Combining Ability of Common Winter Wheat Cultivars Triticum aestivum L. by Date to Heading and Date to Physiological Maturity

This investigation was carried out with a view of evaluating the combining ability and the heritability regularities of a group of wheat cultivars which differed significantly by their date to heading DH and date to physiological maturity DPM. Six common winter wheat cultivars were combined in a complete diallele crossing scheme. The two traits were represented as number of days from 1st January to the respective date for each of them. During three successive years, the early F1 and F2 hybrid generations were analyzed. They were grown in a randomized design, the distance between the rows being 20 cm and the distance between the plants in each row – 10 cm. Each cultivar was evaluated for combining ability and the breeding value of each combination was assessed for the above two traits. The combining ability and the genetic parameters were calculated using the program Dial 98. Lack of reciprocal effect was established although the mother component strongly affected the phenotypic expression of the two traits. There were significant variations between the investigated cultivars in the expression of the two traits within 5-7 days. The values of GCA were predominant as a rule over the values of SCA in the variation analysis performed on the entire crossing scheme. This was evidence for some dominance of the genes with additive effect of the factors determining the two traits. GCA of each cultivar was directly related to the expression of the two traits, the correlation being as high as 0.95. The heritability of the two traits was analogous and resulted from complex combinations of genes with different effects additive or dominant. The higher the difference between the parental cultivars in a combination by the two traits, the higher the inherited DH and DPM values were. The regularities in the genetic control and the combining ability of the investigated cultivars by DH were completely analogous for the trait DPM, as well. This means that earliness could be easily evaluated by DH. Cultivars Pliska, Vratsa and Obriy had high combining ability towards earlier dates to heading and maturity. Cultivar Pryaspa had the latest dates in the diallele crossing scheme, but its breeding value implied successful breeding of earliness in combination with high productivity.