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Makerere University (2013)

Resistance to the African and spotted stem borers in sorghum in Kenya

Muturi, Phyllis Wambui

Titre : Resistance to the African and spotted stem borers in sorghum in Kenya.

Auteur : Muturi, Phyllis Wambui

Université de soutenance : Makerere University

Grade : Doctor of Philosophy (PhD) 2013

Résumé partiel
Sorghum (Sorghum bicolor, L. Moench) is a key cereal crop to over 500 million people in semi arid tropics. Sorghum production in subsistence farming is low and ranges between 0.5– 0.8 t/ha compared to potential yields of 10 t/ha. Diseases, drought, insect pests and parasitic striga weeds are the most important causes of the low grain yield. Lepidopteran stem borers mainly Busseola fusca Fuller (Noctuidae) and Chilo partellus Swinhoe (Crambidae) are among the economically important insect pests of sorghum and maize in East Africa. Stem borers cause grain yield losses ranging between 15 % - 80% through leaf feeding, deadheart formation, exit holes and stem tunnelling damage. Considering multiple stem borer damage traits is useful since resistance to stem borers is quantitatively inherited thus selecting for resistance based on a single parameter would not be effective. Cultural strategies, biological control, as well as chemical pesticide application have been employed, but are either ineffective or uneconomical for resource constrained farmers. Host plant resistance is an economically viable strategy for stem borer management in cereal production. Sources of resistance to stem borers have been reported and the levels vary from low to moderate. Therefore, it is important to identify sorghum genotypes with higher levels of resistance and with different mechanisms of resistance to diversify the bases of resistance to these pests. In Kenya, little research attention has been accorded to indigenous economically important stem borers like B. fusca in cereals. The reason for chilo is because the pest is highly invasive and persistent and has expanded its distribution to areas where it had not been reported earlier. The objectives of this study were to (1) Identify sources of resistance to B. fusca and C. partellus in sorghum ; (2) Establish the mode of inheritance of resistance traits to B. fusca and C. partellus in sorghum and (3) Map quantitative trait loci associated with resistance traits to B. fusca and C. partellus in sorghum. The first study was conducted in two separate experiments in different agroecologies in Kenya. Evaluation of sorghum genotypes for resistance to B. fusca was conducted in the University of Nairobi, Kabete campus field station. Experiments to identify sorghum genotypes resistant to C. partellus were conducted at the Kenya Agricultural Research Institute (KARI), Kiboko.The reason for conducting these studies in these locations was that the pests causes epidemics on sorghum in these areas. The experiments were carried out in 2010 during long and short rain seasons. Seven East African commercial sorghum cultivars and twenty introduced cultivars from India were evaluated in this study. Test material was sown in α-lattice design, consisting of nine plots in three blocks, replicated twice. Rows were 2 m long and 0.75 m apart, and the spacing between plants within rows was 0.25 m. First instar neonates of B. fusca and C. partellus were obtained from the International Centre of Insect Physiology and Ecology (ICIPE), Nairobi. At 30 days after sowing, five plants in each row were tagged and artificially infested with five larvae/plant using a camel hairbrush. Data collected on percentages was arcsin transformed while that of counts was log transformed before analysis of variance.


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