Incidence,identification and pathogenicity of Cladobotryum mycophilum,causal agent of cobweb disease on Agaricus bisporus mushroom crops in Spain

Between 2008 and 2011, outbreaks of cobweb were observed in commercial white button mushroom (Agaricus bisporus) crops in Castilla‐La Mancha (Spain). In the last 3 years, the presence of the disease has notably increased resulting in serious economic losses. Based on morphological and genetic analyses, the casual agent of cobweb was identified as Cladobotryum mycophilum. A. bisporus mushroom crops were surveyed over a 2‐year period to estimate the incidence of cobweb. The presence of the disease was detected in 32% of the mushroom crops observed, being of particular concern in autumn (44% of crops infected) and winter (37%). As regards the casing material, the percentage of crops affected by cobweb was 34% in crops using mineral casing and 29% in those cased with a peat‐based casing, with no statistical relationship between the casing and the presence of cobweb. Two cropping trials inoculated with C. mycophilum were set up to evaluate the pathogenicity of the causal agent of cobweb in three peat‐based casings (C1, C2 and C3). The effect of cobweb on mushroom productivity was evaluated by comparing mushroom production and the cobweb patches detected in the casing soil. The decrease in total yield of mushrooms attributed to cobweb reached 12.9% with C2, and the crop area colonised by cobweb reached a final percentage of 36% with C3.     

Advances in genetic analysis and biotechnology of the cultivated button mushroom, Agaricus bisporus

During the last decade several major breakthroughs have been achieved in mushroom biotechnology, which greatly enhanced classical mushroom breeding. DNA-based technologies such as restriction fragment length polymorphisms and randomly amplified polydisperse DNA sequences have allowed for a measure of genetic diversity, for the isolation of homokaryons, for the determination of inheritance of nuclear and mitochondrial markers, and for the production of a genetic linkage map. The recent availability of ready-to-use and affordable DNA technologies has resulted in a substantial increase in the number of Agaricus bisporus genes that have been identified and characterized. A major breakthrough was achieved in 1996 when the first successful and stable transformation system of A. bisporus was reported. Together, the availability of an increasing number of known genes and the possibility to produce transgenic mushrooms will result in a better understanding of the molecular, physiological and biochemical processes that are essential for mushroom production, shelf life and quality aspects such as flavor, texture and disease resistance. Some potential targets for strain improvement are discussed, such as the genes involved in brown discoloration, substrate utilization, carbon and nitrogen metabolism, and fruit body development. Received: 19 January 1999 / Received revision: 27 May 1999 / Accepted: 4 June 1999     

Absence of induced resistance in Agaricus bisporus against Lecanicillium fungicola

Lecanicillium fungicola causes dry bubble disease and is an important problem in the cultivation of Agaricus bisporus. Little is known about the defense of mushrooms against pathogens in general and L. fungicola in particular. In plants and animals, a first attack by a pathogen often induces a systemic response that results in an acquired resistance to subsequent attacks by the same pathogen. The development of functionally similar responses in these two eukaryotic kingdoms indicates that they are important to all multi-cellular organisms. We investigated if such responses also occur in the interaction between the white button mushroom and L. fungicola. A first infection of mushrooms of the commercial A. bisporus strain Sylvan A15 by L. fungicola did not induce systemic resistance against a subsequent infection. Similar results were obtained with the A. bisporus strain MES01497, which was demonstrated to be more resistant to dry bubble disease. Apparently, fruiting bodies of A. bisporus do not express induced resistance against L. fungicola.     

Microbially induced diseases of Agaricus bisporus: biochemical mechanisms and impact on commercial mushroom production

The button mushroom, Agaricus bisporus (Lange) Imbach, the most common cultivated mushroom, is susceptible to a wide range of virus, bacterial, and fungal diseases. However, only some diseases were studied for the mechanisms involved in the host–microorganism interaction. This review deals with biochemical mechanisms related to cavity disease (Burkholderia gladioli) and to the interaction between A. bisporus and the causal agents responsible for the most severe diseases, namely the bacteria Pseudomonas tolaasii and Pseudomonas reactans and the fungi Trichoderma aggressivum and Lecanicillium fungicola.     

Differentiation between Commercial Strains of Oyster and Button Mushrooms Using Molecular Markers

Analysis of commercial strains of two edible mushrooms, Pleurotus ostreatus and Agaricus bisporus, using PCR and isozyme electrophoresis techniques allowed us to differentiate groups of genetically similar and distant strains. Among the commercial strains of P. ostreatus, the level of genetic variation was higher suggesting a broader genetic basis employed in breeding of this mushroom. The cultivars and hybrids of A. bisporusshowed a higher level of homology. The isozyme markers (nonspecific esterase, leucinaminopeptidase, and phosphoglucoisomerase) are recommended for identification of the commercial strains of edible mushrooms.     

