Bisporus Var Research Articles

Antioxidant, Antibacterial, and Cosmeceutical Potential of Four Common Edible Mushrooms

Waste generated in mushroom cultivation represents a valuable raw material with health benefits, the use of which contributes to a reduction in food waste and to the circular economy. Hydroethanolic extracts obtained by ultrasound-assisted extraction of four edible mushroom species (Agaricus bisporus var. Portobello, Boletus edulis, Lentinula edodes, and Pleurotus ostreatus) were characterized according to their antioxidant, antibacterial, and cosmeceutical potential. The extract with the best properties was incorporated into a cosmetic cream. Concerning the phenolic contents and antioxidant capacity, the extracts of A. bisporus and B. edulis stood out from the other two due to their higher levels. The compounds p-hydroxybenzoic and gallic acids were present in all mushrooms in the ranges of 0.010 to 2.554 µg/g DW and 0.032 to 0.112 µg/g DW, respectively. The extract of B. edulis inhibited all the bacterial isolates, with minimum inhibitory concentration values ranging from 5 to 20 mg/mL for Gram-positive and 10–20 mg/mL for Gram-negative strains. In the anti-hyaluronidase assay, A. bisporus extract (10 mg/mL) was the most effective, with 74.4 ± 7.5% enzyme inhibition, and was selected for incorporation into the cosmetic cream. The cream with A. bisporus extract showed significantly higher phenolic contents and antioxidant capacity than the cream without the extract. Overall, our results support the high value of mushroom reuse as a source of natural antioxidants in the cosmetic industry.

Experimental Outcrossing in Agaricus bisporus Revealed a Major and Unexpected Involvement of Airborne Mycelium Fragments.

Agaricus bisporus var. bisporus, the button mushroom, has a predominantly pseudohomothallic life cycle. Most of its spores are heterokaryotic and give rise to fertile heterokaryons. However, previous studies have suggested that outcrossing should not be rare in wild populations. In order to discover how outcrossing occurs, we experimentally favored it between aerial propagules of a fruiting donor mycelium and a delayed receiver mycelium that only invaded culture trays. Two donor/receiver pairs were studied, and potentially hybrid basidiomata collected on the receiver trays were analyzed with a mitochondrial marker, two unlinked nuclear CAPS markers, then haplotype markers based on DNA sequences obtained after PCR cloning of the rDNA ITS region and the fruk gene. For one of the two pairs, most basidiomata were hybrids between the donor and the receiver. Genotyping of the hybrids revealed only two genotypes consistent with outcrossing involving airborne mycelium fragments rather than basidiospores. The resident receiver heterokaryon that provided its mitochondria to the hybrid basidiomata is suspected to have had a trophic contribution to their growth and successful fruiting. The high level of heterozygosity and the cultivar introgression previously revealed in wild populations of this pseudohomothallic species may result from outcrossing involving airborne pieces of mycelium.

Chemical Constituents and Molecular Mechanism of the Yellow Phenotype of Yellow Mushroom (Floccularia luteovirens).

(1) Background: Yellow mushroom (Floccularia luteovirens) is a natural resource that is highly nutritional, has a high economic value, and is found in Northwest China. Despite its value, the chemical and molecular mechanisms of yellow phenotype formation are still unclear. (2) Methods: This study uses the combined analysis of transcriptome and metabolome to explain the molecular mechanism of the formation of yellow mushroom. Subcellular localization and transgene overexpression techniques were used to verify the function of the candidate gene. (3) Results: 112 compounds had a higher expression in yellow mushroom; riboflavin was the ninth most-expressed compound. HPLC showed that a key target peak at 23.128 min under visible light at 444 nm was Vb2. All proteins exhibited the closest relationship with Agaricus bisporus var. bisporus H97. One riboflavin transporter, CL911.Contig3_All (FlMCH5), was highly expressed in yellow mushrooms with a different value (log2 fold change) of −12.98, whereas it was not detected in white mushrooms. FlMCH5 was homologous to the riboflavin transporter MCH5 or MFS transporter in other strains, and the FlMCH5-GFP fusion protein was mainly located in the cell membrane. Overexpression of FlMCH5 in tobacco increased the content of riboflavin in three transgenic plants to 26 μg/g, 26.52 μg/g, and 36.94 μg/g, respectively. (4) Conclusions: In this study, it is clear that riboflavin is the main coloring compound of yellow mushrooms, and FlMCH5 is the key transport regulatory gene that produces the yellow phenotype.

