First report of Colletotrichum scovillei causing anthracnose fruit rot on Eriobotrya japonicain in Zhejiang province, China.

Abstract

Loquat (Eriobotrya japonica (Thunb.) Lindl.) is a fruit tree of high economic impotance in China. In May 2021, fruit rot on cv. "Baozhu" was observed in Yuhang district (119°40'E, 30°09'N), Zhejiang province, at an incidence of more than 30% within five orchards (the total affected area were about 121, 000 m2). Early symptoms of naturally affected fruits were dark brown, necrotic lesion (Fig. 1 A). Lesions subsequently expanded, and orange conidia were observed (Fig. 1 B). Conidia were transferred using a sterilized needle into sterile water, diluted to several conidia (approximately 10 conidia/µL) in the field of light microscope, and spread onto potato dextrose agar (PDA). After 24 h, single colonies were transferred, and six single-spore strain isolated from different fruits or locations were obtained. Six-day old colonies grown on PDA at 27°C had gray-green centers with white edges, and on the reverse side, the centers were brown (Fig. 1 C). Isolate PPGS2 was selected for further characterization. Conidia were unicellular, smooth-walled, hyaline, cylindrical with one rounded and one acute end, or with both ends rounded and they (n = 30) measured 11.1 to 16.0 µm (mean = 13.3 µm) × 3.0 to 4.6 µm (mean = 4.1) (Fig. 1 D). Appressoria were single or in smalln groups, light brown to dark brown, ovoid or elliptical with a smooth or undulate outline, and measured (n = 30) 4.6 to 8.7 µm (mean = 6.5 µm) × 4.0 to 5.6 µm (mean = 4.9 µm) (Fig. 1 H). These features of PPGS2 were consistent with species of the Colletotrichum acutatum species complex (Damm et al. 2012). For species identification, the internal transcribed spacer (ITS), beta-tubulin (TUB), chitin synthase (CHS-1), calmodulin (CAL), and actin (ACT) genes were sequenced (O'Donnell et al. 2000; Weir et al. 2012). The five sequences were deposited in GenBank (OK054581, OK077960, OK077987, OK077988 and OK077989, respectively). A BLAST search of these sequences showed 99% identity with sequences of the ex-holotype C. scovillei CBS126529 (Damm et al. 2012). The evolutionary tree shown that PPGS2 and C. scovillei CBS126529 were clustered in a branch (SH-aLRT/approximate Bayes test/bootstrap support = 88.6/0.999/96). Combining morphological characteristics with phylogenetic analysis, PPGS2 was identified as C. scovillei. To fulfill Koch's postulates, E. japonica fruit were disinfected with 75% alcohol and air-dried for 5 mins to allow the alcohol to volatilize. A conidial suspension (10 mL of 1 × 106 conidia/ml) of PPGS2 was sprayed onto six fruits, and six fruit sprayed with sterilized water served as controls. The experiment was repeated three times. Fruits were kept on a mist bench at 27°C and 80% relative humidity for 5 days. Inoculated fruit developed dark brown necrotic lesions that later fused and expanded (Fig. 1, E-G), whereas control fruit remained symptomless. C. scovillei was re-isolated from lesions of inoculated fruit. C. scovillei has been reported from fruit of Capsicum sp., Musa sp., Mangifera indica, and Clausena lansium in China (Farr and Rossman 2021). To our knowledge, this is the first report of C. scovillei causing anthracnose fruit rot of E. japonica in China. This disease results in severe economic losses both in the field and after harvest, and it is necessary to develop more effective prevention and control strategies.