Assessment of combining ability for grain yield and its attributing traits in maize (Zea mays L.)

Abstract A comprehensive understanding of combining ability is an emerging focus in hybrid maize research in Nepal. The present study aimed to evaluate the performance of single-cross maize hybrids and to estimate the combining abilities of parental lines for grain yield and its attributing traits. A total of 24 inbred lines, consisting of 20 female inbred lines and four testers, were used in a line × tester mating design to develop 80 single-cross hybrids from March to July in 2022 and 2023. All 24 parents and 80 single-cross hybrids, along with eight checks, were evaluated from October to March of 2022/23–2023/24 in the research field of the National Maize Research Program (NMRP), Rampur, Chitwan, Nepal, using an alpha lattice design with three replications. Analysis of variance revealed significant differences among the genotypes and genotype × year interaction for the number of kernel rows per ear and grain yield. Among hybrids, RL292/RML76 (9480 kg/ha), RML64/RML96 (9080 kg/ha), RL278/CML581 (9047 kg/ha), RML 32/RML17 (9035 kg/ha), and RML46/RML17 (9016 kg/ha) produced the highest grain yield. Similarly, hybrids RL278/CML581 (1939.03), RL84/RML96 (1871.97), RL292/RML76 (1706.56), RL279/RML76 (1449.21) and RL254/RML17 (1238.9) produced the higher and positive (p < 0.05) SCA values for grain yield. Higher positive GCA values for grain yield were found in inbred lines RML145 (976.8), RML32 (893.34), CAL14137 (878.62), RL293 (699.55), RL294 (599.67) and RL143 (454.91). These inbred lines could be utilized to improve grain yield in hybrid breeding program. The predictability ratio ranged from 0.49 (number of kernel rows per ear) to 0.59 (grain yield). Grain yield, ear length, ear diameter, and number of kernels per row had ratios above 0.50, indicating the predominance of additive gene action and the effectiveness of selection based on GCA. Cluster analysis of 80 maize hybrids based on SCA effects grouped them into two main clusters; Group I (44 hybrids, five sub-groups A to E) and Group II (36 hybrids, four sub-groups A to D). The clear separation of these groups suggests the presence of at least two heterotic patterns within the parental lines.