The Perfect Stage of Powdery Mildew of Grapevine Caused by Erysiphe necator Found in Peru.

Abstract

Grapevine (Vitis vinifera L.) has been cultivated in Peru since the sixteenth century to produce wine and grape brandy called "Pisco". Grapevine powdery mildew caused by Erysiphe necator (Schwein.) (formerly Uncinula necator [Schw.] Burr.; anamorph Oidium tuckeri) is currently the most important disease of grapevine in Peru. Table grape producers rely heavily on fungicide applications to manage powdery mildew infections. In Peru, the pathogen is normally found in the anamorphic state, except for one report of the teleomorphic state in 1972 (2) on wine grape varieties. In July 2011, ascomata were observed on table grapevine leaves cv. Sugraone in a commercial field near Huaral in the central coast of Peru. Abundant, mature (black) and immature (brown), globose ascocarps were visible on the abaxial leaf surfaces covered by the anamorphic state of the fungus. The chasmothecia were epiphyllous and ranged from 93.3 to 157.5 μm in diameter. The appendages were hyaline, variable in number (9 to 17), septate, with the apex helicoid when mature, and measuring 310 to 480 μm long. Each ascocarp contained four to seven subglobose asci (55.3 to 76.7 × 36.3 to 52.0 μm) with two to six (mostly three) ascospores. The ascospores were elliptical, hyaline, and measured 20.2 to 25.0 μm long by 11.1 to 17.3 μm wide. The pathogen was identified as E. necator on the basis of the host genus and morphology of the teleomorph (1). The teleomorphic state of E. necator could be a source of primary inoculum before infection by anamorphic conidia occurs, provide the basis for genetic recombination, and lead to more frequent appearance of new races. This could have serious implications for managing fungicide resistance in the pathogen population and may also result in the development of virulence to the resistance of some grape varieties tolerant to powdery mildew infections. In South America, the teleomorph of E. necator has been recently detected in Chile (3), and has caused great concern among grape producers. To our knowledge, this finding represents a first record of the presence of the ascigenous state of the pathogen on table grapes in Peru.