Brown Spot Disease of Peach and Apricot Trees, Pathogenicity and Overwinter

摘要

Brown spot is one of the main diseases to prune fruit production in Iran particularly Khorasan Razavi Province. Lesions appear as black to brownish spots associated with center of dark brown on leaves and twigs that was followed by defoliation, infected buds are dry and darker than other buds. Brown spot is a serious problem in semiarid areas. For identification the causal agent of brown spot disease and the survival of fungus in buildup organs and also its pathogenicity in colonization of the surface, samples were collected from diseased buds, twigs and leaves of peach and apricot trees from infected orchards in Khorasan Razavi during 2007. Washing of buds were carried out by centrifuging. Product of pelleted suspension was cultured on 2% water-agar medium. The fungus was isolated from the lesions of twigs and leaves on PDA and was purified on it. Pathogenicity tests were conducted by inoculating slightly wounded and nonwounded leaves with a conidial suspension adjusted to 1.5><104conidia mL_1. Control leaves were similarly treated with distilled water. The inoculated leaves were placed in a moist chamber. Day and night temperatures were set to 24 and 20°C in light-darkness conditions for 16 and 8 h, respectively. An Alternaria sp. was consistently isolated from diseased twigs, leaves and buds. After 2 to 14 days disease symptoms appeared on leaves associated with appearance of white colonies on surface and the percent of leaves infection was recorded. Control leaves were asymptomatic. Reisolation of the disease agent from diseased organs confirmed the existence of Alternaria alternata (Fr.) keissler as the causal agent of brown spot disease in peach and apricot trees. Also, overwintering of the fungus was observed as conidia and hyphae in buds and shoots and chlamydospore in twig spots. Knowing overwintering form of the fungus will help to control the disease in the following years and will reduce application of fungicides during year. This study is the first report of brown spot disease ofpeach and apricot trees in Iran and is the first documentation of overwintering the fungus in some stone fruit trees.