Fertility in an interspecific rice population and its effect on selection for rhizome length

Fertility barriers, which are common in many wide crosses, can hinder efforts to introgress genes. In this study, we examined an intermated Oryza sativa/Oryza longistaminata population and assessed how fertility barriers affected selection for long rhizomes, a polygenic trait. Rhizomes are typical of O. longistaminata but not found in O. sativa. In the intermate population, we observed that pollen-fertility and self-fertility were generally low but exceptional individuals of high fertility were found in nearly all generations. About 1/5th of the genotypic variation for self-fertility was accounted for by pollen-fertility, based on a significant linear regression. Intermating improved self-fertility more than backcrossing for one generation. Heritability estimates via parent-offspring regression were 17 ± 7% for pollen-fertility and 39 ± 9% for self-fertility. The data indicated that many genes contributed to the fertility barriers. Individuals with relatively high fertility or long rhizomes (>8 cm) were observed infrequently in the intermated population, and there was no evidence of association between low fertility and presence of long rhizomes. By evaluating a large population, we were able to obtain a few rare recombinants that had both self-fertility greater than 10% and long rhizomes.