Peach rootstock differences in ring nematode tolerance related to effects on tree dry weight, carbohydrate and prunasin contents

Abstract

Ring nematode (Criconemella xenoplax: Cx) predisposes peach trees to the disease peach tree short life. Peach genotypes vary widely in survival rates when they are infested with Cx, but all are suitable hosts to 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 compared dry weight, nonstructural carbohydrates (CHO) and prunasin in a highly sensitive (Nemaguard) and a highly tolerant (BY520‐9) peach rootstock inoculated with 0 or 10 Cx (ml soil)−1 in a pot study. Plant responses to the four treatment combinations were evaluated after 11 months of incubation with and without Cx. Cx parasitism reduced dry weight and concentrations of starch and soluble carbohydrates of all organs in Nemaguard, but not in those of BY520–9. Prunasin content was not affected by Cx in either rootstock. Increased partitioning of dry weight and carbohydrate fractions from shoots to roots and shifts in proportional 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 more of its CHO reserves to be partitioned from shoot to root in response to Cx parasitism. When parasitism is severe, reduced levels of CHO in the aboveground portion of the tree could result in tree injury or death at levels of environmental and biological stresses that do not injure healthy trees.