First Report of Trichoderma gamsii Causing Root rot Disease on Panax notoginseng in Wenshan, Yunnan Province of China.

Panax notoginseng (Burkill) F.H.Chen (Sanqi) is a traditional Chinese medicinal plants, and has shown hemostasis, anti-oxidation, neuroprotection and anti-tumor activities (Wang et al. 2014). Wenshan (23°35'24.1" N, 104°19'48.2" E) in Yunnan Province of China, is the main producing area of P. notoginseng. This region has a subtropical monsoon climate, an altitude of around 1200m above sea level, and loam soil. In November 2023, serious symptoms of root rot disease were first observed on 2-year-old P. notoginseng in Wenshan. The P. notoginseng initially exhibits indications of stem browning and leaf yellowing, followed by plant wilting and damping-off, and eventual death. The incidence of diseased plants was up to 20% in a plantation of 4 hectares. Six diseased plants were randomly collected from different regions of a 1000 square meters planting area, and root samples were cut into small fragments and surface sterilized with 1% sodium hypochlorite for 1 min. The root fragments were placed on potato dextrose agar (PDA) and then incubated at 30℃ in the dark. Mycelium tips were observed and transferred onto new plates and finally 18 isolates were obtained from the diseased samples. The colonies of all 18 isolates were white with strong coconut odour, and looked identical in appearance. The growth rate of the isolates was about 2.5cm/d and the whole petri dish (8 cm in diameter) could be covered in 4 days. Conidia formed after another two-day incubation with light. Conidia were smooth, elliptical, 4.1 to 5.2 × 2.9 to 3.6 μm in size (n = 30). DNA was extracted from three representative isolates. The partial region of the rDNA internal transcribed spacer (ITS) and the translation elongation factor (tef1) were amplified with the primers ITS1/ITS4, TEF1/EF728 (Samuels et al. 2006). The blast results showed that the three isolates were identical to each other in their ITS (PP469588) and tef1 (PP544203) sequences and those sequences had 99% (ITS, 580/583bp) and 98% (tef1, 597/609 bp) similarity with those of Trichoderma gamsii (DQ841730 and DQ841722, respectively) (Jaklitsch et al. 2006). For pathogenicity tests, thirty 5-month-old healthy seedlings of P. notoginseng were used and inoculated by root-irrigation of conidial suspension (10⁷ conidia/mL, 20mL per seedling), whereas ten seedlings were treated with distilled water as controls. All seedlings were incubated in pots and set in the test field in Wenshan area from April to June. First symptoms appeared 6 days after inoculation. All inoculated seedlings showed disease symptoms 18 days later after challenge, whereas no symptoms were observed on the controls. The pathogen was reisolated and confirmed to be T. gamsii through molecular identification. The pathogenicity test was repeated three times. T. gamsii was first reported in 2006 (Jaklitsch et al. 2006), and attracted attention mainly on its biocontrol effects (Matarese et al. 2012). It had also been isolated from healthy P. notoginseng as endophyte to produce many different secondary metabolites for potential medical use (Ding et al. 2012). To our knowledge, this is the first report of T. gamsii causing root rot disease on P. notoginseng. P. notoginseng is of great economic value in Wenshan area. In 2017, its production was valued at 16.2 billion Chinese Yuan, with an expanding cultivation (Liu et al. 2020). Thus, it is important to monitor and manage this pathogen on P. notoginseng.