Symptoms mainly damage seedlings and nursery seedlings during mulberry seedlings and sand pre-conditioning. The victim seedlings or cuttings are mostly light brown to brown or dark brown spots on the stem surface near the ground, and a white silk filiform mycelium is produced in the diseased part. The mycelium expands radially and covers the diseased part when serious. The hyphae tangled together to form a dark brown rapeseed sclerotia. After the formation of small sclerotia, the white mycelium gradually disappeared. During this period, the cortex of the diseased section festered, and was easily peeled off. The filamentous fibers were exposed. The diseased leaves turned yellow and withered, and the severe plant died.
The pathogen, Sclerotium rolfsii Sacc., is known as S. sclerotiorum and belongs to the fungus Subgenie Fungi. The sexual state is Athelia rolf-sii (Curzi) Tu. & Kimbrough. It is called Rhizoctonia and belongs to Basidiomycotina fungus. The mycelium was white, lush and radiant in PDA medium. The mycelium was 2–8 μm thick. The branches did not form a right angle with a septum. The sclerotia are milky white at first, then light yellow to dark brown or tan, spherical to ovoid, 1-2 mm in size, and the surface is smooth and shiny. The sclerotia consisted of three layers of cells, with an outer layer of tan, pseudo-parenchyma under the epidermis, and a sparse tissue in the middle. Sclerotia are not associated with mycelium and are easily detached.
Transmission routes and disease conditions The pathogens use sclerotia to overwinter on the surface or in fertilizers containing residues. When the temperature and humidity are suitable for the following year, the mycelium grows from the sclerotia and infects the stem base of the mulberry seedling. Afterwards, the mycelium grows again along the earth seam and spreads to the neighboring plant or diseased plant for direct re-infection. The onset temperature is 30 to 35°C. The disease is easy to develop in the southern mulberry cultivation area. In production, sand preserving sand plugs with plastic film insulation and moisturizing are susceptible to disease. The incidence of continuous cropping in the nursery is heavy.
Control methods (1) Choose Gaosha block to reproduce mulberry seedlings 4 (2) Use clean river sand pre-preparation cuttings to reduce or control its incidence. (3) Disinfection of pharmaceuticals, use 50% carbendazim WP 500 times or 36% thiophanate-methyl suspending agent 600 times, spray the sand wet, and cover with plastic film for 7-8 days. Preserve the pretreatment cuttings; also use the fungicide to soak the sand plugs for 20-30 minutes, which can reduce the incidence of white peony disease.
Rongcheng Jingyi Oceanic Technology Company Limited , https://www.jingyifoods.cn