Inheritance of Strain Instability (Sectoring) in the Commercial Button Mushroom, Agaricus bisporus

Abstract

The button mushroom, Agaricus bisporus, is a commercially important cultivated filamentous fungus. During the last decade, the button mushroom industry has depended mainly on two strains (or derivatives of these two strains). Using one of these highly successful strains (strain UI) we examined the phenomenon of strain instability, specifically, the production of irreversible sectors. Three "stromatal" and three "fluffy" sectors were compared with a healthy type Ul strain and with a wild-collected isolate. Compost colonization and fruit body morphology were examined. The main objective of this study, however, was to examine the meiotic stability of the sectored phenotype. Single basidiospores were isolated and subjected to a grain bioassay in which the ability to produce sectors was measured. Our results were as follows: (i) basidiospore cultures obtained from a wild-collected isolate showed no tendency to produce sectors; (ii) approximately 5% of the basidiospore cultures obtained from healthy type Ul strains produced irreversible sectors in the grain bioassay; (iii) the five primary sectors examined produced basidiospore cultures, half of which produced normal-looking growth in the grain bioassay and half of which produced some degree of sectoring; and (iv) the one sectored isolate that represented the F2 generation gave ratios similar to the 1:1 ratio observed for the Fl cultures.

Characterization of experimentally induced, nonaflatoxigenic variant strains of Aspergillus parasiticus

“…In addition, all these nonaflatoxigenic strains displayed a pleiotropic phenotype that involved changes in conidiophore development and sporulation patterns. These isogenic sec ϩ and sec pairs remain an interesting model system for strain degeneration (15,18). They may also be useful tools in providing an insight into the correlation between secondary metabolism and morphological development in filamentous fungi.…”

“…Similar correlations between morphological changes and loss of virulence or secondary metabolite production have been commonly reported for filamentous fungi, but no satisfactory explanation has been found for most cases of strain degeneration. Proposed theories include chromosome instability, heterokaryosis, cytoplasmic inheritance, and the presence of transposable elements (14,18).…”

Identification of the Genes Involved in the Fruiting Body Production and Cordycepin Formation ofCordyceps militarisFungus

“…Fungal culture degeneration is usually irreversible and inheritable, and can result in great commercial losses [ 19 , 20 ]. In C. militaris , culture degeneration was reflected with poor fruiting body production.…”

Simple Colorimetric Method for Detecting Degenerate Strains of the Cultivated Basidiomycete Flammulina velutipes (Enokitake)

“…The primary objective of this study was to develop a simple method for detecting degenerate Flammulina velutipes (Enokitake) cultures. Cultural degeneration of cultivated strains of Enokitake similar to the degeneration observed for Agaricus bisporus (1,2) has become a serious problem in Japan. Previous efforts to evaluate the fruiting potential of Enokitake have been made using isozyme electrophoresis profiles, randomly amplified polymorphic DNA, and mitochondrial DNA restriction fragment length polymorphism, but there was no clear correlation between the results of these experiments and the degenerate symptoms.…”