First report of rot disease in Prunus salicina var. taoxingli fruit caused by Fusarium lateritium in China.

Abstract

Shengzhou nane (Prunus salicina var. taoxingli) as main cultivated plum in Zhejiang province, China, ripened in summer and was susceptible to microbial infection during the maturation stages because of high ambient temperature. In July 2022, Shengzhou nane fruits were found with symptoms of dark skin and grey-white lesions on surface, and an average incidence of approximate 16% (data obtained from investigation of ten trees in each orchard, and fifty fruits in each tree) in four orchards in Shengzhou city, Zhejiang province, China. To isolate the pathogen, four symptomatic partially rotted fruits (about 25%) from four orchards were collected. The plum tissue from the margin of lesions was excised into small blocks (4×4×3 mm). Eight blocks were disinfested with 70% ethanol for 30 seconds and 2% NaClO for 3 minutes, rinsed at least twice with distilled water, and incubated on PDA medium supplemented with 30.0 μg/mL Chloramphenicol at 25°C for 5 days in darkness until sporulation. Using single-spore isolation, four uniform isolates were obtained. The purified mycelium of isolates on PDA were milky white, the reverse on agar was dark pink. Colonies grew with a mean mycelium growth rate of 4.62 ± 0.38 mm per day on PDA. Macroconidia was shaped like a sickle and the size was 27.27 ± 3.43×4.54 ± 0.39 μm (n=50) with 2 to 3 septate. No microconidia and chlamydospores were observed. These morphological characteristics were consistent with previous descriptions of Fusarium lateritium (F. lateritium) species (Yun et al. 2013). Molecular identification was performed by sequencing nuclear ribosomal internal transcribed spacer region (ITS) gene with ITS1/ITS4 (White et al. 1990) and translation elongation factor-1α (TEF) with EF1-728F/EF1-986R (Carbone and Kohn. 1999). The representative sequences were submitted to Genbank (Accession Nos. OP315081 for the ITS and OP394153 for the TEF-1α). Blastn result indicated that ITS and TEF-1a sequences shared 99.28% and 100% similarity with two strains of F. lateritium (GenBank Accession Nos. MK311296.1 and JF740854.1). To fulfill Koch's postulates, the isolated F. lateritium (TXL-IT5) with a conidial suspension (1×106 spores per mL) was inoculated on ten fresh harvested healthy mature Shengzhou nane fruits (20 μL per fruits) after surface sterilization. The control fruits were inoculated with 20 μL distilled water. The experiment was repeated three times.Fruits were kept in a sealed plastic boxes at 25 °C with 90% relative humidity in dark. Four days after inoculation, all inoculated fruits were infected and appeared the same symptoms which were found in naturally infected fruits while those in the control group remained symptomless. The pathogen was re-isolated from symptomatic rotten fruits using above-mentioned method and was identified asF. lateritiumbased on morphological characteristics as well asITS and TEFgene sequences. In addition, this pathogen was reported to infect Dalbergia tonkinensisin north Vietnam (Nhung et al. 2018), causing shoot dieback of Acer negundo in northeast Poland (Patejuk et al. 2022), and rot of Chinese cherry during postharvest storage (Wang et al. 2020). However, to the best of our knowledge, this is the first report of F. lateritium causing rot on Shenshou nane fruits. Our findings serve as a warning for scientists and growers who should pay attention to this disease and take effective control strategies to reduce epidemics of this disease in China and other regions.