Abstract

Grapevine leaf spot caused by Pseudocercospora vitis is important at the end of the vegetative cycle of Vitis labrusca and its hybrids, but studies on this pathosystem and its monocyclic components are scarce. The objective of this work was to determine the favorable conditions for the development of the pathogen and to study the resistance levels in 10 grapevine cultivars. The germination of P. vitis conidia was evaluated at temperatures from 4 to 35 °C, germ tube size from 8 to 33 °C and weight of colonies of the pathogen from 10 to 40 °C. Wetness periods of 3 to 48 h were also evaluated for germination at temperatures from 10 to 40 °C. In five cultivars of V. labrusca and five hybrids inoculated with P. vitis, the incubation period and the progression of disease severity under controlled conditions were compared. The optimal temperature for germination of P. vitis was at 28 °C and 27 °C for germ tube growth. For mycelial weight the optimum temperature was 26.4 °C. The highest germination of the pathogen occurred with wetness of 45.5 h and temperature of 29.6 °C. The incubation period in the cultivars ranged from 26 to 51 days. The disease progress curve showed differences among cultivars tested, ‘Concord’ and ‘BRS Vitoria’ being the most resistant. In plants inoculated at 25 °C, the number of lesions increased over time, stabilizing at 42–47 days after inoculation and from here no new lesions appeared, only lesions expansion was observed.

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