THE PATTERN OF FLOWERING, SEED SET, SEED GROWTH AND RIPENING ALONG THE EAR OF LOLIUM-PERENNE

A greenhouse pot experiment was conducted to elucidate the pattern of decreasing seed set and seed dry weight found from the basal to the up per spikelet in Lolium perenne L. ears and-very markedly-acropetally w ithin a spikelet. The changes in fresh and dry weight of the seed afte r anthesis were monitored for 12 positions within the ear. To determin e the duration of seed growth, the spatial and temporal patterns of fl owering and ripening along the ear were assessed. The proximal florets of the central spikelets flowered first, and the upper spikelets in t he ear flowered before the basal spikelets, with flowering proceeding acropetally within a spikelet. The upper spikelets ripened earlier tha n the basal ones, and the seeds within a spikelet ripened simultaneous ly. These patterns of flowering and ripening along the ear resulted in different durations of seed growth along the ear. Thus from the proxi mal to the distal seed within a spikelet the duration of growth decrea sed by 26%, the rate of growth fell by 48% and seed set and seed dry w eight also fell sharply. Of the total variation in maximum, final seed dry weight within the ear, 4% could be attributed to the difference i n seed dry weight between spikelets and 89% to differences in seed dry weight within spikelets. Differences in duration and rate of seed gro wth and seed set were also much smaller between spikelets than within spikelets. About 60% of the differences in seed dry weight along the e ar were attributable to differences in growth rate and about 30% to di fferences in the duration of seed growth. The relative growth rate did not differ between seeds in different positions. The main factor dete rmining seed growth rate was the dry weight of the ovule at anthesis, which declined sharply from the proximal to the distal floret within a spikelet. Analysis of the fructose, glucose, sucrose and starch conce ntrations showed that seed growth was not limited by the availability of sucrose nor by the ability of the seeds to convert sucrose into sta rch. These conclusions were supported by results from a second greenho use experiment in which all ovules in 50% of the spikelets were remove d at anthesis. Dry weight of the remaining seeds increased by only 15% .