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.     

Comparative studies of the quality of fresh and stored mushrooms of Agaricus bisporus with two tropical Agaricus bitorquis strains

Three white strains of mushroom were grown for quality assessment tests, a commercial Agaricus bisporus strain SOMYCEL U3 currently popular in most major mushroom producing countries and two tropical Agaricus bitorquis strains, ATCC 32675 and AGC W20. Mushrooms were harvested as stage 2 mushrooms (closed buttons with universal veil intact) and stored at 18°C (± 0.5°C) for 5 days during which time colour development, the rate of fruitbody maturation and weight loss were assessed. Throughout the storage period, a reflectance colormeter was used to monitor colour changes on the tops and sides of mushroom fruitbodies. The tops of both A. bitorquis strains were significantly more yellow than the A. bisporus strain, whereas the sides were significantly less yellow. Overall, the A. birorquis strain AGC W20 was clearly the least discoloured and least yellow at the time of harvest. Although all the three strains tested gave similar fresh weight losses during storage, i.e. approximately 10% per day, ATCC 32675 exhibited a very slow maturation rate. Both U3 and AGC W20 matured at a similar much faster rate forming open cups within the 5 day storage period. ATCC 32675 also showed the least increase in the degree of discolouration with time, whether readings were taken from the sides or tops of mushrooms. A breeding programme to combine the most salient features of AGC W20 (an intensely white mushroom at harvest, high yielding with distinct flush pattern) and ATCC 32675 (very slow maturation rate during storage) is suggested.     

Examining the health effects and bioactive components in Agaricus bisporus mushrooms: a scoping review

There is evidence from both in vitro and animal models that the consumption of edible mushrooms has beneficial effects on health. It is unclear whether similar effects exist in humans and which bioactive compounds are present. This review synthesises the evidence on the world's most commonly consumed mushroom, Agaricus bisporus to (i) examine its effect on human health outcomes; and (ii) determine the nutrient density of its bioactive compounds, which may explain their health effects. A systematic literature search was conducted on the consumption of A. bisporus, without date and study design limits. Bioactive compounds included ergosterol, ergothioneine, flavonoids, glucans and chitin. Two authors independently identified studies for inclusion and assessed methodological quality. Beneficial effects of A. bisporus on metabolic syndrome, immune function, gastrointestinal health and cancer, with the strongest evidence for the improvement in Vitamin D status in humans, were found. Ultraviolet B (UVB) exposed mushrooms may increase and maintain serum 25(OH)D levels to a similar degree as vitamin D supplements. A. bisporus contain beta-glucans, ergosterol, ergothioneine, vitamin D and an antioxidant compound usually reported as flavonoids; with varying concentrations depending on the type of mushroom, cooking method and duration, and UVB exposure. Further research is required to fully elucidate the bioactive compounds in mushrooms using vigorous analytical methods and expand the immunological markers being tested. To enable findings to be adopted into clinical practice and public health initiatives, replication of existing studies in different population groups is required to confirm the impact of A. bisporus on human health.     

Assessment of genetic relatedness among commercial and wild strains of Agaricus bisporus using repetitive extragenic palindromic sequences and polymerase chain reaction

The genetic relatedness among 18 strains of Agaricus bisporus was assessed based on the fragment pattern analysis obtained by the amplification of genomic DNA by BOX, ERIC (ERICIR-I/ERIC2) and REP (REP1RI/REP2I) gene sequences. Based on the banding patterns of PCR-amplified products, eight putative groups among the 18 commercial and wild strains were recognized. REP-PCR generated multiple distinct products showing considerable variability among the strains with ERIC and REP elements successfully enabled detection of wild and commercial A. bisporus. Strains originating from the same geographical location were not always genetically related. To our knowledge, this was the first relevance study of biodiversity in commercial and native populations of A. bisporus by using the REP-PCR technique. The results confirmed the usefulness REP-PCR typing in intraspecific genetic variation assessments of the button mushroom. High level of Iranian wild strains distance with the commercial cultivars approves their importance as a promising new source of diversity in A. bisporus breeding program.     

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.     

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.     

