First Report of Rhexocercosporidium panacis Causing Rusty Root of Panax ginseng in Northeastern China

Abstract

In northeastern China, Asian ginseng (Panax ginseng) roots exhibited reddish brown lesions of various sizes, irregular shapes, and diffuse margins, typical of rusty root disease. The lesions remain superficial, smooth, and limited to the epidermal and peridermal tissues. In September 2013, 10 symptomatic roots were collected from each of three fields in Jilin and Heilongjiang provinces. One piece of symptomatic skin tissue from each root was excised, surface-disinfested in 1% NaClO for 3 min, rinsed three times with sterile water, and then placed on tetracycline-amended (50 μg/ml) potato dextrose agar. After incubation at 22 ± 1°C in the dark for a week, small olivaceous black colonies developed from the symptomatic tissue from five of the 30 samples. No spores were observed. A single hyphal tip of each colony was transferred to a fresh V8 agar plate to purify the culture. Two-week-old colonies on V8 agar were olivaceous gray, and 42 to 46 mm in diameter with an outer white margin (3 to 5 mm wide). Conidia produced in V8 broth after 3 weeks with a 12-h photoperiod were straight and hyaline, cylindrical or subcylindrical with no or one septum. Mature conidia were 12.8 to 21.8 × 2.2 to 4.5 μm (mean 18.2 × 3.0 μm, n = 100 conidia for each of three isolates). Three isolates selected randomly were further identified by analyzing the partial sequences of the ITS region of rDNA with primers ITS4 and ITS5 (5), and partial sequences of β-tubulin with the primers tub2F and tub2R (1). Sequences of the three isolates (GenBank Accession Nos. KJ149287, KJ149288, and KJ149290 to 93) showed 99% to 100% homology with previously identified and deposited Rhexocercosporidium panacis isolates (DQ2499992 and DQ457119) for both loci (3). Therefore, the three isolates were identified as R. panacis and deposited in China General Microbiological Culture Collection Center (CGMCC3.17259 to 61). Pathogenicity of R. panacis in Asian ginseng was investigated using these three isolates as described previously with slight modifications (4). Bare roots of 3-year-old Asian ginseng were surface-disinfested as described above, and inoculated with mycelial plugs (4 mm diameter) cut from the margin of actively growing colonies of the isolates on V8 agar. Three mycelial plugs were placed on each root at 3-cm intervals and four roots (replicates) were inoculated for each isolate. Four additional roots were inoculated with non-colonized agar plugs as control. The treated roots were placed on moist filter paper in an enamel tray. The plates were sealed with plastic wrap to prevent desiccation and incubated in the dark at 18 ± 1°C. Four weeks post inoculation, all the inoculated ginseng roots showed red-brown lesions, which turned to dark red or black over time. R. panacis was recovered from symptomatic roots for all isolates and confirmed by ITS sequence analysis. The mock-inoculated control roots remained symptomless and no R. panacis was isolated. The inoculation experiment was repeated and showed the same results. R. panacis was reported in 2006 to infect roots of Panax quinquefolius (2,3,4). To our knowledge, this is the first report of R. panacis causing rusty root of P. ginseng. References: (1) P. R. Hirsch et al. Mycol. Res. 104:435, 2000. (2) Z. K. Punja et al. Can. J. Plant Pathol. 35:503, 2013. (3) R. D. Reeleder. Mycologia. 99:91, 2007. (4) R. D. Reeleder et al. Phytopathology 96:1243, 2006. (5) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

Planting American ginseng (Panax quinquefolius L.) caused soil acidification and bacterial and fungal communities changes

“…In addition, Mortierella was the most abundant fungal genus in this research. Previous studies have con rmed that Mortierella can be isolated from the roots of red-skin Asian ginseng (P. ginseng) [51]. Our results suggest that the relative abundance of Mortierella increases with the years of American ginseng cultivation, and that even reached more than 30% in the fourth year of planting ginseng.…”

Diversity of Microfungi in a High Radon Cave Ecosystem

“…It should be noted the high presence of endophytic fungus ( Talaromyces, Porodiplodia vitis, Aureobasidium pullulans ) and fungal species associated with roots and decaying plant material ( Rhexocercosporidium panacis and Tritirachium dependens) in Sala de Entrada ( Lu et al, 2014 ; Vanam et al, 2018 ; Crous et al, 2019 ). Therefore, their presence near the entrance was related with roots and the transport of organic matter from outside.…”

Deciphering Microbiome Related to Rusty Roots of Panax ginseng and Evaluation of Antagonists Against Pathogenic Ilyonectria

“…These microorganisms, including bacteria and fungi, have a strong impact on the fitness of plants (Vandenkoornhuyse et al, 2015). Most of previous studies about ginseng rusty root were based on culture-dependent methods (Reeleder and Brammall, 1994; Reeleder et al, 2006; Lu et al, 2014, 2015). However, the relationship between microbial community of ginseng and rusty disorder is still unclear.…”