Differential physiological responses of resistant and susceptible grape cultivars to Eutypa dieback.

Eutypa lata is a fungal pathogen of grapevine that causes widespread economic damage and threatens vineyard longevity worldwide. This study was initiated to further understanding of how grapevines resist E. lata infections, using an integrated approach combining inoculation assays in the greenhouse with physiological and biochemical measurements. Resistant 'Zinfandel' and susceptible 'Syrah' grapevines were subjected to control and inoculation treatments, and assessed for gas exchange, water status, photosynthetic biochemistry, hydraulic conductivity, wood chemistry, and fungal spread (lesion length). Infection reduced leaf photochemical function and gas exchange in Zinfandel and increased these variables in Syrah (P<0.05). Infection produced shorter lesions in Zinfandel (P<0.05), suggesting that down-regulating gas exchange limited pathogen spread by reducing the carbon supply to the pathogen or fungal movement in the transpiration stream. Neither cultivar up-regulated wood defense compounds in response to infection, but proanthocyanidin and catechin levels were constitutively higher in Zinfandel, and stilbenoid and flavonoid contents were constitutively higher in Syrah (P<0.05). Altogether, this study is the first to show that, counterintuitively, down-regulating physiological function in response to infection improves long-term resistance to E. lata. Screening responses in photochemical function or gas exchange could provide a high-throughput alternative to measuring lesion lengths in assessing resistance.