Effects of Photoperiod, Temperature and Asynchrony between Thermoperiod and Photoperiod on Development to Panicle Initiation in Sorghum

Abstract

The duration of the vegetative phase (i.e. days from sowing to panicle initiation) in sorghum (Sorghum bicolor (L.) Moench) is affected by photoperiod and temperature. Plants of several contrasting genotypes of sorghum were grown in controlled-environment growth cabinets with either synchronous or asynchronous photoperiods and thermoperiods. Apical development was recorded. Diurnal asynchrony between photoperiod and thermoperiod reduced durations to panicle initiation when the temperature warmed after lights went on and cooled after lights went off, but increased these durations when the temperature warmed before lights went on and cooled before lights went off. These effects were shown in the maturity lines 60M and SM100 and also in the USA cv. RS610 and the Sudanese landrace IS22365, but their magnitude varied with genotype, photothermal regime, and the degree of asynchrony. The greatest effect was detected in IS22365 grown at 30/21°C (12 h/12 h) with a 12 h d−1photoperiod when the temperature warmed 2.5 h before lights went on and cooled 2.5 h before lights went off, when the duration from sowing to panicle initiation was 69 d compared with 37 d in the control (synchronous photoperiod and thermoperiod in each diurnal cycle)