Tolerance to dry bubble disease (Lecanicillium fungicola) in Iranian wild germplasm of button mushroom (Agaricus bisporus)

Agaricus bisporus is the most widely cultivated mushroom. The mushroom crop is subjected to several fungal diseases. Dry bubble disease caused by Lecanicillium fungicola is among notorious diseases of A. bisporus. This study aimed to assess phenotypic resistance to dry bubble disease among A. bisporus wild strains, collected from Iran regions. The reliability of resistance evaluations regarding disease incidence and intensity was well documented. The extraordinary tolerance of some wild strains to even high degrees of inoculum concentrations (10⁷ and 10⁸ spore/m² mushroom growth bed) of the pathogen in compare to commercial cultivars approved potentials of the wild germplasm in breeding programs for resistance. Also, the potential of some Microsatellite loci for the molecular-based rapid screening of tolerance was established by attributing SSR loci of phenotypically tolerant strains to QTLs for dry-bubble resistance-related traits.     

Recent advances in Agaricus bisporus polysaccharides: Extraction,purification, physicochemical characterization and bioactivities

Agaricus bisporus (A. bisporus), known as a cultivated mushroom or button mushroom, is a very important edible and medicinal basidiomycete fungus. The numerous health benefits of A. bisporus may be related to their polysaccharides, which have significant dietary value and bioactivity, including immunity stimulation and high antioxidant, anticancer, hepatoprotection, anti-inflammation and anti-obesity functions. In general, the extraction method of A. bisporus polysaccharides (ABPs) is relatively simple, and the yield from enzyme-assisted extraction is the highest among various extraction methods. The monosaccharide composition analysis revealed that ABPs mainly consist of glucose, galactose, fucose and xylose, which each have a backbone composed of (1→6)- and (1→4)-linked α-glucan or alternating (1→4)- and (1→6)-linked β-glucan. The biological activity of ABPs may vary significantly depending on their source, composition, structural properties, and purity, and it is highly correlated with molecular weight (MW) and the monosaccharide components. Therefore, this review aims to introduce the extraction methods, chemical structure, and biological activity of ABPs which may provide a theoretical basis for the further development and utilization of polysaccharides and have important reference value for the future study of the relationship between structural features and biological activities.     

Quantitative trait locus mapping of yield-related components and oligogenic control of the cap color of the button mushroom, Agaricus bisporus

As in other crops, yield is an important trait to be selected for in edible mushrooms, but its inheritance is poorly understood. Therefore, we have investigated the complex genetic architecture of yield-related traits in Agaricus bisporus through the mapping of quantitative trait loci (QTL), using second-generation hybrid progeny derived from a cross between a wild strain and a commercial cultivar. Yield, average weight per mushroom, number of fruiting bodies per m(2), earliness, and cap color were evaluated in two independent experiments. A total of 23 QTL were detected for 7 yield-related traits. These QTL together explained between 21% (two-flushes yield) and 59% (earliness) of the phenotypic variation. Fifteen QTL (65%) were consistent between the two experiments. Four regions underlying significant QTL controlling yield, average weight, and number were detected on linkage groups II, III, IV, and X, suggesting a pleiotropic effect or tight linkage. Up to six QTL were identified for earliness. The PPC1 locus, together with two additional genomic regions, explained up to 90% of the phenotypic variation of the cap color. Alleles from the wild parent showed beneficial effects for some yield traits, suggesting that the wild germ plasm is a valuable source of variation for several agronomic traits. Our results constitute a key step toward marker-assisted selection and provide a solid foundation to go further into the biological mechanisms controlling productive traits in the button mushroom.     

Abnormal meiosis in bisporic strains of white button mushroom Agaricus bisporus (Lange) imbach

A formerly developed method of microspreading of mushroom basidial nuclei was applied to study meiotic prophase I in bisporic white button mushroom (Agaricus bisporus) strains. Meiotic recombination and assemblage of axial structures (axial elements and synaptonemal complexes) of chromosomes in meiotic prophase I are interrelated. It is known that the frequency of meiotic recombination is reduced in the bisporic A. bisporus variety. We showed that formation of axial structures of meiotic chromosomes in bisporic strains of this mushroom was disrupted. The anomalous phenotypes in spread prophase nuclei are diverse. In leptotene and early zygotene, many nuclei contain abnormal, often short, and, as a rule, few chromosomal axial elements. The abnormalities in the formation of synaptonemal complexes at the zygotene-diplotene stage are of the same kind and even more pronounced. We discovered an important feature of meiosis in A. bisporus associated with fruit-body morphogenesis. Meiosis starting in basidia (meiocytes) of young closed fruit bodies is accompanied by disruption of chromatin condensation in prophase I and, probably, is arrested. After partial veil breakage, the course of meiosis normalizes. Preparations with clearly observable chromosomal axial structures can be obtained only at this stage of fruit-body development.     

