THE EFFECT OF PHOTOPERIOD ON INTERVAL BETWEEN PANICLE INITIATION AND FLOWERING IN RICE

An understanding of response of crops to photoperiod is essential for accurate prediction of their phenological development. This study aime d to determine whether photoperiod influences the duration from panicl e initiation (PI) to flowering in rice (Oryza sativa L.). In a greenho use experiment, plants of 12 cultivars were grown under three short-da y (SD) conditions 10, 11 and 12 h day(-1) or under three long-day (LD) conditions 13, 14, and 15 h day(-1) until PI, after which half of the plants at SD were transferred to a 3-h longer photoperiod and half of the plants at LD were moved to a 3-h shorter photoperiod. Duration fr om PI to flowering was positively correlated with the photoperiod expe rienced after PI; the effect of a 3-h change in photoperiod varied fro m negligible in some cases to more than 10 days in others. No consiste nt carryover effect of photoperiod before PI on the PI-to-flowering du ration was detected. As expected, the total main-culm leaf number was influenced by photoperiod before PI, but not thereafter. Although the leaf number varied greatly both among cultivars and among pre-PI photo periods, the number of unexpanded leaves at PI was nearly constant, wi th an average of about three leaves. This study further supports the e arlier experimental finding that rice photoperiod sensitivity continue s some days after PI, suggesting the inadequacy of the assumption in c rop simulation model CERES-Rice that the PI-to-flowering duration is i nfluenced only by a carryover effect of pre-PI photoperiod. (C) 1998 E lsevier Science B.V. All rights reserved.