Control of early development in winter and facultative wheats in contrasting field environments

Abstract

The major factors influencing the development of wheat are responses to vernalisation and to photoperiod, and intrinsic earliness. This study sought to determine how these factors influence the development of field-grown winter and facultative wheats of Australian origin, which tend not to be highly responsive to photoperiod. Of particular interest was the relationship between response to vernalisation and the switch from vegetative to reproductive growth. The effect of these developmental factors in influencing field development was established by correlating measurements from controlled and field environments. Three field environments were studied at 2 sites, a February and an April sowing at Temora (NSW, Australia), and a November sowing at Tel Hadya (Syria). Both sites were around 35� latitude. These environments differed in the duration from sowing to the onset of vernalising temperatures in winter. The onset of vernalisation was most delayed in seedlings for the February sowing at Temora. Vernalisation commenced earliest in seedlings for the November sowing at Tel Hadya, and was then presumed to proceed most rapidly. The 3 development factors were measured in 17 wheat genotypes. These data had been published previously; however, measurements of integrated response to vernalisation were re-expressed in new units, and the experiment was repeated, to attain greater precision. Measurement of each developmental factor was correlated with the timing of double ridge, terminal spikelet, and the beginning and end of spikelet site accumulation in each field environment. Where vernalisation was most delayed after sowing, the strongest correlation was between integrated response to vernalisation and the duration from sowing to double ridge. Where vernalisation was most rapid after sowing, the strongest correlation was between intrinsic earliness and the duration from sowing to the beginning of spikelet site accumulation. This study suggests lack of vernalisation most strongly delays the timing of double ridge in winter wheats, and masks the effect of intrinsic earliness which otherwise influences early development. These findings reconcile the significance of the timing of double ridge with previous quantitative studies of early development in winter and facultative wheats.