Defoliation frequency and genotype effects on stolon and root reserves in white clover

Abstract

The effect of defoliation frequency (1 or 3 defoliations over a 42-day period) on the starch, water soluble carbohydrate (WSC), and nitrogen contents of 3 white clover cultivars (Haifa, Irrigation, and S184) was examined. The clover plants consisted of single stolons growing in a sand/scoria mix in an unheated glasshouse and fertilised weekly with a nitrogen-free solution.

Starch concentrations ranged from 1·3% in frequently defoliated Haifa to 15·3% in infrequently defoliated S184 plants. However, there was no interaction between cultivar and defoliation frequency, with the starch concentration in S184 (11·2%) being twice that in Irrigation (6·0%) and 3 times that in Haifa (3·8%). The starch concentration was also less with frequent (3·7%) than with infrequent (10·3%) defoliation. The starch was localised in the old stolon material (12·2%), with lower levels of starch in both the young stolon (6·0%) and roots (4·0%). Furthermore, the cultivar and defoliation frequency effects on the starch concentrations were most pronounced in the old stolon. More frequent defoliation also resulted in a small reduction in the WSC and nitrogen concentrations in both the young and old stolons of Haifa, but not of Irrigation. It was concluded that although starch reserves were the principal method of reserve storage in white clover, WSC and nitrogen reserves will form a relatively large fraction of the reserve pool when starch reserves are depleted under conditions such as frequent defoliation.