Establishment of subterranean clover (Trifolium subterraneum L.) in New Zealand 1. Hardseededness and autumn germination

Abstract

Studies of the germination of subterranean clover (Trifolium subterraneum L.) were conducted in a controlled environment and on a northerly facing hill site at 520 m in the South Island, New Zealand. Seed of cv. Mt. Barker with an initial hard seed content of 97%, stored in soil at the hill site or at room temperature, sampled for germination testing at 15°C every 2 weeks gave a low level of germination even after long periods stored outside in soil from February through to June. Germination increased from 7–10% in February to 13–16% in June. The same seed sown in soil in February at the hill site reached a final germination of 23–24%. Insects and competition from existing vegetation were not a cause of poor establishment. Identical seed subjected to an alternating 15/35°C temperature regime gave almost twice the germination (44%) after 3 months of treatment. Forty-four percent of seed remained hard. The seed of five other cultivars of subterranean clover given similar treatment increased germination 3-8-fold during the course of exposure. The majority of seed that failed to germinate in the above experiments did so because of the development of a seed coat impervious to water, i.e., they were “hard” seeds although they were still viable. The natural regeneration of nine cultivars of subterranean clover was examined at the hill site. By mid April seedling numbers ranged from 65/m² for ‘Clare’ to 285/m² for ‘Mt Barker’. Five cultivars had substantial amounts of seed remaining in the ground ungerminated, ranging from 54% for ‘Woogenellup’ to 92% for ‘Howard’. Seed of five of these cultivars subjected to a fluctuating 15/35°C temperature regime softened steadily. Significant differences in the rate of softening indicate that there may be scope for selection between cultivars. These results and evidence from other subterranean clover evaluations suggest that the lack of the agricultural success of this species in New Zealand may be the result of production of a high proportion of hard seed, which remains hard and therefore fails to germinate in the autumn.

Keywords:

• Trifolium subterraneum
• subterranean clover
• germination
• establishment
• legumes
• hardseed
• environment × genotype interaction