Ginseng (Panax ginseng C.A. Meyer) is a treasure of traditional Chinese medicine resources and has been used in food, health care products, and medicines in China for over 4,000 years. Jilin Province is the largest producing region in the world. Ginseng root rot disease caused by Fusarium spp. is the chief disease of ginseng with more than 25% incidence. Infected ginseng roots could not be used, which brought economic losses, and the species of the pathogens were not clear. The above-ground leaves of infected ginseng plants became red in the early stages and later wilted or died. All parts of root including rhizome, taproot, and fibrous root can be infected. Brown lesions were mainly formed on the surface and expanded gradually. Finally, multiple lesions converged and caused root rot. Diseased roots collected in June 2012 from 4-year-old ginseng (cv. Damaya) from Jingyu County and Jiaohe City, Jilin Province. Six isolates were obtained by cutting the roots into 5 mm3 pieces, disinfecting in 3% NaOCl for 3 min, and isolating on half-strength acidified potato dextrose agar (PDA). All isolates were purified from single spore. They produced white and cottony aerial mycelium cultured on PDA, microconidia were in the majority, oval or reniform, and length ranged from 5.97 to 12.01 μm. Macroconidia were in the minority, fusiform to conical, usually 3 to 5 septa, length ranged from 13.99 to 26.50 μm, thin-walled, with a hooked apical cell and a foot-shaped basal cell. A variety of structures of chlamydospores were produced, in chains or in pairs, basidixed or in the middle of the hyphae. Preliminary conclusions were made according to the morphological characteristics, which were consistent with the descriptions of Fusarium redolens (2). All the isolates of Fusarium spp. were accurately identified based on molecular biological methods of rDNA internal transcribed spacer (ITS) and the elongation factor (EF1-α) gene sequences analysis. ITS sequences analysis (GenBank Accession No. KF499035) resulted in a 100% match for one accession of F. redolens (X94169) by BLAST in the NCBI nucleotide database, and EF1-α gene (KF499036) had 100% similarity with 12 accessions of F. redolens (e.g., AF324319) by BLAST in the FUSARIUM-ID database (1). All isolates of F. redolens were tested for pathogenicity on ginseng root in vitro and healthy plants in a greenhouse, respectively. The surface of healthy ginseng roots were washed and disinfested in 70% alcohol for 3 min and plant in flower pots with sterile sand and sorghum grain infested with 14-day-old isolates and no inoculation as the control. Each experiment was repeated three times. Root rots were assessed 21 days after planting and all the isolates consistently caused root rot on inoculated plants, taproot and fibrous root exhibited brown to black root rot and plant wilting, whereas no root rot was observed in the controls and the pathogen was successfully re-isolated. The results were confirmed by the in vitro and healthy plant inoculation of ginseng root. F. redolens was identified previously as F. oxysporum, but recent molecular studies have shown that they are distant species in phylogenetic analysis (3). To our knowledge, this is the first report of F. redolens causing root rot of ginseng in China.
References: (1) M. D. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (3) K. O'Donnell et al. Mycologia 90:465,1998.
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