Seed production in cluster clover (Trifolium glomeratum L.). 2 Effect of sowing time and sowing rate on flowering time, abortion, seed size, and hardseededness

Abstract

An ecotype of cluster clover (Trifolium glomeratum L.) common to the wheatbelt of Western Australia was sown in pure undefoliated swards at rates in the range 2-256 kg/ha, on 2 dates to give growing seasons 13 and 18 weeks in length. Irrigation was phased out at the time of flowering of late-sown plots. The treatments generated a scale of seed production in cluster clover from 148 kg/ha (43 000 seeds/m2) to 1640 kg/ha (389 000 seeds/m2). Delayed sowing was more important in reducing seed production than was increasing sowing rate. By comparison with the early-sown plots, the late-sown plots had less above-ground biomass at flowering (2053 v. 2728 kg/ha); 48-66% fewer inflorescences per m2; a shorter vegetative phase (9 days); fewer seeds per inflorescence (26 v. 31); and lesser seed mass (337 µg v. 436 µg). There was little effect of the treatments on hardseededness except that hardseededness after 1 season in the field was higher in seeds from late-sown swards at high sowing rate (58%) than from late-sown swards at low sowing rate or early-sown swards (40%). Neither sowing rate nor sowing time influenced the within season pattern of hardseed breakdown. The results indicate that cluster clover is capable of massive seed production, and that even under highly stressed conditions seed production is maximised by a high reproductive allocation and small seed size. Despite conditions which reduced seed production by up to 90%, cluster clover is able to maintain its seed quality. Relatively few inviable seeds are produced and hardseededness is either unaffected or enhanced.