Effects of selection for dark respiration rate on enzyme genotypes in Lolium perenne

Two lines of perennial ryegrass (Lolium perenne) that had previously been selected for 'fast' and 'slow' rates of leaf dark respiration were examined to determine whether selection had differentiated allelic or genotypic frequencies of five polymorphic enzyme loci, and determine whether respiration rates differed among genotypes. The lines were differentiated for genes coding for phosphoglucose isomerase (PGI) and UDP-glucose pyrophosphorylase (UDP). Respiration rates were heterogeneous among UDP and 6-phosphogluconate dehydrogenase (6PGD) genotypes. Founder effects may have produced the genetic differentiation of lines at the PGI locus as we detected no differences among genotypes for respiration rates. The genetic differentiation among lines for UDP was consistent with differences in dark respiration among genotypes. Although we detected large differences (75%) in dark respiration rate among 6PGD genotypes in the fast respiring line, selection did not differentiate the lines at this locus.