Influence of Date of Tiller Origin on Leaf Extension Rates in Perennial and Italian Ryegrass at 15 °C in Relation to Flowering Propensity and Carbohydrate Status

Rates of leaf extension were observed in different tiller age classes in a perennial and an Italian ryegrass genotype following different dates of transfer from a cold glasshouse to a 15 °C growth room. The capacity for enhanced leaf extension observed when plants were transferred in the early part of the year was common to tillers of all ages, and was higher in tillers which subsequently flowered than in those which did not. The reduction in extension rates following later dates of transfer was observed at the same time in all tiller classes in both genotypes, and the difference between tillers which flowered and those which did not tended to disappear. The capacity for rapid leaf extension was lost after about 3 weeks of 16 h d at 15 °C, but could be partially restored by short-term exposure to a temperature of 5 °C and an 8 h day. These results clearly indicate that tillers which are capable of flowering are not necessarily capable of rapid rates of leaf extension and suggest that the reverse is also true. There was a negative relationship between the percentage of soluble carbohydrate present as fructan, which increased over the season as a whole, and rates of leaf extension at 15 °C, which declined, but there was no indication that rates of leaf extension were related either to percentage of total soluble carbohydrate or of fructan