PEACH ROOTSTOCK DIFFERENCES IN RING NEMATODE TOLERANCE RELATED TO EFFECTS ON TREE DRY-WEIGHT, CARBOHYDRATE AND PRUNASIN CONTENTS

Ring nematode (Criconemella xenoplax; Cx) predisposes peach trees to t he disease peach tree short life. Peach genotypes vary widely in survi val rates when they are infested with Cx, but all are suitable hosts t o Cx. Differences among peach genotypes in carbohydrate depletion and release of cyanide from prunasin degradation have been correlated with sensitivity to Cx, but cause and effect relations are not known. We c ompared dry weight, nonstructural carbohydrates (CHO) and prunasin in a highly sensitive (Nemaguard) and a highly tolerant (BY520-9) peach r ootstock inoculated with 0 or 10 Cx (ml soil)(-1) in a pot study. Plan t responses to the four treatment combinations were evaluated after 11 months of incubation with and without Cx. Cx parasitism reduced dry w eight and concentrations of starch and soluble carbohydrates of all or gans in Nemaguard, but not in those of BY520-9. Prunasin content was n ot affected by Cx in either rootstock. Increased partitioning of dry w eight and carbohydrate fractions from shoots to roots and shifts in pr oportional composition of individual sugars occurred in Nemaguard but not in BY520-9. These results are consistent with the hypothesis that Nemaguard is more sensitive to Cx than is BY520-9 because it allows mo re of its CHO reserves to be partitioned from shoot to root in respons e to Cx parasitism. When parasitism is severe, reduced levels of CHO i n the aboveground portion of the toe could result in tree injury or de ath at levels of environmental and biological stresses that do not inj ure healthy trees.