First Report of Fusarium incarnatum-equiseti Species Complex Causing Fruit Rot of Peach (Prunus persica) in China

Peach (Prunus persica [L.] Batsch; Rosaceae) is an economically important deciduous fruit. China is the largest producer of peaches, providing >50% of world production. Fruit rot is a devastating problem both pre- and postharvest. In May 2019, 882 infected peach fruits covered with white fluffy masses and brown necrotic lesions were observed among 4,500 fruits investigated in a commercial orchard in Jinshan, Shanghai, China. Disease incidence was ∼20%. Infected fruits were collected and kept in separate paper bags. Small sections (5 × 5 mm) were excised from the boundary of necrotic and healthy tissues, surface sterilized with 70% ethanol for 30 s and 5% NaOCl for 90 s, rinsed twice with sterilized distilled water (DW), and aseptically placed onto PDA. After 2 days of incubation at 26°C, sections from new colonies were transferred onto fresh PDA and purified by the single-spore method (Yang et al. 2008). Colonies on PDA had white aerial mycelia at first that turned off-white to light yellow after 5 days. No microconidia were observed. Seven morphologically similar isolates were obtained and representative isolate FQ01 analyzed. Macroconidia were five to seven septate with a tapered and elongated apical cell and prominent foot-shaped basal cells. Apical cells were conically elongated, and basal cells were prominently shaped, 20.1 to 47.2 × 2.5 to 2.9 μm. Macroconidia were produced from monophialides on branched conidiophores. Chlamydospores were abundant in clumps or chains, ellipsoidal to subglobose with thick and roughened walls. The isolated strain was identified morphologically as a member of the Fusarium incarnatum-equiseti species complex (FIESC) (Leslie and Summerell 2006). To confirm identity of FQ01, the internal transcribed spacer (ITS) region and the translation elongation factor 1-α gene (EF1-α) were amplified using primers ITS1/ITS4 (White et al. 1990) and EF1-728F/EF1-986R (Carbone and Kohn 1999), respectively. Total genomic DNA was extracted using the E.Z.N.A. Fungal DNA Mini Kit (Omega Bio-tek) according to the manufacturer’s instructions. Resultant sequences of FQ01 were obtained and submitted to GenBank (MN133053 for ITS and MN133052 for EF1-α). BLASTn analyses showed that sequences shared 99.83% identity with a sequence of F. equiseti for ITS (MH879250.1) and 100% with a sequence of F. equiseti (MK692895.1) for EF1-α. Further BLAST search in the FUSARIUM-ID database indicated that the sequences shared 100% identity with a sequence of FIESC for ITS (FD_01695) and 98.58% with a sequence of FIESC for EF1-α (FD_01627) (Geiser et al. 2004). Pathogenicity tests were conducted on wounded and nonwounded peach fruits with mycelial plugs and conidial suspension, respectively. Ten healthy and surface-sterilized fruits (cv. I9) were wounded using a sterilized needle and inoculated with mycelial discs (6 mm). Ten surface-sterilized nonwounded peach fruits (cv. Qiumi) were sprayed with a 10⁵ conidia/ml suspension. For the control, wounded and nonwounded fruits were inoculated separately using agar plugs and DW, respectively All fruits were enclosed in plastic bags and incubated in a growth chamber at 26°C, 90% relative humidity, and 12 h/12 h light (10,000 lux)/dark. After 5 days, the inoculated sites on wounded fruits had brown and sunken lesions. On nonwounded fruits, brown rot and white fluffy mycelia were observed after 1 week. No symptoms were observed on control fruit. The fungus was reisolated from the lesions of the inoculated plants and verified morphologically. This is the first report of FIESC on peach fruits in China. Owing to the range of mycotoxins produced, members of the FIESC are not only saprophytes and opportunistic plant pathogens but also highly associated with human and animal disease (Leslie and Summerell 2006). The pathogen presents a severe threat to peach quality and production, so further research should be implemented to find effective management strategies to prevent and control it.