Podosphaera clandestina causes powdery mildew on sour cherry in Iran

Abstract

During 2014-2016, symptoms and signs of a powdery mildew disease were observed on the leaves and twigs of sour cherry (Prunus cerasus) in orchards from Firouragh in the Khoy region (West Azarbaijan province) of Iran. Young leaves and twigs were covered with a powdery growth consisting of mycelium and the asexual reproductive structures of a powdery mildew species. Affected leaves were curled upward and smaller than uninfected leaves, while affected twigs were stunted and often defoliated. The fungus was identified as belonging in the genus Podosphaera, based on morphological characteristics of its asexual state. Chasmothecia were not observed. The PCR amplification and sequencing of its ITS-rDNA revealed that the causal agent was Podosphaera clandestina. This is the first record on the occurrence of P. clandestina on sour cherry in Iran.Keywords Chasmothecia . Fibrosin bodies . ITS-rDNA . Prunus cerasusSour cherry (Prunus cerasus) belongs in the subgenus Cerasus in the family Rosaceae. The presumed center of origin for this species is Eastern Europe and southwest Asia, where it originated as a natural hybrid between Prunus avium and Prunus fruticosa (Horvath et al. 2008). Sour cherry is a popular fruit tree in many countries including Iran. According to the statistics of Food and Agriculture Organization (FAO) of the United Nations, in 2013 Iran ranked the fifth in sour cherry production in world with an annual production of 106,972 t (FAOSTAT 2013). Although sour cherry is undemanding and very robust, a number of fungal plant pathogens including Monilinia laxa and Stigmina carpophila cause economic crop loss on this host in Iran (Ahmadpour et al. 2009;Leghvani et al. 2016). During 2014-2016, symptoms and signs of a powdery mildew disease were observed on sour cherry trees in orchards of Firouragh in the Khoy region (West Azarbaijan province), Iran. Infected leaves and twigs were collected in paper bags and transported to the mycology laboratory at the Plant Pathology Department, University of Tabriz, Iran. Five specimens were inspected under a stereomicroscope and fungal structures were mounted in distilled water on a glass slide, covered with a coverslip then examined. Microscopic observations were made using an Olympus-BX41 light microscope. Thirty measurements were taken of the relevant parameters of the conidiophores and conidia and 95% confidence intervals were derived for the measurements with the extremes given in parentheses. An Olympus digital camera system (DP 25) and software to analyze photographs was used to capture high-resolution photographs of microscopic fungal structures. A herbarium specimen was deposited in the Fungal Herbarium of the Iranian Research Institute of Plant Protection (IRAN 16861F).The white powdery coating consisted of mycelium, conidiophores and conidia. The infected terminal leaves were smaller than uninfected terminal leaves with the leaf margins curled upward; infected leaves occasionally became necrotic and defoliated (Fig. 1a-b). The sunken irregular lesions (4-)...

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