Growing banana from “seeds”

Bananas are an important crop for global trade and nutrition where they are intensively cultivated, but few efforts exist to breed superior bananas. One of the reasons for this is that humans have intensively “selected” against seeded bananas and it is difficult or impossible to pollinate many banana varieties and successfully produce seeds.

Finding seeds in breeding plots in Namulonge, Uganda. Photo by IITA

Many of the most important banana varieties are triploid, which means that they carry an extra copy of each chromosome compared to the normal diploid. Being a triploid means that it is difficult for normal chromosome pairing and segregation to make fertile eggs or pollen, which results in most triploids being nearly sterile. Sterile bananas are great for people who don’t like to crack their teeth on banana seeds, but mean that bananas have to be multiplied via vegetative propagation, similar to propagation of potatoes, sweet potatoes, cassava, and selected varieties of other fruit trees or ornamental species.

Gardeners are familiar with “seed potatoes,” small potato tubers that are planted to produce a potato crop. Bananas do not form tubers; new plants derive from “suckers” that emerge from the lower banana stem (corm). These suckers can be uprooted and used to plant new banana plants. Similar to potato tubers, these suckers were a part of the original mother plant, which means that they potentially carry whatever disease pathogens or pests had infested the mother plant. Therefore, banana suckers are one of the main means of transport and spread of certain disease-causing agents, including important fungi, bacteria, and viruses.

Nematodes and pests can also hitchhike on banana suckers to infest the new crop. Not only does such hitchhiking result in early infection/infestation of new banana plants in a farmer’s field, but transporting long distances may help introduce a new disease or pest problem in a new location. This dual hazard of reduced yield potential of already infected planting material that may introduce new pests and diseases emphasizes the need for superior disease-free planting material produced through a “seed system” designed to minimize the risks of spreading pathogens and pests.

Banana bicycle transport, Burundi
Banana bicycle transport, Burundi. Photo by IITA

The traditional means of obtaining banana planting material (“seed”) is to acquire suckers from one’s own banana garden, from a neighbor, or from a more distant source. This method served to spread common varieties around the world and to multiply them in their new locations. This system can be modified to produce more banana suckers or shoots by manipulating banana corms to allow more buds to sprout. One such method that is described here is called macropropagation. A higher tech procedure to rapidly produce many plants in just a few generations of propagation is called tissue culture. In tissue culture, plants are first surface sterilized and then grown in aseptic culture in test tubes using an artificial growth medium based on a gelling agent like agar. The tender tissue-cultured plants can then be planted in the field after rooting and hardening under protected conditions.

Seed systems for producing clean planting material can be operated at various levels of technology and efficiency. In some cases, plant health could be improved by merely raising the awareness of the negative impact of planting “sick” suckers. Where infected plants look visibly different from healthy plants, either because of reduced vigor or visual disease symptoms in infected plants, the propagator could practice negative selection against “sick” plants or positive selection for “healthy” plants (or both). Such plants could be multiplied faster by applying a rapid propagation method such as macropropagation. However, while low-tech and affordable for farmers, such a system does not eliminate problems that cannot be detected by visual observation. Unfortunately, many diseases and pests fall into this category for at least part of their infection cycle.

For crops such as cereals, seed certification systems were developed to assure varietal purity, and later expanded to include freedom from weed seeds and seed-transmitted pathogens. Since most pathogens are seed-transmissible for vegetatively-propagated crops like potato or banana, disease management is the major focus of most seed potato certification programs and banana multiplication programs. Modern technology has provided diagnostic tests to detect significant pathogens. These tests are similar to those used in modern laboratories to diagnose human diseases, and can be expensive. For this reason, it is more efficient to test a small number of plants and multiply those that were negative for all pathogens tested in the battery of diagnostic tests.

It is possible to use tissue culture to efficiently and rapidly multiply plants that tested “clean” in the pathogen testing. Most potatoes eaten in the Western world are just a few field generations removed from tissue-cultured plants used to produce “seed potatoes” in screened glasshouses to start the seed production cycle. Similarly, most dessert bananas in the global export trade are from plants originally propagated in tissue culture from plants that tested clean for known banana diseases. A modified form of tissue culture can also be used to eliminate pathogens from plants that did not test clean, after which they can be propagated to produce “seed” planting material. There is great potential to improve the health of banana plantations in the developing world through increased use of this technology.

Tissue culture is the process of growing plants that have been surface sterilized and planted in test tubes or similar containers in sterile medium that contains all the nutrients they need to grow. This is almost always done in indoor laboratory facilities and the medium also contains the sugars needed to grow, since there isn’t enough light for photosynthesis.

