EFFECT OF TEMPERATURE ON TIME TO PANICLE INITIATION AND LEAF APPEARANCE IN SORGHUM

Leaf-tip appearance and duration from planting to panicle initiation ( PI) are important developmental processes in cereals. This study was c onducted to determine the effect of air temperature on rates of leaf-t ip appearance and 1/PI for sorghum [Sorghum bicolor (L.) Moench]. Nine genotypes were grown in pots at mean temperatures of 17 to 33 degrees C and photoperiods of 11.0 to 12.3 h d(-1) in glasshouses. Leaf-tip a ppearance was recorded every 3 to 5 d and PI determined by apical diss ection. The optimum temperature (T-o) for 1/PI was between 26 and 27 d egrees C and supra optimal temperatures delayed PI in all genotypes. T he base temperature (T-b) ranged from 6 to 10 degrees C but only one g enotype had a T-b significantly different from a common value of 8.5 d egrees C. Growing degree days (GDD) for PI among genotypes at sub-opti mal temperatures varied from 411 to 592 (P < 0.001) above a T-b of 8.5 degrees C. Warmer temperatures (>27 degrees C) reduced the rate of le af-tip appearance in five genotypes; in the remaining genotypes the ra te of leaf appearance was effectively constant at mean temperatures be tween 23 and 33 degrees C. There was no significant difference (P > 0. 20) among genotypes in the phyllochron, which was 57 GDD above a T-b o f 8.5 degrees C. The final number of leaf-tips was constant within gen otypes at mean temperatures of 18 to 30 degrees C, but varied among ge notypes from 11.8 to 17.3. In conclusion, the T-b and T-o for 1/PI wer e approximately 8.5 and 27 degrees C and there was variation in 1/PI b ut not in the rate of leaf-tip appearance among the genotypes studied.