Mating-Type Locus Organization and Mating-Type Chromosome Differentiation in the Bipolar Edible Button Mushroom Agaricus bisporus.

In heterothallic basidiomycete fungi, sexual compatibility is restricted by mating types, typically controlled by two loci: PR, encoding pheromone precursors and pheromone receptors, and HD, encoding two types of homeodomain transcription factors. We analysed the single mating-type locus of the commercial button mushroom variety, Agaricus bisporus var. bisporus, and of the related variety burnettii. We identified the location of the mating-type locus using genetic map and genome information, corresponding to the HD locus, the PR locus having lost its mating-type role. We found the mip1 and β-fg genes flanking the HD genes as in several Agaricomycetes, two copies of the β-fg gene, an additional HD2 copy in the reference genome of A. bisporus var. bisporus and an additional HD1 copy in the reference genome of A. bisporus var. burnettii. We detected a 140 kb-long inversion between mating types in an A. bisporus var. burnettii heterokaryon, trapping the HD genes, the mip1 gene and fragments of additional genes. The two varieties had islands of transposable elements at the mating-type locus, spanning 35 kb in the A. bisporus var. burnettii reference genome. Linkage analyses showed a region with low recombination in the mating-type locus region in the A. bisporus var. burnettii variety. We found high differentiation between β-fg alleles in both varieties, indicating an ancient event of recombination suppression, followed more recently by a suppression of recombination at the mip1 gene through the inversion in A. bisporus var. burnettii and a suppression of recombination across whole chromosomes in A. bisporus var. bisporus, constituting stepwise recombination suppression as in many other mating-type chromosomes and sex chromosomes.

Antibacterial and Antioxidant Activity of Different Extracts of Some Wild Medicinal Mushrooms from Nigeria.

This study assessed the antioxidant properties and antibacterial effects of hot water, cold water, and ethanol extracts of Agaricomycetes mushrooms Trametes betulina, Pleurotus ostreatus, Agaricus bisporus var. albidus, and A. bisporus var. avellaneus against Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. The mushroom extracts were assessed for total phenolic content as well as 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydrogen peroxide scavenging activities. The multiantibiotic resistance index (MARI) of the bacterial isolates was assessed and the antimicrobial activity of the mushroom extracts was assayed with the agar disc diffusion method. The agar well diffusion assay was performed to determine their minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The test bacteria were multidrug resistant against antibiotics, with P. aeruginosa having the highest MARI followed by K. pneumoniae and E. coli. Cold water extracts showed a better antibacterial effect compared to the others and a concentration/effect correlation was observed (from 5 to 500 mg/mL). Ethanol extracts from P. ostreatus and hot water extracts from T. betulina were the most effective in inhibiting and lysing E. coli and K. pneumoniae, respectively, at a MIC and MBC of 3.90 mg/mL. The tested extracts, especially P. ostreatus extract, showed high DPPH and hydrogen peroxide scavenging potential as well as high total phenolic content compared to standard antioxidants. This study showed that the screened agaricomycetous mushrooms possess antibacterial activity against bacterial pathogens as well as antioxidant activity due to their high phenolic content.

