Banana breeding activities aim at broadening the genetic base of the East African highland banana (Musa spp., AAA) and "Pisang awak" cooking/beer banana (Musa spp., ABB) gene pools. Through breeding strategies, we develop improved genotypes and populations and select better cultivars with host plant resistance to diseases and pests, high and stable yield, improved agronomic traits, and acceptable fruit quality. There are different Musa breeding schemes adopted by various institutions. A simplified Musa breeding scheme used at IITA is shown below (Fig. 1). In this scheme, triploid varieties are crossed with wild diploids to produce tetraploids (4x) with the desired characteristics. The tetraploids are crossed with improved diploids to produce triploid hybrids.

Musa germplasm collection, maintenance, and characterization

Genetic diversity available from indigenous and exotic germplasm can be used to introduce new useful traits and create new gene combinations. This can contribute to the development of hybrids that are high yielding, and disease- and pest-free. The East African highland banana germplasm does not have genes that are resistant to the major pests and diseases of banana. Enlarging, preserving, and documenting the characteristics of new germplasm is the first research agenda point in IITA’s banana breeding program (Fig. 2). Different plants are assessed for their agronomic traits, and resistance to the major diseases and pests of banana.

Breeding for black sigatoka resistance in bananas

Of all the fungal leaf diseases affecting banana, back sigatoka is considered the most important disease throughout the world. Although chemical control of black sigatoka is possible, it is expensive and not suitable for small-scale farmers. The production and cultivation of resistant cultivars is generally considered as the most appropriate intervention for controlling black sigatoka. IITA has been developing plantains and East African Highland bananas hybrids with resistance/tolerance to black sigatoka for many years. Consequently, 14 black sigatoka-resistant plantain hybrids have been registered and placed in the public domain and a number of East African highland banana-derived hybrids with resistance to black sigatoka are being evaluated in farmer’s fields in Uganda. Some of these hybrids are also resistant to plant-parasitic nematodes and banana weevils.

Effect of varietal mixtures on incidence and severity of black sigatoka

Black sigatoka is one of the most destructive diseases of bananas worldwide and has been reported to cause 30–40% yield reductions. Development and deployment of resistant varieties has been reported to be the most feasible and sustainable strategy to control the disease for the resource-poor farmers. Research in other crops has shown that growing susceptible genotypes in a mixture with resistant genotypes reduces severity and disease spread. This phenomenon is now being investigated in banana at IITA. Three IITA black sigatoka resistant hybrids, 7798S-2, 9494S-10, and 9750S-13, and one susceptible landrace, Mporogoma, have been planted in a mixture, and the incidence and severity of black sigatoka are being monitored.

Field assessment of banana genotypes resistant to Fusarium wilt

Fusarium wilt is a serious threat to the production of exotic bananas in the East African region. It affects mainly "Sukali ndizi" (AAB), a dessert banana, and "Pisang awak" (ABB), an important cultivar for beer making. "Sukali ndizi", or apple banana, has a potential as an export commodity for Kenya and Uganda. Host resistance has been reported to be the most effective, economic, and practical long-term option for managing Fusarium wilt. Therefore, field screening for resistance to Fusarium wilt is worthwhile. Different cultivars respond differently to the disease, and only a few cultivars exhibit high levels of resistance to Fusarium wilt.

Germplasm screening for Xanthomonas campestris pv, Musacearum

Banana bacterial wilt (BBW), caused by Xanthomonas campestris pv, Musacearum (Xcm), is the most devastating disease emerging in the East African region. Wilting and premature ripening of the fruits are some of the typical symptoms of the disease. Initially identified in Ethiopia, the disease emerged in Uganda in 2001 and has been identified in Rwanda and the Democratic Republic of Congo. It now threatens Kenya, Tanzania, and Burundi. In response to the BBW threat, the banana breeding program of IITA set-up trials to screen different banana (elite and local) genotypes in the disease "hot spot" area in Mukono district. Differential reactions have been observed among the genotypes (Fig 3). Most of the genotypes rapidly succumbed to the disease, while a few did not. In a few cases, some genotypes recovered from the disease. The response of some genotypes to the disease and their subsequent recovery is quite remarkable, warranting further investigations.

Testing a technique for screening banana hybrids for resistance against banana weevils

The banana weevil (Cosmopolites sordidus) is the most important insect pest constraining banana production in East Africa. The development of resistant cultivars is seen as the long-term and more sustainable control strategy for banana weevils. Breeding for resistance to banana weevils has however not featured prominently in any breeding program. This is probably because of the absence of good sources of resistance, and lack of a simple screening method for banana weevil resistance, preventing breeders to rapidly pinpoint resistance across the germplasm available. The crop has a long growth cycle and therefore needs quick yet reliable methods of screening. Therefore, a rapid bucket screening method is being evaluated using three known resistant and three known susceptible banana cultivars (Figs 4 and 5). Preliminary findings show that the method is promising and can be adopted for use.

Breeding for drought tolerance in bananas

Drought is one of the most serious constraints to agriculture and is responsible for substantial losses in crop yield. The majority of the farmers especially in the developing countries rely solely on rains for agricultural production leading to unpredictable yield. Growing cultivars with drought tolerance and using proper production practices can mediate the impact of drought on production. Banana, being a food security and income-earning crop, needs to be bred for drought tolerance. Different banana genotypes, such as East African highland landraces; Cavendish bananas; and diploid, triploid, and tetraploid hybrids, were planted in the semi-arid district of Soroti in eastern Uganda to evaluate their drought tolerance (Fig. 6). Genotypes that will show tolerance to drought stress will be selected for advanced evaluation and consequently used for breeding purposes.