Phenotypic variation and sampling for leaf conductance in wheat (Triticum aestivum L.) breeding populations

Recent studies have demonstrated an association between increased stomatal conductance and genetic improvement of yield potential of wheat. However, t he sensitivity of stomata to changes in environmental conditions makes scre ening of large populations for leaf conductance difficult in a breeding pro gram. A rapid and inexpensive viscous air-flow porometer has recently been developed to accurately measure leaf conductance in amphistomatous species. This porometer has potential to assist in the rapid screening of cereal po pulations aimed at identifying families with high leaf conductance and pote ntially high yield potential. In this study, random F-2:4, BC2F2:4, and BC2 F5:7 progeny from crosses between low and high stomatal conductance wheat v arieties were assessed for leaf conductance using the viscous air-flow poro meter in two field environments. Significant (p < 0.05) genotypic variation was observed for leaf conductance in both the F-2:4 and BC2F2:4 population s, and there was some evidence for transgressive segregation towards higher conductance in the BC2F2:4 population. Phenotypic distributions for leaf c onductance among progeny were approximately normal suggesting quantitative inheritance, while heritability on a family-mean basis ranged between 26 an d 73% indicating potential for genetic gain from selection for leaf conduct ance. A relatively greater leaf-to-leaf sampling variance highlighted the n eed for measurements on more leaves per plot in order to increase the preci sion of comparisons among family means, especially in early generations. In creasing the number of leaves sampled in each plot should pose little probl em for plant breeders because successive leaves can be measured rapidly (ca . five leaves/minute) with the viscous air-flow porometer.