Mushroom Culture

Pathogenic Diseases of Mushrooms

B) PATHOGENIC DISEASES OF MUSHROOMS

1. DRY BUBBLE DISEASE OF MUSHROOMS: ( Pathogen : Verticillium fungicola Preuss. Hassebr )

Common Name: Brown spot , fungus spot , Verticillium disease , La mole , Dry bubble

• It is a most common and serious fungal disease of mushrooms. Sometime it may cause complete failure of the crop within 3-4 weeks.

Symptomatology:

• Numerous localized,light brown depressed spots appear on the mature sporophores. After coalition, these spots form irregular brown blotches with white fungal spore mass or grey mouldy fuzz covering the surface giving a dirty look.
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Fig. 13.30 to 13.32 shows: (a&b) The brown spot symptoms of dry bubble disease on fruit bodies, (c) the microscopic structure of the pathogen with verticillate branching and conidia at the tips

Epidemiology:

• The fungus is soil borne and spores can survive in the soil for one year.It also perpetuates through resting mycelium from dried bulbils and spent compost.

Causal Organism:

• Numerous one celled, thin walled, hyaline, oblong to cylinderical conidia ( 3.5 – 15.9 x1.5-5 µ ) are produced on lateral or terminal , verticillately branched , relatively slender and tall conidiophores ( 200 – 800 x 1.5 – 5.0 µ ). Conidia accumulate in round clusters surrounded by a sticky mucilage. The fungus remains live in the soil for a long time.

Control methods:

• Use of properly sterilized casing mixture, cook out of spent compost with steam at 71 º C for 8-10 hours and its disposal at a distant place, isolation and removal of infected sporophores from the cropping room, spray of fungicides like Dithane M-45 ( 0.2% ) or Carbendazim ( 0,05 % ) on cropping beds at 10 days interval, complete hygiene, proper pasteurization of compost etc, have been recommended.

2. WET BUBBLE DISEASE OF MUSHROOM: ( Pathogen: Mycogone perniciosa Magn. )

Common name of the disease: The disease is also known as wet bubble, La mole, bubble, Mycogonedisease or white mould

• It is a serious and devastating disease of white button mushroom all over the world .
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Symptoms:

• The pathogen appears as a white mould attacking primordia and turning them into a soft whitish ball of mycelia. Early infection causes formation of sclerodermoid masses or forms whereas late infection causes production of mushrooms with thickened stipes and deformation of gills. At the later stage amber coloured fluid containing spores and bacteria ooze out from the brown and rotting interior of these bubbles sometime giving bad odour.
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Fig. 13.34 to 13.36 Shows: (a&b) Bubble structures of Mycogone perniciosa formed on mushroom beds (c) warty chlamydospore and single celled conidia borne on the conidiophores

Etiology:

• The disease is caused by a fungus Mycogone perniciosa Magn which is having white, compact, felt like mycelium; hyphae branched, interwoven, septate, hyaline, 3.5 µm broad . Conidiophores short, slender, branched, hyaline measuring 200 x 3-5 µm having sub-verticillate to verticillate branches bearing thin walled, one celled conidia measuring 5-10 x 4-5 µm . It also forms large, dark, 2 celled chlamydospores with its upper cell warty, thick walled, globose, bright coloured measuring 15-30 x 10-20 µm; lower cells hyaline, smooth measuring 5-10 x 4-5 µm . It is the imperfect form of Hypomyces perniciosa .
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Fig. 13.37 shows: Dry bubble in Oyster mushrooms

Sources of Infection:

• Mycogone perniciosa is a soil borne fungus and enters the mushroom house through casing material, spent compost, infected trashes which are air as well as water borne or mechanically transmitted through men, mites, flies ,tools and containers . The aleurospores produced cause secondary infection but since chlamydospores survive for a considerable period in casing soil ( more than 3 years ), it may serve as the primary source of infection . A bed temperature of 25 º C and pH range of 6.0 to 8.4 are favourable for the pathogen.

Control methods:

• Proper sterilization of casing soil with live steam or formalin, use of plastic pots or common salt for early covering of the infected fruit bodies so as to prevent further spread of the disease, complete hygiene, cook out of the cropping beds / bags at the end of the crop with live steam at 71º C for 10 – 12 hours, fumigation of the cropping room with formaldehyde and spray of fungicides like Bavistin or Mertect (0.5% ) immediately after casing etc; are the measures recommended for controlling this disease.

3. COBWEB DISEASE OF MUSHROOMS: ( Pathogen- Cladobotryum dendroides ( Bull : Merat )

Common names of the disease : Mildew, soft decay, Dactylium disease, Hypomyces mildew disease

Symptoms:

• It is cobweb like in appearance which appears as a small, white patches on the casing soil and then spreads to the nearest mushroom by a fine grey white mycelium . A floccose white mycelium covers the stipe, pileus and gills eventually resulting in decomposition of entire fruit bodies and change to slightly pinkish cover . at a later stage.
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Etiology:

• Cladobotryum dendroides ( Dactylium dendroides ) is the imperefect stage of Hypomyces rosellus . The hyphae are prostrate, branched, septate, hyaline with approximately opposite branches which divide above into usually those pointed branchlets; conidia multicelled, usually three or more connected cells which occur singly or in clustered form, terminally positioned at the end of branches often seen in a Verticillium like fashion; conidiophores are erect, similar or branched; conidia measuring 20-30x 5-12.5 µ in size.

Fig. 13.39 to 13.41 shows: (a&b) Mouldy growth of mycelium of Cladobotryum dendroides covering casing surface and engulfing the fruit bodies,
(c) Conidiophore bearing 2-3 celled conidia at the tips

Sources of infection and spread:

• It is a soil inhabiting fungus and introduced through casing ingredients, worker’s hands, spores or mycelia surviving in the spent compost. It further disseminates through workers’ hands, equipments and tools, air, water splash, mushroom flies etc. A bed temperature of 20 ^º C and above with high relative humidity have been found to be favourable for rapid development of the disease and maximum damage.

Control methods:

• Complete hygiene, careful removal of cut mushroom trashes and young dried mushrooms; proper sterilization of casing mixtur , covering of infected pinheads with plastic cups or common salt are recommended.

4. TRICHODERMA BLOTCH OF MUSHROOM:

• The most common green mould fungus Trichoderma viride also infects the fruiting bodies by engulfing them and producing brown spots or blotch symptoms causing considerable loss . The details have already been described under the head green mould.