INCIDENCE OF VERTICILLIUM WILT ON OLIVE IN APULIA AND GENETIC DIVERSITY OF VERTICILLIUM DAHLIAE ISOLATES FROM INFECTED TREES

Abstract

To collect information on the incidence of Verticillium wilt of olive in Apulia (southern Italy), about 6,000 woody samples from 1,390 young and old olive orchards were analysed. Moreover, 565 soil samples from commercial orchards and nurseries located all over Apulia region were tested for the presence of V. dahliae microsclerotia. Verticillium wilt was found in the 18% of the surveyed orchards, mainly in seaside-located intensive plantations, which are usually intercropped with vegetables susceptible to V. dahliae. However, the disease was also found in young plantations established on soil which resulted free of the pathogen, thus indicating a role of the propagating material in the spread of the disease. On the whole, 16% of surveyed fields and 50% of nurseries were contaminated by the pathogen. Overall, the results suggest that preventive diagnostic tests of leafy cuttings, soil and soil mix are mandatory to obtain V. dahliae-free propagative material to limit the spread of the disease. The analysis of more than 60 V. dahliae isolates by RAPD-PCR technique indicated a low level of genetic diversity in the Apulian population of the pathogen from infected olive trees. A distinct cluster including few isolates was found, but no correlation could be established among the isolates and olive cultivars and location. Molecular tests to characterize the pathotype of V. dahliae from infected trees indicated that all the isolates belong to the non-defoliating pathotype, except one for which the results were not conclusive.