Volume 12 Part 2 Article 70: Isolation, Characterization and Studies of Bacterial Mummy Disease of Agaricus brunnescens

Volume 12 Part 2 Article 70
Year 1989
Title: Isolation, Characterization and Studies of Bacterial Mummy Disease of Agaricus brunnescens
Authors: D.A. Betterley and J.A. Olson


Mummy disease of Agaricus brunnescens Peck [= Agaricus bisporus (Lange) Imbach] is a sporadic or occasionally endemic disease which can severely affect both yield and quality of mushrooms on certain farms. The disease tends to be more severe on shelf or deep trough farms where rapidly spreading forms of the disease are potentially unrestricted. Tray, bag, or pre-spawned block growers with the capability of separating compost into units generally experience less severe problems. However, tray farms are also susceptible to losses. In the U.S. and Canada, certain farms experience sporadic outbreaks. Other farms have little or no experience with mummy disease. Olivier (1987) reports low incidence in recent years in France, perhaps due to the predominance of bag (and tray) growmg systems. In Great Britain, Fermor (1987), Fletcher et al. (1986) and Oxley (1985) report mummy incidence, with a few farms encountering persistent problems. Mummy disease occasionally causes serious losses on Australian farms (Fahy and Lloyd, 1983).

The disease was first reported in the U.S. in 1935 (Tucker and Routien, 1942; Kligman and Penny, 1943). These and subsequent investigations described symptoms and the transmissible nature of the disease by infected compost, casing or mycelium (Storey, 1954; Kneebone, 1959; Merek, 1960). Causal agents could not be identified. The disease was shown not to be transmitted by spores by Kneebone (1959). Tucker and Routien (1942) described various species of bacteria and fungi from diseased tissue, but an association of one or more of these with the disease was not established. A constant association between an intracellular Pseudomonas species and diseased rhizomorph and sporophore tissue was established by Schisler et al. (1968). The bacteria were identified as closely related to Pseudomonas tolaasii (= P. fluorescens biotype G). Bactena grown in liquid culture and inoculated into spawn resulted in disease symptoms in mushroom beds. Others investigating the disease have confirmed the presence of intracellular bacteria in diseased tissue (van Zaayen and Waterreus, 1975; Oxley, 1985), and Oxley noted localized hyphal swelling. Suspected causal agents have been identified as P. fluorescens biotype G by Fahy (1981), Fahy and Lloyd (1983) and Oxley (1985). Except for a report of an Australian isolate reproducing symptoms when sprayed onto beds at casing (Fahy, 1981), further attempts to reinfect and reproduce disease symptoms have not been successful (Royse and Wuest, 1980; Oxley, 1985).

This investigation reports the isolation and characterization of bacteria associated with mummy disease, reinfection tests, and comparison with the original mummy strain from Schisler et al. (1968)

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