Grain yield, stem borer and disease resistance of new maize hybrids in Kenya

Evaluation of 30 maize hybrids for yield and resistance to stem borers and foliar diseases in four agroecologies in Kenya was conducted in 2009. There were significant differences among the hybrids in leaf damage, number of exit holes, tunnel length and grain yield in Kiboko. The maize hybrids CKPH08014, CKPH08025, and CKPH08026 showed the least leaf damage, exit holes and tunnel length, similar to the resistant check. Although ten hybrids yielded over 8 t/ha, two hybrids, CKPH09001 and CKPH08033, gave the highest yield of 8.99 and 8.86 t/ha, respectively, in Kiboko. There were significant differences among the hybrids in resistance to leaf rust and maize streak virus in Kakamega. The intensity of foliar diseases was high in Kakamega compared to the other sites. All hybrids appeared resistant to the foliar diseases at Kakamega. On the average, the highest yield of the hybrids was recorded in Kiboko (7.5 t/ha) followed by Kakamega (6.1 t/ha), and the least at Embu (3.5 t/ha), and Mtwapa (3.14 t/ha). The performance of the hybrids varied from site to site, with CKPH09002 and CKPH09003 performing well at Mtwapa, CKPH09001 at Kiboko, CKPH08039 at Embu, CKPH 08002 and CKPH08010 at Kakamega.Key words: Host plant resistance, maize, pest management, stem borer, foliar disease

Genotype by environment interactions and yield stability of stem borer resistant maize hybrids in Kenya

In a maize breeding program, potential genotypes are usually evaluated in different environments before desirable ones are selected. Genotype x environment (G x E) interaction is associated with the differential performance of genotypes tested at different locations and in different years, and influences selection and recommendation of cultivars. Twenty one stem borer resistance maize hybrids and four commercial checks were evaluated in six environments in Kenya under infestation with Chilo partellus and Busseola fusca to determine the G x E interactions and stability of the hybrids. Analysis of variance was conducted for grain yield, days to flowering and plant and ear height. Stability for grain yield was determined using genotype plus genotype by environment interaction (GGE) biplot analysis. Variances due to genotype, environment and G x E interaction effects were highly significant for all traits. The GGE biplot showed that four experimental hybrids and two commercial checks had positive PC1 score indicating above average performance across environments. However, 10 experimental hybrids and two commercial checks had negative PC1 score, suggesting poor average performance. Experimental hybrids, CKIR07004 and CKIR07013, were highly desirable in terms of grain yield (>7.5 t/ha) and stability across environments. These hybrids could be released in Kenya and similar environments.Key words: Genotype x environment (G x E) interactions, maize, stem borer resistant hybrids, stability

Testing public Bt maize events for control of stem borers in the first confined field trials in Kenya

Transgenic maize (Zea mays L), developed using modified genes from the bacterium Bacillus thuringiensis (Bt), controls stem borers without observable negative effects to humans, livestock or the environment, and is now sown on 134 million hectares globally. Bt maize could contribute to increasing maize production in Kenya. Nine public Bt maize events of cry1Ab and cry1Ba genes were tested in confined field trials site (CFTs) to assess the control of four major Kenyan stem borer species. Leaf damage rating, number of exit holes and tunnel length were scored in the field evaluations. Leaf area consumed and mortality rates among stem borers were scored in the leaf bioassays in a Biosafety Level II laboratory, located at the Kenya Agricultural Research Institute (KARI), National Agricultural Research Laboratories (NARL). Field evaluations showed that Bt maize controlled Chilo partellus with mean damage scores of 1.2 against 2.7 for the non-Bt CML216 control. Laboratory bioassays showed high control for Eldana saccharina and Sesamia calamistis, with mean larval mortality of 64 and 92%, respectively. However, substantial control was not observed for Busseola fusca. These results showed that Bt maize could control three of the four major stem borers in Kenya with mortality records of 52.7% for B. fusca, 62.3% for E. saccharina and 85.8% for S. calamistis. Additional Bt genes need to be sought and tested for effective stem borer control in all maize growing ecologies in Kenya.Key words: Maize, Bt, stem borers, confined field trials

Control of Busseola fusca and Chilo partellus stem borers by Bacillus thuringiensis (Bt)-&#948-endotoxins from Cry1Ab gene Event MON810 in greenhouse containment trials

