First Report of Cylindrocladiella peruviana Associated with Grapevine Black Foot Disease in China.

Black foot disease is one of the Grapevine Trunk Diseases (GTDs) that occurs in many grape growing regions and causes vine decline. Black foot disease has been reported in China in 2021 (Ye et al. 2021). In May 2022, serious root rot and nearly half brown necrosis in cross section were observed in several grapevines (Vitis vinifera cv. Cabernet Sauvignon) in Xianyang County, Shaanxi Province, China, with the incidence of 2% in 0.267 hectares. Samples (12-year-old vines) of symptomatic root were collected and taken back to the laboratory. Small fragments from the margin between healthy and diseased tissue were cut into 5 mm × 5 mm pieces. The surface was sterilized using 2% NaOCl for 2 min, followed by 75% ethanol for 30 s and rinsed three times with sterilized water. After the small pieces were dried on sterilized filter paper, they were placed onto potato dextrose agar (PDA) plates with lactic acid at 25°C for 2-3 days. The pure culture was obtained by single spore isolation. In this study, two strains were associated with black foot disease. Colony characteristics were observed in 7-day PDA plates, with cotton wool mycelium and light yellow to brown colony in reverse. Conidia were cylindrical to peanut shaped, 0-1 septa and blunt round at both ends. Size of the conidia was 7.12 to 13.89 × 2.55 to 5.16 µm (average 9.82 × 3.41 µm, n=50). For molecular phylogenetic analysis, genomic DNA of the two strains (JZB3320008 and JZB3320009) was extracted. PCR amplification was performed using four phylogenetic regions (ITS, tub2, tef1 and his3) amplified with primers ITS1/ITS4 (White et al. 1990), T1/Bt2b (O'Donnell and Cigelnik 1997; Glass and Dnoaldson 1995), EF-688F/EF-1251R (Alves et al. 2008) and CYLH3F/CYLH3R (Crous et al. 2004), respectively. Maximum likelihood (ML) inference phylogenetic tree was constructed to confirm the identity of the two strains. ML tree reveals that the two strains clustered with Cylindrocladiella peruviana with 100% bootstrap support value. The sequences of four regions were deposited in GenBank (accession numbers OQ202205-OQ202206 for ITS, OQ225938-OQ225939 for tub2, OQ225936-OQ225937 for tef1 and OQ225934-OQ225935 for his3). Based on the morphological characteristics and molecular phylogenetic analysis, the two strains were identified as C. peruviana. To confirm the pathogenicity, the rooted cuttings (cv. Marselan) in the greenhouse were inoculated by immersing the roots in the conidial suspension (106 conidia/mL; volume, 300 mL) for 30 min, while the control was immersed in sterilized water (volume, 300 mL) for the same time. Nine plants were inoculated with C. peruviana and the same number was used as the control. These grapevines were kept in the greenhouse at 25°C. After 14 days of inoculation, the aboveground of inoculated plants showed symptoms with red leaves, while the control showed no symptoms. After 34 days of inoculation, the inoculated plants showed the reduction of the number of foliage and reduced vigor. They died with brown stem base and vascular discoloration in longitudinal section, while the control showed no symptoms. Cylindrocladiella peruviana was re-isolated by the discoloration regions and the Koch's rule was verified. To our knowledge, the pathogen has been reported in Spain and California (Agustí-Brisach et al. 2012; Koike et al. 2016). This is the first report of Cylindrocladiella peruviana causing grapevine black foot disease in China. We will better diagnose and prevent the disease in the future.