Seed number, seed size and seed diversity in Washington lupin (Lupinus polyphyllus Lindl.)

Over 20 000 seeds of the Washington lupin (Lupinus polyphyllus Lindl.) were examined and measured in an experiment carried out over a 10 year period (1989-1999). Four different groups of Washington lupin seeds were found: dark, patterned, grey and light seeds. During the 10 year experiment, the total average number of seeds per plant decreased from 2654 (1990) to 1220 (1999), there was a slight decrease in seed weight per plant and an increase in the average weight per seed. There was a clear seed size/number trade-off at the intraspecific level. The relative proportions of each seed group also changed with patterned seeds becoming dominant (50 % at the beginning and 90 % at the end of the experiment), grey seeds remained constant (constituting 10 % of the total seeds) and the proportion of both dark (33 % at the beginning and 5 % at the end) and light (10 % at the beginning and 5 % at the end of the experiment) seeds decreased. Six hundred and sixty nine seeds were found to have a different testa ornamentation; they were distributed among the different groups as follows: 48 % patterned seeds, 29 % dark seeds, 12 % grey seeds and 11 % light seeds. There were no significant differences in the physical dimensions of the ornamented seeds compared with all other seeds. The results suggest that the Washington lupin is a mixture of different species and botanical forms; this is discussed in relation to possible selection pressures to produce both smaller and larger seeds. The possibility that changes in tests ornamentation are influenced by genes controlling the synthesis of the seed coat pigment is discussed. (C) 2000 Annals of Botany Company.