Food for Thought: Genetic Gains in Banana and Plantain Breeding in Africa

Africa planted 6.3 million ha with bananas and plantains equivalent to 57.9% of the global 10.9 million ha used for these crops. The continent produced 48.2 million tons of the favorite fruit worldwide or 30.4% of the total global harvest of 158.4 million tons, with an average yield of 7.6 t/ha versus a world average of 14.6 t/ha in 2019. The harvests for both fruit crops are primarily from relatively small field plots or household backyard gardens. Pathogens, pests, declining soil fertility, human population pressure, changes to work or reduced labor supply, among other factors, account for the relatively low productivity noted in both banana and plantain. Their main diseases are black Sigatoka leaf spot (or black leaf streak), fusarium wilt, and bacterial wilts, while insects such as banana weevil and parasitic nematodes are the main pests.

These giant, perennial herbs, which belong to the genus Musa, are grown year-round in West African lowlands and East/Central African mid-altitudes and highlands, which are secondary centers of global diversity for the triploid (2n = 3x = 33) plantain and East African highland banana cultigens, respectively.  There are five clone sets among East African highland banana; namely, Nfuuka, Musakala, Nakabulu, Nakitembe, and Mbidde. They are defined by bunch type plus orientation, fruit size plus shape, male bud tip, and floral bracts in the male inflorescence rachis of the first four clone sets, while the cultivars of the last have a bitter and stringent pulp that shows sticky brown excretions. Inflorescence type and fruit number plus size define plantain sub-groups; i.e., French, French Horn, False Horn, and Horn plantains, which are further subdivided by pseudostem height and leaf number into giant (> 38 leaves), medium, and small cultivars (< 32 leaves).

The key goal for the crossbreeding of banana and plantain is to release sterile triploid hybrids after the recombination of fertile cultivars and species that meet farmers’ needs and consumers’ demands, showing host plant resistance to pathogens and pests. Although the breeding of banana cultivars for the export trade began about a century ago in Trinidad, most banana export cultivars grown today are still selections from somatic mutants of the group Cavendish, which show a very narrow genetic base as noted following DNA fingerprinting.

Banana and plantain crossbreeding is a technically challenging undertaking because several hurdles delay the rapid breeding progress. These include low reproductive fertility, triploidy, slow propagation, space (6 m2 per plant), and time (2 years from seed to seed) necessary for bringing new hybrids into the field for testing and selection. It takes about 1000 seeds, produced after more than 1000 hand pollinations of 200 plants (0.12 ha), to obtain one selected tetraploid plantain-banana hybrid per year. Nonetheless, in 1987, the International Institute of Tropical Agriculture (IITA) began breeding hybrid plantains with black Sigatoka resistance and high yield potential in its High Rainfall Station (Onne, Rivers State, Nigeria). The main outputs of this endeavor have been the release of tetraploid (known by the acronym PITA) or secondary triploid (TM3x) plantain hybrids that are grown today in West Africa (e.g., ‘PITA 3’ in Côte d’Ivoire or ‘PITA 14’ in Nigeria) and elsewhere in the tropics (including the tetraploid banana hybrid ‘BITA-3’). The bred germplasm’s cost-benefit impact was estimated as 10:1 over fungicides during periods of adequate production. This advantage may decrease to 5.5:1 during scarcity periods that dramatically influence plantain prices in Nigeria. Likewise, diploid-derived plantain (TMP2x) and banana (TMB2x) hybrids were released as pre-breeding germplasm for use in breeding, e.g., to develop the East African highland secondary triploid matooke banana hybrids known as NARITAs. These hybrids ensued from a joint enterprise between the National Agriculture Research Organization of Uganda (NARO) and IITA beginning in 1994. NARITAs are being grown today in Uganda and will soon be released in Tanzania.

Plant breeding programs must deliver high rates of genetic gain (ΔG) to address Sustainable Development Goal 2, “Zero Hunger,” of the UN’s Agenda 2030 due to the continuous demand for more food under a changing climate. The One CGIAR crop breeding programs aim to deliver above 1% of genetic gains resulting from testing and selection.  Using available breeding trial data from IITA and partners, genetic gain per cycle for bunch weight (a proxy for total yield) were estimated. The selection cycle time (from seed to seed) was different for plantains and matooke bananas. For example, it took 5 years from the cross of a plantain cultivar (C0) to the release of the TMPx (C1), and a further 5 years for releasing TM3x (C2) through germplasm registrations (placing in the public domain) in the journal HortScience during the 1990s. From the available matooke cultivars, prior crossbreeding (C0) to primary tetraploid hybrids (C1) took 10 years and from C1 to secondary triploid bred-germplasm (C2) or NARITAs it also took another 10 years. Thus, the estimated genetic gains per year for matooke bananas and plantains are 1.4% and 2.5%, respectively. The latter was adjusted to 2.1% when considering breeding trials of TM3x released in the early 2000s and grown in the Nigerian plantain belt. Supplementary information and data are provided here.

As noted by the late Dirk R. Vuylsteke, who together with Banana Breeder Rony Swennen began Musa crossbreeding in Africa during the second half of the 1980s, “A broad-based, improved Musa germplasm with pest/disease resistance will be a major component to achieve sustainable production of this vegetatively propagated, perennial crop. Such germplasm can be produced through conventional crossbreeding, enhanced by the utilization of innovative methods for the introduction of additional genetic variation. Also, the increased use of molecular markers will accelerate the process of recurrent selection of improved Musa germplasm and, hence, facilitate the development of new hybrids. The prospects of banana and plantain breeding are unlimited and increased efforts will at once initiate a new phase of Musa evolution.”

Author: Rodomiro Ortiz, Swedish University of Agricultural Sciences

Data sources

Aba, S.C., P.K. Baiyeri & R. Ortiz. 2021. Soil fertility dynamics and yield responses of four plantain genotypes to different nutrient management systems in Nsukka, southeastern Nigeria. Fruits. In press.

Batte, M., B. Uwimana, R. Swennen, A. Brown, H. Persson Hovmalm, M. Geleta & R. Ortiz.  2019.  Heterobeltiosis in banana and genetic gains through crossbreeding.  International Tropical Agricultural Conference (TropAg). Brisbane, Australia, 11–13 November 2019. Proceedings 36, 193; https://doi.org/10.3390/proceedings2019036193

Ortiz, R., D. Vuylsteke, H.K. Crouch & J. Crouch. 1998. TM3x: triploid black sigatoka resistant Musa hybrid germplasm. HortScience 33, 362–365.