Stem borers, Busseola fusca (Fuller) Noctuidae, Lepidoptera and Chilo partellus (Swinhoe) Pyralidae, Lepidoptera, are serious insect pests of maize. However, genotypes showing exclusive resistance to each of these borers and with resistance to both species have not been identified in Kenya. The objective of this study was to evaluate tropical maize inbred lines for resistance to the two species. 112 maize inbred lines were artificially infested with the stem borers at three sites in Kenya. Each row of each line received three different treatments in different parts, namely infestation with B. fusca larvae, infestation with C. partellus larvae, and protection with beta 25 g/L cyfluthrin pesticide. Data was collected on leaf feeding damage rating, cumulative stem tunnel length, number of exit holes, number of dead-hearts, stalk strength and selected agronomic traits. There were significant differences among the test genotypes, (p<0.01) for resistance to B. fusca and C. partellus, for all the traits measured. The results also showed that most of the test genotypes were susceptible to B. fusca and less so to C. partellus. Twenty one (21) lines showed resistance to both B. fusca and C. partellus in at least two sites, and only four lines showed resistance to both species across the locations. Among all the test genotypes, 26 lines showed resistance to C. partellus only, while five entries had resistance to B. fusca only. Furthermore, 84 and 28 entries showed susceptibility to B. fusca and C. partellus, respectively. The others were categorized as either moderately resistant or moderately susceptible to either species. The identified inbred lines variously resistant to B. fusca and C. partellus may be used as parents in hybrid breeding programmes that emphasize stem borer resistance or as sources of resistance in breeding programs.
In Kenya, stem borers destroy an estimated 13.5% of farmers' annual maize harvest. Maize transformed using Bacillus thuringiensis (Bt) derived genes controls stem borers without negative effects to humans, livestock or the environment. The effectiveness and sustainability of Bt transgenic technology in the control of stem borers depends on the levels of concentration of the Bt δ-endotoxins in plant tissues. Kenya introduced Bt maize events to test the efficacy of Bt maize in controlling stem borers, and to develop high-yielding and locally adapted Bt maize germplasm for farmers. The objective of this study was to assess under greenhouse conditions the concentration levels of Bt δ-endotoxins in the leaf tissues of the parents, the F 1 , and the F 2:3 populations of tropical maize, as a measure of stability and sustainability. Kenya introduced Bt maize events to test the efficacy of Bt maize in controlling stem borers, and to develop high-yielding and locally adapted Bt maize germplasm for farmers. The objective of this study was to assess under greenhouse conditions the concentration levels of Bt δ-endotoxins in the leaf tissues of the parents, the F1, and the F2:3 populations of tropical maize, as a measure of stability and sustainability. Two public Bt maize lines (Event 216 and Event 223) containing the cry1Ab::ubi gene were crossed with two non-Bt maize inbred lines, CML144 and CML159, to assess how the concentrations of Bt δ-endotoxins are transmitted from parents to F 1 and to F 2 generations. The mean concentration of Bt δ-endotoxins (μg/g) was 4.93 and 4.63 in Events 216 and 223 respectively. As expected, F 1 generations of all the crosses had similar concentrations of Bt δ-endotoxins. However, the F 2 generations showed a spread of concentrations. These findings may imply that genotypes with a higher mean concentration of Bt δ-endotoxins also have a lower level of plant damage traits expressed. In addition, these observations indicate that the cry1Ab gene was dominant and was inherited following the Mendelian segregation and that Events 216 and 223 could be utilized as reliable sources of resistance to stem borers in maize breeding programmes.
The spotted stem borer, Chilo partellus, Swinhoe (Lepidoptera, Crambidae) is one of the most destructive insect pests of maize in tropical environments. However, the combining ability and heterotic orientation of the germplasm for grain yield and borer resistance is limited. The objective of this study was to determine combining ability and heterotic orientation of new maize inbred lines under C. partellus infestation. Sixty six (66) inbred lines were crossed to two single cross testers in a line x tester mating scheme. The 132 testcross hybrids and four checks were evaluated at three locations in Kenya under C. partellus infestation. General and specific combining ability effects were significant for C. partellus stem borer resistance traits and grain yield, suggesting the importance of both additive and non-additive gene effects for these traits. Heterotic classification of lines was done based on both heterosis and specific combining ability data. Based on heterosis for grain yield data at Embu, 15 lines were allocated to group A, 18 to group B and 12 to group AB. At Kakamega, 26 lines were oriented towards group A, 19 to group B and 9 to group AB. At Kiboko, 15 lines were inclined towards group A, 18 to group B and 11 to group AB, whilst the remainder could not be classified. Based on the SCA estimates, at Embu, 10 lines revealed positive SCA effects with both testers and were considered to be AB-oriented while 8, and 1 lines were oriented towards A, and B, respectively. A similar trend was detected at Kakamega and Kiboko. The identified lines and heterotic groups would be used by hybrid maize programs where C. partellus stem borers occur exclusively or in league with other stem borers.
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