Selective, rapid and simultaneous determination of ergosterol and ergocalciferol in mushrooms by UPLC-Q-TOF-MS

An ultra-performance liquid chromatography coupled to atmospheric pressure chemical ionization-quadrupole time-of-flight mass spectrometry method has been optimized and validated for the determination of ergosterol and ergocalciferol in mushroom samples, using cholecalciferol as surrogate standard.The separation was carried out with a Synergi Hydro-RP column (100 mm x 3.00 mm i.d, 2.5 μm particle size), (Phenomenex, CA, USA) column, thermostated at 35 °C. The mobile phase was 0.1 % formic acid aqueous solution and methanol in gradient elution mode and it was achieved in 5 min approximately. Detection was achieved by atmospheric pressure chemical ionization in positive mode and quadrupole time-of-flight mass spectrometry. Desolvation and interface temperatures were set at 500 °C and 150 °C, respectively. The recoveries obtained were within 92–105 % for ergosterol, 77–81 % for ergocalciferol and 83–87 % for cholecalciferol. Method limits of detection were 0.4 and 0.5 μg g−1 for ergosterol and ergocalciferol, respectively, and method limits of quantitation were 1.2 and 1.3 μg g−1 for ergosterol and ergocalciferol, respectively.A rapid and simple extraction procedure using small amount of sample (100 mg) with hexane was optimized and the method was applied to the determination of ergosterol and ergocalciferol in white button mushrooms (Agaricus bisporus var. bisporus) exposed to UV irradiation. Results were compared to the corresponding non-irradiated mushrooms.

Whole Genome Sequence of the Commercially Relevant Mushroom Strain Agaricus bisporus var. bisporus ARP23.

Agaricus bisporus is an extensively cultivated edible mushroom. Demand for cultivation is continuously growing and difficulties associated with breeding programs now means strains are effectively considered monoculture. While commercial growing practices are highly efficient and tightly controlled, the over-use of a single strain has led to a variety of disease outbreaks from a range of pathogens including bacteria, fungi and viruses. To address this, the Agaricus Resource Program (ARP) was set up to collect wild isolates from diverse geographical locations through a bounty-driven scheme to create a repository of wild Agaricus germplasm. One of the strains collected, Agaricus bisporus var. bisporus ARP23, has been crossed extensively with white commercial varieties leading to the generation of a novel hybrid with a dark brown pileus commonly referred to as ‘Heirloom’. Heirloom has been successfully implemented into commercial mushroom cultivation. In this study the whole genome of Agaricus bisporus var. bisporus ARP23 was sequenced and assembled with Illumina and PacBio sequencing technology. The final genome was found to be 33.49 Mb in length and have significant levels of synteny to other sequenced Agaricus bisporus strains. Overall, 13,030 putative protein coding genes were located and annotated. Relative to the other A. bisporus genomes that are currently available, Agaricus bisporus var. bisporus ARP23 is the largest A. bisporus strain in terms of gene number and genetic content sequenced to date. Comparative genomic analysis shows that the A. bisporus mating loci in unifactorial and unsurprisingly highly conserved between strains. The lignocellulolytic gene content of all A. bisporus strains compared is also very similar. Our results show that the pangenome structure of A. bisporus is quite diverse with between 60–70% of the total protein coding genes per strain considered as being orthologous and syntenically conserved. These analyses and the genome sequence described herein are the starting point for more detailed molecular analyses into the growth and phenotypical responses of Agaricus bisporus var. bisporus ARP23 when challenged with economically important mycoviruses.

Aminokiselinski sastav i antioksidacijska aktivnost odabranih gljiva Bosne i Hercegovine

Many studies highlight the health benefits of mushrooms, which are consequently becoming more and more interesting for researchers. The content of amino acids (AA), total phenolic content (TPC), and antioxidative activity (AAc) were determined in wild as well as cultivated mushrooms. The AA included: L-tryptophan (Trp), L-arginine (Arg), L-cysteine (Cys), L-methionine (Met), L-alanine (Ala), L-phenylalanine (Phe), L-lysine (Lys), L-valine (Val), L-glycine (Gly), and L-leucine (Leu). The wild mushrooms: Lactarius piperatus, Amanita caesarea, Lactarius deliciosus, Lycoperdon pyriforme, Macrolepiota procera, and cultivated mushrooms: Agaricus bisporus, Boletus aestivalis, Cantharellus cibarius, Pleurotus ostreatus, and Agaricus bisporus var. avellaneus were investigated in this study. The AA was determined by HPTLC method and quantified with a Camag TLC scanner and WINCAT software by scanning the plates at 540 nm. The TPC was spectrophotometrically estimated as gallic acid equivalents/g of fresh weight according to Folin-Ciocalteu’s method. The radical scavenging activity (RSA) of mushroom extracts was determined by DPPH assay. The highest content of Ala, Gly, Phe, Lys, Val, and Leu was found in Pleurotus ostreatus. The total phenolic content (mg GAE/g) in investigated mushrooms ranged from 1.90 to 35.56, and the % RSA ranged from 43.88 to 90.17. This study promotes the consumption of food rich in bioactive compounds, mushrooms being among such food. Further research on mushrooms from Bosnia and Herzegovina and their benefits in the overall maintenance of human health and protection from age-related diseases is necessary.

