Unusually High Frequency of Cross-Pollination Between Rice Landraces Shiuli and Kharah with Coincident Flower-Opening Times

Cross-pollination in cultivated rice (Oryza sativa L.) is rarely reported to exceed 2%. This low cross-pollination frequency (CPF) is conducive to success-fully maintaining the purity of rice landraces for many generations. We were therefore surprised to notice a dramatic loss of genetic purity in some of the pure line landraces in many farmers’ fields. Having ruled out the possibility of mixing of seeds from dif-ferent varieties, we surmised this rapid loss of genetic purity to be due to a somewhat higher degree of cross-pollination, and conducted a carefully designed expe-riment with suitably chosen pairs of landraces. We report here an unusually high (>81%) CPF seen in a pair of landraces whose flower opening times (FOTs) were coincident. Our control experiment on a pair of landraces with non-overlapping FOTs failed to detect any cross-pollination. This preliminary report sug-gests that the crucial importance of FOT diversity in landraces in determining CPF has not been recognized in designs of previous reports of crossing experiments, resulting in a severe underestimation of CPF in cultivated rice under natural conditions.