DNA polymorphisms in commercial and wild strains of the cultivated mushroom,Agaricus bisporus

Summary DNA from the cultivated mushroom, Agaricus bisporus, was cloned into the bacteriophage lambda vector EMBL3 creating a partial genomic library. Ten random clones from the library were used to probe for restriction fragment length polymorphisms (RFLPs). Six of the ten probes detected polymorphisms and were used to demonstrate variation in wild and cultivated strains of the mushroom. These results suggest that RFLPs could form a basis for genetic finger-printing and subsequent strain protection in A. bisporus. In single spore progeny, RFLPs were used to demonstrate normal meiotic segregation and to differentiate between homokaryons and heterokaryons. RFLPs therefore have great potential in the development of the genetics and breeding of this commercially important species.     

Resource allocation ability of wild isolates of Agaricus bisporus on conventional mushroom compost

Abstract: Twenty-one wild isolates from two distinct sites and six cultivated strains of Agaricus bisporus were cultivated on a conventional mushroom compost. Their degradative abilities were studied by measuring 12 extracellular enzyme activities produced during mycelial growth. Differences in production of enzyme activities and in compost colonisation were observed between the three groups of strains and within each group. They were used to define the mechanisms of resource allocation in mushroom compost. The ability to grow and produce sporophores on mushroom compost appeared to be linked with the production of a balanced pool of enzymes including moderate levels of polysaccharidases active on straw cell walls and of enzymes able to degrade microbial biomass and microbial products.     

Occurrence of Verticillium fungicola var. fungicola on Agaricus bitorquis Mushroom Crops in Spain

Diseased fruit bodies of Agaricus bitorquis, with similar symptoms to those caused by dry bubble on Agaricus bisporus, were observed in some Spanish crops during summer 1999. Isolates of Verticillium fungicola from A. bitorquis and A. bisporus were submitted to different temperatures and to prochloraz–Mn sensitivity tests. All the isolates collected from A. bitorquis and A. bisporus were identified as V. fungicola var. fungicola. Artificial infections of A. bisporus and A. bitorquis with V. fungicola var. fungicola are also described in the present study. The appearance of natural infections of V. fungicola var. fungicola in A. bitorquis crops could well be due to the growing temperatures used in Spain, which are considerably below those used in other countries.     

Effect of packaging conditions on the growth of micro-organisms and the quality characteristics of fresh mushrooms (Agaricus bisporus) stored at inadequate temperatures

Mushrooms were packed in two polymeric films (perforated and non-perforated PVC) and stored at 17 degrees C and 25 degrees C. The carbon dioxide and oxygen content inside the packages, aerobic mesophiles, Pseudomonas spp., faecal coliforms, Escherichia coli, anaerobic spores and major sensory factors (colour, texture, development stage and presence of moulds) were determined. The non-perforated packages had the highest contents of CO2 (6-7%), the lowest contents of O2 (0.013-0.17%) and the most desirable quality parameters (texture, development stage and absence of moulds). Pseudomonas spp. counts were around 1 logarithmic unit lower in mushrooms packaged in non-perforated film as the O2 concentrations were lower than in perforated film. The mushrooms themselves were inoculated with an enterotoxin A-producing strain of Staphylococcus aureus, packaged in overwrapped trays and stored at 17 and 25 degrees C. Staphylococcus aureus did not grow in the samples stored at 17 degrees C. Only slight growth was observed in mushrooms packaged with non-perforated film after 1 day at 25 degrees C. No enterotoxin was detected in any package. Faecal coliform counts were <2 log cfu g(-1). Escherichia coli was not isolated in any of the samples. At 25 degrees C, counts of anaerobic spores of around 2 log cfu g(-1) were detected in those mushrooms packaged in non-perforated film.     

Hydrogen peroxide concentrations detected in Agaricus bisporus sporocarps and relation with their susceptibility to the pathogen Verticillium fungicola

A dry bubble is an undifferentiated structure that forms in place of mushrooms when cultures of Agaricus bisporus are contaminated by Verticillium fungicola. Hydrogen peroxide concentrations were measured in lyophilised samples of bubbles and healthy sporocarps from cultures of genetically related strains of A. bisporus. The strains the more resistant to the pathogen had the higher levels of H2O2 concentration measured in the bubbles, but the differences in the healthy sporocarps were not significant. That is an indication of a higher reaction to the pathogen in the forming sporocarps of A. bisporus strains associated with their partial resistance to V. fungicola.     

