Bioreactors for the rapid mass micropropagation of yam

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Morufat Balogun, m.balogun@cgiar.org

The tissue culture technique using meristems followed by serial nodal cultures can be effective for producing high quality seed yam but its use is limited by the slow rate of regeneration and propagation in a conventional semi-solid culture medium. Conventional tissue culture employs manual introduction into culture vials. However, the slowness of yam propagation in vivo also occurs in vitro where cultures for some genotypes can take more than 1 year to regenerate from meristems. This low multiplication rate limits the use of in-vitro produced plantlets; there are also losses during acclimatization and transplanting. Other limitations resulting in low propagation rates are frequent sub-culturing which increases labor costs, culture container size (hence nutrients), and sub-optimal culture aeration and uptake (Cabrera et al. 2011).

As part of its objective to develop technologies for the high ratio propagation of high quality seed yam, YIIFSWA is set to standardize in vitro propagation techniques using conventional and temporary immersion technologies. In most crops tested (pineapple, cocoa, potato, and others), the Temporary Immersion Bioreactor system (TIB) increased propagation rates (Watt 2012) through culture aeration combined with automation, both of which increase productivity.

The TIB technology involves the timed immersion of plant tissues in a liquid medium to allow for the aeration of cultures. Each unit is a bioreactor—an enclosed sterile environment provided with inlets and outlets for air flow under pressure—and therefore circumvents the limitations associated with conventional tissue culture. Although the TIB system requires the interplay of plant physiology and the chemical and physical sciences, growth rate is significantly enhanced therein since gas exchange is guaranteed (Watt 2012).

IITA’s TIB system is a “twin flask” type (Adelberg and Simpson 2002), having 1 container for the medium and the other for the cultures. It has potentials for both plantlet and yam microtuber production which will facilitate the production of quality breeders’ seed yam from which healthy foundation and certified seed yam will be multiplied. IITA’s TIB is established with 128 units and, when running at full capacity, can produce at least 12,000 seed yam in 1 year. It is programmable and remotely controlled online. It can also be used to fast-track genetic improvement through accelerated in-vitro variations and selection. Seed yam from this technology will be bulked in IITA’s aeroponics facility; other end-users include researchers, farmers, and public/private seed companies.

References

Adelberg, J.W. and E.P. Simpson. 2002. Intermittent Immersion Vessel Apparatus and Process for Plant Propagation. Internl. S/N: PCT/US01/06586.

Cabrera, M., R. Gómez, E. Espinosa, J. López, V. Medero, M. Basail and A. Santos. 2011. Yam (Dioscorea alata L.) microtuber formation in Temporary Immersion System as planting material. Biotecnologia Apl. 28: 4.

Watt, M.P. 2012. The status of temporary immersion system (TIS) technology for plant micropropagation.African Journal of Biotechnology 11: 14025-14035.

 

Novel yam propagation technologies: the aeroponics system

Norbert Maroya, n.maroya@cgiar.org, Morufat Balogun, Lava Kumar, Robert Asiedu, and Beatrice Aighewi

Norbert Maroya, Project Coordinator, YIIFSWA; Morufat Balogun, Agronomist (YIIFSWA); Lava Kumar, Virologist and Head, Germplasm Health Unit; Robert Asiedu, R4D Director for West Africa, IITA; and Beatrice Aighewi, Seed Systems Specialist, YIIFSWA

The multiplication ratio of yam in the field is known to be very low (less than 1:10). The methods developed to address this limitation include the minisett technique, vine propagation, and micropropagation using in vitro culture of apical meristems and nodal cuttings. These methods are well suited to rapid multiplication of seed tubers for new and other recommended varieties, and are also amenable to the application of sanitary methods that ensure high seed quality. Other methods of rapid propagation developed at IITA include production of microtubers from plantlets in vitro, and the production of seed tubers using slips (sprouts) and peels. Other technologies also exist but are not yet being used for yam.

Three new technologies targeted to be implemented for seed yam propagation are aeroponics system (AS), temporary immersion bioreactor system (TIBs), and photoautotrophic culture (PC). These technologies are being tested under the Bill & Melinda Gates Foundation-funded project “Yam Improvement for Income and Food Security in West Africa (YIIFSWA)”. These technologies are known to be effective for other vegetatively propagated and horticultural crops for high ratio propagation and assurance of high seed quality. However, their cost-effectiveness for yam propagation is yet unknown. Very recently two of these technologies, AS and TIBs, have been established at IITA-Ibadan, Nigeria. Progress achieved with AS is summarized in this article.

What is an aeroponics system?
The basic principle of AS is growing plants in air in a closed or semi-closed environment without the use of soil or an aggregate media and spraying the plant’s roots with a nutrient-rich solution (mist environment). The techniques of growing plants without soil were first developed in the 1920s by botanists who used primitive aeroponics to study plant root structure. The aeroponics system has long been used as a research tool in root physiology (Barker 1922). Carter (1942) was the first researcher to study air culture growing and described a method of growing plants in water vapor to facilitate examination of roots. Went (1957) named the air-growing process in spray culture as “aeroponics”.

The International Union of Soil-less Culture defines aeroponics “as a system where roots are continuously or discontinuously in an environment saturated with fine drops (a mist or aerosol) of nutrient solution” (Nugali et al. 2005). AS has been used successfully in producing several horticultural and ornamental crops (Biddinger et al. 1998). It has also been applied successfully in Korea for potato seed tuber production (Kang et al. 1996; Kim et al. 1999). At the International Potato Centre (CIP) in Peru, yields of over 100 tubers/plant were obtained using aeroponics technology (Otazu 2010). Aeroponics technology is also being tested in several African countries for the production of potato mini tubers (Lung’aho et al. 2010).

IITA’s experience in propagating yam in AS

Seed yam production using aeroponics was initiated recently. A consultant from Kenya helped to establish an AS of 14 boxes of four tables each in an existing screenhouse at IITA, Ibadan, Nigeria, with an adjacent powerhouse as a source of the spray of nutrient-rich solution to the roots.

From yam seedlings transplanted in July 2012, vine cuttings were made on 6 to 19 December 2012 and planted in black plastic pots for pre-rooting. The pre-rooted vines were transplanted in AS on 26 to 28 February 2013. Vine cuttings were collected from other seedlings transplanted on 28 August 2012 and planted directly in AS on 1 March 2013.

Both pre-rooted and direct-planted vines have continued to grow normally in AS with the development of new shoots and roots. The two types of plants produced viable minitubers which were harvested in June 2013. The key finding in this experiment is the ability to root vine cuttings in AS. Within 10 days more than 50% of the vines produced roots and in 3 weeks 85–100% of the direct-planted vine cuttings produced roots in AS. If a yam plant is certified clean, one can directly collect vine cuttings from such plant for propagation in AS through vine cuttings.

This is the first report of successful yam propagation in AS. Also all previous studies on AS for potatoes or horticulture crops used transplants of rooted plantlets and not unrooted vine cuttings. This is the first experience using yam vine cuttings in AS. The minitubers harvested in June 2013 were planted in August 2013 and sprouted well.

Many of the farmer-preferred yam genotypes are also being evaluated in AS. Direct vine cutting of variety Puna—a popular cultivar in Ghana—was planted in AS on 10 July 2013 and harvested on 6 November 2013 (4 months).

