Banana nectar as a medium for testing pollen viability and germination in Musa

A quick and reliable method for evaluating pollen quality is essential in a breeding program, especially in a crop such as banana that is characterized by high male and female sterility. In this study the germination and viability of banana pollen was evaluated in a sucrose solution and diluted banana nectar. Twenty banana accessions were used to evaluate pollen germination in the two media after 3 and 24 h. Nineteen genotypes (95%) showed significantly higher pollen germination potential (PGP) in diluted nectar than in 3% sucrose solution. The accession TMB2x 8075 - 7 showed no significant pollen germination in nectar and sucrose. Eleven genotypes (55%) showed significant increase in pollen germination by increasing the time of incubation whereas pollen germination for nine genotypes (45%) was not affected by increase in incubation time. Nectar from different banana clones influenced pollen germination suggesting a genotype effect for pollen germination in Musa

A screening method for banana weevil (Cosmopolites sordidus Germar) resistance using reference genotypes

The banana weevil (Cosmopolites sordidus Germar) is a serious pest in most banana-growing areas of the world. Host-plant resistance is considered to be the most feasible and sustainable method for itscontrol. However, a quick and effective method for screening banana genotypes for resistance against the banana weevil to facilitate selection and/or development of resistant genotypes is lacking. The objective of the study was to develop an early screening method for weevil resistance by using a set of reference genotypes. Three susceptible genotypes (‘Atwalira’, ‘Namwezi’ and ‘Kibuzi’) and three resistant genotypes (‘Calcutta 4’, ‘Yangambi Km5’ and ‘TMB3x1968-2’) were used in screen-houseexperiments to assess weevil resistance/susceptibility. Healthy plantlets of the above genotypes were established in buckets in a screen house. Ten adult weevils (5 females and 5 males) were introduced at the base of each plant and the bucket was covered with a weevil-proof mesh. Weevil damage of the corms was estimated as a percentage at 35 and 60 days after the weevil introduction by estimating the peripheral and cross-section corm damage. The resistant genotypes had significantly lower (p < 0.05)peripheral and total cross-section corm damage, and less larvae than the susceptible genotypes. These results indicated that these genotypes can be used as reference genotypes in evaluating resistance or susceptibility against the banana weevil. These experiments were completed in five to seven months, depending on the source of planting material, as compared to field-screening experiments for the banana weevil that can take up to three or more years

Ploidy level of the banana (Musa spp.) accessions at the germplasm collection centre for the East and Central Africa

Banana germplasm collections serves as a source of useful genes for banana breeding. However, insufficient and/or inaccurate information on the ploidy level of the germplasm renders its utilization in breeding difficult. The objective of this study was to determine and validate the ploidy level of 120 banana accessions in the ex situ germplasm collection centre for the East and Central Africa, located in Mbarara, Uganda. Flow cytometric analysis of the nuclear DNA content was used to determine the ploidy level of the accessions. Results indicate that accessions: Bura, Diana, Kambani-Rungwe, Paji and Pagatau, and Rungwe that were previously classified as diploids are actually triploids, whereas Selangor previously known to be a diploid is a tetraploid. Accessions such as Galeo, Mwitupemba and Ntindi 1 that were previously classified as triploids were found diploids. GT, FHIA 25 and Muzungu Mwekundu that were considered as tetraploids, were found triploids. The information generated will guide correct placement of these accessions in the regional germplasm collection centre for the East and Central Africa and their utilization in banana breeding

Banana Xanthomonas wilt: a review of the disease, management strategies and future research directions

Banana production in Eastern Africa is threatened by the presence of a new devastating bacterial disease caused by Xanthomonas vasicola pv. musacearum (formerly Xanthomonas campestris pv. musacearum). The disease has been identified in Uganda, Eastern Democratic Republic of Congo, Rwanda and Tanzania. Disease symptoms include wilting and yellowing of leaves, excretion of a yellowish bacterial ooze, premature ripening of the bunch, rotting of fruit and internal yellow discolorationof the vascular bundles. Plants are infected either by insects through the inflorescence or by soil-borne bacterial inoculum through the lower parts of the plant. Short- and long-distance transmission of thedisease mainly occurs via contaminated tools and insects, though other organisms such as birds may also be involved. Although no banana cultivar with resistance to the disease has been identified as yet,it appears that certain cultivars have mechanisms to ‘escape’ the disease. Management and control of the disease involve methods that reduce the inoculum’s density and spread of the pathogen. Removalof the male bud (de-budding) has proven to be very effective in preventing the disease incidence since the male bud appears to be the primary infection site. The economic impact of banana Xanthomonaswilt is not fully understood but its impact on food security in the region is very significant. While germplasm screening for the disease is ongoing, efforts to genetically engineer resistance in somebanana cultivars are also making good progress. This paper presents a review of the disease and management strategies that have been successful in curtailing its spread

