CROP LOAD AND WATER-STRESS EFFECTS ON DAILY STEM GROWTH IN PEACH (PRUNUS-PERSICA)

We investigated crop load and water stress effects on diurnal stem ext ension growth of field-grown peach (Prunus persica (L.) Batsch) trees. Neither the presence of fruit nor reduced irrigation significantly al tered the timing of diurnal fluctuations in stem growth rate. Stems wi th subtending fruit had significantly reduced growth compared to stems with no subtending fruit. Crop load had no significant effect on rela tive stem extension rates and the majority of the reduction in absolut e growth was the result of a smaller zone of elongation in fruit-beari ng stems than in stems with no subtending fruit. Fruit removal did not increase growth rates within 24 h. When irrigation was reduced, the l ength of the stem elongation zone and total daily stem growth were sig nificantly decreased relative to well-irrigated controls and the decre ases were highly correlated with stem water potential. Compared with w ell-irrigated controls, relative stem extension rates of water-stresse d trees were reduced at several times during the 24-h period, but the degree of reduction was not proportional to the difference in stem wat er potentials between the treatments.