Variation in skikelet initiation and ear development of old and modern Australian wheat varieties

Abstract

A chronological series of 14 economically important varieties of wheat was sown at two sites in Western Australia. Frequent samples were taken until the terminal spikelet stage. At each sampling, the stage of apex development of the main shoot was scored and number of emerged leaves and total number of primordia were counted. At terminal spikelet stage, numbers of leaves and spikelets were counted separately. Development was faster at Perth, which was on average more than 1 °C warmer than Wongan Hills. When analysed in terms of thermal time, development of varieties with an intermediate-length life-cycle was similar at both sites, as were rates of primordium initiation. Development of the earliest varieties was also similar at both sites until about the double-ridge stage, when herbicide was applied to the Wongan Hills experiment. This caused malformation of the floral apex and slowed down development compared with Perth. The latest varieties developed more quickly at Wongan Hills, possibly because they may have a vernalisation response. Thermal time from sowing to double-ridge stage ranged from 424 to 958°Cd and to terminal spikelet from 591 to 1196°Cd. Between 8 and 14 leaves were initiated, the number of leaves being strongly correlated with the time to double-ridge and terminal-spikelet stage. The rate of spikelet initiation varied from 0.08 to 0.03 (°Cd) −1, and both rate and duration of spikelet initiation were also strongly correlated with number of leaves. There was no correlation with number of spikelets. The association between number of leaves and shoot apex development may have important implications for breeding high-yielding early genotypes, as further reduction in the number of leaves on the main shoot may reduce tillering potential. It may be possible to use thermal time to predict both stages and rates of development in the earlier varieties. Differences in response of the later varieties between sites needs further investigation.