Production of bulbils of yam in AS

The second set of experiments was done using only vine cuttings of plants produced in a glasshouse. To increase the size of mini tubers, two new fertilizers—potassium sulfate (K2SO4) and Triple Super Phosphate—were added to the existing nutrient solution. Between 45 and 60 days after vine cuttings were planted in AS we observed that many varieties of both D. rotundata (white yam) and D. alata (water yam) had produced bulbils. All the bulbils produced by D. rotundata were growing with new shoots and roots; it was the same for D. alata with most bulbils increasing in size. Bulbils mainly harvested from D. rotundata were planted in plastic bags, sprouted, and are growing normally.

Percentage of bulbils formed per genotype on AS

Genotypes

Number of plants

% of plants with bulbils

TDa 291

32

9.4%

TDa 98/01176

53

18.9%

TDr 02475

47

42.6%

TDr 89/02665

18

72.2%

TDr 95/18544

50

22.0%

TDr 95/19158

12

16.7%

TDr 95/19177

26

11.5%

Total

238

26.1%


Challenges

Ideally the AS environment should be kept free from pests and diseases so that the plants will grow healthier and quicker than plants grown in a soil medium. However, current arrangements do not provide an ideal environment due to lack of control on temperature and pest and disease infestation. Plants generated in AS were frequently infested (19 to 29%) by Colletotrichum sp. (both leaves and stem), Sphaerosporium sp. (stems) (typically saprophytic), and Fusarium sp. (stems). Steps are being taken toward reducing the heat inside the screenhouse with industrial fans and providing adequate shade. Measures are also being implemented to control infestation of fungal pathogens.

Conclusion

Despite the relatively recent (less than one year) attempt to propagate yam in AS, some of the results obtained so far are very encouraging and impressive. They have clearly shown that AS does not necessarily need rooted plantlets/vines for yam propagation. Micro-tubers, bulbils, and mini-tubers can be produced respectively within 2 and 4 months after vine cuttings are planted in AS.

References

Barker BTP. 1922. Studies on root development. Long Ashton Res. Station Ann. Rep. 1921: 9-57.

Biddinger E.J., Liu C.M.. Joly R. J, Raghothama K.G. 1998. Physiological and molecular responses of aeroponically grown tomato plants to phosphorous deficiency. J. Am Soc. Hortic. Sci. 123: 330-333

Carter W.A. 1942. A method of growing plants in water vapor to facilitate examination of roots. Phytopathol. 732: 623-625.

Lung’aho C., Nyongesa M., Mbiyu M.W., Ng’ang’a N.M.. Kipkoech D.N., Pwaipwai P., Karinga J. 2010. Potato (Solanum tuberosum) minituber production using aeroponics: another arrow in the quiver? In: Proceedings of the 12th Biennial Conference of the Kenya Agricultural Research Institute.

Kang J.G., Kim S.Y.; Om Y.H., Kim J.K. 1996. Growth and tuberization of potato (Solanum tuberosum L.) cultivars in aeroponic, deep flow technique and nutrient film technique culture films. J. Korean Soc. Hort. Sci. 37: 24-27.

Kim H.S., Lee E.M., Lee M.A., Woo I.S., Moon C.S., Lee Y.B., and Kim S.Y. 1999. Production of high quality potato plantlets by autotrophic culture for aeroponics systems. J. Korean Soc. Hort. Sci. 123: 330-333.

Nugali Yadde M.M., De Silva H.D.M., Perera, R., Ariyaratna D., Sangakkara U.R. 2005. An aeroponic system for the production of pre-basic seed potato. Ann. Sri Lanka Department Agric. 7: 199-288.

Otazú V. 2010. Manual on quality seed potato production using aeroponics. International Potato Center (CIP), Lima, Peru. 44 p. ISBN 978-92-9060-392-4. Produced by the CIP Communication and Public Awareness Department (CPAD)

Went F.W. 1957. The experiment control of plant growth. New York.

Prof Felix Nweke: Staying true to the course

Prof Felix Nweke about himself: I was born in Eastern Nigeria as an Igbo man but I consider myself an African right now. My training background is agricultural economics. I am a professor by occupation, retired some years back. Just call me “Prof.”

How did you get into root and tuber crops research & development?
I like that question because yam and cassava are the rhythm of my life from the beginning; I was born growing and eating them. When I was born where I was born we woke up in the morning, ate cassava fufu, then went to the field. Later in the afternoon we ate yam and continued to work in the field until dusk. We went home and ate cassava again for dinner; we did this day in, day out and it was good at that time.

As I grew up and went to school I was attracted to agriculture by the then Government of Eastern Nigeria which offered scholarships. My interest was in mathematics but my parents could not pay my university education costs from growing yam and cassava. At the University of Nigeria, Nsukka, which is in the yam belt of the world, what was taught was not called yam and cassava but those crops were still part of everyday life.

When I completed the undergraduate program and after my Biafran experience, I went to Michigan State University (MSU) for postgraduate studies. There, I was spared working on and eating cassava and yam but on return to the University of Nigeria, Nsukka, as a teacher I got immersed in the influence of those crops once again. The first research program I conducted was a project titled “Yam-Based Cropping System of Eastern Nigeria”; it was as if I had no choice but work on yam.

Can you explain the benefit and value of yam to you.
I envy my parent’s generation and rhythm of life for its routine and stable life pattern. That is the positive side. But there is a negative side to the life of that generation; I told you we ate cassava in the morning, yam in the afternoon, and cassava again at night. That story is true but yam was not always available, especially during the hungry season (after planting yam). During the hungry season we ate cassava morning, afternoon, and night. At the time, it meant nothing to me; but today if I have to worry about what my grandchildren would eat the next day, I would probably go what some people of the Caribbean describe as “separat”, i.e., mind and body going separate ways.

My parents worried about what we would eat the next day. Today, not everybody can afford even to eat cassava three times a day. I know families that live under leaking roofs, if you can call it a roof at all; I know families that cannot afford painkillers when a member is sick. When I walk in the streets I see beggars all the time. I do not give to them because private charity does not solve the social inequality problem. I pursue social justice by doing my work with honesty, courage, and commitment; in that way everybody can benefit from my work. If successful, my work on yam and cassava research will benefit everybody. That is what I got from my childhood experience of poverty and deprivation, which are still the experience of many people today.

What make yam and cassava so interesting?
Cassava and yam are interesting to me because they are rooted in my blood; if you cut me, I shall bleed cassava and yam. I could have migrated to the US and worked on wheat or corn but that will be a betrayal; by working on yam and cassava I am staying true to the course; I am giving back to what made me what I am and I feel good doing that.

Those crops are important to people of sub-Saharan Africa as a whole. There is a lot of value in these crops; we know that about cassava in Africa because that is a crop that is now well studied. It is clear that cassava has a lot of food and monetary values while its value as feed and industrial raw material remains potentials as far as Africa is concerned.

On the other hand, yam is not studied and people do not understand the crop. The monetary value to farmers who produce yam is quite high; when farmers grow yam they can sell all of it because they cannot afford their own yam. The money they get from it is more valuable to them than the yam; they use that money to buy cheaper foods like cassava.

It is often said that yam has cultural values, but people have a superficial understanding of that value. When a farmer distinguishes himself in yam production, he becomes a reference point in his community; when he speaks, people listen. He plays a key role in community mobilization and leadership. Rites of thanksgiving, passage, appeasement, and petition that are performed with yam as a ritual object among several yam-producing people of West Africa sustain the traditional social values in which the existence of the people, individually and communally, is rooted.

