Person: Gakunga, J.
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Gakunga
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Gakunga, J.
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- Genetic gains in grain yield through genomic selection in eight bi-parental maize populations under drought stress(CSSA, 2015) Beyene, Y.; Semagn, K.; Mugo, S.N.; Tarekegne, A.T.; Babu, R.; Meisel, B.; Sehabiague, P.; Makumbi, D.; Magorokosho, C.; Oikeh, S.O.; Gakunga, J.; Vargas Hernández, M.; Olsen, M.; Prasanna, B.M.; Banziger, M.; Crossa, J.
Publication - Performance and grain yield stability of maize populations developed using marker-assisted recurrent selection and pedigree selection procedures(Springer, 2016) Beyene, Y.; Semagn, K.; Mugo, S.N.; Prasanna, B.M.; Tarekegne, A.T.; Gakunga, J.; Sehabiague, P.; Meisel, B.; Oikeh, S.O.; Olsen, M.; Crossa, J.A marker-assisted recurrent selection (MARS) program was undertaken in sub-Saharan Africa to improve grain yield under drought-stress in 10 biparental tropical maize populations. The objectives of the present study were to evaluate the performance of C1S2-derived hybrids obtained after three MARS cycles (one cycle of recombination (C1), followed by two generations of selfing (S2), and to study yield stability under both drought-stress (DS) and well-watered (WW) conditions. For each of the 10 populations, we evaluated hybrids developed by crossing 47–74 C1S2 lines advanced through MARS, the best five S5 lines developed through pedigree selection, and the founder parents with a single-cross tester from a complementary heterotic group. The hybrids and five commercial checks were evaluated in Kenya under 1–3 DS and 3–5 WW conditions with two replications. Combined across DS locations, the top 10 C1S2-derived hybrids from each of the 10 biparental populations produced 0.5–46.3 and 11.1–55.1 % higher mean grain yields than hybrids developed using pedigree selection and the commercial checks, respectively. Across WW locations, the best 10 hybrids derived from C1S2 of each population produced 3.4–13.3 and 7.9–36.5 % higher grain yields than hybrids derived using conventional pedigree breeding and the commercial checks, respectively. Mean days to anthesis of the best 10 C1S2 hybrids were comparable to those of hybrids developed using the pedigree method, the founder parents and the commercial checks, with a maximum difference of 3.5 days among the different groups. However, plant height was significantly (P < 0.01) different in most pairwise comparisons. Our results showed the superiority of MARS over pedigree selection for improving diverse tropical maize populations as sources of improved lines for stress-prone environments and thus MARS can be effectively integrated into mainstream maize breeding programs.
Publication - Combining ability of maize inbred lines resistant to Chilo partellus (Swinhoe) in the mid-altitude environment of Kenya(Academic Journals, 2012) Gakunga, J.; Mugo, S.N.; Njoroge, K.; Olubayo, F.Gene action conditioning important traits in maize is useful to breeders in order to design appropriate breeding methods. A study was conducted to determine the combining ability of 10 maize inbred lines adapted to Kenya?s mid-altitude environment and being resistant to spotted stem borer, Chilo partellus. The inbred lines were crossed in a diallel scheme and the resulting 45 single crosses were evaluated under conditions of artificial infestation at four locations in Kenya in 2008 and 2009. Data were recorded on grain yield, foliar damage, exit holes and tunnel length to plant height ratio. Significant differences (P<0.001) for foliar damage, exit holes, tunnel length to plant height ratio, and grain yield were found. General combining ability (GCA) and specific combining ability (SCA) gave significant differences for grain yield and exit holes. There was discord in GCA between grain yield and resistance traits among lines. The most favorable SCA for grain yield occurred in hybrid 5 × 7, while hybrids 7 × 10, 3 × 5 and 4 × 8 were superior in resistance. Our results suggest that the development of C. partellus resistant maize varieties should consider both grain yield and stem borer resistance traits. This study identified additive gene action as important in controlling stem borer resistance, stem borer resistant inbred line donors and elite single crosses.
Publication - Testcross performance of doubled haploid maize lines derived from tropical adapted backcross populations(Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di Ricerca per la Maiscoltura, 2011) Beyene, Y.; Mugo, S.N.; Pillay, K.; Tadele Tefera; Ajanga, S.; Njoka, S.; Karaya, H.; Gakunga, J.Doubled haploid (DH) lines produced by in vivo induction of maternal haploids are routinely used in maize breeding. The present study was carried out to assess the performance of 75 doubled haploid maize testcrosses and six checks tested across four locations in Kenya for grain yield, agronomic traits and reaction to major leaf diseases. The 75 DH lines were derived from the backcross (BC1) plants of two CIMMYT bi-parental crosses. Significant location, genotype and genotype x location effects were observed for grain yield and anthesis-silking interval (ASI). Genotypes were significantly different for reaction to leaf blight and gray leaf spot. Location explained 69% of the total phenotypic variance while both genotype and genotype by environment interaction effects contributed 4% each. Fifteen DH testcross hybrids yielded better than the best commercial check, WH505 (5.1 t/ha). The best DH testcross hybrid (CKDHH0223) averaged over the four locations yielded 29.5% higher than WH505. These results indicate that maize testcrosses developed from DH lines produced as high a grain yield and as acceptable agronomic traits as the commercial hybrids developed through conventional pedigree methods. The DH lines identified in the study may be useful for improving yield and disease resistance in maize breeding programs in eastern and southern Africa.
Publication - Yield stability of stem borer resistant maize hybrids evaluated in regional trials in east Africa(Academic Journals, 2012) Beyene, Y.; Mugo, S.N.; Tadele Tefera; Gethi, J.; Gakunga, J.; Ajanga, S.; Karaya, H.; Musila, R.N.; Muasya, W.; Tende, R.; Njoka, S.Twenty-seven stem borer-resistant maize hybrids and three checks were evaluated in 14 locations in Kenya and Ethiopia to study the genotype x environment interaction (GEI) and yield stability. An analysis of variance was conducted for grain yield, number of days to silking, plant height, ear height and grain moisture content, and reaction to turcicum leaf blight, gray leaf spot, maize streak virus diseases and common rust. The yield stability and adaptation pattern of genotypes were examined with genotype plus genotype x environment (GGE) interaction biplot. Variations due to location, genotype and GEI effects were highly significant for all traits. Location variance among the hybrids was the most important source of variation for all traits, accounting for 58 to 90% of the total variance. The genotypic variance was higher than the GEI variance for turcicum leaf blight, plant height and silking date. The GEI variance was higher than the genotypic variance for grain yield, ear height, gray leaf spot, common rust and grain moisture content. The GGE biplot showed that 50% of the entries had positive PC1 scores suggesting above average performance, and 50% of them had negative PC1 scores indicating below average performance. Based on the mean grain yield and stability parameters, hybrid CKIR07003 (5.5 t/ha), CKIR07004 (5.5 t/ha) and CKIR07005 (5.6 t /ha) were identified as high-yielding and stable genotypes, and could be nominated for national performance trials for commercial release in various countries.
Publication - Combining ability of maize (Zea mays L.) inbred lines resistant to stem borers(Academic Journals, 2011) Beyene, Y.; Mugo, S.N.; Gakunga, J.; Karaya, H.; Mutinda, C.J.M.; Tadele Tefera; Njoka, S.; Chepkesis, D.; Shuma, J.M.; Tende, R.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.
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