The effect of photoperiod on interval between panicle initiation and flowering in rice

Abstract

An understanding of response of crops to photoperiod is essential for accurate prediction of their phenological development. This study aimed to determine whether photoperiod influences the duration from panicle initiation (PI) to flowering in rice ( Oryza sativa L.). In a greenhouse experiment, plants of 12 cultivars were grown under three short-day (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 from PI to flowering was positively correlated with the photoperiod experienced after PI; the effect of a 3-h change in photoperiod varied from negligible in some cases to more than 10 days in others. No consistent carryover effect of photoperiod before PI on the PI-to-flowering duration 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 photoperiods, the number of unexpanded leaves at PI was nearly constant, with an average of about three leaves. This study further supports the earlier experimental finding that rice photoperiod sensitivity continues some days after PI, suggesting the inadequacy of the assumption in crop simulation model CERES-Rice that the PI-to-flowering duration is influenced only by a carryover effect of pre-PI photoperiod.