How to prevent and control bacterial brown blotch in edible fungi?

I. Pathogen and conditions for occurrence

The bacterium causing bacterial brown blotch in edible fungi is Pseudomonas tolaasii, which is widely distributed in nature. This pathogen multiplies very easily under conditions such as high-temperature, high-humidity cultivation sites and poor ventilation. Reproduction accelerates when the temperature is above 18°C or the relative air humidity is above 85%. During the fruiting period, spraying water carrying the pathogen onto fruiting bodies, poor ventilation and excessively high humidity in the mushroom bed, prolonged water accumulation on the surface of mushroom caps and the substrate surface, repeated cultivation of the same mushroom type and the same variety in the greenhouse for several years, and condensation water gathering on the greenhouse film and dripping onto the mushroom bags or fruiting bodies can all cause the disease. The disease can also float in the air and be spread by mushroom flies, nematodes and workers.

II. Main symptoms

1. Substrate contamination. On the surface of agar medium contaminated by bacteria, colonies visible to the naked eye form; the colonies appear wrinkled and irregularly raised from the surface inward, and then rot and become moldy. In bagged substrate contaminated by bacteria, the water content increases in the early stage, with a sour odor; in the later stage the substrate rots and the sour odor becomes stronger.

2. Fruiting body contamination. On fruiting bodies infected by the pathogen, irregular brown spots form on the surface of the mushroom caps, round or diamond-shaped, relatively uniform in size, with neat edges, slightly sunken in the middle, and a thin layer of bacterial ooze on the surface. If the lesion is lightly scraped with a fingernail, the flesh underneath can be seen to remain white. In severe infections, a single cap may have dozens to hundreds of lesions, the fruiting body becomes dry and wrinkled and stops growing, and it rots when there is too much water.

III. Integrated control

1. Ensure mushroom house hygiene. Keep the cultivation site away from chicken and duck poultry sheds, and strictly prohibit scattering fertilizer and contaminated mushroom sticks around the area to ensure a clean environment. Regularly disinfect the facilities inside the mushroom house; the bed frames and supporting materials should be removed, sprayed and brushed with bleaching powder, then dried in the sun, and the floor of the mushroom house should be disinfected by scattering bleaching powder at a concentration of 150 mg/L. Before the mushroom bags enter the greenhouse, fumigate the mushroom greenhouse with 10-15 g/cubic meter sulfur and keep it closed for 2-3 days, with relative humidity kept below 85%. During the fruiting period, the relative humidity in the mushroom house should not be too high; ventilation should be strengthened to keep the air fresh. In addition, the greenhouse is best covered with anti-drip plastic greenhouse film.

2. Choose high-quality substrate. Choose substrate free of pests, diseases, miscellaneous fungi and mold; in the substrate formula during the high-temperature season, wheat bran should be no more than 10%, cornmeal is best not added, and an appropriate amount of lime should be added. The water content of the substrate should be no more than 65%; during the spawn running period, the relative air humidity in the mushroom house should be no more than 70%, and the casing soil material should be disinfected with formaldehyde.

3. Choose good varieties. Choose excellent varieties with strong resistance to contamination, master the cultivation season well, and inoculate and run spawn at the proper time, so that spring planting should not be too late and autumn planting should not be too early.

4. Strengthen water management during the fruiting period. During the fruiting period, the mushroom house should be kept on the dry side, and ventilation should be strengthened while ensuring appropriate humidity. During the pinhead stage, do not spray columnar water onto small pinheads; spray in a fine mist and pass over quickly, and it is best to use water stored for 1 day before use and disinfected with bleaching powder (concentration 150 mg/L), avoiding water accumulation on the substrate or fruiting bodies.

5. Handling of diseased mushrooms. Once fruiting bodies in the greenhouse are infected by the pathogen, they should be removed promptly, including infected young mushroom buds. When removing diseased mushrooms, the mushroom roots should be removed and the substrate surface should be cleaned thoroughly to ensure that nutrients in the substrate are not consumed.

6. Chemical control. ① When the disease is mild, spray 2000-fold diluted agricultural streptomycin on the lesions. ② Spray fruiting bodies infected with the disease with 150 mg/kg available chlorine to reduce the incidence rate. ③ Spray the substrate surface or fruiting bodies with 3000-fold diluted "Mushroom Guardian" solution once every 7-10 days, and mix the substrate with 3000-fold diluted "Mushroom Guardian" to prevent infection throughout the entire growth period. ④ Spray the fruiting bodies with 2000-fold diluted "Mushroom Disease Conqueror" solution.