What does the future of yam look like to you?
The future of yam looks bright to me. Today, yam is costly to produce because of Stone Age technologies that dominate the yam crop sector. Yam production, harvesting, and storage technologies are primitive. Why? The answer is that there has not been significant investment in yam research and development. Yam is produced and consumed in West Africa, mostly, that is. West African governments do not care and in that case the Western world does not bother.

But the situation is beginning to change with the funding of YIIFSWA by the Bill & Melinda Gates Foundation. In a regional agricultural research on a crop produced and consumed with rudimentary technology, US$12 million over five years is seed money. But it is an important seed money because it is the first of its kind and it will grow to help break the low technology bottleneck in the yam crop sector.

People have talked about the extinction of yam because of its primitive production and handling technologies. Such people should understand that as long as there are yam eaters, yam would be produced. Yam has a bright future because in spite of high costs, West Africans have continued to produce and eat yam. More importantly, with the US$12 million funding for YIIFSWA, the international donor community is beginning to appreciate the various values of yam.

What is yam’s added value?
It is not easy to think clearly of those added values with the present high cost of yam production. Converting yam to starch, liquor, ethanol, etc., will be irrational behavior because there are cheaper sources of those products. If yam is discovered to possess some high medicinal value, which no other plant has, such as a substance that can cure common diseases that have so far defied cure such as diabetes, various cancers, HIV/AIDS, etc., then the crop can be rationally diverted to such use.

How would you then describe the yam of the future?
This is a good question but the answer is not direct because of the different purposes that yam serves which may be conflicting in terms of the nature of yam that serves each purpose. Long ago, I think it was in 1980, the future of yam was the subject of a panel discussion at the Triennial Conference of the ISTRB-African Branch at IITA. The answer to the question ought to consider the different requirements for the various uses for yam. But there is a bottom line and that is cost; the yam of the future must be delivered for the various uses at reduced cost. Yam has no rival as a ritual object in cultural rites in producing communities, but that use alone cannot sustain yam in the future. Yam as food has a wide range of competitors some of which are produced at very low costs following high levels of investments in research and development in the Western countries. As those alternative foods become cheaper, people will switch to them.

You have been associated with IITA for so many years. What do you see as its strengths and what areas need more focus?
I have been associated with IITA since 1977. When I returned to Nigeria from graduate school at Michigan State University, the first place I had a job was the University of Nigeria, Nsukka, as a teacher. A university teacher in agriculture has responsibility for teaching, research, and extension. But the university did not have money for research and I did not want my research responsibility to suffer.

I had a senior colleague in graduate school who was a scientist at IITA, his name was Fred Winch. Fred passed away a few years ago; I do want to remember him. I used Fred’s facilities to carry out the study of “Yam-Based Cropping Systems of Eastern Nigeria” which I referred to earlier. Kun Tekail, who was Director of the Farming Systems Program at IITA, asked me to come to IITA as a full Scientist. I declined because I was enjoying what I was doing in Eastern Nigeria. He then appointed me as a Honoris Causa Scientist at IITA. I continued to work with IITA resources as an honorary scientist until 1987 when I caved in to pressure from Larry Stiffel to join IITA as a full scientist.

I was employed at IITA as a yam economist to work with yam agronomists. Dunstan Spencer was the director of the Resource and Crops Management Program in which I was based. A few months after I came to IITA Dunstan assigned the COSCA project leadership to me and I moved from working on yam to working on cassava. I left IITA in 1997 but I have continued to work on cassava.

There is an agricultural problem that IITA needs to address. That problem is neglected perhaps because of the assumption that Africa’s agricultural development will necessarily follow the path of other regions’ agriculture. For example, in Africa R and D effort is focused on achieving a Green Revolution because of the success of Green Revolution in Asia and South America. But are Africa’s needs and circumstances the same as those of Asia and South America? In Africa, a different kind of revolution is needed to pave the way for a Green Revolution; that is Mechanical Revolution. In the 21st century African agriculture based on the hand hoe cannot compete with the rest-of-the-world agriculture. I am not talking of tractor mechanization but improved farm tools that are designed by engineers working in Africa and maintainable by local artisans.

How do you perceive the impact of IITA’s work on roots and tubers for farmers in Africa?
Whoa! Tremendous! In Nigeria, scientifically determined yield of cassava was 15 tons per hectare in the 1990s following wide adoption of IITA’s high-yielding mosaic resistant TMS varieties. There was an estimate that in Nigeria alone, the additional value in terms of gari from these high-yielding mosaic resistant TMS varieties was enough to feed 29 million people annually. We have information which shows that the price of cassava products relative to the price of other commodities dropped in the 1990s, which meant increased income to consumers who paid less for cassava food products such as gari. At the same time, because of reduced cost, farmers are making more money. IITA’s effort on cassava including the biological control, mosaic disease control, and the high-yielding varieties produced tremendous value in terms of income to millions of cassava producers and consumers.

How do you picture Africa in the next 50 years?
Income will improve in Africa and people will be better off materially. The meaningfulness of that in terms of improved welfare depends on how much the measures that create the wealth interfere with the fundamental values of the African people. I wish to see a significant decline in the present high levels of poverty, deprivation, and inequality in Africa. Retaining African social values while improving the economic conditions of the masses of the people will be the better of two worlds.

How will agriculture play a role in doing that?
Improved agricultural productivity will mean improved income for farmers through reduced production costs and for consumers through reduced food prices. Improved productivity in agriculture will generate feed and industrial raw materials and help expand employment opportunities in the industrial sector. Large farms could be depended on to improve agricultural productivity but they can convert small farmers into farm laborers. Measures to improve agricultural productivity should protect small farms to allow even distribution of increased farm income from improved productivity.

In the ISTRB symposium 2 years ago, you were given the Lifetime Achievement award. What does that award mean to you?
The Award for Lifetime Achievement in research on roots and tuber crops was given to me by peers in the ISTRC and that makes it satisfying. One of the reasons I was given the award is the pan-African cassava research project in which I served as Project Leader while I was a scientist at IITA, i.e., the Collaborative Study of Cassava in Africa or COSCA study. I do not claim the award for myself alone even though it was given in my name.

The COSCA study involved 63 scientists from all over the world not just Africa. The study was the idea of Dunstan Spencer, John Lynam, and others whom I do not even know. Soon after I came to IITA in 1987 as a Yam-Based Systems Economist, the new COSCA study was assigned to me to execute. CIAT, NRI, International Child Health Institute, and MSU are among collaborating institutions from outside Africa. National agricultural research centers of Cote d’Ivoire, Ghana, Nigeria, Democratic Republic of the Congo, Tanzania, and Uganda played critical roles.

What is the value of a medal like this award? Igbo wisdom says that “if you say thank you to somebody, the person will do more.” Saying thank you is inexpensive but it is an inspirer. Besides, awards such as this one can open doors; Prof Felix Nweke, winner of Lifetime Achievement Award, is at the door, please let him in. I am going to make effective use of this effect to do more work on cassava and yam in Africa. That is what the award means to me.

