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Powdery mildew, caused by Golovinomyces orontii and Podosphaera xanthii, is a widespread disease that causes important losses in cucurbit production. To determine the aetiology and the epidemiology of cucurbit powdery mildew disease in the North of Italy, observations on the occurrence of the main disease-causing fungal species were conducted during the 2010, 2011 and 2012 growing seasons. Samples of infected leaves of zucchini, melon and pumpkin plants, either from field or greenhouse crops, were collected every 15-18 days from May to September/October. To identify the fungal species, both morphological observations based on the asexual stage and molecular identifications by a Multiplex- PCR reaction with species-specific primers were performed. Climatic parameters of temperature and relative humidity were also monitored. Pearson's correlation coefficient and Principal Component Analysis showed a negative significant correlation between the two species, and a peculiar epidemiological behaviour was also observed: the earlier infections were caused by G. orontii, which was the predominant species till the end of June-middle of July. At this time, this species progressively decreased in frequency and was replaced by P. xanthii that became the main species infecting cucurbits till the end of the growing season. As the two species have different ecological requirements, these seasonal variations in the cucurbit powdery mildew species composition could possibly be explained by the influence of temperature and relative humidity on the pathogen epidemiology during the growing season but also by the different overwintering strategies adopted by the two species. [ABSTRACT FROM AUTHOR]

Powdery mildew is a widespread disease that causes important losses to cucurbit production. The main agents of the disease are Podosphaera xanthii and Golovinomyces orontii. To determine the occurrence of chasmothecia as overwintering forms of both fungal species in northern Italy, powdery mildew-infected samples from cultivated cucurbits were collected in different locations of the provinces of Bologna and Mantova during 2010, 2011 and 2012. Only the sexual stage of P. xanthii was found, indicating that in northern Italy, contrary to what reported from other areas of the Mediterranean basin, the pathogen overwinters as chasmothecia. In parallel, to determine the frequency and distribution of both MAT 1-1-1 and MAT 1-2-1 P. xanthii idiomorphs, a multiplex-PCR with MAT idiomorph-specific primers was carried out on 147 monoconidial isolates obtained from infected leaf samples. The obtained frequencies were tested for random mating. Results showed a MAT ratio that tended to 1:1, supporting the finding of the sexual stage thus suggesting the occurrence of actively mating populations and that sexual reproduction plays a significant role in the life cycle of P. xanthii in this area. The lack of G. orontii chasmothecia suggests that this species might have alternative overwintering strategies. [ABSTRACT FROM AUTHOR]