Determination of spikelet number in wheat. III.* Effect of varying temperature on ear development

Abstract

The effects on rate of development and spikelet number per ear in eight wheat cultivars grown at various temperatures (16/9, 23/16, and 30/23°C for 8/16 hr) throughout or transferred from one temperature to another at floral initiation were studied under normal (12.5–14.0 hr) and 24 hr photoperiods. Under a 24 hr photoperiod, the durations of the vegetative, spikelet and elongation phases, and spikelet number per ear decreased as the temperature increased from 16/9 to 30/23°C in all cultivars. The rate of spikelet initiation increased as temperature increased from 16/9 to 23/16° in most cultivars, but further increase in temperature caused a variable response. Under a normal photoperiod, increasing the temperature from 16/9 to 23/16°C changed spikelet number little, but further increase in temperature decreased it in most cultivars. The rate of initiation increased, but the durations of the vegetative, spikelet and elongation phases, and the apex length at floral initiation decreased in all cultivars as the temperature increased from 16/9 to 23/16°; with further increase in temperature, the rate of initiation, apex length and duration of the elongation phase decreased in most cultivars, but the durations of the vegetative and spikelet phases either increased or changed little. Variation in the number of spikelets per ear in relation to variation in the factors considered to be its possible determinants is discussed with a view to understanding the control of spikelet number. ___________________ *Part II, Aust. J. Agric. Res., 28: 575 (1977).