Combining ability of yield and yield components in S7 maize lines

Maize (Zea mays L.) is the fourth most important cereal after wheat, barley and rice in Iran (Ahmadi et al., 2018). Given the future demand of corn as a food for humans and as a feed for livestock, there is a continuous need to evolve new hybrids with high yield. To achieve this, combining ability study is one of the best options (Reddy Yerva et al., 2016). Griffing diallel method (Griffing, 1956a;b) is one of the methods that examines how genetic control of traits in parents. It also evaluates the general and specific combining ability of parents and hybrids. The purpose of this study was to estimate the general and specific combining ability of parents and hybrids.

In order to estimate the gene action and heritability of important agronomic traits, five S7 maize lines were crossed in a 5×5 half-diallel and F1 hybrids derived from them were cultivated in a randomized complete block design with three replications at the Research Farm of Graduate University of Advanced Technology, Kerman, Iran in 2017. Number of ear, grain number per row, grain row number, grain number per ear, ear length, 100-grain weight and grain yield per square meter were evaluated. Analysis of data for general and specific combining ability was carried out following Griffing (1956) method IV model I using DIALLEL-SAS05 program (Zhang et al., 2005).

Analysis of variance showed that there was a significant difference between genotypes for all studied traits that showed the role of additive and non- additive effects in controlling these traits. The low ratio of GCA variance to SCA for the grain row number and number of ear traits, and in other words, the lack of significant GCA variance of these traits showed that genetic control of these traits has a non-additive effect. General (GCA) and specific (SCA) combining ability variances for grain number per row, grain number per ear, ear length, 100-grain weight and grain yield per square meter were significant at 1% probability level, indicating the control of these traits by additive and non-additive effects of genes with a greater proportion of additive gene effects.

The results of this study showed that although genes with both additive and non-additive effects played a role in controlling of yield and its component traits. In controlling traits of ear number and rows, the role of non-additive effects was greater. Whereas, other traits were more controlled by the additive gene effects. The Line14 had positive and significant GCA for the yield trait and most of its related traits, which indicated that the line could be used in breeding programs to improve yield and increase it. The results also showed that the P1 × P2 and P3 × P5 crosses had positive and significant SCA for yield and its related traits, so these hybrids might be the best for improving and increasing maize grain yield.