Rate of leaf appearance in sugarcane, including a comparison of a range of varieties

Leaf appearance rate is a major determinant of canopy establishment, radiation interception and therefore yield. The effect of genotype on leaf appearance rate in sugarcane is largely unknown. Leaf appearance rate was recorded for the mainstems of pot grown sugarcane plants of nine commercial varieties, over 10 months in Townsville, Australia. Bi-phasic linear, polynomial and power-law models were fitted to data describing leaf appearance with thermal time. The bi-phasic model (previously used for sugarcane) had a single large change in phyllochron for which no biological explanation is apparent. Polynomials were less likely to predict leaf appearance accurately outside the range of fitted data. The power-law model gave a continuously increasing thermal time between the appearance of successive leaves (phyllochron) and was used to compare the varieties. An increasing phyllochron for the first 15 leaves could be explained, in part, by the increasing length of lamina each successive leaf had to grow through. However, an explanation for an increasing phyllochron throughout ontogeny has yet to be found. The rate of leaf appearance was significantly different between the varieties. After 5000 degrees Cd the number of leaves predicted to have appeared ranged from 35 to 46. These variety specific parameters make an important contribution to describing how different varieties produce leaf area.