Y. Z. Zhao, Laboratory of Fungi, College Plant Protection, Shenyang Agricultural University, Shenyang 110161, China;
D. Wang, Nematology Institute of Northern China, College Plant Protection, Shenyang Agricultural University, Shenyang 110161, China; and
Z. H. Liu, Laboratory of Fungi, College Plant Protection, Shenyang Agricultural University, Shenyang 110161, China
Crataegus pinnatifida Bge. var. major N. is a time-honored herbal medicine and an important economic fruit that is processed into various foods. Cultivated fields are mostly situated in northern China. In August 2012, a fruit brown rot disease on mature plants was found in Fushun, Liaoning Province, China. This disease reduced the yield and the quality of fruits; the incidence of fruits affected in each tree was between 20% and 35%. The initial stage of infection was marked by regular or irregular light brown spots turning dark brown and gradually supporting many grey fluffy tufts of mycelium. At last, the lesions expanded, causing the fruits to become rotted or withered. The pathogen was isolated from infected fruits by a tissue isolation method (1) and cultured on potato dextrose agar (PDA) at 25°C under 12 h light/12 h dark for 7 days. The colonies reached 60 to 75 mm in diameter after 7 days and were pale green or pale yellow with a neat greyish white margin; the aerial mycelium sometimes formed annulations. The conidia were single, hyaline, lemon-shaped or oval, and 11.3 ± 1.4 (8.0 to 16.5) × 6.4 ± 0.8 (5.1 to 7.6) μm; sporulation was sparse and stromata that formed after 15 days were abundant, black, and spherical to elliptical in shape. Conidiophores were simple or branched, bearing a single conidium on the tip. The internal transcribed spacer (ITS) region of rDNA amplified with primers ITS1 and ITS4 was directly sequenced in both directions. The ITS1-5.8S-ITS2 sequence of rDNA was 100% identical to Monilinia yunnanensis (GenBank Accession No. HQ908788.1), which is distinguished from the closely related M. fructigena (AF150679.1) and M. polystroma (JX315717.1). The pathogen was identified as M. yunnanensis on the basis of morphological characteristics (2) and the ITS sequence of rDNA (2,3). Pathogenicity tests were performed on detached healthy fruits. Four fruits were wounded with a sterilized nail and inoculated by placing a PDA plug of mycelia on upper surfaces of the fruits. Another four fruits treated with sterile PDA plugs served as a control. Fruits were cultured in petri dishes with a 12-h photoperiod at 25°C and 90% relative humidity. The initial symptoms on inoculated fruits were observed after 5 days, while no symptoms showed on the controls. The pathogen was reisolated from the inoculated fruit and identified as M. yunnanensis by the above methods. While M. yunnanensis has been reported to cause brown rot on peach (2), to our knowledge, this is the first report of M. yunnanensis infecting C. pinnatifida Bge. var. major N. in China.
References: (1) Z. D. Fang. Research Methods of Plant Disease, 1998. (2) M. J. Hu et al. Monilinia species causing brown rot of peach in China. PLoS ONE. Online publication. doi:10.1371/journal.pone.0024990, 2011. (3) G. C. M. van Leeuwen et al. Mycol. Res. 106:444, 2002.