Combining Ability of Certain Agronomic Traits in Quality Protein Maize under Stress and Nonstress Environments in Eastern and Southern Africa

Abstract

Growing maize (Zea mays L.) hybrids tolerant to drought and low‐nitrogen (N) stress would significantly reduce yield losses occurring in Africa. This study evaluated the performance of quality protein maize (QPM) F1 hybrids, and general (GCA) and specific combining ability (SCA) of QPM inbred lines for grain yield and other agronomic traits under stress and nonstress environments. A diallel cross of 15 QPM inbred lines was evaluated under drought and low‐N stresses and optimal conditions in a total of 17 environments in Eastern and Southern Africa. Significant variations were observed among the hybrids for all measured traits. TZMI703 × (6207QB/6207QA), GQL5 × (6207QB/6207QA), and CML511 × (6207QB/6207QA) were identified as the best single crosses across environments. The GCA and SCA mean squares were significant for all measured traits, indicating that additive and nonadditive genetic effects were important in this set of genotypes under all test environments. The GCA effects were more important under drought stress, and SCA effects were more important under low‐N and optimal conditions for grain yield. There was preponderance of GCA effects for most agronomic traits tested in all environmental conditions. Inbred lines CML159SR, GQL5, CML159, and CML312SRQ exhibited favorable GCA effects for grain yield under stress and optimal conditions, indicating that the genetic systems controlling a given trait under different conditions are at least partially similar. Cross combinations with favorable SCA effects for grain yield and other traits were also identified. Generally, this study provided evidence that good performance can be achieved under stress and nonstress conditions in QPM germplasm.

Analyses of Combining Ability and Genotype‐By‐Environment Interaction of Quality Protein Maize Inbred Lines Adapted to Tropical‐Highlands

“…The mean squares due to GCA and SCA were highly significant for most traits. This finding is in line with previous diallel studies on QPM inbred lines (Pixley and Bjarnason, 1993;Bhatnagar et al, 2004;Wegary et al, 2011;Wegary et al, 2014). Significant GCA  environment interaction is an indication of variation in the GCA effects of lines under different environments, suggesting the need to select different parental lines for hybrid development at specific environments.…”

“…Mean performances of inbred lines, hybrids, high-parent heterosis, and general combining ability (GCA) values for grain yield (Mg ha −1 ), evaluated in the six environments. traits (Pixley and Bjarnason, 1993;Bhatnagar et al, 2004;Musila et al, 2010;Elmyhum, 2013;Wegary et al, 2014). Genotype-environment interactions were significant for most traits, resulting in rank differences of the genotypes.…”

“…The lines KIT32 and FS60, however, had crossover interaction showing rank differences at Holetta and Kulumsa in their GCA effects for GY (Fig. Therefore, while selecting for early-maturing genotypes, maintaining a balance between earlier maturity and higher yield is worth considering (Pswarayi and Vivek, 2008;Wegary et al, 2014). These parents could then make complementary and wellbuffered single crosses as seed parents for three-way cross hybrid development under diverse environments.…”

Grouping of early maturing quality protein maize inbreds based on SNP markers and combining ability under multiple environments

“…In addition, Musila et al (2010) reported the preponderance of additive gene action for grain yield, anthesis date, ASI and EPP in adapted early maturing QPM inbred lines evaluated under low-N, drought, and optimal environments. In contrast, Wegary et al (2013) reported GCA effects to be more important under drought, while SCA effects were more important under low-N and optimal conditions for grain yield. The differences in the results reported in the studies may be due to the fact that the inbred lines used in the different studies were derived from diverse germplasm sources and these might have had some genes with different modes of action (Badu-Apraku et al, 2013).…”

“…This suggested that additive gene action for grain yield and other agronomic traits was the most important contributor to the heritable variation in agronomic traits in these genotypes. Results of other studies have indicated preponderance of additive over nonadditive gene action (Vasal et al, 1993a,b;Bhatnagar et al, 2004;Musila et al, 2010;Wegary et al, 2013). However, such important information is completely lacking on the gene action conditioning the grain yield of IITA's early QPM inbreds under drought, low-N or Striga infestation.…”