First Report of Didymosphaeria rubi-ulmifolii causing Wood Rot of peach (Prunus persica) in China

China is the largest producer of peaches (Prunus persica) in the world, with an annual yield accounting for over 50% of the world peach product. In January 2019, a severe wood rot disease of peach was observed in Hefei City, Anhui Province of China. Mean disease incidence was estimated as 10% in 5-ha orchards. Typical symptoms were characterized by wood internal vascular discoloration and canker on stems. Seven samples were collected from symptomatic stems of peach trees and cut to small pieces (4 × 4 mm) from the margin of the lesions, and they were surface disinfected in 75% ethanol for 20 s and 2% NaClO for 1 min, followed by rinsing three times with sterilized water, placed on potato dextrose agar (PDA), and incubated at 25°C. In total, six representative fungal colonies were isolated from infected stems on PDA medium and named as GF1 to GF6. Colonies on PDA showed brown at the early stages and turned to black after 5 days. Conidia were ellipsoid or short cylindrical, continuous, sometimes separate, olivaceous, and 3.4 to 4.6 × 2 to 2.3 μm. Total DNAs of the three isolates were extracted for PCR sequencing using primers for the rDNA internal transcribed spacer (ITS) (ITS1/ITS4, ITS1/ITS2, and ITS4/ITS5) and TUB2 (βT2a/βT2b) (Arredondo-Santoyo et al. 2018; Damm et al. 2008). ITS sequences (MN932144, MN947626, and MN944552) and TUB2 (BankIt2303021) were deposited in GenBank. BLAST searches showed ITS sequences had over 99.65% sequence similarity with Paraconiothyrium brasiliense strain KH1W (MK779925.1), STE-U 6300 (EU295651.1), and CBS 254.88 (JX496058.1), respectively. The sequences of TUB2 showed 97.98% similarity with P. brasiliense TUB2 sequences (LT796975.1). Based on the morphological and molecular analysis (Verkley et al. 2004), we confirmed the newly isolated strains belong to Didymosphaeria rubi-ulmifolii (basionym: P. brasiliense) (Ariyawansa et al. 2014). Pathogenicity trials were conducted on 5-year-old P. persica trees. Two-year-old healthy shoots were surface sterilized with 70% ethanol. Conidial suspension (50 μl, 5 × 10⁶ conidia/ml) was added into the wound (a hole of 2 to 2.5 mm deep). Control branches were treated with sterilized water. The inoculated plants were maintained at 25 ± 3°C with 95% humidity for 14 days. All those treated with isolates showed lesions of branches, but not the water-treated control plants. Reisolation was performed from symptomatic branches, and their identities were confirmed using the above-mentioned methods. All tests were performed three times, and pathogenicity tests employed five plants for each strain. To our knowledge, this is the first report of D. rubi-ulmifolii causing canker disease on peach species in China.