Estimation of pollen dispersal distance in Job's tears (Coix lacryma-jobi L.) by using red leaf sheath as a morphological marker.

Job's tears (Coix lacryma-jobi L.) is grown widely in Asian countries and a crop that can fertilize with own pollen and pistils. The grains are used not only for food but also for medicinal purposes. The grain of many cultivars contains glutinous endosperm; only grains with this glutinous endosperm are suitable for use as medicine in Japan. Many wild types have non-glutinous endosperm and can easily cross with cultivar under natural environmental conditions. Because the non-glutinous endosperm trait is dominant to that of glutinous endosperm, F₁ seeds produced by crosses between a cultivar and a wild type have non-glutinous endosperm. To reduce the rate of unwanted crosses, we investigated the pollen dispersal distance by using a red leaf sheath as a morphological marker. When plants were cultivated in rows 70 cm apart, the crossing rate was about 25%-35%. As the distance increased, the crossing rate decreased at a rate that could be fitted to a power approximation in fields without intervening plants and to an exponential equation in fields with intervening plants. Our data could be used as guidelines for preventing unwanted crossing with wild types when growing cultivars.