Photosynthetic damage caused by grapevine rust (Phakopsora euvitis) in Vitis vinifera and Vitis labrusca

Abstract

Grapevine rust Phakopsora euvitis is an important disease in tropical and subtropical grapevine-producing areas, and both American (Vitis labrusca) and European (Vitis vinifera) grapevine species are sensitive to rust. Grapevine rust can cause early plant defoliation, reducing photosynthesis and photoassimilate supply and storage. This study evaluated the photosynthetic damage induced by varying grapevine rust intensities in leaves of V. vinifera cv. Moscato Giallo and V. labrusca cv. Niagara Rosada. The disease effect in tissues adjacent to the lesion, called virtual lesion (β), was estimated for photosynthetic variables, considering measurements taken in both healthy and diseased tissues. The average lesion size was higher in V. vinifera (0.66 mm2) than in V. labrusca (0.24 mm2). A water-soaked halo around the lesion was observed only in V. vinifera. The β-values estimated for the photosynthetic rate were 4.99 for V. labrusca and 5.93 for V. vinifera, taking into account the water-soaked and sporulating areas. When considering only the sporulating area, the β-value increased to 11.49 in V. vinifera. Grapevine rust had similar negative effects on photosynthesis in both species with increasing disease severity. While stomatal conductance was slightly affected, the pathogen caused significant reductions in the effective quantum efficiency of photosystem II and the instantaneous carboxylation efficiency of V. vinifera and V. labrusca with increasing disease severity. The β-value of instantaneous carboxylation efficiency was higher in V. vinifera (9.26) than in V. labrusca (4.76). In conclusion, Phakopsora euvitis dramatically affects photosynthesis in both V. vinifera cv. Moscato Giallo and V. labrusca cv. Niagara Rosada, causing large virtual lesions and substantial damage to the photochemical and biochemical reactions associated with CO2 assimilation.