What would you say is the highlight of your career?
This question can hardly be answered with dispassion; self-assessment is more often than not underrated or overrated depending on one’s level of humility. Nevertheless, I consider that the highlight of my career is demonstrated in the accomplishments of the people with whom I have grown up professionally. These are not only students whom I taught in the classrooms or those whose higher degree dissertations I supervised; there are several of those. But having worked closely with Prof Carl Eicher of Michigan State University for the past 50 years beginning in 1963 at the University of Nigeria, Nsukka, I assimilated what I consider his finest professional value. Carl Eicher is like a magnet that draws young professionals to him and he grows with them, in some cases for life. Many of the people I have grown with that way are highly accomplished professionally and they are all over the world, not just in Africa. That is the highlight of my career and it could not have been better.

Tony Sikpa: Commercializing yam in Ghana

Anthony Sikpa is the president of the Federation of the Associations of Ghanaian Exporters (FAGE). His group includes producers, exporters, and farmers. The federation currently has 13 associations with up to a couple of hundred members each. He also works with people in the horticulture sector producing vegetables, papaya, pineapple, and yam. He has been involved in organizing the group and doing advocacy work as president. He is an exporter of commodities such as cotton seed, cashew, coffee—both processed and raw materials, and other products.

How did you get involved in yam development?

Yam has been of interest to us and Ghana has been exporting yam for many years. So when the government approached IITA and ITC to help them develop a sector strategy for yam, it was interesting. Initially I was not involved because I did not handle yam but the association members asked me to lead them from the private sector angle. So I worked together with Dr Antonio Lopez (IITA) and Nelson (ITC), and we designed a participatory approach in crafting the strategy and in implementing and evaluating the whole process. This meant getting everybody in on one house: farmers, researchers, policy makers, exporters, traders, and financiers, under one roof. We talked, addressed issues, and came out with six broad objectives; how to improve the planting material, how the research and private sector will support the crop, how to help yam farmers in producing products using improved technologies, and how to market yam? Because we can’t just take anything into the market, we introduced ‘quality certification’ along the way to test the product.

The exercise was very useful. For the first time the misconceptions along the value chain were addressed. A farmer had the opportunity to ask scientists “why don’t you produce this type of material for me?” The approach really addressed the need of each person in the room.

For me, it helped to tell the public sector to create an environment for the private sector to lead and work with them.

Where are we going with the strategy?
This strategy is very important. The document provides a future road map, priorities and areas for investment/resource allocation, including milestones to assess the progress. The beauty of the strategy which makes me happy is that it is not dependent on one person to make it work. The farmers can go to the researchers to get the varieties. Fortunately we have IITA also to approach for new varieties. The exporter now clearly knows that he has work from the market; what the market requires and its standard. So he should prepare himself for the market.

We have used the strategy to position yam as an input for the industry. We should not just see yam as a food for the table. Yam can be used for different types of products including wine, in pharmaceuticals, etc. These are the ways we want to project yam so that we create a bigger demand for yam, and researchers would have to produce different varieties to suit the different needs of people. We will then be making yam as an industrial crop and create a bigger demand for it.

How are you involved with YIIFSWA?

I took advantage of the YIIFSWA meeting in Kumasi to go and tell them what we are doing in the yam sector and to also get their support for what we are doing. Maybe some of the products such as the new seeds and technology that would come out of the project could be made available to us in executing our strategy. I also told them about the gap that I saw: the emphasis on seed production was too much. We need to go beyond that into processes, coming out with new varieties for different uses. That is where they thought I could be useful and they invited me to join the technical advisory for the first time.

What are the lessons for other countries in Ghana’s experience of developing a yam sector strategy?

Others can learn from us. You cannot go into export without knowing which market you want. The export market has different strings; you need to look at the size of the market and use that to determine your production methods and even the varieties you want to produce. The variety that is in big demand is Pona. It has a very short shelf life and is delicate. You have to put all this into consideration when transporting it. You must package it well. The researchers need to take their time to study this. This project would help us to collaborate with, for example, our Nigerian brothers for us to be able to show them a few things we are doing that they can do. We know the way we use yam is different from the way they use yam. If they want to export yam, they need to go for smaller sizes for easy packaging because we measure in weight and not in hip or sizes.

What are the challenges in commercialization of yam?

The major challenge is in numbers and regularity. If you look at the trend in marketing now, in supermarkets they don’t want to buy small quantities because the supermarket has a chain, so you need to produce the volume required. If you can do this, you won’t have problem.

Aggregation. For instance you have so many farmers producing yam, you need someone to aggregate and make sure the quality is the same. The supermarket would not buy from you again if you get it wrong because they have a responsibility to their consumers to assure their safety. I will keep on saying certification. You cannot put any product in the European market without certification. They would look for international certification like the rainforest alliance as this would give them access to the international market. Another thing is transportation. You need to transport your product directly because if you don’t it will get cooked.

What is your vision for yam in Africa?

My vision for yam is to put it where potato is. Potato is everywhere. When people bring yam to town and package it into yam flour, then we’ll have done what this project is set out to do.

Would you have any advice to young farmers?

The young farmers should be happy and should grasp this opportunity of coming into agriculture now. It is a new learning. They should not be afraid of scientists; they should go to them with trust and patience.

Yam genetic resources conserved at IITA

Badara Gueye (B.Gueye@cgiar.org) and Michael Abberton

Within CGIAR, IITA has the mandate for the collection, characterization, and exchange of yam species. IITA’s Genetic Resources Center (GRC) thus holds a major yam international germplasm collection in trust under the Multilateral System of the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA).

With 3,872 accessions, the IITA yam collection is the world’s largest, including nine of the major cultivated species: Dioscorea rotundata, D. alata, D. bulbifera, D. cayenensis, D. dumentorum, D. esculenta, D. preussii, D. manganotiana, and D. praehensilis. Conserved in the field and through an in vitro genebank, it represents a large genepool for yam crop improvement to help the crop reach its full potential for food and income for poor farmers. To meet this objective, GRC is working on many themes for harnessing yam genetic resources in collaboration with a range of partners. The first one is the filling of genetic gaps to ensure the availability of a broader yam gene pool. In 2014, we are carrying out germplasm collection in Nigeria and Benin Republic. The entire yam collection is conserved in the IITA field bank at Ibadan, Nigeria, and the use of outstation sites offers different conditions for the regeneration of recalcitrant lines, which reduces germplasm losses. More than one-third of the yam collection is duplicated in the in vitro medium-term storage facility at IITA-Ibadan. The development of a yam cryopreservation protocol will allow long-term conservation.

To promote the use and distribution of yam germplasm, especially in breeding, the entire yam collection was characterized using agromorphological descriptors, leading to the identification of a core collection. Increasing collaboration with the yam breeders, germplasm health specialists, and national partners is ongoing to carry out genetic resources evaluation including for market demanded traits. Molecular tools and advanced phenotyping methods are also being employed to further characterize the germplasm and further promote its use. All the data are made available and accessible worldwide and efforts are ongoing to increase the proportion of quarantine pathogen free yam genetic resources for more distribution across borders. Viruses are important pathogens of yam, therefore germplasm use will also be promoted through production of virus-free material for exchange and production of planting material. Virus elimination methods (heat treatment, cryotherapy and chemotherapy) are being explored to establish a reliable protocol for yam virus cleaning.

GRC plays also a major role in training and capacity building of national programs with respect to collection, conservation and characterization of genetic resources of yam.

