Abstract
As part of a study on the heading characteristics of sorghum spp., the effects of temperature changes on the final leaf number and the leaf emergence rate on the mainstem were examined by changing the sowing date and planting year, using 57 commercial cultivars. The responses in the number of leaves to temperature varied substantially among different cultivars. On the basis of the degree of the response, cultivars could be clearly classified into two groups;in one group, the number of leaves obviously increased with a temperature increase, and in the other group, the temperature changes did not have a significant effect on the number of leaves. Moreover, each of the two groups could be further classified into four and three sub-groups based on the degree or pattern of the responses, respectively. Although the leaf emergence rates based on calender days increased with an increase in growth temperature, those based on an effective heat unit summation above 12℃ were approximately constant, regardless of thetemperature changes. The heat unit summations required for the emergence of one leaf was 36.5℃ in sorghum and sorghum × sudangrass, and 40℃ in sudangrass.
