Volume 12 Part 2 Article 67
Title: Influence of Spawn Incubation Temperature of Agaricus bisporus (Lange) Sing. on La France Disease Symptomatology
Authors: P.J. Wuest and J.A. Mataka
La France disease is a serious disorder of the cultivated mushroom, Agaricus bisporus (Lange) Smg. Numerous symptoms have been ascribed to La France disease (2, 4, 6, 14, 15), and some are noted: (a) mycelia may disappear from the compost or casing resulting m barren areas and serious crop losses; (b) a delay in first break harvest; (c) sporophores grow from below the casing rather than on the casing surface. Symptomatic sporophores vary in morphology and this symptomatology includes thin, elongate, and slightly bent stipes, sometimes bearing a small pileus. Colonies which originated from symptomatic sporophore tissue plated onto a solid medium frequently are buff-colored, and exhibit a slow, appressed growth on agar in comparison with the white, fluffy vigorous isolates from healthy sporophores (10).
Another perplexing aspect of La France disease is the occurrence of mycelial colonies and sporophores acting as symptomless carriers of virus-like particles.
Hollings, Gandy, and Last (6) reported that “the apparently normal mushrooms surrounding areas containing obviously diseased mushrooms were found to be symptomless carriers, and were a rich source of virus”. Following serial transfer on malt agar over a 19-month period, Nair (10) found that a previously symtomatic isolate could not be distinguished morphologically from its corresponding healthy isolate, although the virus-like particles were still present.
Kneebone et al. (7) demonstrated that tissue cultures derived from symptomatic sporophores can appear to be normal in gross morphology or growth rate, yet give rise to symptomatic sporophores when planted as spawn in compost. Spawn has been considered a source of inoculum in the onset of La France disease (8, 11), and recent reports add substance to this perspective.
Temperature is known to affect symptom expression of viral infections. Also, mycelial growth of A. bisporus is limited to a very narrow range of temperatures close to 24°C (17). During spawn preparation mycelium can be subjected to nonoptimal growth temperatures. The role of unfavorable spawn incubation temperature in La France disease etiology is unknown. Therefore, these experiments examined the effect of incubation temperature on healthy and infected isolates during spawn preparation on La France symptomatology.Please login to download the PDF for this proceeding.