Inheritance of Adult Plant Resistance to Leaf Rust in Five Egyptian Bread Wheat Cultivars

Abstract

The inheritance of wheat resistance to leaf rust caused by Puccinia triticina (Rob. Ex. Desm) was studied under field conditions at El-Nubaria Agric. Res. Station during 2003/04, 2004/05 and 2005/06 growing seasons. Ten crosses were made among the five Egyptian bread wheat cultivars, i.e. Sakha 94, Gemmeiza 9 and Giza 168 (resistant), Gemmeiza 7 (moderately resistant) and Giza 139 (highly susceptible) to determine quantitatively the inheritance mode and gene action of leaf rust resistance. The F1's and F2's of the ten crosses and their respective parents were evaluated for adult-plant response to leaf rust infection under field conditions at El-Nubaria during 2005/06 growing season, using three components of resistance, i.e. FRS (%), r-value and AUDPC.Analysis of variance (ANOVA) for combining ability effects showed highly significant variance due to general combining ability (GCA) and specific combining ability (SCA) effects for the three leaf rust resistance components, revealing the importance of additive as well as non-additive type of genetic variance in controlling the inheritance of these traits. Nevertheless, the higher values for the GCA variance than those of SCA variance indicated the predominance of an additive component over the dominant one for the three leaf rust resistance parameters; FRS (%), r-value and AUDPC. This result is in conformity with that, the additive component (D) of genetic variance was greater in its magnitude than their corresponding dominance values (H1) and (H2), suggesting the importance of additive gene action in the inheritance of wheat leaf rust resistance components of the study and confirmed the above result.The average of dominance (H1/D) ½ was less than unity for each component of resistance, which indicated that presence of partial dominance in the expression of wheat resistance to leaf rust. However, due to the positive values of (F), it could be suggested that the resistant cultivars in the half-diallel crosses seem to carry more dominant alleles than recessive ones for leaf rust resistance. In addition, there are at least two functioning groups of gene pairs controlling the two epidemiological parameters AUDPC and r-value in both F1 and F2. Meanwhile, final rust severity (FRS%) was governed by three gene pairs in F1 and F2. High heritability values in each broad and narrow sense were estimated for the three adult-plant resistance components. Thus, selecting resistant genotypes may be useful in the early generations, but it would be more effective if delayed to the later ones.