Susceptibility of red, black and purple raspberry cultivars to three Phytophthora species under greenhouse and field conditions

Raspberry cultivars were evaluated for their susceptibilities to Phytophtho ra fragariae var, rubi under greenhouse and field conditions and to P. citr icola and P. megasperma in the greenhouse only. Results from the field and greenhouse evaluations were qualitatively similar for most cultivars but di sease was more severe in the greenhouse trials, making it difficult to dist inguish moderately resistant cultivars. 'Latham' and the related cultivars, 'Boyne', 'Killarney' and 'Nordic', showed excellent resistance to P, fraga riae var. rubi under field conditions, confirming that this trait is highly heritable. 'Latham' also showed good resistance to the same pathogen in th e greenhouse trials, but appeared much more susceptible to P. citricola and P. megasperma under these conditions, which involved periodic episodes of soil flooding. In the greenhouse trials, two black raspberry (Rubus occiden talis) cultivars, 'Jewel' and 'Bristol', showed levels of resistance to P. fragariae var, rubi that were equivalent to that of 'Latham', suggesting th at this plant species might represent a previously-unrecognized source of r esistance to the pathogen.