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POSTERS: Plant defense response

Photosynthetic cost associated with the inducible defences to Plasmopara viticola in grapevine
Antonio Fernandes Nogueira Junior - University of Sao Paulo. Rafael Vasconcelos Ribeiro- University of Campinas, Merle Traenkner- Georg-August University of Goettingen, Lilian Amorim- USP, Andreas Von Tiedemann- Univ of Goettingen

Downy mildew, caused by Plasmopara viticola, is the most destructive disease of Vitis vinifera worldwide. Grapevine breeding programs had introgressed P. viticola resistant traits into V. vinifera genotypes and yielded downy mildew resistant hybrids. The objective of this work was to estimate the cost, at leaf level, of inducible responses to the infection of P. viticola on resistant cultivars (Solaris, Cabernet Blanc, and Phoenix) as well as to determine and to compare the limitations to photosynthesis imposed to P. viticola in resistant and susceptible cultivars. The net photosynthetic rates (An) were reduced (-15%) in inoculated ‘Solaris’ plants, even before the appearance of hypersensitive response-like cell death. A similar pattern was noticed in ‘Cabernet Blanc’ and ‘Phoenix’ plants. The susceptible cv. Riesling did not show any variation in leaf gas exchange before the appearance of visual symptoms. However, drastic reductions in An and stomatal conductance were found in ‘Riesling’ plants after 12 days of inoculation. Decreases in the maximum Rubisco carboxylation rate were noticed in ‘Riesling’ plants after pathogen inoculation, which was not found in ‘Solaris’. Damage to the photochemical reactions of photosynthesis was likely associated with the oxidative burst found in resistant cultivars within the first 24 hours after the inoculation. Taken together, our data revealed that the defense response against P. viticola causes a photosynthetic cost to grapevines, which is not reversible even 12 days after the pathogen infection. (Funding - FAPESP 2017-02432-6)