环境因子对双孢蘑菇损伤敏感性的影响（英文）

在机械损伤过程中,白色双孢蘑菇极易被损伤并迅速褐变,使得机械采收的鲜菇质量低下,并且影响机械采收技术的应用和发展。机械采收双孢蘑菇的褐变程度(损伤敏感性)受栽培环境条件的影响。本文应用因子设计分析的方式研究多个因子对双孢蘑菇机械损伤敏感性的影响。以4个菌株为材料测试3个环境因子对双孢蘑菇损伤敏感性的影响,即覆土的厚度(分为2.5cm和5cm两个水平),覆土的湿度(分为干覆土和正常覆土两个水平),以及菇房内的相对湿度(分为80%和87%两个水平)。目的是找出能够在不敏感菌株和敏感菌株间产生最大敏感性差异的环境条件,由此得到的环境条件将应用到后续的群体分离分析中以得到最大的敏感性变异率。根据方差分析结果得出基因型(菌株)和覆土厚度是影响损伤敏感性的显著性因子,因子间相互作用显著。能够在不敏感菌株和敏感菌株间产生最大的损伤敏感性差异的环境条件为正常湿度的5cm厚覆土材料和87%的菇房内相对湿度。     

低温保鲜的双孢蘑菇硬度与生理特性变化

研究双孢蘑菇Agaricus bisporus在4 ℃环境下贮藏3、6、10、14 d后生理品质的变化情况。结果表明,在4 ℃低温保鲜环境下双孢蘑菇的硬度下降较慢,延缓了可溶性蛋白质和POD、SOD、CAT等酶的降解,V?含量在第3天迅速下降后,一直保持稳定的水平,MDA含量在贮藏第10天才迅速上升。说明低温保鲜对双孢蘑菇贮藏过程中的品质保持具有积极的正向作用,可延长双孢蘑菇的货架期。     

Relative contribution of nematodes (Caenorhabditis elegans) and bacteria towards the disruption of flushing patterns and losses in yield and quality of mushrooms (Agaricus bisporus)

Laboratory tests of bacteria isolated from the body surface, or from the gut, of a saprophagous rhabditid nematode Caenorhabditis elegans infesting mushrooms (Agaricus bisporus) showed that some bacteria enhanced nematode reproduction and that others inhibited it. As some bacteria were shown to inhibit mycelial growth of the mushroom, the effects of Acinetobacter calcoaceticus var. anitratus, Enterobacter cloacae and Serratia liquefaciens, either alone or in combination with C. elegans, on the flushing patterns, quality and yield of A. bisporus (strain Horst U3) were studied. Bacteria alone had little effect on flushing patterns whereas C. elegans delayed the onset of mushroom production and significantly disrupted the growth pattern of crops, with mushrooms appearing more regularly and not within obvious flushes. Inoculation with bacteria resulted in ‘browning’ of mushrooms that was even more pronounced in C. elegans treatments. Characteristic distortion of sporophores was observed only in the presence of C. elegans. Nematodes commonly colonised sporophores. Bacteria affected the size of nematode populations both on the sporophores and in the casing. Significant yield loss occurred; up to 10% when bacteria were inoculated, up to 27.8% when C. elegans was inoculated, and up to 35% with both bacteria and nematodes. Synergism between C. elegans and A. calcoaceticus var. anitratus was observed; the combination resulted in significantly greater reduction in mushroom yield than any other treatment. It is concluded that bacteria contribute to yield loss and quality deterioration in A. bisporus but that the effects are far greater in the presence of C. elegans.     

Several pseudomonads,associated with the cultivated mushrooms Agaricus bisporus or Pleurotus sp., are hemolytic

Pseudomonas tolaasii, causing brown blotch disease on cultivated mushrooms, and yielding a white line precipitate towards P. “reactans”, has been shown to induce lysis of erythrocytes. Some Finnish strains isolated from diseased mushroom fruit bodies, although harboring the typical features of P. tolaasii, proved to be distinct, and have been allocated to a nov. sp. P. costantinii. We examined in these study whether all brown blotch causing agents were hemolytic. The induction of erythrocytes lysis seemed to be a rather common feature of mushroom associated-pseudomonads, especially for strains involved in the production of a white-line-in agar.     

Use of molecular markers to differentiate between commercial strains of the button mushroom Agaricus bisporus

Agaricus bisporus is an edible basidiomycete cultivated industrially for food production. Different spawn and mushroom producers use genetically related A. bisporus strains frequently marketed as different products. In this paper we show that the use of suitable molecular markers reveals the high level of genetic homology of commercial strains of A. bisporus, and allows, at the same time, to distinguish between them. In the course of this work, a molecular marker potentially linked to the agronomic character 'mushroom weight' has been identified by bulked segregant analysis.     

Lignocellulose degradation during the life cycle of Agaricus bisporus

Abstract Lignocellulose degradation was monitored during the complete life cycle of the edible mushroom Agaricus bisporus grown on composted straw. Lignin and cellulose degradation were assayed by the use of ¹⁴C-labelled lignin and cellulose. Agaricus degraded both polymers but cellulose degradation was more extensive. Cellulolysis increased markedly at fruit body production and was greater still in non-axenically fruited cultures. No large change in the rate of lignin degradation occurred during the life cycle.     

