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, the sensitivity of stomata to changes in environmental conditions makes screening of large populations for leaf conductance difficult in a breeding program. 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 populations aimed at identifying families with high leaf conductance and potentially high yield potential. In this study, random F2:4, BC2F2:4, and BC2F5:7 progeny from crosses between low and high stomatal conductance wheat varieties were assessed for leaf conductance using the viscous air-flow porometer in two field environments. Significant (p< 0.05) genotypic variation was observed for leaf conductance in both the F2:4 and BC2F2:4 populations, and there was some evidence for transgressive segregation towards higher conductance in the BC2F2:4 population. Phenotypic distributions for leaf conductance among progeny were approximately normal suggesting quantitative inheritance, while heritability on a family-mean basis ranged between 26 and 73% indicating potential for genetic gain from selection for leaf conductance. A relatively greater leaf-to-leaf sampling variance highlighted the need for measurements on more leaves per plot in order to increase the precision of comparisons among family means, especially in early generations. Increasing the number of leaves sampled in each plot should pose little problem for plant breeders because successive leaves can be measured rapidly (ca. five leaves/minute) with the viscous air-flow porometer.