Downy mildew (Plasmopara viticola) is the most important disease in all grape-growing areas of the world. The disease can cause yield losses of up to 100% in production. P. viticola presents a high level of genetic variability and clear distinctions between populations from different geographic regions. The occurrence of cryptic species in Brazil has not been reported yet. Oospores (survival structure originating from sexual reproduction) represent the main source of inoculum for primary infections in temperate climates. Beyond the rule of primary inoculum, oospores can contribute to epidemic progress throughout the growing season. Studies about the spatio-temporal progress disease and the occurrence of sexual reproduction and population genetic variability of P. viticola in tropical and subtropical regions are limited. The knowledge about these assumptions could contribute to understand the epidemic process of downy mildew in these climatic regions. The aims of this researcher are (i) evaluate the temporal and spatial progress of downy mildew to compare with the dynamic epidemic in Brazil; (ii) investigate the population diversity of P. viticola from Georgia-USA, and São Paulo State-Brazil to understand the role of primary and secondary infections in downy mildew epidemics; (iii) and verify the occurrence of sexual reproduction of P. viticola during the growing season in subtropical climates to infer about its role in epidemic dynamics. To evaluate the spatio-temporal progress of downy mildew, disease incidence and disease severity will be performed weakly. The data will be fitted by mathematic models using non-linear regression analysis. The spatial progress will be analyzed by the dispersion index (D) and by the modified Taylor's power law. By combined regressions the results obtained from Georgia-USA will complement those obtained from the experiments performed in São Paulo-Brazil. Population diversity will be characterized molecularly. Single-lesion isolates from different combinations of vineyards, cultivars, and regions of São Paulo State will be collected and will be analyzed by polymerase chain reaction (PCR) with specific primers, and cleaved amplified polymorphic sequence (CAPS), which will allow the recognition of the different cryptic species (clades) of P. viticola, if present. The characterization of infections caused by sexual and asexual reproduction of P. viticola will be performed by microsatellite markers. Leaf samples of the variety 'Niagara Rosada' (Vitis labrusca) will be collected from the experimental vineyard in Piracicaba-SP at three different times during the growing season. Simple sequence repeat (SSR) markers will revealed if there is polymorphism within the samples collected from the infected vineyard. These results should reveal the role of sexual and asexual reproduction structures in downy mildew epidemic in tropical and subtropical regions.
News published in Agência FAPESP Newsletter about the scholarship: