The use of genetic engineering has transformed agriculture, and food production and development by providing options and solutions where none existed before—to the benefit of billions of the world’s inhabitants.

Tripathi discusses work with staff at Namuloge, IITA-Uganda. Photo by IITA

IITA and its partners have been using genetic transformation as a crop improvement tool to help produce more and better food staples. The Institute—with partners such as the National Agricultural Research Organization (NARO) of Uganda, Academia Sinica (Taiwan), and the African Agricultural Technology Foundation (AATF) in Kenya—is at the forefront of research “designing” a genetically modified banana that is resistant to the worst bacterial disease so far—Banana Xanthomonas Wilt (BXW). Entire banana fields can be destroyed, especially those planted to Pisang awak, a susceptible exotic variety widely grown to make banana beer.

Bananas are a major staple in East Africa produced mostly by smallholder subsistence farmers. Uganda is the world’s second leading grower with a total annual production of about 10.5 million tons. It is Africa’s biggest producer and consumer of bananas and plantains.

Most growers cannot afford costly chemicals to control the many pests and diseases that affect banana cultivation. As diseases continue to spread, demand grows for new improved varieties.

Bacterial wilt caused by Xanthomonas campestris pv. musacearum is threatening banana production and the livelihoods of these smallholder growers, and solutions have to be found fast before it could destabilize food security in the region.

Work on developing a GMO banana has been ongoing since BXW was first reported in 2001. The disease has been identified in the Eastern Democratic Republic of Congo, Rwanda, Kenya, and Tanzania, and is widespread in Uganda. It attacks almost all varieties of bananas, causing these countries an annual loss of over US$500 million. These can be reduced bunch weights or absolute yield loss or clean planting material is unobtainable for new plantations.

Banana Xanthomonas wilt-infected plants. Photo by IITA

“Developing resistant varieties is a long-term but more sustainable way to control pests and diseases. Improving the plant’s defense mechanism against BXW through genetic engineering is still the best line of defense because of its many advantages,” commented molecular geneticist Leena Tripathi based in IITA-Uganda, Kampala. “Farmers are reluctant to employ labor-intensive disease control measures.”

“Genetic engineering offers many opportunities for improving existing elite varieties not amenable to conventional cross-breeding, such as bananas. It allows breeders to develop new varieties quickly through the introduction of cloned genes into commercial varieties.”

Transgenic bananas possess a gene or genes that have been transferred from another plant species. The term “transgenic plants” refers to plants created in a laboratory using recombinant DNA technology.
Tripathi said that the development of stable and reproducible transformation and regeneration technologies has opened new horizons in banana and plantain breeding. The development of transgenic banana and plantain has been reported by several groups, but a commercial transgenic banana variety is yet to be released.

There are no cross-fertile wild relatives in many banana-producing areas. Most edible bananas and plantains are male and female sterile. The clonal mode of propagation makes the risk of gene flow from banana to another crop species not an issue.

IITA’s in vitro screening method for early evaluation of resistance to BXW uses small tissue culture-grown plantlets. This method can be used by breeders for screening Musa germplasm with larger numbers of cultivars for resistance to BXW and other bacterial diseases.

Currently, most transformation protocols for banana use cell suspensions, Tripathi said. Establishing cell suspensions is a lengthy process and cultivar dependent. At present, the major barrier in transforming East African Highland Bananas (EAHB), a cooking banana from Uganda, is the limited success in producing embryogenic cell suspension cultures from a wide range of cultivars. IITA scientists in collaboration with NARO have developed a rapid and efficient protocol using a cultivar-independent transformation system for improving Musa species including EAHB. This new technique has paved the way for the development of a transgenic banana using transgenes from sweet pepper that confer resistance against BXW.

Tripathi explains how the technology works: the ferredoxin-like amphipathic protein (pflp) and hypersensitive response-assisting protein (hrap), were isolated from the sweet pepper, Capsicum annuum. These are novel plant proteins that intensify the harpinPSS-mediated hypersensitive response (HR). These proteins have a dual function: iron depletion antibiotic action and harpin-triggered HR enhancement. The transgenes were shown to delay the hypersensitive response induced by various pathogens in nonhost plants through the release of the proteinaceous elicitor, harpinPss in various crops including dicots such as tobacco, potato, tomato, broccoli, orchids and monocots such as rice. Elicitor-induced resistance is not specific against particular pathogens, hence it is a very useful strategy.

The pflp genes encode for ferrodoxin, which exists in all organisms, and is therefore common in human diets. This protein is safe for human consumption and the environment. The pflp and hrap genes are owned by Taiwan’s Academia Sinica, the patent holder. IITA has negotiated a royalty free license through the AATF for access to the pflp and hrap genes for use in the production of BXW-resistant varieties in sub-Saharan Africa.

Hundreds of transformed lines of various banana cultivars have already been generated, and are under screening for disease resistance under laboratory conditions. The most promising will be evaluated for efficacy against BXW in confined field trials under different farming systems by national partners with IITA. The transgenic lines will be tested for environmental and food safety, in compliance with target country biosafety regulations, risk assessment and management, and seed registration and release procedures. The project will also study public perceptions, consumer preferences, and the acceptability of transgenic banana in Africa to guide commercialization and wide use.

“Wide-scale deployment of genetically modified, farmer-preferred banana varieties in African countries would succeed only with effective interinstitutional partnerships, particularly with advanced research institutions, AATF, national committees on biosafety, nongovernmental organizations, and private tissue culture companies,” explained Tripathi. “This project will enhance the capacity of partners from the national agricultural research and extension systems in genetic transformation of banana, molecular biology, and biosafety. High-yielding BXW-resistant banana will bring greater productivity for smallholder farmers in East Africa and improved food security.”