Black Knot [ Apiosporina Morbosa(Schw.)] Resistance in Imported and Domestic Prunus DomesticaL. Germplasm and Cultivars

Abstract

Black knot Apiosporina morbosa(Schw.) (BK) is an important fungal disease of Prunus domesticaand other Prunus species in North America. BK causes economic losses in the plum growing regions of northern and eastern U.S., and eastern Canada. Relatively few P. domesticacommercial cultivars are resistant to BK. Evaluation of resistance to BK in P. domesticaplums including an evaluation of infection of new shoot growth following pruning was carried out over four years. The 43 genotypes evaluated included 23 accessions from the U.S. National Plant Germplasm System (NPGS)-Davis, California and cultivars and selections from the U.S., Canada, and Europe. Based on the evaluations, genotypes were classified as highly resistant, moderately resistant, susceptible or highly susceptible. Highly resistant genotypes, without visible symptoms made up 44% of the germplasm evaluated and of these, 68% were accessions from the U.S. NPGS collection. While the inheritance of resistance remains to be determined, these evaluations indicate that sources of high level resistance are available in P. domesticathat can be utilized in breeding highly resistant commercial cultivars.