Abstract:

“Pre-harvest sprouting” in rice is usually caused by high temperature and humility or continuous raining. It has frequently happened in F₁ in hybrid rice seed production. Those “Pre-harvest sprouting” or “Physiologically germinated” seeds are of lower quality, by which the hybrid rice seed production is badly affected, and the problem usually happens every three years. 20% or even 50% yield in the seed production losts by “Pre-harvest sprouting” in the Yangtze River and the South West areas. It is estimated that “Pre-harvest sprouting” causes an average decrease of seed activity by 10%.
A recombinant inbred line (RIL) population comprising 304 lines derived from a cross between indica rice (Oryza sativa L.) cultivars Zhong-156 and Gumei-2 was used to study the physiology of pre-harvest sprouting.
Based on the data of “Sprouting rate in panicle” and “Sprouting rate in grain”, two kinds of lines namely easy-sprouting lines and hardly-sprouting lines were selected to investigate their physiological differences when pre-harvest sprouting happened.
The experiment was conducted in a special field with higher temperature and higher humidity microclimate. The results indicated that female parent GM-2 was easier to produce pre-harvest sprouting than the male parent ZH-156, GA₁ content and amylase activity in GM-2 grains were higher than that in ZH-156. However, ABA content in GM-2 grains was lower than that in ZH-156. Higher temperature and higher humidity facilitated the GA₁ increment from milk ripe stage to yellow ripe stage, GM-2 and the easy-sprouting lines showed a even higher span of increase tendency than ZH-156 and the hardly-sprouting lines, which enhanced amylase activity and led to pre-harvest sprouting. This may be the physiological basis for pre-harvest sprouting induced by higher temperature and higher humidity, and these special characters must be inherited from their parents.

Key words: Pre-harvest sprouting, Physiological analysis, Hybrid rice seed F₁, Amylase activity, Recombinant inbred lines