Estimation of gene effect and combining ability of some maize traits under normal and low irrigation conditions by diallel method

Maize (Zea mays L.) is considered as one of the most important cereals in the field of world production. Water stress due to water shortages and its various forms is one of the main and most common limiting factors of crop yield, especially in arid and semi-arid regions of the world. Therefore, in corn, identification, selection and use of tolerant cultivars against drought stress in order to prevent the reduction of crop yield is considered as one of the most important and essential issues in breeding programs. Breeding of high-yield and good quality cultivars is one of the main goals of the breeding program which requires comprehensive information about the genetic structure of the parents, as well as their general and specific combining ability, the level of heterosis, genes action, and their interaction with each other and the environment. Therefore, the present study was conducted to evaluate the gene effects, heritability and the control of yield and its components in drought stress conditions compared to normal conditions in corn. In order to select suitable breeding methods and take an effective step in the production of high yielding maize cultivars.

In order to estimate the gene action and heritability of important agronomic traits, five S7 maize lines in a 5×5 half-diallel cross with F1 hybrids derived from them in a randomized complete block design with two replications in two normal conditions (irrigation intervals of 5 days) and drought stress (8 days irrigation) were cultivated 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 plant were evaluated in two conditions. The data were analyzed by analysis of variance and regarding the significance of the variance of treatments, the analysis was performed using Griffing's second method. In order to carry out the diallel analyzes by Griffing's second method in two normal and drought stress conditions and combined analysis of variance was used SAS command.

Combined analysis of variance showed that there was a significant difference between genotypes, environment and genotype×environment interaction for all studied traits, indicating the genetic differences between lines and corn hybrids. The results of combined variance analysis showed a significant interaction effects between general and specific combining ability with the environment, which indicates the different of inheritance of traits in each environment. The results of diallel analysis by second Griffing method under normal conditions indicated that the grain number per row, grain row number, grain number per ear and ear length more controlled by non-additive effects of genes, while these traits more controlled by additive effects of genes under water scarcity conditions.

The results of this study showed that although genes with both additive and non-additive effects played a role in controlling the traits, the contribution of each of these effects was different in controlling each of the traits. Also, the control of these traits was different in both normal and drought stress conditions, and the genes controlling these traits differed from environment to environment. The KSC704-S7-7 line showed positive and significant general combining ability for grain yield and most related traits in both conditions which can be used in breeding programs to improve grain yield and increase it. In addition, the P2×P4 cross under water scarcity conditions and the P1×P3 cross under normal conditions, which showed positive and significant specific combining ability for grain yield and most related traits, are introduced as the best hybrids for improvement and increase of maize grain yield for water scarcity and normal conditions, respectively.