Symptoms and Control Methods of Anthracnose in the Medicinal Plant Panax notoginseng (Tianqi)

Symptoms The disease can occur at the seedling stage and the adult plant stage. Infection at the seedling stage causes damping-off or top blight. At the adult plant stage, it mainly affects leaves, petioles, stems, flowers and fruits. Infected leaves initially develop circular or nearly circular yellow-brown spots with a distinct reddish-brown margin; later the diseased areas tend to rupture and perforate. Infected petioles and stems develop spindle-shaped, yellow-brown, sunken spots, causing the petioles to coil or the stems to twist. Infection of the stem base causes lodging of adult plants or rot of the rhizome. Infection of pedicels and flower discs leads to drying of flowers and seeds. Infected fruits also develop nearly circular yellow sunken spots, causing the fruits to turn brown and rot.

Pathogen Colletotrichum gloeosporioides Penz. and C. dematium (Pers.) Grove, known as the anthracnose fungus and the black-line anthracnose fungus respectively, both belonging to the Deuteromycotina fungi. On PDA, C. gloeosporioides colonies are initially white, later turning grayish-white, with light gray aerial hyphae; the conidial masses are initially white, later pale red; setae are numerous; conidiophores are branched; conidiogenous cells are phialidic, producing conidia in a phialidic manner; conidia are colorless, single-celled, sickle-shaped, with a pointed apex and a bluntly rounded base, 19-23 x 2.5-4.0 (μm); appressoria are abundant, dark brown, elliptical, circular or club-shaped, with mostly regular margins. For C. dematium, see anthracnose of dwarf lilyturf.

Transmission routes and disease conditions The pathogen overwinters as mycelium in the cortex of the soft fruit of the seed or attached to the surface of the red seed (seed); the residual stubs of the sheep-gut head and dead leaves are also major overwintering sites of the disease. The disease is mainly transmitted by red seeds, causing the above symptoms, and infected red seeds carrying the pathogen become the primary infection source the following year. In the field, the pathogen mainly occurs during the rainy season; generally, under high temperature and high humidity in June-July, the disease spreads rapidly, and continuous overcast and rainy weather, sultry weather after rain, and overly dense planting easily induce an epidemic of the disease.

Control methods (1) Clean the field in winter and promptly burn diseased residues. (2) Adopt a formulated fertilization technique, apply sufficient well-rotted organic fertilizer, and increase the application of phosphorus and potassium fertilizers to improve disease resistance. (3) Seed (red seed) treatment. Soak the red seeds in a 150-fold dilution of 43% formalin for 10 minutes, remove the soft fruit skin, and then dress the seeds with 0.5%-1.5% of 75% thiophanate-methyl or 70% thiophanate-methyl wettable powder. Alternatively, mix 75% thiophanate-methyl 400-fold solution with 45% zineb wettable powder 200-fold solution at 1:1 and soak the seeds for 2 hours, which gives excellent control efficacy. (4) Rain-shelter cultivation is recommended. During the rainy season, cover the top of the shade shed with plastic film to prevent rainwater from wetting the plants, significantly reducing the disease incidence. (5) Adjust and repair the canopy or use shade netting to control light transmittance. For Panax notoginseng seedlings, the light transmittance of the shade shed should be adjusted to 17%-25%, and for 2-4-year-old plants to 20%-35%; in early spring or late autumn each year, the light transmittance may be slightly higher. (6) During the emergence stage or before and after rain, promptly spray 45% zineb wettable powder 400-fold solution, or 75% thiophanate-methyl wettable powder 1000-fold solution, 50% carbendazim wettable powder 800-1000-fold solution, 25% tanteling wettable powder 500-fold solution, or 25% benomyl emulsifiable concentrate 900-fold solution.