A detailed analysis of the recombination landscape of the button mushroom Agaricus bisporus var. bisporus

The button mushroom (Agaricus bisporus) is one of the world’s most cultivated mushroom species, but in spite of its economic importance generation of new cultivars by outbreeding is exceptional. Previous genetic analyses of the white bisporus variety, including all cultivars and most wild isolates revealed that crossing over frequencies are low, which might explain the lack of introducing novel traits into existing cultivars. By generating two high quality whole genome sequence assemblies (one de novo and the other by improving the existing reference genome) of the first commercial white hybrid Horst U1, a detailed study of the crossover (CO) landscape was initiated. Using a set of 626 SNPs in a haploid offspring of 139 single spore isolates and whole genome sequencing on a limited number of homo- and heterokaryotic single spore isolates, we precisely mapped all COs showing that they are almost exclusively restricted to regions of about 100kb at the chromosome ends. Most basidia of A. bisporus var. bisporus produce two spores and pair preferentially via non-sister nuclei. Combined with the COs restricted to the chromosome ends, these spores retain most of the heterozygosity of the parent thus explaining how present-day white cultivars are genetically so close to the first hybrid marketed in 1980. To our knowledge this is the first example of an organism which displays such specific CO landscape.

Deciphering the ability of Agaricus bisporus var. burnettii to produce mushrooms at high temperature (25 °C)

The button mushroom Agaricus bisporus is cultivated almost worldwide. Its cultivation is standardized and a temperature of 16–19°C is needed during the fruiting period. The development of A. bisporus cultivars able to fruit at higher temperature (FHT) represents a promising alternative to reduce energy costs during cultivation in hot countries as well as in temperate countries during the hot season. A. bisporus var. burnettii is able to fruit at 25°C. Understanding the biological mechanisms that underlie such a thermo-tolerance is a prerequisite to further development of breeding strains. The foundation of the FHT ability of the var. burnettii was dissected using a combination of candidate gene approaches and genetic tools. Transcript profiling of A. bisporus var. burnettii at two developmental stages (primordium P and sporophore SP) under two fruit-producing temperature conditions (17°C and 25°C) were established by cDNA-AFLP. The expression patterns were more similar within the same stage at the two different temperatures rather than between stages under the same temperature. Only one transcript-derived fragment (TDF) sequence differentially expressed between temperatures was recovered but it could not be further characterized. Twenty-nine TDF sequences differentially expressed between development stages were obtained. The phenotypic assessment of an intervarietal A. bisporus var. bisporus×A. bisporus var. burnettii progeny demonstrated the complex inheritance of the FHT trait. Two quantitative trait loci (QTL) involved in the number of fruit bodies yielded at 25°C were found on LG II and LG VI. Two functional candidate genes known to be potentially involved in A. bisporus thermo-tolerance, a heat shock protein (HSP70) gene and a gene coding for a para-aminobenzoic acid synthase (PABA), were found in the vicinity of the QTL on LG II. Several positional candidate genes have been also identified in the confidence interval of the QTL on LG VI and are promising for further fine mapping purpose.

The intraspecific variability of mitochondrial genes of Agaricus bisporus reveals an extensive group I intron mobility combined with low nucleotide substitution rates.