Lecanicillium fungicola: causal agent of dry bubble disease in white‐button mushroom

Lecanicillium fungicola causes dry bubble disease in commercially cultivated mushroom. This review summarizes current knowledge on the biology of the pathogen and the interaction between the pathogen and its most important host, the white‐button mushroom, Agaricus bisporus. The ecology of the pathogen is discussed with emphasis on host range, dispersal and primary source of infection. In addition, current knowledge on mushroom defence mechanisms is reviewed. Taxonomy: Lecanicillium fungicola (Preuss) Zare and Gams: Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreales; Order Hypocreomycetidae; Family Cordycipitaceae; genus Lecanicillium. Host range: Agaricus bisporus, Agaricus bitorquis and Pleurotus ostreatus. Although its pathogenicity for other species has not been established, it has been isolated from numerous other basidiomycetes. Disease symptoms: Disease symptoms vary from small necrotic lesions on the caps of the fruiting bodies to partially deformed fruiting bodies, called stipe blow‐out, or totally deformed and undifferentiated masses of mushroom tissue, called dry bubble. The disease symptoms and severity depend on the time point of infection. Small necrotic lesions result from late infections on the fruiting bodies, whereas stipe blow‐out and dry bubble are the result of interactions between the pathogen and the host in the casing layer. Economic importance: Lecanicillium fungicola is a devastating pathogen in the mushroom industry and causes significant losses in the commercial production of its main host, Agaricus bisporus. Annual costs for mushroom growers are estimated at 2–4% of total revenue. Reports on the disease originate mainly from North America and Europe. Although China is the main producer of white‐button mushrooms in the world, little is known in the international literature about the impact of dry bubble disease in this region. Control: The control of L. fungicola relies on strict hygiene and the use of fungicides. Few chemicals can be used for the control of dry bubble because the host is also sensitive to fungicides. Notably, the development of resistance of L. fungicola has been reported against the fungicides that are used to control dry bubble disease. In addition, some of these fungicides may be banned in the near future. Useful websites: http://www.mycobank.org ; http://www.isms.biz ; http://www.cbs.knaw.nl     

Attraction of female fungus gnats,Lycoriella ingenua,to mushroom‐growing substrates and the green mold Trichoderma aggressivum

To evaluate the attractiveness of several mushroom‐growing substrates to the female mushroom fly Lycoriella ingenua (Dufour) (Diptera: Sciaridae), a pest of the cultivated white button mushroom, Agaricus bisporus (JE Lange) Emil J Imbach (Agaricales), we developed a two‐choice, static‐flow olfactometer. Behavioral assays using this olfactometer indicated that mushroom compost with A. bisporus mycelia growing in it was not more attractive than compost lacking growing mycelia. We also found that female flies were more attracted to compost lacking A. bisporus mycelia than to the actual commodity, the white button mushroom fruiting bodies. Flies were not, however, attracted to sterilized compost, suggesting the attraction is due to volatiles produced by microbial metabolism in the compost. We also found that female L. ingenua flies were attracted to the mycoparasitic green mold Trichoderma aggressivum Samuels & W Gams (Hypocreales). Flies preferred mushroom compost that had T. aggressivum growing in it over compost lacking T. aggressivum, providing an experimental outcome consistent with the anecdotal belief that L. ingenua flies are vectors of T. aggressivum spores that can infest mushroom‐growing houses.     

Comparative effects of Steinernema feltiae (Nematoda: Steinernematidae) and insecticides on yield and cropping of the mushroom Agaricus bisporus

In a mushroom crop (Agaricus bisporus) affected by a very low level of sciarid fly (Lycoriella auripila) infestation, the effects of an indigenous isolate of insect-parasitic nematode (Steinernema feltiae) and of two commonly used insecticides (diazinon and diflubenzuron) were studied. When compared with untreated plots, nematodes applied to the casing had no adverse effects on mushroom yields whereas insecticides decreased yields. At a rate of 3 × 10⁶ infective juveniles per tray (surface area = 0.56 m²), S. feltiae elicited increases of 28.5% and 19% in the mean total numbers and weights of mushrooms respectively. Treatment only with diflubenzuron resulted in 14.6% and 6% reductions in mean total numbers and weights of mushrooms, respectively; treatment with both diazinon and diflubenzuron caused 18.5% and 9.4% losses. Application of nematodes generally reduced the mean weight per mushroom whereas insecticides increased it; nematodes delayed the onset of mushroom production (first flush) whereas diflubenzuron delayed the third and fourth flushes. Nematode contamination of sporophores was minimal when S. feltiae was applied at casing. Although their numbers declined with time, the nematodes persisted, in the casing layer, throughout the cropping period of seven weeks. It is concluded that yield benefits associated with nematode application can result mainly from nematode effects on A. bisporus and not solely from suppression of a damaging pest population.