Traits responsible for variation in pollination and seed set among six rice cultivars grown in a miniature paddy field with free air at a hot, humid spot in China

Severe rice sterility induced by high temperatures occurred in the Yangtze Valley of China in the summer of 2003; the cause for an increase in its occurrence is believed to be global warming. Proposed traits for maintenance of high fertility in rice under conditions of high temperature were: (1) long dehiscence formed at the basal part of the anther at the time of the flowering; (2) early time flowering; and (3) decreased panicle temperature. The objective of this study was to clarify whether or not these three possible traits are effective on the seed set of rice under free-air hot condition in this region. These traits were examined in a miniature paddy field in 2005-2006 with six cultivars that had shown variation in seed set rates in the Yangtze Valley in 2003. The effects of the cultivars on these three traits were significant as revealed by the analysis of variance. Percentage seed set was significantly correlated with the length of basal dehiscence (r = 0.682, n = 12, p = 0.015) across cultivars under normal high temperature, but not with the other traits. Analysis of covariance showed that year (fixed variable), length of basal dehiscence (covariant variable) and daily maximum temperature (covariant variable) explained 82.1% of variance in seed set rate across the cultivars. Moreover, the percentage of sufficiently pollinated florets was correlated with both the length of basal dehiscence and seed set percentage. From these results, we conclude that long basal dehiscence is an effective trait in maintaining seed set under high atmospheric temperatures in the paddy fields in this region and that the long basal dehiscence enables high seed set rate through the stable pollination. (C) 2010 Elsevier B.V. All rights reserved.