Response of Rice to Small Differences in Length of Day

Abstract

DORE1 has recently reported the response of a Malayan rice, an ‘indica’ variety of Oryza sativa L., to small differences in photoperiod. I have obtained similar results with West African upland cultivated rices, varieties of Oryza sativa L. and Oryza glaberrima Steud. The latter is the main indigenous rice cultivated in Northern Nigeria. Monthly sowings (May to October) of two varieties of O. glaberrima in Ibadan—latitude 7° 26′ N.—showed marked variation in time to ear emergence from sowing date, the later sowings flowering earlier. The time between sunrise and sunset at Ibadan varies from 11 hr. 40 min. in December to 12 hr. 33 min. in June.