Estimate of outcrossing rates in a rice plant (Oryza sativa L.) under field conditions using a purple grain rice cultivar, Okunomurasaki

Abstract

We studied outcrossing in a rice plant under field conditions over five years, to clarify the relationship between outcrossing, pollen flow, and meteorological factors. We employed two cultivars to discriminate hybrid grains: Okunomurasaki, a non-glutinous cultivar with purple grains, was used as the donor, and Himenomochi, a glutinous cultivar, was used as the recipient. Therefore, we could accurately discriminate hybrid grains by the presence of two phenotypic markers—the xenia grain and the leaf color of the F1 plant. The results indicated that outcrossing occurred when the difference in the heading date between the donor and recipient was 11 days or less. And it did not occur when the difference was 13 days or more. In 2004 and 2007, hybrid grains were detected at a distance of 20 m or more from the donor. The wind speed during the flowering period of the donor was higher in both of these years than during the other three years of the study period. This suggested that outcrossing often occurred when the flowering period of the donor and recipient overlapped and the wind speed was high. In addition, outcrossing was considerably depressed when the difference in the day of heading between the donor and recipient was large.