Mushroom Culture

Bacterial Diseases of Mushrooms

C) BACTERIAL DISEASES OF MUSHROOMS
1. Bacterial blotch and bacterial pit diseases of white button mushroom:
Symptoms:

• Circular but irregular, yellowish spots appear superficially on or near margin of the cap of a wet mushroom which enlarge rapidly under high humidity conditions and coalesce to form bigger rich chocolate brown spots that are slightly depressed and slimy.

Causal organism:

• The pathogen Pseudomonas tolaasii can devastate the crop of button mushroom and Psilocybe sp. The bacterium has cylinderical ( Bacilli ) and spherical forms ( Cocci ) with its cells measuring 0.4-0.5x1.0-1.7 µ in size, with either one or more flagella ( motile hairs ) attached at one or both the ends for locomotion. The bacterium is gram negative in character
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Fruit bodies showing blotch symptoms

Epidemiology:

• The casing ingredients and air borne dust particles are the primary sources of infection .Under high humidity and damp conditions, bacterial population increases on cap surfaces and cause the disease. The bacterium remains suppressed in the compost, casing , tools and debris under dry conditions, but it becomes active under high humidity conditions and further spreads through worker’s hands, tools, mushroom spores, debris, water splash, flies, mites etc.

Control methods:

• Avoid heavy water sprays during rainy season, introduce fresh air immediately for about one hour after water spray and ensure that water droplets do not remain on the cap surface, remove all the diseased fruit bodies and spray bleaching powder ( 0.015 % ) on the cropping beds at 7 days interval.

II. Bacterial disease of Oyster mushroom:

Yellow Blotch:

• The yellow blotch disease of Pleurotus spp. is caused by Pseudomonas agarici.

Symptoms:

• Disease appears as blotches of various sizes in pilei, yellow hazel brown or organic in colour. The infected fruit bodies turn yellow and remain stunted, turn slimy and start giving foul smell.
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Fig. 13.43 shows: Symptoms of yellow blotch disease of Pleurotus sp.Caused by Pseudomonas agarici

Control methods:

• Same as suggested for controlling bacterial blotch disease of button mushroom.

3) VIRAL DISEASES OF MUSHROOMS:

• Diseases due to mushroom viruses are also known as La France, Die back disease and Mummy disease .

Symptoms:

• The viral diseases are not detectable during spawn – run stage; the initiation of pinheads is inhibited and vigour of mycelium severely reduced; yield is drastically reduced, mushrooms appear with distorted shape, delay occurs in appearance of first flush, sporophores with elongated stem and small caps giving drum stick like appearance and tilted towards one side appear, mushrooms appear in patches, prematrure opening of veils, watery stipe and streaking in the stipe. In case of oyster mushroom, dwarfing or elongation of stem has been observed whereas, no detectable symptoms appear in infected Volvariella sp.

Sources of Infection:

• Infected mycelium and spores released from infected mushrooms are the primary sources of infection. These viruses further disseminate through worker’s hands, equipments, infected spawn / mycelium present in the trays / bags and spent compost etc.

Control methods:

• Complete hygiene, use of disease free spawn, frequent disinfection with formaldehyde, aeration strictly through high efficiency filters, cook out of exhausted compost at the end of the crop with live steam at 70-71 º C for 10-12 hours, regular disinfection of equipments, wearing clean and changed clothes everytime while entering a mushroom house, harvesting of mushrooms before opening when the veil is intact, visitors to be discouraged, wooden trays and shelves to be washed regularly with 4 % sodium pentachlorophenate solution, growing of resistant strains like A. arvensis and A . bitorquis have been recommended.