Ecological niche models of grapevine downy mildew formae speciales suggest differential range expansions under climate change

Hannah Scheppler
Graduate (PhD)
Andrea Gschwend
Horticulture and Crop Science

Plant pathogens are one of the biggest threats to global food security under future climates, and grapevine downy mildew (Plasmopara viticola) is perhaps the most detrimental disease among vineyards. Grapevine fungicide regimes are expensive to growers and lead to considerable ecological damage to surrounding landscapes.  Grapevine downy mildew pressure has been modeled at the field-level in epidemiological studies, but it is unclear how the species distribution will change under future climates. Additionally, the P. viticola species complex contains three formae speciales that infect cultivated grapes, and studies of their distribution differences will greatly inform future breeding efforts. Multi-omics approaches have been heavily utilized to discover P. viticola-specific disease resistance genes in wild grapes to exploit for crop improvement. Over 25 downy mildew resistance (Rpv) loci were discovered in wild grapevine species. Downy mildew infection outcomes vary depending on pathogen isolate identity, as well as host resistance gene variation, which is a major caveat to plant disease resistance investigations that study only one pathogen isolate or plant population. This poses a problem for breeders when selecting loci for host resistance to a pathogen species as a whole, which includes a multitude of variants. Additionally, it is not always clear what pathogen variant(s) will be the next local threat under future climates from a geographical perspective. Considering the pathogen isolate specificity of grapevine Rpv loci, as well as the vast intraspecific variation in P. viticola, is it sustainable to breed for resistance to all downy mildew variants? Here I propose that grapevine downy mildew resistance genetics should be considered in the lens of P. viticola formae speciales range expansions, which will aid breeders in selecting germplasm resistant to future local pathogen variants. I present preliminary data from a maximum entropy model showing niche divergence among three P. viticola formae speciales that infect cultivated grapevines, suggesting that marker-assisted selection for specific downy mildew formae speciales-resistance should be performed based on local disease variant threats.