VARIABILITY OF SEED-SET IN ALFALFA AND CORRELATIONS WITH SOME POLLEN AND OVULE CHARACTERISTICS
A random sample of 30 named alfalfa (Medicago sativa L.) cultivars representing diverse genetic material was investigated for relationships among the following traits: frequency of seed-set (seeds per flower) after self-pollination, frequency of seed-set after cross-pollination, abundance of pollen, viability of pollen, germinated pollen tube length, ovule number, and ovule size. In each cultivar, 100 reciprocal crosses and selfs were made by hand in the greenhouse, with emasculation when appropriate. A second experiment re-used the plants of 11 cultivars for specific inter- and intra-cultivar crosses to estimate the relative importance of maternal and paternal effects on seed-set. In the first experiment, seed-set of crosses did not correlate with any other factors, and the seed-set of selfs was only slightly correlated with pollen viability. An analysis of broad sense heritabilities indicated a very low heritability for seed-set of selfs (H = 0.11), and relatively high heritability for seed-set of crosses (H = 0.74). The difference in rates of seed-set for crosses and selfs on the same plant also had high heritability (H = 0.66). The mechanisms controlling seed-set with selfing and with crossing appeared to be different. In the second experiment, correlation analysis indicated that the maternal parent had over five times the influence of the paternal parent on the frequency of seed-set.