Susceptibility of pear (Pyrus communis) cultivars for different strains of Venturia pirina

Abstract: Pear scab, caused by the fungus Venturia pirina, is one of the most important diseasesin European pear, especially in organic culture systems. In order to develop adapted controlstrategies there is a need for a better knowledge of pear susceptibility/resistance to scab and theplant pathogen interaction. Therefore, we performed inoculations of pear cultivars with differentV. pirina strains. Germination of conidia and appressorium formation in a compatiblecombination were observed on in vitro plants 8 and 12 hours after inoculation, respectively. Thegrowth of the fungus on the leaf continued even until 14 days after inoculation with ramificationsof the germination tube and several appressoria from one spore. The same observations weremade after inoculation of pear leaves with Venturia inaequalis. For the cultivars Conference,Doyenné du Comice and Durondeau clear differences in susceptibility were found afterinoculation of grafted plants in the greenhouse according to the origin of the scab strain. Onlystrains isolated from the cultivar itself could give sporulation on leaves. Strain specificity amongcultivars was less pronounced for chlorosis than for sporulation. Specific symptoms were foundon Durondeau (sporulation on twigs) and on Doyenné (pin points after inoculation withConference isolates).