The agronomic significance of seed quality in combining peas (Pisum sativum L.)
Field emergence trials in NE Scotland of 29 commercial seed lots (80&'37 germination) from five cultivars of combining pea (Consort, Countess, Progreta, Bohatyr and Orb) in 1989, and of 26 of these lots in 1991, revealed large differences in field emergence indicative of differences in vigour. Laboratory germination (NG) was poorly related to the field emergence potential (FEP) of lots. The tetrzolium staining (TZ) test, mean time to germination and probit theoretical initial germination (K_i) were the best overall predictors of FEP. Seed leachate tests (electrical conductivity and N content) gave a good indication of the FEP of lots within individual cultivars but, because of the inherently lower solute leakage from lots of cv. Progreta, correlations for all cultivars together were poor. The influence of sowing date and harvest date on seed quality in combining peas was investigated in a study over two years (1990 and 1991). Only when the date of sowing was very late (mid-May) did it have any measurable deleterious effect on seed quality. Time of harvest had, in contrast a highly significant effect on seed quality; premature harvesting produced seed of poor quality, and although delays in harvest beyond the stage of maximum seed quality had little effect on the viability and vigour of cleaned seed, the yield of such seed was severely reduced. The ability to germinate normally after drying was maximal in seeds harvested at the end of seed-fill (seed moisture content &'61 56&'37) in both seasons. Maximum seed vigour, as assessed by leachate conductivity, TZ, controlled deterioration, K_i and field emergence tests, was, however, in the 1991 trial, reached much later at between 11 and 18 days after the end of seed-fill (smc &'61 23-36&'37). Finally, experiments on plants grown under conditions of minimal competition showed no effect on seed vigour on plant growth and yield that could not be explained by differences in the rate of germination and emergence.