Gene Action of Canopy Temperature in Bread Wheat under Different Environments.

Wheat is commonly grown in regions where yields are limited by low seasonal rainfall. Progress through plant breeding has been achieved by using physiological traits in the selection process to complement conventional breeding for yield. New screening tools are necessary to be tested in terms of their ability to express the genetic variation in the population, with minimum environmental influence and low genotype x environment interactions. Canopy temperature (CT) has been proposed as a screening tool for predicting high wheat yield in rainfed environments. However, CT reliability was questioned when evaluated in different environments. Yet little is known of genetic control. The objective of this study was to determine the gene action and heritability for CT in bread wheat. The wheat populations used for this study were obtained by crossing Weebill4//Gim/Lira, Weebill4/Prinia, Weebill4/SW89.5193, SW89.5193/Attila and SW89.5193/Prinia. Parents were chosen according to their contrasting CT. Plants of the parental lines (P1 and P2), backcrosses (BCP1 and BCP2), F1, and F2:4 families were grown in Ciudad Obregon, Mexico, during three cycles (2004-07) under heat irrigated, drought, and irrigated conditions. CT measurements were taken during vegetative and grain-fill phases. Analysis of variance was conducted using SAS mixed linear model procedure. Genetic estimates for quantitative traits were estimated according to Gusmini, Wehner and Donaghy (2007). Main genetic components consisted of additive variance (a) and dominance variance (d). Interaction components (epistasis) were described as additive x additive (aa), additive x dominance (ad), and dominance x dominance (dd). Means and variances of P1 and P2, F1, BC1, BC2, and F2 derived populations were used to generate the models. The estimated parameters were used to test the goodness of fit to the different genetic models. We accepted the models that fitted the data (chi-square > 0.05) and consisted of significant components (t-test < 0.05).