Fine mapping of a heading date QTL, Se16 (t), under extremely long day conditions in rice

Heading date (flowering time) is a key trait that determines the yield and the adaptability of rice varieties. In the past 20 years, a number of genetic studies have been carried out to elucidate the genetic control of rice heading date, and many important genes have been cloned. These genes were identified under natural day (ND) conditions; however, little is known about the heading behavior under extreme day-length conditions. In this study, we identified a japonica variety, Sasanishiki, that showed sensitivity to extremely long days (ELD). Its heading date was significantly delayed for about 20 days under artificial ELD conditions that were achieved by setting a light emitting diode (LED) lamp beside a paddy field. We found that the late heading phenotype of Sasanishiki was induced when the day length was more than 14.75 h, and the LED light intensity was above 2 µmol m −2 s −1 . Genetic analysis revealed that the photoperiod sensitivity of Sasanishiki was controlled by a dominant locus, temporarily named Se16 (t). It was fine mapped to a 30.4-kb interval on chromosome 3, containing five predicted genes, including PHYC , a phytochrome encoding gene of rice. Our findings provide new information on the heading date under ELD conditions in rice.