Significant progressive heterobeltiosis in banana crossbreeding

Open Access Journal; Published online: 27 Oct 2020Background Heterobeltiosis is the phenomenon when the hybrid’s performance is superior to its best performing parent. Banana (Musa spp. AAA) breeding is a tedious, time-consuming process, taking up to two decades to develop a consumer acceptable hybrid. Exploiting heterobeltiosis in banana breeding will help to select breeding material with high complementarity, thus increasing banana breeding efficiency. The aim of this study was therefore to determine and document the level of heterobeltiosis of bunch weight and plant stature in the East African highland bananas, in order to identify potential parents that can be used to produce offspring with desired bunch weight and stature after a few crosses. Results This research found significant progressive heterobeltiosis in cross-bred ‘Matooke’ (highland cooking) banana hybrids, also known as NARITAs, when grown together across years with their parents and grandparents in Uganda. Most (all except 4) NARITAs exhibited positive heterobeltiosis for bunch weight, whereas slightly more than half of them had negative heterobeltiosis for stature. The secondary triploid NARITA 17 had the highest heterobeltiosis for bunch weight: 249% versus its ‘Matooke’ grandparent and 136% against its primary tetraploid parent. Broad sense heritability (across three cropping cycles) for yield potential and bunch weight were high (0.84 and 0.76 respectively), while that of plant stature was very low (0.0035). There was a positive significant correlation (P < 0.05) between grandparent heterobeltiosis for bunch weight and genetic distance between parents (r = 0.39, P = 0.036), bunch weight (r = 0.7, P < 0.001), plant stature (r = 0.38, P = 0.033) and yield potential (r = 0.59, P < 0.001). Grandparent heterobeltiosis for plant stature was significantly, but negatively, correlated to the genetic distance between parents (r = − 0.6, P < 0.001). Conclusions Such significant heterobeltiosis exhibited for bunch weight is to our knowledge the largest among main food crops. Since bananas are vegetatively propagated, the effect of heterobeltiosis is easily fixed in the hybrids and will not be lost over time after the release and further commercialization of these hybrids

Association genetics of bunch weight and its component traits in East African highland banana (Musa spp. AAA group).

Bunch weight increase is one of the major objectives of banana improvement programs, but little is known about the loci controlling bunch weight and its component traits. Here we report for the first time some genomic loci associated with bunch weight and its component traits in banana as revealed through a genome-wide association study. A banana-breeding population of 307 genotypes varying in ploidy was phenotyped in three locations under different environmental conditions, and data were collected on bunch weight, number of hands and fruits; fruit length and circumference; and diameter of both fruit and pulp for three crop cycles. The population was genotyped with genotyping by sequencing and 27,178 single nucleotide polymorphisms (SNPs) were generated. The association between SNPs and the best linear unbiased predictors of traits was performed with TASSEL v5 using a mixed linear model accounting for population structure and kinship. Using Bonferroni correction, false discovery rate, and long-range linkage disequilibrium (LD), 25 genomic loci were identified with significant SNPs and most were localized on chromosome 3. Most SNPs were located in genes encoding uncharacterized and hypothetical proteins, but some mapped to transcription factors and genes involved in cell cycle regulation. Inter-chromosomal LD of SNPs was present in the population, but none of the SNPs were significantly associated with the traits. The clustering of significant SNPs on chromosome 3 supported our hypothesis that fruit filling in this population was under control of a few quantitative trait loci with major effects

Banana nectar as a medium for testing pollen viability and germination in Musa

A quick and reliable method for evaluating pollen quality is essential in a breeding program, especially in a crop such as banana that is characterized by high male and female sterility. In this study the germination and viability of banana pollen was evaluated in a sucrose solution and diluted banana nectar. Twenty banana accessions were used to evaluate pollen germination in the two media after 3 and 24 h. Nineteen genotypes (95%) showed significantly higher pollen germination potential (PGP) in diluted nectar than in 3% sucrose solution. The accession TMB2x 8075 - 7 showed no significant pollen germination in nectar and sucrose. Eleven genotypes (55%) showed significant increase in pollen germination by increasing the time of incubation whereas pollen germination for nine genotypes (45%) was not affected by increase in incubation time. Nectar from different banana clones influenced pollen germination suggesting a genotype effect for pollen germination in Musa

The triploid East African Highland Banana (EAHB) genepool is genetically uniform arising from a single ancestral clone that underwent population expansion by vegetative propagation

East African Highland bananas (EAHBs) are a subgroup of triploid (AAA genome) bananas of importance to food security in the Great Lakes region of Africa. Little is known about their genetic variation, population structure and evolutionary history. Ninety phenotypically diverse EAHB cultivars were genotyped at 100 SSR microsatellite markers to investigate population genetic diversity, the correlation of genetic variability with morphological classes, and evolutionary origins since introduction to Africa. Population-level statistics were compared to those for plantain (AAB) and dessert (AAA) cultivars representing other M. acuminata subgroups. EAHBs displayed minimal genetic variation and are largely genetically uniform, irrespective of whether they were derived from the distinct Ugandan or Kenyan germplasm collections. No association was observed between EAHB genetic diversity and currently employed morphological taxonomic systems for EAHB germplasm. Population size dynamics indicated that triploid EAHBs arose as a single hybridization event, which generated a genetic bottleneck during foundation of the EAHB genepool. As EAHB triploids are sterile, subsequent asexual vegetative propagation of EAHBs allowed a recent rapid expansion in population size. This provided a basis for emergence of genetically near-isogenic somatic mutants selected across farmers and environments in East Africa over the past 2000 years since EAHBs were first introduced to the African continent