Germination, emergence and surface establishment of wheat and ryegrass in response to natural and artificial hydration-dehydration cycles

Abstract

The emergence and establishment of wheat and annual ryegrass (Lolium rigidum) from seeds that had been hydrated and dehydrated in such a way as to double the speed of their germination was examined in controlled environments. In addition, the effects of rain on the germination characteristics of surface-sown ryegrass were monitored for 4 months during summer and autumn. Seed pretreatment was of no benefit to the establishment of wheat seedlings. Ryegrass seedlings from pretreated seeds emerged earlier and 3 weeks after sowing had higher dry weights than controls. When conditions in the seed-bed favoured establishment for only a short time, some pretreated seeds of ryegrass established where none of the controls did. It is concluded that seed pretreatment has potential application in autumn or winter establishment of pasture grasses, but not of wheat. Initially, the effect of rain insufficient for establishment was to increase the potential germinability of ryegrass by reducing dark dormancy, but seed viability decreased later. A proportion of the seeds previously exposed to rain always germinated before controls. The ability of naturally dispersed seeds to establish depends not only on the timing of establishment rains, but on the cumulative length of the wet periods that occurred before the break of season.