Effects of Caenorhabditis elegans (Nematoda: Rhabditidae) on yield and quality of the cultivated mushroom Agaricus bisporus

Thirteen species of saprobic rhabditid nematodes (11 genera) were identified from samples of compost and casing material collected from mushroom farms in the British Isles. Caenorhabditis elegans, the most frequently found saprobe, was mass-produced monoxenically and its effects on the cultivated mushroom, Agaricus bisporus (strain U3) were studied. C. elegans did not multiply in well-prepared, pasteurised, spawned compost, whereas casing material proved to be a highly suitable environment for its reproduction. An initial casing inoculum of 10⁶ nematodes/crate of compost (7.5 kg), caused a significant reduction in mushroom yield. Losses in total mushroom yields of 11%, 20% and 26% were caused by initial inoculum rates of 10⁶, 10⁷and 2 × 10⁷ nematodes/crate, respectively. Yields were negatively correlated with the initial nematode inoculation level and regression equations were derived. The nematode treatments caused fewer mushrooms to be produced and an absence of the usual distinctive flushing patterns. C. elegans caused considerable deterioration in mushroom quality and characteristic distortion of mushrooms. Individual sporophores were mis-shapen, notched and had brown or violet coloured grills. Up to 3.8%, 6.7% and 10.8% of total weight and 3.5%, 5.4% and 8% of total numbers of mushrooms were distorted at the three highest nematode inoculum rates tested. Weights and numbers of distorted mushrooms were positively correlated with the initial nematode population. C. elegans commonly colonised sporophores.     

Differences in microfibrils in the walls of Agaricus bisporus secondary mycelium

Thick fibres mainly located in longitudinal and parallel arrays were observed on the outer surface of vegetative mycelial walls of Agaricus bisporus treated to remove the polysaccharide mucilage. When thick fibres were removed from the cell wall, by alkali treatment, thin fibres with predominantly transverse orientation were observed. The former have been identified to be composed of α-glucan and the latter of chitin. Both different types of fibres constitute the skeletal components of the wall in which matrix materials are embedded.     

Pseudomonas tolaasii and tolaasin: comparison of symptom induction on a wide range of Agaricus bisporus strains

Abstract A wide range of Agaricus bisporus , including commercial, wild and hybrid strains, were tested for resistance to brown blotch disease caused by Pseudomonas tolaasii . Effects of toxin and living bacteria were compared. Wild and hybrid A. bisporus ranged in the same order from very poorly to highly susceptible whatever the inoculum type used, tolaasin or bacteria. Symptom aspects induced by both inocula were visually identical, but some differences occurred in response intensity. The data suggest that toxin is probably not the only factor involved in symptom development.     

Selection of Trichoderma strains capable of increasing laccase production by Pleurotus ostreatus and Agaricus bisporus in dual cultures

Aims:  To select Trichoderma strains for enhanced laccase production in Pleurotus ostreatus or Agaricus bisporus cultures.
Methods and Results:  Laccase production by P. ostreatus and A. bisporus was evaluated in liquid (axenic) and solid (dual cultures) malt extract medium. Oxidation of ABTS, DMP and syringaldazine was evaluated in order to assess the potential of Trichoderma strains to enhance laccase production by basidiomycetes. Selected Pleurotus–Trichoderma interactions yielded higher increases in laccase volumetric activity and an additional laccase isoform was produced. By contrast, Agaricus–Trichoderma interactions lead to smaller increases on laccase volumetric activity, probably as result of repression (or degradation) towards one of the laccases isoforms.
Conclusions:  The strains of P. ostreatus and A. bisporus assessed in this work showed good potential as laccase producers. The Trichoderma -mediated biological stimulation of laccase production by P. ostreatus and A. bisporus is relevant in order to develop highly productive processes.
Significance and Impact of the Study:  Extracellular laccases from basidiomycetes are produced only in small amounts. It is therefore important to increase process productivity for potential industrial applications. The results from this study enable the selection Trichoderma strains capable of increasing laccase production by P. ostreatus or A. bisporus in dual cultures.     

Influences of compost and casing layer depths on the mechanical properties of mushrooms

The mushroom growing bed consists of an underlying compost which is covered with casing (a peat and chalk or lime mixture) to induce fruit-body formation. The influences of the depths of the compost and casing layers on the mushroom texture, susceptibility to bruising, and ease of detachment from the growing bed surface were investigated. Textural properties were determined on cubes of cap tissue and detachment torque was determined by using an instrumented rotating suction cup which was lowered on to the caps. The proportion of mushrooms which detached at the base from the bed surface was recorded, since this is an important parameter for an automatic (robotic) harvesting system. Shallow casing resulted in mushrooms that were firmer and less likely to deform plastically, but that showed greater discolouration after a standard bruising treatment. Shallower casing also increased the proportion of mushrooms that detached at the base. Increasing the depth of compost produced firmer mushrooms, significantly increased the detachment torque and reduced the proportion of mushrooms detached at the base. The proportion of mushrooms that detached at the base correlated negatively with the plastic deformation of cap tissue. A positive correlation was found between mushroom dry matter content and tissue firmness.