Growth and development of a range of grain-sorghum cultivars in three tropical and sub-tropical environments

Abstract

Seven grain-sorghum ( Sorghum bicolor (L.) Moench) cultivars of varying maturity were grown at three locations in northern Australia (15°39′S, 24°30′S and 27°30′S) with three different sowing dates at each location (September/October, December and March). Dates of emergence, floral initiation, anthesis and maturity were recorded. Tillers and fully expanded leaves were counted at regular intervals. Crop dry-matter production, grain-yield, grain-yield components and leaf area were measured. Temperature and daylength were the major factors governing the duration of growth phases, with daylength assuming greater importance in the later-maturing cultivars. For similar sowing dates, development was faster in the tropics than in the sub-tropics. Empirical relationships were derived between rate of development in each phase and both temperature and daylength. There was a large variation among cultivars in the number of tillers. Fewer tillers were produced in the tropics and the least number was produced in the December-sown crops when the temperature was highest. Tillering was thus inversely related to temperature. The number of tillers was also directly related to growth rate between floral initiation and anthesis, and it is suggested that this was an expression of availability of assimilate for tiller development. Grain-yield was related to the total plant dry-matter increment between anthesis and maturity. Grain number, which was closely related to yield, was related to temperature and the solar-radiation integral between floral initiation and anthesis. Growth rate was shown to be correlated with radiation flux during this period.