For further information visit: http://www.iita.org/genetic-resources.

Countering yam anthracnose threat in West Africa

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From yam production and postharvest constraints to opportunities

D.B. Mignouna, d.mignouna@cgiar.org, T. Abdoulaye, A. Akinola, and A. Alene

Food insecurity remains a huge concern in West Africa. Agriculture, without doubt remains the main source of food and livelihood. Over the past two decades, agricultural yields have stayed the same or declined. Although there has been a recent rise in agricultural productivity, it derived more from expanded planting areas for staple crops than from yield increases. Thus, increasing and sustaining agricultural productivity should be a critical component of programs that seek to reduce poverty and attain food security in the region.

Yam (Dioscorea spp.), a vegetatively propagated crop cultivated for its underground edible tubers, is the mainstay for about 300 million people in West Africa. It is a very important food and income source for millions of producers, processors, and consumers in the region. About 48 million tons are produced annually in this subregion on 4 million ha. The five major yam-producing countries (Bénin, Côte d’Ivoire, Ghana, Nigeria, and Togo) account for 93% of the world’s production, with Nigeria alone accounting for 68% of global production (36 million t on 3 million ha) with 31.8% of the population depending on yam for food and income security. The crop contributes substantially to the amount of protein in the diet, ranking as the third most important source, much more than the more widely grown cassava, and even higher than some sources of animal protein. Hence, yam is important for food security and income generation with a domestic retail price of US $0.49/kg. Yam is also integral to the sociocultural life in the subregion.

In present-day Nigeria, yam is still culturally significant because it plays an important role in betrothal ceremonies or traditional marriages. It is one of the significant items a suitor presents to his in-laws to obtain their approval to marry their daughter. Some grooms are compelled to present as many as 40 pieces of long and fat yam tubers, aside from gallons of palm oil, baskets of kola nuts, bags of salt, and other sundry items, the nonprovision of which could invalidate the union. The cultural importance of yam is higher in some regions in Nigeria as it is a crop celebrated annually during the New Yam Festival, with rituals to thank the god of agriculture, to seek its blessings for a bumper harvest in the forthcoming years. Yam is produced more in the middle belt zone of Nigeria and is consumed more in the South, but those making commercial gains from its sales are core northerners from the North West, the North Central, and the North East.

Despite its importance in the economy and lives of many people, the crop faces several constraints that significantly reduce its potential to support rural development and meet consumers’ needs for improved food security and enhanced livelihood. Constraints limiting yam production and postharvest handling need to be identified to provide a basis for appropriate interventions. This was the reason behind the interventions through the Yam Improvement for Income and Food Security in West Africa (YIIFSWA) project. YIIFSWA was initiated to work with other stakeholders in West Africa to identify the opportunities of interventions that could potentially help to increase productivity in the region. This report documents production and postharvest constraints and opportunities in yam.

Using Nigeria and Ghana as cases, important worldwide yam-producing countries, a study was carried out using a multistage, random sampling procedure in selecting a total of 800 and 600 households, respectively. All surveyed households were interviewed using a structured questionnaire.

Survey results indicated that a range of factors limited yam production and storage. These include insect pests, diseases, water-logging, drought, rodents, low soil fertility, shortage of staking material, inadequate input supply and storage facility, land shortage, high cost of labor, lack of improved varieties, and others such as theft (Fig. 1).

High cost of labor stands out as the most pressing problem in all the surveyed zones, both in Nigeria and Ghana. For instance, mounding as a seedbed preparation method, is laborious, and hence expensive. But apart from mound making all yam production operations are labor intensive because they are performed with hand hoes, machetes, and digging sticks without any form of a labor-saving technology.

Another main constraint are insect pests and diseases. The unavailability and high cost of good quality disease-free seed yam had been on one hand a result of pests and diseases and on the other hand a serious hidden constraint due to the fact that farmers do not purchase seed yam. Other important constraints mentioned were the inadequate input supply that was very pronounced in Ghana, low soil fertility more reported in Nigeria, rodents and drought (Ghana), water-logging (Nigeria), lack of improved varieties more prominent in Ghana, shortage of land and staking material (Ghana), and others such as theft that were not negligible in both countries.

It is clear that there are shared priority constraints in the two countries, indicating no specificity of problems by country. The YIIFSWA research agenda needs to be informed by the constraints facing yam farmers and based on these the following interventions were identified: (i) Key investments for lowering farmers’ production cost using agricultural research (breeding, agronomy) and extension (improved agronomic and management practices; and (ii) Managing pests and diseases.

As regards opportunities, yam could be be a formidable force in the fight against poverty, hunger, and deadly diseases if research and development measures are implemented to develop and disseminate technologies that can bring the crop into central focus in national food policies. This will enable it to benefit from policy programs that can drive down production costs. Yam is a preferred food in the region; some varieties, especially yellow varieties, are sources of betacarotene. The crop is produced mostly for sale, and it is increasingly becoming a major source of foreign exchange in the region as an export crop.

Therefore, YIIFSWA, through its initiatives, should ensure that all constraints are turned into opportunities for all the yam value chain players in general and farmers in particular.

Enhancing yam improvement for West Africa

Hiroko Takagi

EDITS Project: JIRCAS International Collaborative Research for West African crops

In the past, most agricultural investments and international agricultural research in Africa were focused on developing major cereals and crops for export. Recently, however, the focus has shifted to approaches to diversify agricultural innovations in defined locations to contribute to productivity and profitability increase and achieving sustainable food security to overcome poverty and malnutrition. In addition to so-called “major global crops”, attention has also been placed on many more crops that are regionally or locally important for nutrition and income and that are often underresearched but are nutritious, valued culturally, adapted to local environments, and contribute to diversifying regional agriculture systems.

The Japan International Research Center for Agricultural Sciences (JIRCAS), together with several Japanese research institutions and IITA, initiated in 2011 a 5-year collaborative research project called “Evaluation and Utilization of Diverse Genetic Materials in Tropical Field Crops (EDITS)”. The project focuses on yam (EDITS-Yam) and cowpea (EDITS-Cowpea), and aims to generate a solid understanding of the available wide genetic resources in these West African traditional crops, and develop efficient evaluation techniques for effective crop improvement. The outputs from these collaborative efforts are expected to contribute to breeding programs in West Africa.

JIRCAS is playing a key role by linking the Japanese scientific capacities to African communities through IITA, which is the entry point for many overseas research institutions to overcome the various constraints in African agriculture. The knowledge and techniques gained from the collaborative research project is expected to enhance the development of improved yam and cowpea varieties that can help promote rural livelihoods in West Africa.

EDITS-Yam

Yam is a traditional staple crop of significant economic and sociocultural importance in West Africa. The demand for yam is projected to increase, mostly due to population growth in the region. However, little improvement of farm yields has been registered in this crop in the last few decades, indicating an urgent need for more investment in yam research and development. To increase its productivity and enhance the income generation capacity of small-holder farmers, research-for-development should focus on increasing productivity through improved varieties and production technologies to meet the regional needs.

The last couple of years saw a breakthrough in genome sequencing technologies, and in the application genomic information to plant breeding. Genome analysis and improved molecular techniques would tremendously facilitate germplasm characterization, genetic mapping and tagging, and functional genomics of yam. These new tools, if incorporated into the breeding program, will pave the road for effective genetic improvement of yam. Since April 2011, JIRCAS together with the Iwate Biotechnology Research Center (IBRC) and IITA, has been implementing EDITS-Yam to develop and use advanced genomic and molecular tools to enhance germplasm evaluation and improvement for D. rotundata in West Africa.

