Histopathology of Phakopsora euvitis on Vitis vinifera

Abstract

Rust (Phakopsora euvitis) is an important fungal disease in grapevines grown in tropical and subtropical regions. Epidemiological works have been conducted on plant disease resistance, however, little is known about defense mechanisms of resistance to the disease. Leaves of Vitis vinifera cv. Moscato Giallo were inoculated with P. euvitis and lesions were formed with pustules surrounded by water-soaked halo 17 days after inoculation. Foliar tissue of injured and sound material was fixed and submitted to histological techniques. Emergence of pustules from stomata was observed. In water-soaked halo, hyphae of fungus were not observed. In this region, foliar blade presented mesophyll modified by cell hypertrophy with reduction of intercellular spaces and accumulation of pectic compounds. Hypertrophied cells showed parietal thickenings in the cellulose and pectin layers. In the areas delimited by water-soaked halo in the pustule region, the fungus grew vigorously in intercellular spaces of chlorophyll parenchyma; however, vascular bundles also restricted the advance of fungus where sheath cells present parietal pectic thickenings. Therefore, although Vitis vinifera cv. Moscato showed rust symptoms on leaves, pathogen colonization was limited by the formation of water-soaked haloes and vascular bundles, which resulted in minor injuries along the foliar limbo.