Browsing by Author "Tarekegne, Amsal"

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    Exploiting Grain-Filling Rate and Effective Grain-Filling Duration to Improve Grain Yield of Early-Maturing Maize
    (Crop Science, 2013) Gasura, Edmore; Setimela, Peter; Edema, Richard; Gibson, Paul T.; Okori, Patrick; Tarekegne, Amsal
    Early-maturing maize (Zea mays L.) genotypes yield 15 to 30% less than late-maturing genotypes. One strategy for improving grain yield in the early-maturing group involves assessment of grain-filling traits as secondary traits for selection for high grain yield. In this study, we investigated the possibility of using grainfilling rate and duration for improving grain yield in early-maturing tropical maize. Forty-four hybrids generated using North Carolina design II were evaluated at CIMMYT-Zimbabwe during the 2011/2012 season under irrigated and nonirrigated environments. Although grain-filling rate and effective grain-filling duration were negatively correlated, several hybrids were distinctly above the trend line. The earliest-maturing hybrid took 127 d to reach physiological maturity and produced grain yields comparable to those of the medium-maturing genotypes (7 t ha-1). It had a high grain-filling rate of 2.40 g per plant d-1 (18% higher than those of the lowyielding hybrids) and a relatively longer effective grain-filling duration. Grain-filling rate and effective grain-filling duration had high coefficients of genetic determination, positive correlations with grain yield, low error terms, and low genotype × environment interactions, making them appropriate selection traits for improved grain yield. The study shows that it is possible to develop high-yielding early- to medium-maturing maize hybrids based on favorable combining ability values for grain-filling rate and duration.
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    Genetic distance among doubled haploid maize lines and their testcross performance under drought stress and non-stress conditions
    (Euphytica, 2013) Beyene, Yoseph; Mugo, Stephen; Semagn, Kassa; Asea, Godfrey; Trevisan, Walter; Tarekegne, Amsal; Tefera, Tadele; Gethi, James; Kiula, Barnabas; Gakunga, John; Karaya, Haron; Chavangi, Andrew
    In contrast to conventional inbreeding that takes up to seven generations to develop inbred lines, the doubled haploid (DH) technology allows production of inbred lines in two generations. The objectives of the present study were to: (a) evaluate testcross performance of 45 doubled haploid lines under drought stress and non-stress conditions (b) estimate heritabilities for grain yield and other traits and (c) to assess the genetic distance and relationship among the DH lines using 163,080 SNPs generated using genotyping-by-sequencing (GBS). The 45 hybrid and five checks were evaluated using a 10 9 5 alpha lattice in six drought stress and nine well-watered environments in Kenya, Uganda, and Tanzania. Differences in trait means between the drought stress and well-watered conditions were significant for all measured traits except for anthesis date. Genetic variances for grain yield, grain moisture, plant height and ear height were high under well-watered environments while genetic variance for anthesis date, root lodging and stalk lodging were high under drought stress environments. Combined analyses across drought stress and well-watered environments showed that ten top hybrids produced 1.6–2.2 t/ha grain yield under well-watered condition and 1–1.4 t/ha under drought stress condition higher than the mean of the commercial checks. Genetic distance between pairwise comparisons of the 38 of the 45 DH lines ranged from 0.07 to 0.48, and the overall average distance was 0.36. Both cluster and principal coordinate analysis using the genetic distance matrix calculated from 163,080 SNPs showed two major groups and the patterns of group was in agreement with their pedigree. Thirteen (13) of the best hybrids are currently in National Performance Trials testing, an important step towards commercialization in Kenya, Tanzania and Uganda.
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    Variability of grain-filling traits in early maturing CIMMYT tropical maize inbred lines
    (Crop Science, 2019) Gasura, Edmore; Setimela, Peter S.; Tarekegne, Amsal; Icishahayo, David; Edema, Richard; Gibson, Paul T.; Okori, Patrick
    This paper examines the relationship between positive deviance and entrepreneurial networking among small and medium enterprises (SMEs). Using a mixed method approach combined self-administered questionnaires and interview guide covering 228 SMEs in Uganda, the cross-sectional nature of this study revealed key nuances about SMEs. The research findings confirmed a significant positive relationship between positive deviance and entrepreneurial networking among SMEs in Uganda. The findings also revealed that: SME owner/ managers should create enabling environment for people with divergent views to interact with each other to innovate new practices, such as accessing resources from the networks; managers should initiate new policies for error management to allow employees room to learn from mistakes; managers should acquire new skills of leadership skills to manage and utilize the knowledge and skills of positive deviants. This research therefore contributes to existing scholarship by providing nuances in the study of positive deviance and entrepreneurial networking among SMEs in Uganda through employing a complexity approach that transcends previous academic focus on social network theory.