Floral traits to enhance outcrossing for higher hybrid seed production in rice: present status and future prospects

High seed cost is a major factor limiting the adoption of hybrid rice in South and Southeast Asian countries. A practical way to improve hybrid seed production is to increase the outcrossing rate in rice. Several studies reveal that perennial wild Oryza species have a higher outcrossing rate than annual species. Among various traits that influence outcrossing, pistil characteristics are the most crucial in improving the seed set on the male sterile parent in hybrid seed production. Wild species are known to have wide genetic variability for stigma length, anther length, and percent stigma exsertion. This review establishes the need to exploit new genetic resources, through both classical and molecular breeding approaches, to improve seed production. It also reviews the genetic variability of floral characteristics, the genetics of floral traits that influence outcrossing, and progress made in understanding these traits using biotechnological approaches, the effect of environment on floral traits and the resulting prospects for improving hybrid rice seed production.