Sanitation is extremely important, since a single mold spore is enough to contaminate a test tube. Tissue-cultured plants are generally tested for pathogens before commencing the multiplication cycle so that infected plants are not multiplied. The small banana plantlets produce small suckers that can be detached and planted as new plants, or an experienced technician can cut sections that contain buds that will grow. Extra shoots can sometimes be induced by cutting through the growing points so that multiple plants develop from single buds. This process can be repeated every 5-8 weeks so that a single plant can produce many new plantlets in a relatively short period of time.Bananas are sometimes unstable in tissue culture and mutant versions can develop. For this reason, most multiplication labs try to limit the number of multiplication cycles before renewing their cultures from field plants observed to have all the correct traits for that variety.

When tissue-cultured plants are rooted in soil, hardened, and then planted back in the field, they can be more susceptible to some pests and diseases than the original plant was. To restore natural levels of resistance, these plants can be reinfected with the endophyte microorganisms that normally coexist with bananas, similar to the gut bacteria that are important for human intestinal health (see related article on endophytes).

Macropropagated banana plant in chamber. Photo by IITA

Macropropagation falls somewhere between tissue culture and traditional systems of distributing suckers. In macropropagation, large suckers from healthy banana plants are removed and the roots and soft stem portion (pseudostem) of the sucker are cut away to expose the buds of the corm (the hard stem portion at the base of the sucker). The bare corms are briefly dipped in boiling water to kill any nematodes (micro-worms) that were not removed when cutting off roots. Small cuts are made through the buds to encourage development of multiple sprouts from each bud. The apical (top) bud is often removed because it can suppress development of lower buds. The corm is then covered with moist wood shavings and incubated in a small plastic-covered chamber for a few weeks to encourage shoot development.

Primary shoots can be rooted and used as planting material, or cut off and the growing point again cut to promote additional shooting. Shoots that develop are broken off with a bit of hard stem and roots attached, placed in small nursery bags in a similar high humidity chamber for a few days to allow root development, and finally moved to a nursery for hardening. Hardened plants can be planted in the field, similar to suckers or hardened plants from tissue culture.

Banana roadside market in rural southwest Uganda. Photo by IITA
Banana roadside market in rural southwest Uganda. Photo by IITA

A major drawback of macropropagation is that rustic or low-tech methods of detecting pathogens have not been developed, so this method can propagate infected plants if they were chosen as mother plants. Both macropropagated plants and tissue-cultured plants have less food reserves than suckers and require more care (compost/manure, watering) after planting than suckers. Careful siting of “mother gardens” established from tissue-cultured plants in clean areas may be the best way to produce suckers for macropropagation.

Traditional seed systems have produced most of the nearly 6 billion banana and plantain plants in Africa currently spread over nearly 4 million hectares of farm and gardens. Many of these are in excellent condition; others have become infected with one or more banana diseases and need to be replaced. Since new banana diseases have been introduced to Africa in the last century, and many diseases have increased in distribution and prevalence, greater care needs to be practiced to multiply “healthy seed”.

Breeding programs are nearly ready to release new varieties with resistance to some of the disease problems.

A combination of new and old seed systems can improve the overall health of new plantings by providing healthy plants of both preferred older varieties and resistant new varieties.

IITA’s research on macropropagation is supported by the Directorate General for Development Cooperation (Belgium) and Agricultural Productivity Enhancement Program (APEP-USAID) Uganda Agricultural Productivity Enhancement Project.

Banana and Plantain Systems

Bananas drawg
Grown by smallholder farmers, bananas and plantains are major food staples and two of the leading cash crops, both in the East African Great Lakes zone and the West African humid lowlands. Diverse banana cultivars are grown for a number of uses, including brewing (juice bananas), cooking and roasting, as well as sweet dessert bananas. Banana starch, flour, and chips are processed banana products whose markets are yet to be fully developed. Because of its cash crop status, farmers are more likely to adopt high-level management technologies in order to intensify production and yet sustain the natural resource base in the systems. Clearly, much progress can be realized with more profitable and sustainable banana systems.

Since the 1970s, reports of low and declining banana yields have been widespread. Some have attributed this phenomenon to constraints such as soil degradation, pests, poor crop husbandry, and drought. In this project, the hypothesis is that these constraints are, to a large extent, interlinked. Although each constraint can, on its own, potentially cause serious yield decline, the complex interactions between a number of them compound yield losses.

The overall purpose of the banana and plantain project is to enhance the performance of banana and plantain systems within smallholder farms in sub-Saharan Africa.

The main project objectives are:

  • To increase knowledge on ecosystems, social systems, and commodity chains related to banana and plantain production in
  • To research ways to improve profitability of banana and plantain systems in Africa
  • To improve the quality of banana- and plantain-based food products

Erostus Njuki Nsubuga: Lessons on partnership

AGT CEO and Managing Director Erostus Nsubuga
AGT CEO and Managing Director Erostus Nsubuga

R4D Review interviewed Erostus Njuki Nsubuga, the chief executive officer and managing director of Agro-Genetic Technologies Ltd (AGT), to get his insights on the IITA-AGT partnership. AGT is the first and only private commercial tissue culture (TC) laboratory in Uganda and so far the biggest single supplier of banana TC planting material in East and Central Africa. It produces up to 8 million tissue culture plantlets per year, of which 1 million are banana plants.

