OVERCOMING OF THE RESISTANCE IN RESISTANT GENOTYPES OF DRY PEA (PISUM SATIVUM) BY AN ISOLATE OF ERYSIPHE PISI IN ITALY

Abstract

Powdery mildew (PM), caused by Erysiphe pisi DC, is the major disease of dry pea in southern Italy and the use of resistant cultivar is the best choice to control it. Screening field trials were conducted with eleven pea genotypes in four different farms located in the typical pea-growing areas of the Campania region (Scafati, Caserta, Acerra and Eboli). All resistant varieties showed no symptoms in three (Scafati, Acerra and Eboli) of the tested environments, whereas at Caserta, three of the cultivars i.e. Fallon, SW Carousel, and ISCI 7/06-2, which are reported to carry the powdery mildew resistance gene er1 showed symptoms, whereas the resistance of cv. Stirling was confirmed. Following artificial inoculation under greenhouse conditions, the three above cultivars supposed to carry er1 gene showed severe PM symptoms when exposed to the fungal isolate EpCE2 from Caserta. No symptoms were obtained with the other three isolates tested. The cv. Stirling maintained its resistance both in the field and greenhouse. Morphological and molecular analyses of the fungus that induced disease on resistant cultivars proved that the isolates used as inoculum belong to E. pisi. This result was confirmed by the molecular analysis performed on the leaves of resistant cvs Fallon, SW Carousel and ISCI 7/06-2 inoculated with the EpCE2 isolate from Caserta. Thus, the resistance conferred by the er1 gene can be broken and further investigations are needed to clarify the different behavior of resistant cultivar. To our knowledge, this is the first time that breaking of er1 resistance is reported in Italy.