Intraspecific mitochondrial variability was studied in ten strains of A. bisporus var. bisporus, in a strain representative of A. bisporus var. eurotetrasporus and in a strain of the closely related species Agaricus devoniensis. In A. bisporus, the cox1 gene is the richest in group I introns harboring homing endonuclease genes (heg). This study led to identify group I introns as the main source of cox1 gene polymorphism. Among the studied introns, two groups were distinguished according to the heg they contained. One group harbored heg maintained putatively functional. The other group was composed of eroded heg sequences that appeared to evolve toward their elimination. Low nucleotide substitution rates were found in both types of intronic sequences. This feature was also shared by all types of studied mitochondrial sequences, not only intronic but also genic and intergenic ones, when compared with nuclear sequences. Hence, the intraspecific evolution of A. bisporus mitochondrial genome appears characterized by both an important mobility (presence/absence) of large group I introns and by low nt substitution rates. This stringent conservation of mitochondrial sequences, when compared with their nuclear counterparts, appears irrespective of their apparent functionality and contrasts to what is widely accepted in fungal sequence evolution. This strengthens the usefulness of mtDNA sequences to get clues on intraspecific evolution.

Diversity in the ability of Agaricus bisporus wild isolates to fruit at high temperature (25 °C)

The button mushroom Agaricus bisporus commercially cultivated requires 16–19 °C during the fruiting period. Wild strains are also present in natural habitat, and in light of their wide range of geographic distribution reported, from boreal region to tropical region, questions on the development adaptation to temperature arose. Isolates from various geographic areas were screened for their ability to fruit at higher temperature (FHT ability) than commercial cultivars. The FHT trait discriminated at the varietal rank. Agaricus bisporus var. eurotetrasporus was unable to develop any sporophores whilst A. bisporus var. burnettii adapted perfectly to 25 °C for fruiting, suggesting that the FHT ability is a fixed trait in these varieties. In contrast, FHT ability of A. bisporus var. bisporus appeared variable and correlated neither with climate/microclimate nor with habitat. However, FHT ability taken as a whole appeared higher in North American populations than in European ones. Some A. bisporus var. bisporus isolates revealed a good potential for cultivation at 25 °C.

Quantitative genetics to dissect the fungal–fungal interaction between Lecanicillium verticillium and the white button mushroom Agaricus bisporus

Lecanicillium fungicola (formerly Verticillium fungicola) is responsible for dry bubble disease in the white button mushroom Agaricus bisporus. Selection for resistance to this pathogen raises an important challenge for mushroom breeders. We have investigated the inheritance of resistance to dry bubble under artificial inoculation in three independent experiments, using a progeny of 89 hybrids derived from an intervarietal A. bisporus var. bisporus×A. bisporus var. burnettii cross. Overall, phenotypic correlations were highly significant between the different experiments. Principal component analysis, together with analysis of variance results stated that the disease reactions were accurately assessed using the percentage of bubbles (PB) and the percentage of spotty cap mushrooms (PS) separately rather than with the combination of both. An original contribution of this study lies in the effective use of area under the disease-progress curve (AUDPC) to describe the dry bubble resistance. The continuous phenotypic distribution observed for the resistance traits suggested that tolerance to dry bubble was under polygenic control. Heritability estimates for either PB or AUDPC were high (0.67–0.86) while it was inconsistent for PS (0.33–0.68) suggesting a strong impact of the environment on this latter trait. Earliness and latent period were found highly correlated with disease incidence. The earliest strains appeared to be the most resistant ones. These results contribute to disentangle the complex fungal–fungal A. bisporus / L. fungicola interaction and to provide genetic basis as a prerequisite for mushroom breeding program.

