Gene action for leaf conductance in three wheat crosses

Selection for altered stomatal conductance has potential to improve wheat grain yields in dry and well-watered environments. Yet the slow speed with which conductance is typically measured has limited studies reporting genetic parameters for leaf conductance. A viscous air-flow porometer that measures resistance to mass flow through a leaf was used to provide rapid estimates of leaf conductance. These estimates were obtained prior to anthesis on irrigated plants representing different generations of crosses between the low conductance parent, Quarrion, and 3 high conductance varieties, Hartog, Genaro 81, and Matong. Sampling for leaf conductance was done between 08 00 and 12 00 hours under cloud-free conditions. Significant (P < 0.01) genetic differences were observed between generation means for conductance measured in different crosses and on different days. Gene action was complex with both additive and non-additive (dominance and additive-based epistasis) genetic effects important for expression of leaf conductance. There was a greater reduction in leaf conductance for Quarrion and backcross-Quarrion progeny with sampling later into the day. In turn, genetic variances for leaf conductance increased with later sampling. Family-mean heritabilities varied in size (0.06-0.70), depending on cross and time of sampling. It is suggested that breeders selecting for altered leaf conductance maximise genetic gain by delaying screening of populations until later in the day, and repeat measurements across a minimum of 2 days. Large populations of inbred families should be evaluated in order to minimise confounding through dominance and increase the probability of recovering families containing desirable non-allelic gene combinations.