Browsing by Author "Makumbi, Dan"
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Item Grain yield performance and flowering synchrony of CIMMYT’s tropical maize (Zea mays L.) parental inbred lines and single crosses(Euphytica, 2016) Worku, Mosisa; Makumbi, Dan; Beyene, Yoseph; Das, Biswanath; Mugo, Stephen; Pixley, Kevin; Ba¨nziger, Marianne; Owino, Fidelis; Olsen, Michael; Asea, Godfrey; Prasanna, Boddupalli M.Maize production constraints in sub-Saharan Africa (SSA) are being addressed by CIMMYT and partners through an array of projects, focusing on developing and evaluating parental inbred lines and single-crosses as well as formulating, evaluating and releasing high-yielding and stress resilient hybrids adapted to different agro-ecologies. The objectives of the present study were to (1) evaluate the grain yield performance of parental elite inbred lines developed over the years, and single crosses; and (2) ascertain the flowering synchrony among inbred lines and singlecross hybrid parents. Parental inbred lines and singlecrosses were evaluated at seven locations in two countries in 2014. Combined analysis of variance revealed differences (P\0.01) among genotypes for grain yield (GY) and among different years/era of release of the inbred lines. The improvement in GY of inbred lines was estimated to be 1.4 %per year. Under irrigated conditions GY of some single-cross hybrids was over 16 t ha-1. Some single-cross and inbred line parents showed acceptable flowering synchrony, good producibility, and stable performance across testing environments, suggesting that these have high potential for seed production. Further research is needed to determine the physiological and morphological characteristics that contributed to the GY improvement in the parental inbred lines. Information generated from this study will enhance the use of CIMMYT’s tropical mid-altitude parental germplasm by breeders working in both private and public breeding programs for developing and deploying high-yielding maize hybrids for the benefit of small-scale farmers in SSA.Item Identification and diversity of tropical maize inbred lines with resistance to common rust (Puccinia sorghi Schwein)(Crop Science, 2020) Sserumaga, Julius Pyton; Makumbi, Dan; Assanga, Silvano O.; Mageto, Edna K.; Njeri, Susan G.; Jumbo, Bright M.; Bruce, Anani Y.Common rust (CR) caused by Puccinia sorghi Schwein is one of the major foliar diseases of maize (Zea mays L.) in Eastern and Southern Africa. This study was conducted to (i) evaluate the response of elite tropical adaptedmaize inbred lines to Puccinia sorghi and identify resistant lines (ii) examine associations between CR disease parameters and agronomic traits, and (iii) assess the genetic diversity of the inbred lines. Fifty inbred lines were evaluated in field trials for three seasons (2017–2019) in Uganda under artificial inoculation. Disease severity was rated on a 1–9 scale at 21 (Rust 1), 28 (Rust 2), and 35 (Rust 3) days after inoculation. Area under disease progress curve (AUDPC) was calculated. The genetic diversity of the lines was assessed using 44,975 single nucleotide polymorphism markers. Combined ANOVA across seasons showed significant (P < .001) line mean squares for the three rust scores andAUDPC.Heritabilitywas high for Rust 2 (0.90), Rust 3 (0.83), and AUDPC (0.93). Of the 50 lines, 12 were highly resistant to CR. Inbred lines CKL1522, CKL05010, and CKL05017 had significantly lower Rust 3 scores and AUDPC compared to the resistant check CML444 and are potential donors of CR resistance alleles. The genetic correlations between CR disease resistance parameters were positive and strong. A neighbor-joining (NJ) tree and STRUCTURE suggested the presence of three major groups among the lines, with lines highly resistant to CR spread across the three groups. The genetic diversity among the highly resistant lines can be exploited by recycling genetically distant lines to develop new multiple disease resistant inbred lines for hybrid development and deployment.Item Molecular characterization of tropical maize inbred lines using microsatellite DNA markers(Maydica, 2014) Sserumaga, Julius P.; Makumbi, Dan; Ji, Hyeonso; Njoroge, Kiarie; Wanjohi Muthomi, James; Chemining’wa, George N.; Si-myung, Lee; Asea, Godfrey; Kim, HakbumAn insight on diversity and relationships among germplasm is important in any breeding program for crop improvement. The main objectives of our study were to: (i) determine the level of genetic diversity within mid altitude maize inbred lines resistant to weevils, aflatoxin accumulation and drought, (ii) to suggest potential heterotic groups using their genetic structures and distance based on cluster analysis with the aim to generate broad based source germplasm for mid altitude maize breeding program with combined traits of importance against Aflatoxin accumulation. In this study, 25 SSR markers were used to finger print forty two maize inbred lines to assess the genetic diversity, genetic relationships, and their population structure. A total of 184 alleles were identified at all the loci with an average of 7.36 and a range between two and 19 alleles per locus. The major allele frequency varied from 0.17 to 0.90 with an average of 0.49 while the minor allele frequency varied from 0.10 to 0.83 with an average of 0.51. The gene diversity values varied from 0.18 to 0.92 with an average of 0.65. Average heterozygosity percentage of the inbred lines was 4%, ranging from 0% to 2%, indicating the low level of heterozygosity within the inbred lines. The average polymorphism information content (PIC) was 0.61. A dendrogram constructed using unweighted Neighbour Joining algorithm suggested three heterotic groups among the inbred lines. The three heterotic patterns based on the SSR markers need to be verified by field testing to confirm what appears to be promising alternative heterotic patterns. The fixed pattern detected using SSR markers could potentially contribute towards effective utilization of the inbred lines for the exploitation of heterosis and formation of genetically diverse sources population.Item Reproductive efficiency and breeding potential of East African highland (Musa AAA-EA) bananas(Field Crops Research, 2006) Ssebuliba, Ruth; Talengera, David; Makumbi, Dan; Namanya, Priver; Tenkouano, Abdou; Tushemereirwe, W.; Pillay, MichaelThe East African highland banana (Musa spp. AAA) is an economically important food crop. The crop is affected by a number of diseases and pests. Genetic improvement of the crop is hindered by very low seed set and poor seed germination. The objective of this study was to compare seed set, seed quality and embryo rescue rates of hybrid seeds obtained from 20 East African highland banana cultivars crossed with a fertile diploid species, Musa acuminata spp. burmannicoides ‘Calcutta 4’, as a male parent. There was great variation in seed set, seed quality and in vitro embryo germination rates among the cultivars. Although 72% (range = 47–88%) of the seeds appeared normal externally characterized by black hard integuments, only 59% (range = 35–81%) contained embryos, of which 9% (range = 0–22%) germinated. This study demonstrated that hard-seededness alone does not signify the presence of an embryo and should not be regarded as a measure of seed fertility in East African highland bananas. Cultivars ‘Entukura’, ‘Enzirabahima’ and ‘Kabucuragye’ of the ‘Nfuuka’ clone set were superior in terms of seed set, presence of seeds with embryos and culturability of embryos. These cultivars are recommended as female parents for a crossing program in the improvement of East African highland bananas. The low embryo rescue rates suggest that hybrid seeds derived from East African highland banana possess factors that cause high embryo abortion. This may be ascribed to endosperm breakdown, which can release toxins.