Temporal variations in the cucurbit powdery mildew species composition in Northern Italy

Cucurbit powdery mildew is a widespread disease that causes important losses in cucurbit production. Observations on the occurrence of Podosphaera fusca and Golovinomyces cichoracearum were conducted in the years 2010 and 2011 in Bologna and Mantova provinces to determine the epidemiology and etiology of powdery mildew in these important areas of cucurbit production. Samples of infected leaves of zucchini, melon, cucumber, pumpkin and watermelon crops, in field and greenhouse conditions, were collected every two weeks from May to October. To distinguish the two species, morphological observations of conidia germ tubes, presence/absence of fibrosin bodies in 3% KOH and observation of chasmothecia were conducted. Molecular identification of both pathogens were carried out with a Multiplex-PCR, using species-specific primers designed on the ITS region of both species and performed on a DNA pool isolated from infected leaves. The preliminary results show that the earlier infections are by G.cichoracearum, that seems to be the predominant species till the middle of July when it progressively disappears and P.fusca becomes the main species infecting cucurbits till the end of October. Only chasmothecia of P.fusca were collected in October-November. This peculiar behavior could suggest a seasonal alternance in the cucurbit powdery mildew species composition that could explained both by the different climatic requirements of the two species and by their different overwintering strategies. Further investigations are in progress to confirm these results.