FACTORS INFLUENCING THE DEVELOPMENT OF BREAD WHEAT PLANT TYPES TO BE GROWN IN THE TRANSITIONAL ZONE IN NORTHERN SYRIA

This study sought to identify factors that influence wheat development in the transitional wheat growing zone of northern Syria. Three devel opment factors were studied, intrinsic earliness, and responses to ver nalization and to photoperiod. Two sets of wheat were studied, each co mposed of lines with differing combinations of development factors. Se t 1 comprised 20 parental and breeding lines utilized by the CIMMYT/IC ARDA facultative and winter wheat breeding program based at Tel Hadya. Set 2 comprised 19 parental and breeding lines utilized by an Austral ian winter wheat breeding program based at Temora. Field development w as recorded in greatest detail at one site, Tel Hadya, using the state of differentiation of the apex of the main tiller of sampled plants. To extend findings, development was also recorded as the time from sow ing to ear emergence for later sowings of wheat at Tel Hadya, and in s ewings at four other regional sites. The significance of each developm ent factor was tested in multiple regressions that predicted either st age of apical development at Tel Hadya, or time to ear emergence in al l trials. It was found that intrinsic earliness was the major factor a ssociated with development, in both sets of wheat. Response to photope riod had a much smaller and less consistent effect. Response to vernal ization had least effect on development, possibly because low temperat ure in winter delayed development for a longer period than was require d to fully vernalize winter wheats. Our results suggested it may not b e directly relevant whether spring or winter wheats are grown in the t ransitional zone of northern Syria. The desired phenotype for the regi on, of slow development prior to double ridge, then fast development t o ear emergence, cannot be simply achieved from combinations of the th ree development factors. Selection for improved adaptation to the regi on must continue to rely on direct field observations.