Nsubuga wants to see AGT become well established and profitable by increasing its capacity to provide the region with quality TC planting material at affordable prices and introducing other services such as plant and soil analysis, and produce organic fertilizers. His dream is for AGT to become a one- stop shop that provides total solutions to farmers.

Nsubuga was born in Uganda and spent his early years there. Because of the war, he and his family had to move to other countries in Africa and Europe. He started living on his own at 16, studying in Europe and USA for 24 years to obtain an MSc (Agriculture) and MBA (International Marketing). He worked in international companies and managerial positions for over 20 years but his dream was always to come back, to help his mother who had survived all the wars, to sustain himself and his family, and to contribute to the development of his people and country.

What made you establish AGT?
I had completed one contract and was about to start a new job when I decided to start a TC laboratory at my house. I employed and trained two people to produce TC plants out of my kitchen while I was traveling. At that time (2001–02) banana and coffee wilt diseases were spreading like wildfire in Uganda. It was easy to start with these two crops as there was great demand for disease-free planting material to reduce the spread of diseases and restore healthy plantations. Over time, using my own finances, AGT built a state-of-the-art TC facility and we grew significantly. Our technical team now includes five university graduates and a retired professor. Degree students from Makerere University have been doing their internships at AGT’s laboratory with their programs embedded in our production line.

How did the AGT and IITA partnership come about?
It started when Dr. Thomas Dubois called me out of the blue. IITA was looking for a commercial enterprise to start testing and producing its endophyte-enhanced plants. Under a mutual agreement, AGT and IITA have worked on fine-tuning the enhancement of TC plants with endophytes. We identified and established on-farm trials together, using the same farmers. In the short run, IITA assisted us with laboratory chemicals and AGT also benefited from publicity. In the longer run, production of endophyte-enhanced TC material would be greatly beneficial to AGT and other commercial producers in the region. Now that the original project has expired, we are trying to get this unique product commercialized to supply farmers facing high pest and disease pressure.

Please give some insights on public-private collaboration.
Collaboration can be very important in developing and disseminating research products. For IITA, it has forced them to think commercially from the onset. A good example has been the experimental protocol for endophyte inoculation. After piloting it in my lab, IITA quickly abandoned the use of a nutrient solution in favor of fertilizer-amended soil along the lines of the system used in commercial nurseries. Such partnerships should be developed as early as possible, especially for a technology such as this. This would help AGT to build up its technical, human, and financial capacity to take on the research products once they reach commercialization. Also a very clear agreement has to be drafted and this is sometimes a balancing act.

How could IITA improve its relationship with the private sector?
AGT indicated to IITA that it was open to other research products but wanted to be involved at an early stage. This is what we call a demand-driven research agenda where the consumer is sure of getting research products through private sector involvement. We are now backstopping a socioeconomic study looking at full commercialization of our nurseries in Uganda and Rwanda. At present AGT sells mainly through NGOs and institutions. Direct marketing to farmers would be better.

What lessons have you learned from the partnership with IITA and others?
It is great that research organizations such as IITA have realized the role of private sector involvement in agricultural research and in the product value chain. Such partnerships are relatively new and we still have much to accomplish. Personally, I feel many governments and international research institutions, even IITA, are working too much for the donors, not the farmers. We should tell the donors what needs to be funded. More impact assessment is needed on some research products.

Any suggestions for future collaboration or collaborators?
I hope IITA can do more demand-driven research by including the private sector in the development of research products as early as possible with specific roles for each partner clearly defined.

What do you think makes AGT successful?
I have a professional approach and commitment, with many years of experience in agriculture and entrepreneurship and good relationships, local and international. AGT started when diseases such as banana bacterial wilt and coffee were at their peak, so I was in the right place at the right time.

How else could development organizations and private entities such as AGT help farmers and consumers?
AGT is getting farmers involved in production, distribution, and training by establishing banana nurseries and demonstration gardens owned by local farmers. The farmer then becomes the AGT distributor for that community and the nursery the focal point for training others in modern agricultural practices.

What is your dream for Uganda?
Uganda is the second largest producer but seventy-fifth in banana exports. The Government and all development partners should industrialize this crop and thus lift many out of poverty.

Any thoughts about the world food crisis, food security, GMOs, or development in general?
African countries are the poorest in the world today with many problems. We urgently need biotechnology tools, including GMOs, to address problems. We should not waste time blaming others for creating poverty and hunger but make efforts ourselves to get out of the rut. I still have far to go but I am contributing to the well being of farmers in Uganda and the whole region.