Evaluation of Peach x Almond Hybrids for Fungal Gummosis Resistance

Peach trees in the Southeastern United States are damaged by fungal gummosis (incited by Botryosphaeria dothidea [(Moug.:Fr.) Ces. & De Not.] with a fruit yield reduction up to 40% per tree in severe cases. Previous studies indicated a high level of susceptibility in commercially recommended rootstocks and cultivars. The climatic conditions in the Southeastern United States are conducive to the development of the disease and currently, there are no proven effective cultural or chemical controls for peach fungal gummosis. Our group has evaluated peach germplasm for over 2 decades, searching for sources of resistance to peach fungal gummosis. Preliminary research in our lab indicates that almond, a species closely related and sexually compatible with peach, may provide a new source of genes for resistance to peach fungal gummosis. Preliminary tests comparing commercial quality peach cultivars with peach x almond F1 hybrids indicated the existence of a novel source of resistance to gummosis. Parental genotypes and segregating backcross populations of peach, peach X almond F1 hybrids, and peach X (peach X almond) progeny were evaluated for 3 consecutive years using a previously established rating system based on gumming severity. Selected peach x almond F1 hybrids presented the lowest mean for gummosis susceptibility. Pearson chi-square analysis of the disease rating data suggested a dependent segregation of the populations for gummosis. Further analysis of the standardized residuals deviations identified differences in backcross population 8 (UFSharp x (Flordaguard x almond)).  The phenotypic segregation ratio for fungal gummosis resistance is consistent with the presence of a single dominant locus.  Backcross population 8 has been genotyped for SSR markers sourced from the Prunus reference genome map and Quantitative Trait Locus (QTL) analysis will be performed.