Characterizing an f2 banana diploid population for identifying and validating molecular markers for weevil resistance

The banana weevil (Cosmopolites sordidus Germar) is the most important insect pest of banana and plantain in Africa. Most East African highland bananas (EAHB) are highly susceptible to it. Sources of resistance to most pests and diseases are known to come from wild banana diploids. There is thus a need to exploit the potential of wild banana diploids in improvement of East African highland bananas by studying genetics of resistance of inter diploid crosses that could be used to improve the EAHB. The objectives of this study were a) to identify segregating weevil resistance and agronomic traits in an F2 diploid banana population, b) to determine the inheritance of banana weevil resistance and agronomic traits based on an F2 banana diploid population and c) to optimise SSR markers for nematode resistance for characterizing an F2 diploid banana population against banana weevil resistance. Two diploid parents Musa acuminate Subspecies banksii (kasaska) susceptible to banana weevil and Musa acuminata Subspecies microcarpa (borneo) resistant to banana weevil were crossed to generate an F1 population from which one line was selfed to generate an F2 diploid population. The F2 population was screened against weevil resistance by artificial inoculation in a field where corm sections were inoculated with larvae at first instar and measurements taken for growth parameters after 8 days and in pot experiment where damage parameters were measured. Agronomic parameters were also studied for this F2 diploid banana population. There were significant differences (P<0.05) among the different genotypes for banana weevil resistance traits such as head capsule width (HCW), body length, body weight, larval mortality, total damage, peripheral damage, dead weevils and larvae retrieved. However, weevil damage parameters such as total cross sectional inner and outer damages and total cross sectional damage were non-significant. There were also significant differences (P<0.05) for agronomic parameters such as bunch weight, number of clusters, number of fingers, days to maturity, inner corm hardness and total corm hardness. However there were no significant differences (P<0.05) for number of functional leaves at flowering, number of functional leaves at harvest and youngest leaf spotted. The nature of inheritance for all the larval resistance traits and weevil damage parameters showed a possibility of quantitative inheritance. The chi square test of goodness of fit showed body weight to be in a ratio 15:1 when tested using both resistant and susceptible parents as checks; body weight in ratio of 7:9 with resistant parent as check and 15:1 with susceptible parent as check; larval mortality in ratio of 1:3 ratio with resistant parent as check and 15:1 with a susceptible parent as check; total damage in a ratio of 3:1 with resistant parent as check, peripheral damage in a ratio of 9:7 with resistant parent as check; larvae retrieved in a ratio of 3:1 and dead weevil in ratio of 1:3 tested using a resistant parent as check and 1:15 when using a susceptible parent as a check. Knowing the nature of inheritance of segregating diploid population will assist in improving the susceptible East African highland bananas (EAHB). Among the tested 33 SSR primers, 17 primer pairs amplified the DNA of the parental materials and the F1 progeny implying that they could be used in genotyping the developed diploid population especially under high resolution Gels such as Metaphor agarose or poly acrylamide gelelectrophoresis (PAGE). These markers will aid in early selections of desired cultivars which will shorten the breeding cycle and reduce on the breeding costs.