Control methods of Sclerotinia sclerotiorum in bergamot

Symptoms: damage to fruits buried in sand during storage. Most of the diseased fruit first fell ill in the wound, began to be watery, light brown, rapidly expanded, soft rot, and finally rotted into a pile of mud, the disease produced a large number of black particles, that is, the sclerotia of the pathogen.

The pathogen: Sclerotinias clerotior μ m (Lib.) deBary is called Sclerotinia sclerotiorum, which belongs to the subphylum Cysticercus. The sclerotia produced in the disease part were oval, irregular, initially white, and then turned black on the outside, with a size of 2 Mel 5 × 1 Mel 3 (mm). On PDA, the flora was white, felt-shaped, the mycelium was flat, rough and grew rapidly. The hyphae are colorless, branched, and produce conidiophores. Some small bottle peduncles are irregularly clustered at the top of the conidiophores or at the top of their branches, and the tiny conidia are dense and colorless unicellular. The size of the conidia is only 1.5 × 1 × 2 (μ m), and a large black irregular sclerotia is gradually formed after a week of initial white.

Transmission route and disease condition: overwintering with sclerotia in soil, on diseased remains or mixed in compost. The sclerotia of overwintering sclerotia germinated under suitable conditions to produce ascomycetes. After the ascomycetes matured, the spores were emitted and spread with the wind to infect the surrounding plants in case of the change of air humidity. In addition, sclerotia sometimes produce hyphae directly. The mycelium on the diseased plant had strong infectivity and became the source of re-infection and spread. The hyphae developed rapidly and the pathogenic part rotted. Sclerotia are produced when nutrients are consumed to a certain extent, and sclerotia germinate without dormancy. The disease occurs under cool and humid conditions, and the optimum temperature is 5 ℃ 20 ℃ and 15 min. Ascospores can germinate at 0-35 ℃, and 5-color 10 ℃ is the most favorable. The mycelium could grow at 30 ℃, and 20 ℃ was the most suitable. The temperature of sclerotia formation was consistent with the temperature required for mycelium growth, and 50 ℃ of sclerotia was killed in 5 minutes. The bacteria have strict requirements on humidity. In moist soil, sclerotia only survive for 1 year; long-term stagnant water in soil will die in 1 month; it can survive for more than 3 years in dry soil, but it is not easy to germinate. Sclerotia germination requires high temperature and cool conditions, and the development of ascus needs enough water for 10 days after germination. When the relative humidity is 70%, the ascospores can survive for 21 days; the relative humidity at 100% can only survive for 5 days. It occurred in Guangdong from October to December, and the damage was serious.

Prevention and treatment methods: at the initial stage of the disease, 40% polysulfide suspension 600ml 700 times or 70% thiophanate methyl wettable powder 500Mel 600 times, 50% mixed thiophanate suspension 600 times, 80% carbendazim wettable powder 600m 700 times, 50% propofol wettable powder 1000ml 1500 times, once every 7 times 10 days, continuous prevention and treatment for 23 times.