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.