Author : Nay Aung

Summary : The identification of maize inbred lines to distinct heterotic groups is a critical step in the development of high-yielding hybrids. Combining ability through line x tester analysis, associated with the exploitation of heterosis, is essential for developing maize hybrids that are not only high-yielding but also well-adapted to diverse agro-ecological conditions. This study aimed to assess the genetic parameters associated with heterosis for grain yield and yield attributing traits in maize under highland and lowland conditions. A total of 203 maize inbred lines were genotyped from December 2022 to July 2023 at the Biotechnology Research Section, Department of Agricultural Research (DAR). Forty-five SSR markers were applied to identify distinct heterotic groups. Of the total markers, 53.33% demonstrated high polymorphism, 42.22% showed average polymorphism and 4.44% exhibited low polymorphism. Genetic relationships among the tested maize inbred lines were analyzed using Unweighted Pair Group Method with Arithmetic Mean (UPGMA) clustering, population structure analysis, and principal coordinate analysis (PCoA). These methods effectively categorized the 203 maize inbred lines into two distinct heterotic groups. Seven lines and four testers were selected from the respective heterotic groups and then crossed to produce 28 F1 hybrids and to perform line x tester analysis. These 28 F1 hybrids, along with their parents and five checks (Yezin Hybrid-10, Yezin Hybrid-11, Yezin Hybrid-14, CP-808 and NK-625) were evaluated in a randomized complete block design with three replications at Tatkon Research Farm and Aungban Regional Research Centre, DAR, from May to September 2024 to estimate heterosis levels. Based on general combining ability (GCA) effects, lines L2 (TKN-20-03) and L4 (TKN-20-20) were observed high GCA effects for grain yield and yield attributing traits. Specific combining ability (SCA) effects for 28 crosses revealed that L2 x T1 (TKN-20-03 x Thai-10-04), L2 x T3 (TKN-20-03 x YZCI-16-038) and L4 x T4 (TKN-20-20 x KICF-12-002) exhibited significantly positive SCA effects for grain yield, with the heterosis performance of these three crosses significantly superior than that of the best check, NK-625. Based on the experimental results, the cross L2 x T1 (TKN-20-03 x Thai-10-04) demonstrated adaptable to lowland conditions, while L4 x T4 (TKN-20-20 x KICF-12-002) was better suited for highland condition. The hybrid L2 x T3 (TKN-20-03 x YZCI-16- 038) showed adaptability across highland and lowland conditions. The results indicated that line x tester analysis provided detailed genetic information on the lines, testers, and their combinations, while the Genotype and Genotype x Environment (GGE) biplot approach offered breeders a powerful tool for identifying potential parents and crosses through its graphical representation. This information will support breeders in developing high-yielding maize hybrids that are well­adapted to different agro-ecologies in Myanmar.