THERMAL REQUIREMENTS FOR GERMINATION AND SEEDLING GROWTH OF WHEAT

Two cultivars of wheat, Hartog (a spring type) and Rosella (winter) were sown at 2, 5, 8, 10, 15, 20 and 25-degrees-C on porous sand medium held at constant soil matric potential. The thermal times required for germination, onset of coleoptile elongation and emergence were similar, 27, 35 and 130-degrees-C days respectively, for the two cultivars over the temperature range of 2-25-degrees-C. By extrapolation, the base temperature for germination and coleoptile elongation was 1-degrees-C and for emergence 0.4-degrees-C. The rate of seedling elongation and emergence of both cultivars increased linearly with temperature between 5 and 25-degrees-C. Final percentage germination, final coleoptile length and total emergence of both cultivars were independent of temperature between 8 and 25-degrees-C but were smaller at 2-degrees-C. Differences between the two cultivars were confined to response to low temperature (2-degrees-C) during germination and to high temperature (25-degrees-C) during coleoptile elongation.