EDITS-Yam is designed to strengthen genotyping using molecular tools and develop phenotyping protocols to facilitate yam breeding. The project aims to (1) generate the first reference genome of D. rotundata (Guinea yam), (2) develop and apply genomic information and molecular tools in yam breeding, (3) provide improved tools for biodiversity analysis and identification of potentially useful germplasm, and (4) develop phenotyping protocols for important agronomic traits. The outputs from this collaborative research are expected to contribute to the enhancement of yam breeding activities in the region. Consequently, new improved varieties will provide better food security and income for the small-holder farmers in West Africa and beyond.

Progress in 2011-2013

Sequencing of Guinea yam genome

To enhance Guinea yam breeding by fully exploiting modern genomics tools, generating a reliable reference sequence is a prerequisite. To this end, we have been gathering efforts to obtain the first whole genome sequence (WGS) of D. rotundata. The de novo assembly is currently in its final stage. The reference of genome will be completed soon, and the finding will be shared with the global yam community (Fig. 1).

Whole-genome sequencing-based analysis of diversity in Guinea yam

Next generation sequencing (NGS) allows large-scale genome-wide discovery of genetic markers that are important for genomic and genetic applications such as construction of genetic and physical maps, and analysis of genetic diversity. As a component of the on-going effort to construct the first draft sequence of D. rotundata and accelerate the breeding program, WGS-based genetic diversity analysis of D. rotundata accessions is under way. So far, 10 D. rotundata breeding materials, including five landraces and five breeding lines, have been resequenced. These materials are diverse with respect to traits such as maturity time, yield, tuber quality, and resistance to nematode and Yam mosaic virus (YMV), and have been extensively used as parental lines in the IITA yam breeding program.

Aligning the Illumina paired-end short reads obtained from resequencing of the breeding materials to D. rotundata scaffold sequence allowed genome-wide extraction of single nucleotide polymorphism (SNP) and insertion/deletion (indel) markers, which are being used to estimate the genetic relatedness among the lines/accessions studied and reveal the genetic diversity available to breeders. Findings of this study will have huge implications for genetic and genomic studies in yams, including among others, the application of SNPs, the most abundant genetic markers in genomes, for the development of high throughput genotyping platforms and for marker-assisted breeding. More accessions will be considered for resequencing in the future to mine the diversity in D. rotundata in detail.

Diversity Research Set (DRS) as a tool for diversity evaluation of D. rotundata germplasm

The availability of genotypic and phenotypic tools is critical to understand the diversity present in germplasm collections and enhance the active use of genetic resources. IITA currently holds over 2,000 accessions of D. rotundata. Of these, we selected a subset of experimental materials called Diversity Research Set to develop genotyping and phenotyping tools and protocols for germplasm evaluation.

In principle, DRS should be small in size for ease of handling and to allow a detailed analysis of diversity, but retain most of the diversity present in the original collection both at molecular and morphological levels. Accordingly, 106 accessions have been selected as the DRS-EDITS based on 21 key morphological traits, ploidy level, and SSR polymorphisms. The materials are currently being used for (1) detailed genotyping using DNA markers generated from the ongoing WGS, (2) morphological characterization and identification of key descriptors for regional D. rotundata collection, and (3) detailed phenotyping of economically important traits (Fig. 2)

Developing phenotyping protocols

In yam, as well as other root and tuber crops, phenotyping remains the major bottleneck to fully use genotyping information in germplasm evaluation and breeding. EDITS-Yam is also aiming to develop phenotyping protocols on key traits such as tuber yield, earliness of tuber growth and maturation, starch content and properties in collaboration with agronomists and food science specialists. These protocols, once developed, will be used for large-scale phenotyping applied to genetic and diversity studies (Fig. 3).

The information generated and tools developed in the framework of the EDITS-Yam project are expected to contribute immensely to broadening the knowledge base in yam, thereby facilitating the management of available genetic resources and aiding efficient use of yam germplasm for future improvement of the crop. This project and the collaboration it forged are expected to contribute to raising the profile of yam, and trigger the initiation of more and concerted international approaches to yam research for development. The preliminary outputs from the EDITS-Yam project suggest that there is a need for complementary studies to effectively use genetic and genomic tools being generated for yam improvement. To this effect, possibilities for additional resources are being explored.

Viral disease threats to yam in West Africa

Lava Kumar, l.kumar@cgiar.org

Virus diseases pose serious challenges to seed and ware yam production and also impede international exchange of yam planting material in West Africa, which is home to about 91% of the global edible yam production. Current efforts to control virus threats are directed towards propagation of virus-free seed yam. However, deployment of genetic resistance in farmer-preferred cultivars is critical for sustainable virus disease control in West Africa.

One disease and several viruses

‘Mosaic disease’ is a common disorder caused by several different viruses infecting yam in West Africa. About 17 viruses have been identified in edible and medicinal yam in different parts of the world1. The virus species belonging to the genera Potyvirus and Badnavirus are most widespread. Two potyviruses, Yam mosaic virus (YMV) and Yam mild mosaic virus (YMMV), and several badnaviruses—generically referred as yam badnaviruses (YBVs) —are frequently detected in farmer-grown yam in the West African yam belt that stretches from western regions of Cameroon to Cote d’Ivoire, including Nigeria, Bénin, Togo, and Ghana. About 88% of the global yam production area and 91% of the global production is confined to this region. Six Dioscorea species, viz., D. rotundata (white yam), D. alata (water yam), D. cayenensis (yellow yam), D. dumetorum (bitter yam), D. bulbifera (aerial yam), and D. esculenta (lesser yam) are widely cultivated for food use in West Africa. Virus infections are known in all these species but most prevalent in D. rotundata and D. alata, the two most predominant species covering >70% of the cultivated area in West Africa.

Different viruses cause almost similar symptoms and are difficult to distinguish from one another based on symptoms alone. In general virus symptoms in yam consist of deformation of leaf lamina, mottling, yellowing, vein banding, mosaic pattern on leaves, stunting, and poor growth (Fig. 1). Symptom expression can differ based on the genotype, time of infection, environmental conditions and cultivar. Mixed infection with more than one virus often results in severe symptoms. Although effects of virus infection on tuber size have not been accurately quantified, data from published and unpublished studies suggest about 20 to 50% reduction in tuber yield. In addition, ‘internal brown spot disease’ reported from Côte d’Ivoire is known to cause dry corky necrosis in tubers (Fig. 1b). The cause of this disease is not known, but based on symptoms it is regarded as viral in nature. In addition, badnavirus sequences have been found to be integrated in the yam genome. These are termed as endogenous pararetrovirus sequences (EPRVs) or endogenous yam badnaviruses (eYBVs) and have been detected in almost all yam species grown in West Africa, the Caribbean, and South-Pacific regions2. However, the pathological significance of yam EPRVs is not known.

Virus spread along with plant parts and insect vectors

Viruses infecting yam are systemically distributed in all plant tissues, including tubers. Consequently, tubers, setts, or any plant tissue from infected plants serves as a source for virus spread through vegetative propagation (Fig. 2). In addition, some of the yam viruses are transmitted from plant to plant by insect vectors. For instance, YMV and YMMV are transmitted by aphids and YBVs are transmitted by mealybugs. Insect vectors play an important role in spreading virus from infected plants to uninfected plants. A recent study demonstrated YMV transmission through botanical seeds of yam, albeit only a small percentage of seed serves as virus carriers.

