SEED PRODUCTION IN CLUSTER CLOVER (TRIFOLIUM-GLOMERATUM L.) 1 - FLOWERING TIME, ABORTION, SEED SIZE, AND HARDSEEDEDNESS ALONG BRANCHES

Seed production in cluster clover (Tri;folium glomeratum L.) was inves tigated at the level of the individual inflorescence. Plants were grow n in nursery rows under non-limiting conditions until 150 days after s owing, at which time irrigation was stopped to truncate the growing se ason. The number of florets, and the number, mass, and impermeability of seeds, were determined for each inflorescence along the main branch es, and were related to the date and node of flowering. The interval b etween subsequent flowers increased (3.4 days at node 2 v. 7.3 days at node 7) and the rate of floret abortion increased (14% at node 1 v. 4 9% at node 7) with successive inflorescences along the branch, even wh ile moisture conditions remained favourable. These effects are attribu ted to resource limitation during the latter stages of plant growth. O n the other hand, seeds per floret and seed mass were unaffected by th e node of flowering but declined rapidly once irrigation ceased. Hards eededness was not affected by either node of flowering or date of flow ering, before or after the cessation of irrigation. Mean initial hards eededness from inflorescences produced after irrigation ceased was sli ghtly higher than that from earlier formed inflorescences (99.6% v. 94 .1%, P < 0.001). The results highlight the importance of reproductive timing in an environment with a limited growing season, since seed pro duction fell rapidly once water conditions became unfavourable. They s uggest that seed production in cluster clover is near to its potential while conditions remain favourable, although resource Limitation may reduce the rate of flowering and increase floret abortion as the plant matures. Although unfavourable water conditions may sharply reduce pr oduction of viable seeds, in cluster clover the initial impermeability of those seeds is not affected, possibly a benefit of rapid seed form ation.