First report of Fusarium commune causing root rot of blueberry in Guizhou Province, China.

Abstract

In February 2017, an unknown root disease was observed on blueberry (Vaccinium uliginosum L.) plants in Fenggang county, Guizhou Province, China. Root symptoms began with small necrotic lesions; subsequently, dark brown rot of the tap root and stem base was observed; finally, the whole plant withered and died. Root tissue was obtained from the junction of diseased and healthy tissue, and the samples were rinsed 3 times with sterile water. Then the surface was disinfected in 75% alcohol for 30 s, washed three times with sterile water, washed with 3% (v/v) sodium hypochloride for 3 min, rinsed three times in sterile water and cultured on PDA at 28 ℃ for 3-5 days. Fungal colonies were subcultured on PDA 3-4 times until purified colonies were obtained. Eight isolates exhibiting morphological characteristics of Fusarium were recovered from symptomatic roots. Six isolates showed morphological characteristics consistent with Fusarium commune. The colonies of LMGF6, a representative, on PDA were white and pink, and there was abundant aerial hyphae. Microconidia were cylindrical, usually without septa, with a dimension of 5.0 to 12.0 μm × 2.0 to 3.5 μm; macroconidia were usually 3-septate and 10.5 µm to 36.5 µm × 3.0 to 5.0 μm in size. Chlamydospores were smooth and spherical. DNA fragments were amplified from LMGF1-6 from the internal transcribed spacer (ITS) region using ITS1/ITS4 primers (White et al. 1990), DNA-directed RNA polymerase II second largest subunit (RPB2) gene using 5f2/7cr primers and translation elongation factor 1-alpha (TEF1) gene using EF1/EF2 primers (Zhong et al. 2021; O'Donnell et al. 2022). The sequences were submitted to GenBank (GenBank accession Nos. OP035965 to OP035970 for ITS, OP106349 to OP106354 for RPB2, and OP106355 to OP106360 for TEF1). BLAST analysis showed 100% identity to those of F. commune. Ten plants were used for the experimental and control. The roots of experimental bushes were inoculated with 50 ml of a 1ⅹ106 conidial suspension. The roots of control plants were irrigated with sterile water. The plants were grown under the ambient conditions (monthly average maximum temperature of 30℃, monthly average minimum temperature of 20℃). After 25 days, all inoculated plants showed symptoms similar to those of the natural infection observed, but no lesions were observed on the control plants. The same fungus was successfully reisolated from all of the inoculated plants and was identified as F. commune based on colony morphology, phylogenetic analysis of concatenated ITS-RPB2-TEF1 sequences was performed using MEGA7.0 and pathogenicity tests. To our knowledge, this is the first report of F. commune causing root rot on blueberry plants in Guizhou Province, China.