Infected seed yams contributing to high virus incidence in West Africa

Farmers in West Africa mainly cultivate yam by planting small tubers (seed yam) or pieces of tubers (setts and minisetts) derived from larger tubers, which are sourced from their own harvest, brought from neighbors, or markets. This practice contributes to the accumulation and perpetuation of tuber-borne viruses. Considering that about one quarter of the yam tuber harvest each year in West Africa is used for propagation, the risk of virus perpetuation dramatically increases through infected tubers from generation togeneration. Historical data and recent surveys conducted as part of the Yam Improvement for Income and Food Security in West Africa (YIIFSWA) project estimated an average virus incidence of >70% in almost all the farmers’ fields, reflecting the perpetual use of infected tubers due to lack of availability of virus-free seed yams. Lack of virus resistance in the popular landraces and improved cultivars, poor awareness about viral diseases, and severe shortage of virus-free planting material are other factors that continue this prevailing situation in West Africa. Coordinated action is required to control the unabated spread of yam viruses through use of virus-infected seed yams.

Multipronged approach for yam virus disease control

Virus disease management of clonally propagated crops which are also transmitted by insect vectors requires a multipronged strategy: (i) reduce virus inoculum in the field by phytosanitation (removal and destruction of infected sources) and replacement of infected seed stock with virus-free propagation material, (ii) use resistant cultivars to prevent infection, and (iii) control insect vectors to prevent further spread. Unfortunately, many of these tactics are not being practiced due to lack of appropriate resources such as virus-free seed stock or highly resistant varieties.

YIIFSWA impetus

In the ongoing Bill & Melinda Gates Foundation-funded YIIFSWA initiative, surveys were conducted in the major yam production regions in Ghana and Nigeria to determine the situation of virus incidence and severity during the 2012-13 seasons. Mean virus disease incidence in both countries was greater than 85% and mean severity was 3, based on a 1 to 5 rating scale (1 = no symptoms and 5 = most severe symptoms). Local landraces were dominantly used by farmers compared to released cultivars. Virus diagnostics tests by reverse-transcription polymerase chain reaction (RT-PCR) assays detected YMV in D. rotundata in all the locations, sometimes in mixed infection with YMMV. YBVs were also detected in all the locations, however it was not clear if these positive results were from episomal? infection or eYBVs. Knowledge on virus diversity determined by sequencing of portion of viral genomes was incorporated into the diagnostic test development to further enhance sensitivity and specificity of yam virus diagnostic tools.

Efforts are also ongoing to produce virus-free yam stocks of the most popular farmer-preferred cultivars (landraces and improved cultivars) in Nigeria and Ghana. A suite of macro and micropropagation technologies combined with thermo- and chemotherapy techniques have been employed to generate stocks free of YMV, YMMV, and CMV. Such virus-free stocks have been established for the cultivars Adaka, Aloshi, Alumaco, Ame, Amula, Danachia, Gbangu, Kemi, Makakusa, Obiaturugo, Ogini, Ogoja, TDr 89/02475, and TDr 89/02665. They are being mass propagated for use as nucleus stock for breeder-class seed yam production. Similar efforts are ongoing to generate virus-free stocks of a wider range of D. rotundata and D. alata cultivars. This, in combination with YIIFSWA activities on strengthening the seed yam systems through improved seed production techniques and capacity development is anticipated to regularly infuse stocks of high quality seed yams produced from virus-free sources by specialist seed growers and contribute to productivity gains.

‘Positive selection’ (PS) is another approach piloted as part of YIIFSWA and allied initiatives to prevent reuse of tubers from severely infected plants for seed purpose. PS is a simple on-farm method of selectively harvesting seed yam tubers from healthy looking plants or plants showing mild symptoms, when asymptomatic plants are not available. This eliminates tubers with high virus concentration and infected with multiple viruses, the two conditions responsible for severe symptoms, poor plant performance, and degeneration of seed yams. Implementation of PS over several seasons is expected to reduce virus inoculum in the fields, improves the quality of farmer-saved seed yam, and reduces the need for regular seed replacement. However, this approach requires additional effort in the form of monitoring crops before senescence, tagging, and separate harvesting of tubers from selected plants. Awareness creation among growers about the benefits of PS and training in selection of healthy looking plants is critical to the sustainable implementation of this approach.


Resistant varieties required for sustainable management

Resistant varieties offer the most convenient, economical, and sustainable option for controlling virus diseases. In addition, they are easy for dissemination and adoption. Almost all the popular landrace cultivars were found to be susceptible. Some were found to have tolerance showing mild symptoms at the later crop growth stage (e.g., Amula). Germplasm sources with high levels of host plant resistance to virus diseases have been identified in the Dioscorea landraces3. However, all the improved varieties released as of 2013 were found to be susceptible. Limited breeding efforts for virus disease resistance demonstrated dominantly inherited resistance to YMV in certain D. rotundata crosses4,5, indicating the promise of breeding for developing cultivars with high levels of virus resistance with end-user preferred traits.

Conclusions

Virus diseases pose a major threat to West African yam production, affecting tuber yields and seed yam quality. Reuse of farmer-saved seed in successive seasons has contributed to high virus incidence and seed yam degeneration. In the absence of high levels of virus resistance in farmer-preferred varieties, it is imperative to infuse clean stocks of popular cultivars through seed systems, coupled with approaches such as phytosanitation and positive selection to reduce virus inoculum in the fields. Concerted efforts in this direction started recently through initiatives such as YIIFSWA. However, these efforts need to be complemented with breeding programs to develop cultivars with high levels of resistance and end-user preferred attributes for sustainable control of virus diseases and also to ensure sustainability of quality seed yams.

References

1. Kenyon et al. 2003. An overview of viruses infecting yams in sub-Saharan Africa. In: Eds. Hughes, J. d’A and Odu, B.O. Plant virology in sub-Saharan Africa, Proceedings of a conference organized by IITA, IITA, Nigeria. pp432-439.

2. Seal et al. (2014). The prevalence of badnaviruses in West African yam (Dioscorea cayenensis-rotundata) and evidence of endogenous pararetrovirus sequences in their genomes. Virus Research (in press) [doi:10.1016/j.virusres.2014.01.007]

3. Asiedu R. 2010. Genetic improvement of yam. In: Yam Research for Development in West Africa – Working Papers. IITA-BMGF Consultation Documents, IITA. pp 81-108.

4. Mignouna J. et al. 2002. Identification and potential use of RAPD markers linked to Yam mosaic virus resistance in white yam (Dioscorea rotundata Poir.). Ann. Appl. Biol. 140: 163­169.

5. Odu et al. 2011. Analysis of resistance to Yam mosaic virus, genus Potyvirus, in white guinea yam (Dioscorea rotundata) genotypes. J. Agri. Sci. 56: 1-13.

