Assessment of the response to selection for leaf water conductance in Lolium perenne

Measurements of leaf water conductance (LWC) were made in a growth room on plants previously selected for either high or low LWC as seedlings from two Lolium perenne L. populations. Differences in LWC were maintained between selection groups when measured as older plants, but there were considerable changes in LWC of individual selection groups on remeasurement. The LWCs and the rankings of LWCs of individual genotypes were correlated between experiments, thus demonstrating that selection of genotypes was worthwhile. Thus the possibility of including LWC in selection programmes was established.

Investigations conducted to optimize sampling for LWC are described. It was concluded that little further reduction in the standard error of LWC measurements was obtained by making more than eight measurements per genotype, and it was important to sample on at least four tillers. A new measure for the phenotypic stability of a selection group is proposed, named realized ‘selectivity’. The realized selectivity can be used to estimate the upper value for realized heritability and is about 0.5 for LWC in L. perenne. The values of phenotypic repeatability of LWC are compared with other similar measurements.