Abstract
Seedlings derived from dropped seed of forage rice for whole crop silage at the harvest cause a severe weed problem on the normal rice paddy field in the following year. To alleviate the weed problem, we examined the germination ability of 15-19 cultivars and lines of forage rice and ordinary rice harvested at the yellow ripe stage in 2006-2007 and 2007-2008. The seeds overwintered on the soil surface (SS) or were embedded in a soil depth of 15-cm (ES) in the paddy field. Viability index (VI) represented by germination percentage after wintering divided by that before wintering multiplied by 100 showed a significant difference among varieties in the range of 0-44 and 0-24 in SS and ES, respectively. The VI in ES was lower than that in SS for almost all varieties. There were positive correlations between VI and the degree of seed dormancy before wintering and the correlation coefficients were higher in ES than in SS. Trace of germination was observed in ES treatment after wintering and there were negative correlations between the percentage of trace of germination after wintering and the degree of seed dormancy before wintering. These results suggest that the over-wintering ability of forage rice seed is lower in the varieties having weaker seed dormancy, because they are vulnerable due to easy germination during wintering in the paddy field.
