Verticillium dry bubble

Lecanicillium fungicola

Dry bubble mainly affects three different species of mushrooms: Agaricus bisporusA. bitorquis, and Pleurotus ostreatus. It has been isolated from numerous other basidiomycetes, including a few wild mushrooms. However, there has not been enough research into dry bubble pathogenicity to define an exact host range.

A. bisporus, white button mushroom, is the main host of Verticillium dry bubble disease. Worldwide, 40% of commercially produced mushrooms are A. bisporus. When infecting A. bisporus, dry bubble is unable to infect the vegetative mycelium and can only infect the fruit bodies. This means infection must take place in the casing layer, a layer of material, usually mulch put on top of the mushroom. In general, dry bubble symptoms are dependent on the time point of infection, affecting both the type and severity of the disease symptoms. Symptoms are mild when inoculation occurs during casing layer applications, and severe when inoculation takes place 14 days after the casing layer has gone down after the mushrooms have poked through.

Interactions between the pathogen and the host in the casing layer can either result in stipe blow-out or dry bubble. Early infections can cause stipe blow-out in which part of the fruit body of the mushroom becomes deformed, accompanied by splitting or peeling of the stipe tissue. L. fungicola also causes totally deformed and undifferentiated white masses of mushroom. If inoculation occurs in the late stage of the mushroom life cycle, symptoms include small necrotic lesions on the cap of the mushroom. Other symptoms may include brown, light brown, or gray discolorations on the cap or the stipe of the mushroom. Infection by L. fungicola does not decrease the weight of the mushroom crop, but has the potential to decrease the total number of mushrooms produced. Therefore, dry bubble is thought of mainly as a cosmetic disease.

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