Host and non-host interaction of Venturia inaequalis and Venturia pirina on Pyrus communis and Malus x domestica

Pyrus communis and Malus x domestica inoculated respectively with Venturia pirina and Venturia inaequalis give susceptible or resistance symptoms with large similarities. We addressed the question whether the two species of Venturia could exhibit reciprocal relationships with Pyrus communis and Malus x domestica. Trees of the apple cultivars: 'Gala' (susceptible to V inaequalis) and 'Discovery' (polygenic resistant) and the pear cultivars: 'Pierre Corneille' (susceptible to V pirina) and 'Navarra' (polygenic resistant) were inoculated in the glasshouse with very aggressive monoconidial strains of V inaequalis (EU-B04) and V pirina (Pca). Three days after inoculation, conidia germination, germ tube formation and appressoria differentiation were observed in all combinations. There were no clear differences in the percentage of germinated conidia and the appressoria index between host and non-host interaction. Six days after inoculation, a dense subcuticular network of stromatic strands was observed in the susceptible interaction. The resistant hosts were characterized by a reduced primary stroma and the epidermal cells were modified. In the case of the non-host relationships, much reduced primary stroma with few conidia were observed on the susceptible (to the compatible Venturia species) host only. The leaf reaction was limited to a very small number of cells. Fourteen days after inoculation, macroscopic symptoms of sporulation appeared on the susceptible cultivars. In non-host relationships, no additional modification of the microscopic aspects was observed. In conclusion, in this experiment, non-host interactions with V inaequalis and V. pirina were observed but were reduced to very limited microscopic aspects.