Genetic and temporal variation in wound healing after abscission of peach leaves in relation to peach canker disease

Abstract

Leaf scars from 13 peach cultivars and clones with varying susceptibility to peach canker disease were collected during the period November 1986 through May 1987 and were examined histologically. Leaf scar sections were examined with light and fluorescence microscopy for tissue changes related to wound healing, including depth and width of the polysaccharide-impregnated zone, the timing and tissue depth at which the ligno-suberized layer occurred, the thickness and numbers of cells in the ligno-suberized layer, the longitudinal length of the ligno-suberized layer and whether or not the tissue was complete in longitudinal section through the leaf scar, and the presence and numbers of phellem cells in the wound periderm and whether or not the periderm was complete across the longitudinal section of the leaf scar. The percentage of leaf scars with a complete polysaccharide-impregnated zone varied by date with 94–96% of the leaf scars exhibiting the zone in January and April. The thickness of the polysaccharide-impregnated zone also varied by date, reaching its thickest in January and April. Percentages of lignified leaf scars were mostly similar among cultivars on four of the five dates; however on 1 May, there was considerable variation among cultivars with percent lignification ranging from 0 to 100%. The proportion of leaf scars with lignification was not significantly correlated with the field susceptibility rankings for peach canker disease at any of the five dates. The proportion of leaf scars with complete ligno-suberized layers varied by date only, with the highest values observed on 12 January and 14 May. The lowest values was observed on 1 May, and this was significantly less than that observed on 7 November and 10 April. The highest percentage of leaf scars possessing periderm occurred on 12 January (74%), with all the other dates not significantly different from each other (ranging from 29 to 40%). Analysis of cultivar across all dates combined indicated that Candor generally showed the highest percentages of leaf scars with periderm (64%), and this was significantly higher than Sunhaven (24%), Earlired (14%), and V68101 (13%), which were not different from each other. The proportion of leaf scars with periderm was not significantly correlated with the field susceptibility rankings for peach canker disease at any of the five dates. Key words: Prunus, wounding, Leucostoma.