Another PhD for the Breeding Better Banana project as Michael Batte successfully defends his thesis

Michael Batte successfully defended his PhD thesis titled Increasing efficiency of the breeding pipeline for East African highland bananas on 4 June at the Swedish University of Agricultural Sciences (SLU) Alnarp campus. His studies were sponsored by the Breeding Better Banana project that is led by IITA as part of its capacity building program. This brings the number of completed PhD studies under the project to three.

The project seeks to strengthen banana breeding programs in Uganda and Tanzania and speed up the development of high-yielding and disease-resistant hybrid varieties of the East Africa Highland banana (EAHB). Its focus is on the two most popular cooking banana in the two countries—‘Matooke’ and ‘Mchare’ for Uganda and Tanzania, respectively.

Dr Batte works with IITA in Uganda and his main supervisor was Professor Rodomiro Ortiz from SLU, co-supervised by Dr Helena Persson Hovmalm and Dr Mulatu Geleta, also from SLU. At IITA, his co-supervisors were  Rony Swennen, Brigitte Uwimana, and  Allan Brown.

In his study, Batte looked at innovations to tackle the technical challenges of breeding banana that stem the crop’s low fertility, low seed germination, long selection cycle period, and large space requirement for field evaluation.
He also looked at innovations to improve the efficiency of banana breeding programs to quickly deliver to farmers improved banana, which are high yielding and resistant to production constraints to boost their livelihoods. He analyzed the practices that were used for the first 21 years of the banana breeding program of IITA in Uganda.

He focused on five approaches to tackle this challenge:

• An assessment of the available minimum descriptor list for suitability to characterize the EAHB germplasm.
• Analysis of crossbreeding data of EAHB for the first 21 years (from 1995 to 2015) at IITA as a basis for designing future interventions.
• Path analysis to determine a breeding ideotype for EAHB.
• Estimation of heterobeltiosis (hybrid vigor) for the NARITA hybrids (mostly secondary triploids ensuing from the 4x × 2x).
• Phenotyping a diploid banana population for resistance to the nematode Radopholus similis.

Of the 31 descriptors studied, 10 were found stable but had similar scores in EAHB cultivars and therefore it was not suitable to distinguish between them. The month of pollination did not result in significantly different pollination success, implying that pollination of EAHB can be conducted throughout the year. However, the seed set and rate of germination were still low. Thus, further research about seed production and germination is required.

Years of collaboration between IITA and the National Agricultural Research Organization (NARO) of Uganda had led to the successful development of the first ever hybrids of EAHB, named NARITAs. Twenty-seven NARITAs were selected for further evaluation in the East African region.

Path analysis undertaken in this study revealed that fruit length, circumference, number of hands, and plant cycle number had a direct positive effect on the bunch weight (a proxy for edible yield). Significant progressive, heterobeltiosis for bunch weight was found in all the NARITAs. Half of the NARITAs had negative heterobeltiosis for stature. The diploid population was found to segregate for resistance to R. similis with a phenotypic ratio of 9:3:4 suggesting recessive epistasis.

This research opens perspectives to make the breeding of EAHB more efficient and cheaper.