Combining ability analysis and genes effect for grain yield and its’ components in bread wheat

Wheat is the first important grain in the world and one of the strategic products of the country and the main source of protein and calories. Due to the growing trend of world population, the production and expansion of new varieties, has always been and will always be of interest to wheat breeders in the world. To achieve favorable outcomes in breeding programs, selection of parents based on general combining ability and specific combining ability is so important. Therefore, aim of this study was to investigate the general and specific combining ability of five different wheat cultivars and F1 hybrids derived from them in order to study the genetic structure and heritability of yield and its components to determine the type of breeding method and selection of suitable parents and hybrids.

In this study, five wheat cultivars including Kuhdasht, Karim, Qaboos, Aseman and Line 17, were crossed in a half- Diallel methode in the research farm of the Agricultural Research Station of Gonbad-e Qabous in the 2018-19 crop year. In order to comparative experiment, seeds of 10 F1 generations and parents were planted in a randomized complete block design with three replications in the 2019-20 crop year. Then, traits Days to spike emergence date, Plant height (cm), Spike length (cm), Number of grain per spike, 1000-grain weight (g), Plant yield (g / m2) were recorded /measured.

Significance of analysis of variance indicates the existence of genetic differences between the genotypes and the possibility of continuing the analysis by Diallel method. Based on the results of genetic analysis based on the two method Griffing B models, general and specific combining abilities were significant for all traits, which indicates the simultaneous effect of additive and non-additive effects of genes in controlling traits. However, the share of additive gene effects for all traits except 1000-seed weight was higher than non-additive gene effects. In terms of increasing in spike length, number of seeds per spike, 1000-seed weight and yield, Aseman cultivar was the best compound. Also, Line 17 cultivar with the lowest general combinability was the best one in of early maturity and dwarf traits. The best hybrid for 1000-seed weight and yield was Kuhdasht×line17, that had the highest specific combining ability. The results of the Jinks-Heyman test indicated that hypothesis of the genetic analysis were satisfied only for plant height, number of seeds per spike, spike length, plant yield. Evaluation of genetic parameters by hayman method showed that the parameters D and H1 were significant, but the high contribution of variance D showed that the additive effects of genes action had greatest importance in genetic control of these traits.The rate of specific heritability also varied from 0.63 in number of seeds per spike to 0.93 for plant height.

Result of Griffing and Hayman indicated, additive and non-additive gene effects were effective for all traits. But, the low values of the mean degree of dominance and regression line break in the positive part of the Wr axis and also the significance of the GCA/SCA ratio indicate the high share of additive effects in the control of these traits. Therefore, due to the importance of additive effects, the selection method can be a suitable method to breeding these traits.