A new paradigm for improving yam systems

N. Maroya, R. Asiedu, P. Lava-Kumar, D. Mignouna, T. Abdoulaye, B. Aighewi, M. Balogun, U. Kleih, D. Phillips, A. Lopez-Montes, F. Ndiame, J. Ikeorgu, E. Otoo, N. McNamara; S. Abimiku, Sara Alexander, and R. Asuboah

In West Africa, yam (Dioscorea spp.) plays a very important role as a source of income, food security, and livelihood systems for at least 60 million people. The crop also makes a substantial contribution to protein in the diet, ranking as the third most important source. Farmers engage in yam cultivation for cash income and household food supply. Yam traditionally plays a significant role in societal rituals such as marriage ceremonies and annual festivals, making the crop a measure of wealth. Yams therefore have significance over and above other crops in the region. At the regional level, yam seems to be a superior economic good in all countries. As incomes increase, consumers shift from cassava to yam. This is related in part to regional cultural values and consumer preferences, which is mainly due to the relative ease in consumer food preparation.


Despite its importance in the economy and lives of many people, yam faces many constraints that significantly reduce its potential to support rural development and meet consumers’ needs as an affordable nutritional product. Unavailability and high cost of high quality disease-free seed yam is a major constraint in West Africa. This is followed by high levels of on-farm losses of tubers during harvesting and storage, low soil fertility, and high labor costs associated with land preparation and staking. Other constraints include losses due to diseases caused by viruses and fungi and nematode attack. Scale insects, tuber beetles, and termites affect the tubers in some areas. These effects are experienced more in the dry savannah agroecologies where yam cultivation is rapidly expanding due to the shrinking arable land in the traditional moist humid areas. In addition, the seed yam system in West Africa is mainly informal and entirely market driven.


Yam Improvement for Income and Food Security in West Africa (YIIFSWA) was initiated to increase yam productivity of 200,000 smallholder farmers (90% with less than 2 acres) in Ghana and Nigeria by 40% (2011 to 2016), and deliver key global goods research products that will contribute to the sustainable development of the yam sector.


Early gains

The project started by identifying yam production systems with partners (Fig. 1).

The yam value chain surveys with farmers, marketers (including exporters), transporters, and processors helped to estimate the cost of production of ware and seed yam, analyze costs and benefits of yam transaction, and identify major ware yam supply and distribution routes in both Nigeria and Ghana. Detailed value chain analysis has shown that yam production is a profitable business and yam farmers are able to generate substantial income from the production of tubers. But at the same time, production costs tend to be high (in particular for seed yam and hired labor) and selling prices depend on the season. There is significant price variability between the new yam season (August to October), the peak season (November to April), and the slack season (May to July). During peak seasons there is much yam in the markets but because of unavailability of good storage facilities, yam are sold at the lowest prices (Fig. 3). The gross margins can be negative if farmers get the timing of their harvest wrong, or are unable to sell at times when prices are higher.


YIIFSWA baseline studies conducted in 600 and 800 households, respectively in Ghana and Nigeria, indicated that only 3% and 10% households are headed by females in Nigeria and Ghana. Land was by far the major natural capital for small-holder farmers in yam-growing areas. The average farmland available was about 2.4 ha in Nigeria and 2.7 ha in Ghana. Priority has been given by households to yam over other food and cash crops. The areas under yam cultivation are generally small and the primary objective of small-holder farmers is to meet subsistence needs.

To develop the capacity of farmers organizations (FOs) by linking them to service providers (SPs) that would offer demand-driven services, a profiling exercise was conducted on 77 and 44 FOs and 40 and 17 SPs in Nigeria and Ghana, respectively. Overall, the performance indicators revealed that the selected FOs in Nigeria performed better than the ones in Ghana, in terms of quality of governance, internal management, value chain management, and marketing strategy. However the selected Nigerian FOs performed poorly, compared to Ghana counterparts, in the internal management and operations indicators.


Over 90% of the farmers use tubers harvested from the previous season as ‘seed yam’ or sourced from local markets, which are of poor quality due to pest and disease attack and lack of seed yam replacement. To improve the quality of farmer-saved seed yam, two NGOs—the Missionary Sister for Holy Rosary (MSHR) in Nigeria and Catholic Relief Services (CRS) in Ghana—have taken on the responsibility to train yam growers on seed yam multiplication using minisett technique combined with seed treatment to protect them from nematodes and fungal attack. So far, about 16,784 farmers were trained in Nigeria and Ghana.


The seed and ware yam sanitation challenges were also tackled. Surveys were conducted to identify pest and disease prevalence to establish appropriate strategies to control biotic threats to seed yam and ware yam. Virus diagnostics has been simplified to detect major yam-infecting viruses, Yam mosaic virus (YMV), Yam mild mosaic virus (YMMV), and Cucumber mosaic virus (genus, Cucumovirus), through a multiplex PCR-based assay.


Breeder seed yams produced in 2012 by Crops Research Institute (CRI) in Ghana and National Root Crops Research Institute (NRCRI) in Nigeria were handed over respectively to the Grain and Legume Development Board (GLDB, Ghana) and National Agricultural Seeds Council (NASC, Nigeria) for generation of foundation seed yam.


The breeder seed yam under production in 2013 is 0.8 ha and 0.5 ha, respectively for Nigeria and Ghana. GLDB has taken the challenge in Ghana and has a 1.5-ha foundation seed production site at Afraku (Ashanti region); while in Nigeria NASC selected two private seed companies (Greengold Construct Nigeria Ltd. and Romarey Ventures Nigeria Ltd.) that were engaged in foundation seed yam production for the first time.


New techniques such as aeroponics and temporary immersion bioreactors systems (TIBS) were effectively established at Ibadan. Results of experiments on the use of aeroponics system were encouraging for both pre-rooted planted and direct planting of vine cuttings of D. rotundata and D. alata. The successful growth of yam on the aeroponics system is reported for the first time with production of microtubers and mini-bulbils.


The TIBS is reported on yam in general, and in only one article for D. rotundata. YIIFSWA established a TIBS running on automated computer system with remote control through Internet. The 128 units of TIBs can produce a minimum of 12,800 plantlets per cycle. The running of the TIBs and the aeroponics systems for breeder or foundation seed yam production will speed up the generation of initial stocks of seed yam to supply the formal seed system.


Integrating available technologies, local and improved varieties to increase yam productivity is also another key objective of the project. Improved varieties with good performance in low soil fertility and drought stressed environments, and in staked and no staked system have been identified (table). The integration of landraces with seed selection and treatment, effective weed control, fertilizer application under no-stake system has indicated yields of 50% above the local technology. Studies have also determined that choice of yam varieties could be same for both men and women farmers and sometimes preferences differ.


For an effective operational seed system the capacity building of the players is key. To that effect national training workshops were organized: breeder and foundation seed production training workshop in Ghana and Nigeria; seed yam quality management protocol (QMP), yam virus disease diagnostics. In addition many partners (NASC, GLDB, CRI; SARI, CRS, MSHR, etc.) have organized training workshops for different stakeholders mainly on minisett technique for yam propagation.


Conclusions

In 24 months of project implementation, significant results were achieved on baseline studies, value chain analysis, farmers’ organization profiling, farmers training, and participatory selection of new genotypes. New techniques on high ratio propagation (aeroponics and TIBS), novel methods to develop virus-free planting materials, and the multiplex RT-PCR test for simultaneous detection of major viruses infecting yam, were successfully established. The formal seed yam system has been initiated and training have started. These initial successes are expected to pave a way to tackle greater challenges confronting the seed yam sector in West Africa.