Effect of Defoliation on Growth and Physiological Developments in Tubers of Purple Nutsedge (Cyperus rotundus L.)

Abstract

AbstractThe starch metabolism and hydrolytic enzyme activities in growing tubers of purple nutsedge (Cyperus rotundus L.) in response to defoliation were examined to elucidate the regrowth physiology of the plant. Effects of complete or partial defoliation imposed at 2 or 4 weeks (single defoliation), or 2 and 4 weeks (repeated defoliation) after emergence (WAE) on plant growth were studied.Leaf area and leaf dry weight per plant in the control plots increased with time. In the mother tuber, dry weight and starch content were reduced by 16 % and 18 %, respectively, during the first 2 WAE, and then increased with time. Endoamylase (EC 3.2.1.1) activity of tubers (3.8 units g−1 dry tuber) increased by 42 % during the first 4 WAE, but decreased rapidly up to 8 WAE.Repeated defoliation significantly reduced the regrowth ability of nutsedge tubers when compared to single defoliation and the control. Repeated complete defoliation reduced the leaf area and leaf dry weight by 56 % and 69 %, respectively. The dry weights of mother tuber and total tubers 100 cm −2 were reduced by 41 % and 63 %, respectively, when compared to the control at 8 WAE. Endoamylase activity and starch content in the mother tuber in this treatment were reduced by 72 % and 56 %, respectively. Defoliation did not have any significant effect on the exoamylase activity.Endoamylase is the major starch hydrolysing enzyme in tubers and the activity of this enzyme could be a limiting factor in regrowth of nutsedge tubers. Repeated complete defoliation effectively suppressed the regrowth of purple nutsedge.