Peach Leaf Scar Healing

Plant Pathology Research at The Kearneysville Tree Fruit Research and Education Center

Genetic and temporal variation in abscission zone healing in peach leaves in relation to Leucostoma canker

Leucostoma canker continues to be a major limiting factor in peach production in the northern fruit-growing region of North America, including West Virginia. The fungi that cause peach canker initiate disease in wounds created by pruning, leaf abscission, winter injury, and insect damage. The disease appears as perennial cankers on trunks, scaffold limbs, and branches, and causes crop losses mainly through reduction in bearing surface and premature tree death. Leaf scars have been identified as a major site of entry. Resistance to infection, invasion, and colonization is associated with rate of formation of new tissues associated with defense and repair in the bark. The formation of tissue zones, predominant in either polysaccharides or lignin and suberin, has been demonstrated in peach bark either wounded or wounded and inoculated with the fungi that cause peach canker. Rate of leaf fall and the temperature during the leaf abscission period are considered to be critical factors affecting outbreaks of the disease. There are marked differences among cultivars in rate of leaf fall and rapid leaf abscission has been correlated with moderate levels of pathogen resistance. It is possible that natural infection would be greatly reduced by the selection of breeding lines that exhibited rapid defoliation. Given the potential importance of this observation to peach breeding programs, the objective of the present study was to document the gross tissue changes in the leaf scar following abscission and examine their correlation with the known susceptibility of several different peach cultivars and clonal selections to the peach canker pathogens. Leaf scars from 13 peach cultivars and clones with varying susceptibility to peach canker disease were collected during the period November through May, and were examined histologically. Leaf scar sections were examined with light and fluorescence microscopy for tissue changes related to wound healing. 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 periderm was not significantly correlated with the field susceptibility rankings for peach canker disease at any of the five dates. This study confirmed the presence of genetic variation in wound healing in leaf scars among peach cultivars and clones. However, variation in wound healing parameters, as demonstrated in earlier studies of wounded bark tissue is useful as an expression of partial resistance to Leucostoma spp. only if it can be established that a significant association exists between specific anatomical changes and relative cultivar susceptibility to the pathogens. Unfortunately, this relationship could not be demonstrated over the course of the current investigations.

A. R. Biggs (September, 1996)

See: Biggs, A.R. 1997. Genetic and temporal variation in abscission zone formation in peach leaves in relation to peach canker disease. Canadian Journal of Botany 74:717-722.