Radiation Effects on Rate of Development in Wheat Grown Under Different Photoperiods and High and Low Temperatures

Abstract

This study was designed to examine whether development rate of wheat might be changed by radiation at high temperature and more generally whether development might be varied by changed source: sink ratio. In the genotype studied, when temperature was high (27/22ºC) and especially when the photoperiod was short (9 h), leaf primordia were produced more slowly under low than high natural radiation, and this slowing was reflected in lower final spikelet numbers and in fewer grains per ear. Under the higher source: sink condition of low temperature (17/7ºC), and under either short or long photoperiod, rates of primordia production were not measurably changed by radiation, but more light did result in more spikelets. The lengthening of plastochron intervals (thermal time between the appearance of leaf primordia) associated with low radiation did not translate into significantly increased phyllochron intervals (thermal time between emergence of leaves). However, phyllochron intervals were responsive to both photoperiod and temperature.

Under short photoperiod, source limitation associated with high temperature extended the thermal time to ear emergence. Thus, an increase in temperature from 17/7ºC to 27/22ºC doubled the thermal time to heading from 1241 to 2571 ºCd. Source limitation associated with low radiation also increased thermal time to heading by up to 400 ºCd and calendar time by up to 17 days. Under long photoperiod, where development was rapid, radiation did not change the timing of developmental stages. It is concluded that although development in wheat is generally not source-limited in the traditional environments for cultivation, under high temperatures and shorter photoperiods development may be slowed by limiting source:sink ratios.