B. Uwimana

Trait variation and genetic diversity in a banana genomic selection training population

Banana (Musa spp.) is an important crop in the African Great Lakes region in terms of income and food security, with the highest per capita consumption worldwide. Pests, diseases and climate change hamper sustainable production of bananas. New breeding tools with increased crossbreeding efficiency are being investigated to breed for resistant, high yielding hybrids of East African Highland banana (EAHB). These include genomic selection (GS), which will benefit breeding through increased genetic gain per unit time. Understanding trait variation and the correlation among economically important traits is an essential first step in the development and selection of suitable GS models for banana. In this study, we tested the hypothesis that trait variations in bananas are not affected by cross combination, cycle, field management and their interaction with genotype. A training population created using EAHB breeding material and its progeny was phenotyped in two contrasting conditions. A high level of correlation among vegetative and yield related traits was observed. Therefore, genomic selection models could be developed for traits that are easily measured. It is likely that the predictive ability of traits that are difficult to phenotype will be similar to less difficult traits they are highly correlated with. Genotype response to cycle and field management practices varied greatly with respect to traits. Yield related traits accounted for 31–35% of principal component variation under low and high input field management conditions. Resistance to Black Sigatoka was stable across cycles but varied under different field management depending on the genotype. The best cross combination was 1201K-1xSH3217 based on selection response (R) of hybrids. Genotyping using simple sequence repeat (SSR) markers revealed that the training population was genetically diverse, reflecting a complex pedigree background, which was mostly influenced by the male parents.

Bananas and Plantains (Musa spp.)

Bananas and plantains are one of the most important crops in the world, yet very few hybrids are cultivated. Bananas face considerable pressure from multiple biotic and abiotic stresses, but its genetic improvement is impeded by constraints on seed set due to multiple physiological and reproductive issues. The triploid nature of almost all commercially important bananas requires a complicated breeding scheme involving cross hybridization across ploidy levels and results in poor seed set that reduces the probability of obtaining favorable recombination. The poor seed set is further complicated by issues of parthenocarpy and partial to complete female and male sterility that are not fully understood. While the introduction of genomic resources of this perennial long cycling crop promises to hasten the development of improved cultivars, there is a need to maintain vigorous and committed long-term international breeding programs.

Genomic Prediction in a Multiploid Crop: Genotype by Environment Interaction and Allele Dosage Effects on Predictive Ability in Banana

First empirical evidence of genomic prediction in a multi‐ploidy banana population is presented. The effect of allele dosage single nucleotide polymorphism on prediction accuracy depends on the trait. Use of averaged environmental data improves prediction accuracy. BayesB model can be used across all traits during genomic prediction in banana breeding. The high predictive values show the potential of genomic prediction in banana breeding.

Progress in understanding Pseudocercospora banana pathogens and the development of resistant Musa germplasm

No. 35. Elad Y, Pertot I, 2014. Climate change impacts on plant pathogens and plant diseases. Journal of Crop Improvement 28, 99–139. Escobar-Tovar L, Maga~ na-Ort ız D, Fern andez F et al., 2015. Efficient transformation of Mycosphaerella fijiensis by underwater shock waves. Journal of Microbiological Methods 119, 98–105. Ferreira CF, Silva SO, Sobrihno NP et al., 2004. Molecular characterization of banana (AA) diploids with contrasting levels of black and yellow Sigatoka resistance. American Journal of Applied Sciences 1, 276–8. Plant Pathology (2018) 67, 759–770 Pseudocercospora banana pathogens 767

Suitability of existing Musa morphological descriptors to characterize East African highland ‘matooke’ bananas

Morphological traits are commonly used for characterizing plant genetic resources. Germplasm characterization should be based on distinctly identifiable, stable and heritable traits that are expressed consistently and are easy to distinguish by the human eye. Characterization and documentation of a representative sample of East African highland bananas (Lujugira–Mutika subgroup) was carried out following an internationally accepted standard protocol for bananas. Eleven cultivars were characterized using an existing set of minimum descriptors (31 qualitative and quantitative traits) with the aim of determining stable descriptors and the ability of these descriptors to distinguish among East African highland banana cultivars. There was variation in stability of these descriptors within cultivars and across the 11 cultivars. Only 10 (32%) out of 31 descriptors studied were stable in the 11 cultivars. However, they had similar scores and therefore are not suitable to distinguish between cultivars within this group. Nonetheless, these 10 descriptors may be useful for distinguishing the East African highland bananas as a group from other groups of bananas. A few descriptors were unique to the cultivar ‘Tereza’ and may be used to distinguish this cultivar from other ‘matooke’ cultivars. None of the quantitative descriptors were stable.

Molecular and cytogenetic study of East African Highland Banana

East African highland bananas (EAHBs) are staple food crop in Uganda, Tanzania, Burundi, and other countries in the African Great Lakes region. Even though several morphologically different types exist, all EAHBs are triploid and display minimal genetic variation. To provide more insights into the genetic variation within EAHBs, genotyping using simple sequence repeat (SSR) markers, molecular analysis of ITS1-5.8S-ITS2 region of ribosomal DNA locus, and the analysis of chromosomal distribution of ribosomal DNA sequences were done. A total of 38 triploid EAHB accessions available in the Musa germplasm collection (International Transit Centre, Leuven, Belgium) were characterized. Six diploid accessions of Musa acuminata ssp. zebrina, ssp. banksii, and ssp. malaccensis representing putative parents of EAHBs were included in the study. Flow cytometric estimation of 2C nuclear DNA content revealed small differences (max ~6.5%) in genome size among the EAHB clones. While no differences in the number of 45S and 5S rDNA loci were found, genotyping using 19 SSR markers resulted in grouping the EAHB accessions into four clusters. The DNA sequence analysis of the internal transcribed spacer region indicated a relation of EAHB clones with M. acuminata and, surprisingly, also with M. schizocarpa. The results suggest that EAHB cultivars originated from a single hybrid clone with M. acuminata ssp. zebrina and ssp. banksii being its most probable parents. However, M. schizocarpa seems to have contributed to the formation of this group of banana.