Inheritance of resistance to flower bud thrips (Megalurothrips Sjostedti) in Cowpea

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Flower bud thrips is a major pest of cowpea that causes significant grain yield losses. Chemical control measures are the most widely known form of control to this pest. However, the rapid development of insecticide resistance in thrips population has rendered the chemical treatments ineffective. The development of flower bud thrips resistant varieties is necessary to help curb the situation. Knowledge of inheritance of flower bud thrips resistance is required to accelerate breeding of resistant varieties. Inheritance of resistance to flower bud thrips in cowpea was studied in a cross involving resistant (Sanzi) and susceptible (Bengpla) genotypes, using generation mean analysis. The segregating generations were intermediate between the resistant and susceptible parents and were skewed towards the resistant parent. Reciprocal differences were not detected in the cross suggesting the absence of maternal effect. The results revealed a non-significant departure from zero for parameters A, B and C and a non-significant chi-square (χ2) for joint scaling test indicating adequacy of the additive-dominance model in explaining the mode of inheritance of resistance to flower bud thrips in cowpea. The additive-dominance model revealed that both additive and dominance gene effects contributed significantly to the inheritance of resistance to flower bud thrips suggesting the potential for further improvement of the trait using simple selection and hybridization procedures. Dominance gene effect was negative indicating dominance in the direction of the resistant parent. Negative heterosis over mid-parent was observed for thrips resistance score. Estimates of broad sense and narrow sense heritabilities indicated that environmental effects were larger than genetic effects. The results suggested the imposition of lower selection pressure in order to advance as many high-potential recombinants as possible in a hybridization programme.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Science in Agronomy (Plant Breeding), August-2012