SEED AND SEEDLING STUDIES OF 3 TRIFOLIUM-SUBTERRANEUM VAR BRACHYCALYCINUM LINES, IN A PREDOMINANTLY SUMMER RAINFALL ENVIRONMENT

Field experiments were conducted in a predominantly summer rainfall en vironment to investigate burr burial, seed production, seed characteri stics, seedling emergence and survival, and the effects of time of sow ing on 3 Trifolium subterraneum var. brachycalycinum lines (cv. Clare and 2 local lines). Each line produced more surface than buried burrs; surface burrs were 59% (range 56-62%) of the total number of burrs re covered and produced 59% of the total seed number. Numbers of seeds pe r burr were similar for surface and buried burrs, however, buried seed s were 0.97 mg heavier (P<0.05) than surface seeds. Storage for 5 mont hs at 25/60 degrees C decreased hardseed content of surface seed by 50 % and buried seed by 70%. Surface and buried seeds stored at 25/25 deg rees C for 3 months prior to sowing in trays had a total emergence of <10%, compared with 70% emergence for seeds stored at 25/60 degrees C before sowing. These emergence differences reflected their levels of h ardseededness. Numbers of seeds recovered from the soil were not signi ficantly different among lines, declining from about 4200 seeds/m(2) a fter initial seed set to 150 seeds/m(2) by the following winter, a 97% decrease. Seed production in the second year increased seed reserves to about 8730 seeds/m(2). With no further seed production, levels had declined by 93% in June 1990 and by 99% in May 1991. These data confir m the importance of annual seed production for persistence. Total seed ling emergence in summer-autumn accounted for only 10% of the estimate d seed production in each year. Seedling survival in summer-autumn 198 8-89 was 92.7%, more than double the survival in 1989-90. The effect o f sowing time on flowering was always significant, with time to first flower being highest (196 days) for the earliest sowing in March (P<0. 05), progressively decreasing (P<0.05) to 108 days for the latest sowi ng in July. In March, April and May sowings, inflorescence numbers on the first day of flowering were similar at about 120/m(2), but increas ed markedly (P<0.05) for sowing in June or July. However, for the Marc h and July sowings, number of inflorescences at the 9 November 1990 co unt, were lowest (P<0.05). May or June sowings had the highest number of burrs and seeds (P<0.05), indicating that these may be the best sow ing times for maximum seed production in these Trifolium subterraneum var. brachycalycinum lines.