Presowing Hydration-Dehydration Treatments in Relation to Seed Germination and Early Seedling Growth of Wheat and Ryegrass

Abstract

Seeds of wheat (Triticum aestivum cv. Egret) and annual ryegrass (Lolium rigidum cv. Wimmera) were given a single hydration-dehydration cycle by adding a known amount of water and later air-drying them. Embryos enlarged during this initial hydration, and short periods at high water contents were equivalent to longer periods at lower water contents. After hydration to 145% of seed dry weight (wheat) or to 155% (ryegrass) followed by dehydration back to the original seed weights the speed of germination of both species was approximately doubled because the lag phase of germination was shortened. The proportion of ryegrass seeds that were dark-dormant was reduced if seeds were pretreated in light. Pretreatment did not increase germination synchrony, alter threshold temperatures for germination or enhance seedling growth rates. The viability of pretreated seed declined rapidly at - 15°C and at 50°C. The effect of pretreatment, i.e. early germination, is attributed mainly to embryo enlargement. More rapid imbibition of pretreated seeds may contribute in a minor way to differences in germination time.