Seed weight in Lolium perenne as affected by interactions among seeds within the inflorescence

Little is known about interactions between seeds within the inflorescence o f perennial ryegrass (Lolium perenne L.) and their effect on final seed wei ght. These relations were investigated in two glasshouse experiments using two genotypes, by reducing the number of seeds in an inflorescence at anthe sis. In the first experiment, entire spikelets were removed to study the re lations between seeds in different spikelets. The effects on seed dry weigh t were not proportional to the number of spikelets removed. In one genotype , removal of two-thirds of the spikelets increased seed dry weight of the r emaining seeds by 15%. In the other genotype, such treatment did not increa se seed dry weight. In the second experiment, investigating seed interactio ns within a spikelet, either two proximal seeds or two central seeds were m aintained in a spikelet by removing the other ovules in combination with no or 75% shading. Shading by 75% reduced seed dry weight by about 10%. In th e unshaded treatment, seed dry weight was not affected by ovule removal. Un der shading, the central seeds in a spikelet were about 12% heavier if they grew alone, in contrast to the proximal seeds. The effects of a reduction in seed number on seed dry weight were not related to the final nitrogen co ncentration of seeds. These experiments show that assimilate partitioning a nd the relationship between seeds in the inflorescence of perennial ryegras s are already largely determined at anthesis; increasing seed yield by mani pulations after anthesis is not feasible. (C) 1998 Annals of Botany Company .