Development and Testing of Cultivar-Specific Tillering Coefficients for Sorghum

Abstract

Tillering is an important yield component of grain sorghum [Sorghum bicolor (L.) Moench]. Temperature greatly influences tillering, and variability occurs among cultivars. Growth rate has been used to describe mathematically cultivar tillering abilities for a range of environments. Our objectives were to develop tillering coefficients for a range of temperate and tropical grain sorghum cultivars and to test the accuracy of these coefficients in predicting productive tiller numbers using independent field data. Eight grain sorghum cultivars of temperate (DK 39Y, DK 46, RS 610, and Pioneer 8500) and tropical adaptation (AT x 623 x RT x 430, DK E57, Segaolane, and CSM 63) were grown in a growth chamber at Manhattan under three day/night temperature regimes (20/150C, 25/200C, and 30/250C) to determine the relationship between dry matter required per tiller and daily minimum air temperature. Field experiments at St. John and Manhattan were used to determine the effects of dates and rates of planting on tillering of the same cultivars. The results were used to evaluate the accuracy of the tiller dry matter requirements. Growth chamber results showed that the number of tillers was related linearly to daily rates of dry matter accumulation per plant. These dry matter requirements per tiller were related linearly to daily minimum air temperature, with differences among cultivars. Predicted number of productive tillers per plant was approximately 7 to 12 times actual tiller numbers in the field experiments. This was accounted for by low cultivar-specific tillering coefficients, which were not representative of the dry matter requirement of productive tillers.