Previous testing of several public Bacillus thuringiensis (Bt)-maize events did not show control of the African stem borer (Busseola fusca Fuller), an important stem borer species, without which stewardship would be compromised by the possibility of rapid development of resistance to Bt deltaendotoxins. This study was carried out to test Bt-maize Event MON810 as an option to control all major stem borer species in Kenya. Two Bt-maize hybrids, DKC8073YG and DKC8053YG, both containing Bt Event MON810 of Cry1Ab gene were imported to carry out greenhouse containment trials. The hybrids together with the controls were grown in 10 replications upto the V6 and V8 stages. Infestations on whole plants were carried out at two stages of growth using 5 neonates of the spotted stem borer (Chilo partellus Swinhoe) and B. fusca. Bt-maize Event MON810 hybrids showed resistance to both stem borer species with low leaf damage scores and few surviving larvae recovered from the whole plant. The public Bt-maize Event 223 did not control B. fusca. Deploying Bt-maize Event MON810 may, therefore, be used to control the two species of stem borers. However, the efficacy of Bt-maize Event MON810 will, need to be evaluated under field environments.Key words: Bacillus thuringiensis (Bt) maize, cry1A (b) proteins, stem borers, transgenic

Combining ability of maize (Zea mays L.) inbred lines resistant to stem borers

Ten inbred parents with varying resistance levels to Chilo partellus and Busseola fusca were crossed in a half diallel mating scheme to generate 45 F1 hybrids. The hybrids and five commercial checks were evaluated across four locations in Kenya under artificial and natural infestation in 2009. Genotype (G) by environment (E) interaction (G x E) was non-significant for stem borer leaf damage, number of exit holes and tunnel length, suggesting that screening for stem borer resistance at one location would be adequate. On the other hand, G x E and general combining ability (GCA) x environment interactions were highly significant for gray leaf spot and turcicum leaf blight, indicating an inbred line resistance to a disease in one location may have a different reaction to the same disease in another location. The results of combining ability analysis showed that GCA effects were significant for stem borer resistance traits (leaf damage scores, number of exit holes, and tunnel length) while the opposite was true for specific combining ability (SCA) effects. Parents 5, 2, 6, 9 and 3, were good sources of genes for higher grain yield while parents 1 and 4 were good sources of resistance genes for stem borers. Hybrid 5 x 9 was the best performing hybrid in grain yield (6.53 t/ha) across the locations, while hybrid 1 x 4 was the least performing in grain yield (3.08 t/ha). The source of stem borer resistance identified in the study may be useful for improving levels of stem borer resistance in maize breeding  programs in eastern and southern Africa.Key words: Combining ability, maize, inbred lines, stem borers

Testing public Bt maize events for control of stem borers in the first confined field trials in Kenya

Transgenic maize (Zea mays L), developed using modified genes from the bacterium Bacillus thuringiensis (Bt), controls stem borers without observable negative effects to humans, livestock or the environment, and is now sown on 134 million hectares globally. Bt maize could contribute to increasing maize production in Kenya. Nine public Bt maize events of cry1Ab and cry1Ba genes were tested in confined field trials site (CFTs) to assess the control of four major Kenyan stem borer species. Leaf damage rating, number of exit holes and tunnel length were scored in the field evaluations. Leaf area consumed and mortality rates among stem borers were scored in the leaf bioassays in a Biosafety Level II laboratory, located at the Kenya Agricultural Research Institute (KARI), National Agricultural Research Laboratories (NARL). Field evaluations showed that Bt maize controlled Chilo partellus with mean damage scores of 1.2 against 2.7 for the non-Bt CML216 control. Laboratory bioassays showed high control for Eldana saccharina and Sesamia calamistis, with mean larval mortality of 64 and 92%, respectively. However, substantial control was not observed for Busseola fusca. These results showed that Bt maize could control three of the four major stem borers in Kenya with mortality records of 52.7% for B. fusca, 62.3% for E. saccharina and 85.8% for S. calamistis. Additional Bt genes need to be sought and tested for effective stem borer control in all maize growing ecologies in Kenya

Striga hermonthica parasitism in maize in response to N and P fertilisers

Parasitism by the parasitic weed, Striga hermonthica (Striga), constitutes a major biological constraint to maize production in sub-Sahara Africa. Nutrient deficiency is known to aggravate Striga infestation and in a number of plant species it was recently shown that this may be due to increased secretion of Striga germination stimulants into the soil. The present study was designed to observe the connection between soil fertility, secretion of germination stimulants and Striga infection in maize under greenhouse and field conditions. The experiments were conducted during two successive cropping seasons (2008 and 2009). The greenhouse study showed that maize secretes a number of so far unidentified strigolactones that induce Striga seed germination and the amount of these strigolactones increases upon N and P deficiency. The increased secretion of germination stimulants under N and P deficiency resulted in increased Striga infection in pot experiments. The on-station and on-farm field trials in Western Kenya also showed reduction in Striga infestation with the application of mineral nutrients but the results were less consistent than in the greenhouse. Increasing levels of N showed a fair reduction of Striga in the field especially during the first year, whereas P application did not have much effect in contrast to the greenhouse study where both N and P clearly reduced Striga infection. The likely explanation for this discrepancy is that availability of mineral nutrients under field conditions is less predictable than under greenhouse conditions, due to a number of factors such as soil texture and structure, pH, salinity, drought, leaching and runoff. Hence, further studies are needed on the importance of these factors before a fertiliser application strategy can be formulated to improve control of Striga in maize in the field