Combining Ability and Heterotic Grouping of Advanced Maize (Zea Mays L.) Inbred Lines in the Moisture Stress Areas of Ethiopia

Understanding the combining ability and heterotic grouping of maize inbred lines is essential to the development of high-yielding hybrids in the systematic breeding programs. This study was undertaken to estimate combining ability effects and to classify inbred lines into heterotic groups. A total of 84 entries, comprising 80 F₁ progenies derived from line × tester crosses and four standard checks, along with 42 parental lines, were evaluated using an alpha-lattice design with three replications at Melkassa and Dhera during the 2019/20 main cropping season. Combined analysis across locations revealed highly significant (P < 0.01) and significant (P < 0.05) differences among genotypes for grain yield and most agronomic traits. Analysis of variance for general combining ability (GCA) of lines and testers indicated significant effects (P < 0.01 or P < 0.05) for grain yield, days to 50% silking, plant height, ear diameter, ear length, kernels per row, rows per ear, root lodging, and common leaf rust. Specific combining ability (SCA) effects of line × tester interactions were significant (P < 0.01 or P < 0.05) for grain yield, ears per plant, ear aspect, plant and ear height, ear position, ear diameter, rows per ear, and thousand seed weight. The presence of significant GCA and SCA effects confirmed the existence of substantial genetic variability exploitable for hybrid development. Twenty lines exhibited positive and significant GCA effects for grain yield, with GCA contributing 47.94% to the total variance. Thirty-seven crosses showed positive and significant SCA effects for grain yield, with SCA contributing 49.54% to the total variance. The highest GCA/SCA ratio was observed for ear length (5.2), followed by days to 50% silking (4.5), indicating the predominance of additive gene action in the inheritance of these traits. Based on across-location SCA results for grain yield, 17 lines with negative and significant SCA effects with tester A (CML312) were classified into heterotic group A, while 19 lines with negative and significant SCA effects with tester B (CML395) were classified into heterotic group B. The findings provide valuable information for maize breeding programs, particularly under low-moisture stress conditions. Future efforts should emphasize multilocation evaluation of these genotypes to strengthen heterotic grouping and enhance hybrid development pipelines.