EFFECTS OF CHROMOSOMAL ADDITION ON REACTION NORMS OF TRITICUM-AESTIVUM

A better knowledge of the genetics and degree of variability of phenotypic plasticity is particularly important for the understanding of evolution in natural populations. Also, for agronomically significant plants, plasticity has implications for the yield in different conditions. Phenotypic response to three levels of nitrogen availability was investigated in Triticum aestivum var. Chinese Spring (CS). A CS pure line and seven chromosomal addition lines from a wild relative (Elytrigia elongata) were grown in a greenhouse. Two-way ANOVAs of 19 morphological traits were used to detect the presence of main line effects, main treatment effects, and line x treatment interactions. We found genetic variation for character means in 10 traits, and evidence for plasticity in six traits, but no significant genetic variation for plasticity. A multivariate approach allowed us to summarize the phenotypic variation using three principal factors: the first one relating to reproductive output, the second one to plant size, and the third one to shape of flag leaf and first spike. The first and third factors turned out to be significantly plastic according to the analysis of variance, while the first and second components presented genetic variation. Addition lines of T. aestivum lack genetic variation for plasticity. The mean phenotypic response, however, shows complex genetic effects, with more than one addition chromosome interfering in the control of the average across-treatments phenotype.