First Report of Brown Rot Caused by Monilia yunnanensis on Sweet Cherry in China.

Abstract

Chinese cherry industry has developed rapidly over the past few years, with the planting acreage continuously expanding, from Shandong province to Liaoning, Shaanxi, Hebei, Sichuan etc. Monilia spp. are the most important causal agents of brown rot of cherry, to date, M. fructicola, M. mumecola, and M. fructigena were reported to cause brown rot of cherry in China (Chen et al. 2013; Yin et al. 2014; Liu et al. 2012). In May 2023, fruit of sweet cherry cultivar 'Hongdeng' (Prunus avium L.) with symptoms resembling brown rot were collected from Tongchuan City, Shaanxi Province. Conidia on diseased tissues were spread on a water agar (WA, 1.5% agar and distilled water) medium and isolated with a glass needle under a professional single spore separation microscope (Wuhan Heipu Science and Technology Ltd., Wuhan, China). If no conidia were present, fruit pieces (5 × 5 mm) at the intersection of healthy and diseased tissues were surface sterilized with a sodium hypochlorite solution (1%) for 30 s and washed three times in sterilized water, followed by 75% ethanol for 30 s, then washed three times in sterilized water. After the tissue pieces were dried, they were placed on potato dextrose agar (PDA; 200 g of potato, 20 g of dextrose, and agar at 20 g/L) and incubated at 22 °C for about twenty days to produce spores and then single spore isolation was carried out. Thirty single-spore isolates were obtained and all were morphologically similar. The isolates produced white-gray colonies with even margins and concentric rings of sporogenous mycelium after 3 days incubation, and abundant black-colored stromata on the PDA medium after 15 days of incubation at 22°C. Conidia were one-celled, hyaline, ellipsoid to lemon shape (14.12 × 10.37 μm), with 1-2 germs which is similar to M. yunnanensis on peach. The genomic DNA of the isolates was extracted as described previously (Chi et al. 2009). The pathogen identity was confirmed by multiplex PCR which resulted in a 237bp amplicon, which is diagnostic of M. yunnanensis (Hu et al. 2011). Further sequencing of the internal transcribed spacer (ITS) region 1 and 2 and 5.8S gene (accession number: OR192774) indicated 100% identity with that of M. yunnanensis isolates (accession numbers: MW355895, ON024742). The average daily growth of mycelium on PDA at 22°C was 11.44 mm. Koch's postulates were fulfilled by inoculating 20 mature sweet cherry fruits of cv. 'Van' with mycelial plugs in a drilled hole. After 3 days of incubation at 22℃ in an airtight plastic tray with wet paper, the inoculated fruit developed typical brown rot symptoms. The developing spores on inoculated fruit were confirmed to be M. yunnanensis based on ITS sequence. All control fruit inoculated with a PDA plug remained healthy. M. yunnanensis was first reported as the causal agent of brown rot of peach in China (Hu et al. 2011). Later studies demonstrated that it is also pathogen on other fruits, e.g. hawthorn (Zhao et al. 2013), plum (Yin et al. 2015), apricot (Yin et al. 2017), apple, and pear in China (Zhu et al. 2016). To our knowledge, this is the first report of cherry brown fruit rot caused by M. yunnanensis, indicating the high risk of this species to cherry production, and effective strategies must be taken to prevent the possible control failure in practice.