Structure of Agaricus spp. fucogalactans and their anti-inflammatory and antinociceptive properties

Fucogalactans from Agaricus brasiliensis (EPF-Ab) and A. bisporus var. hortensis (EPF-Ah) were prepared via by aqueous extraction and a purification procedure. EPF-Ab had Mw 19.4×103g/mol and EPF-Ah Mw 31.1×103g/mol. EPF-Ab had a (1→6)-linked α-D-Galp main-chain partially substituted in O-2 by non-reducing end-units of α-L-Fucp. EPF-Ah had a similar main-chain with O-2 substitution, but was partially methylated at HO-3, as well as having 2.5% non-reducing end-units of β-D-Gal. In mice, EPF-Ab gave 39% antinociceptive inhibition (ID50>100mg/kg) and no anti-inflammatory activity. EPF-Ah also gave an inhibition of 39% at ID50 0.33mg/kg and also inhibited by 61% (ID50 5.0mg/kg) total cell migration and by 32% peritoneal capillary permeability, which is related to the anti-inflammatory effect. The small differences in chemical structure in these polysaccharides thus modified their biological activities.

An expanded genetic linkage map of an intervarietal Agaricus bisporus var. bisporus×A. bisporus var. burnettii hybrid based on AFLP, SSR and CAPS markers sheds light on the recombination behaviour of the species

A genetic linkage map for the edible basidiomycete Agaricus bisporus was constructed from 118 haploid homokaryons derived from an intervarietal A. bisporus var. bisporus x A. bisporus var. burnettii hybrid. Two hundred and thirty-one AFLP, 21 SSR, 68 CAPS markers together with the MAT, BSN, PPC1 loci and one allozyme locus (ADH) were evenly spread over 13 linkage groups corresponding to the chromosomes of A. bisporus. The map covers 1156cM, with an average marker spacing of 3.9cM and encompasses nearly the whole genome. The average number of crossovers per chromosome per individual is 0.86. Normal recombination over the entire genome occurs in the heterothallic variety, burnettii, contrary to the homothallic variety, bisporus, which showed adaptive genome-wide suppressed recombination. This first comprehensive genetic linkage map for A. bisporus provides foundations for quantitative trait analyses and breeding programme monitoring, as well as genome organisation studies.

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3-5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

Karyological evidence for meiosis in the three different types of life cycles existing in Agaricus bisporus

In Agaricus bisporus all cytological studies performed until now concerned the pseudohomothallic and bisporic var. bisporus. In the past 12 y two tetrasporic varieties have been described, the heterothallic var. burnettii and the homothallic var. eurotetrasporus. Our aim was to compare the behavior of the nuclei in the vegetative and reproductive cells of the three varieties with light microscopy (Feulgen and DAPI staining) and transmission electron microscopy. Most of the vegetative cells contained 3–5 nuclei in the three varieties. Nuclear migrations through the septum were detected. In the basidia relative locations of nuclei and vacuoles, meiotic spindle alignments, relative content of nuclear DNA and synaptonemal complexes were measured or observed. From the observation of numerous asynchronous second division of meiosis within basidia of var. bisporus and var. burnettii a new hypothesis emerges to explain the nonrandom distribution of the four meiotic products in the two spores of the bisporic basidia. Karyogamy and meiosis similarly occurred in the three varieties. In the case of A. bisporus var. eurotetrasporus this implies that the reproductive mode is sexual and therefore homothallic in the strict sense. The three different types of life cycles are described.

Conservation of genetic linkage with map expansion in distantly related crosses of Agaricus bisporus.

A previous map of the genome of a hybrid strain which had European parents belonging to the secondarily homothallic fungus Agaricus bisporus var. bisporus appeared to be unusually compact, with a particularly recombophobic segment in the central part of chromosome I. A new map of this segment was constructed based on allelic segregations among 103 homokaryotic offspring of an A. bisporus hybrid between a European parent of the var. bisporus and a Californian parent of the heterothallic var. burnettii. Markers completely linked on the previous map were distributed along 28 cM in the new map. These results suggest that the greater recombination rate could be correlated with the outbreeding behaviour of the var. burnettii.

A novel homothallic variety of Agaricus bisporus comprises rare tetrasporic isolates from Europe

Among 400 wild specimens of A. bisporus collected in Europe, only three were tetrasporic. In the case of two of them from France, a previous study showed that one was homokaryotic and hypothetically belonged to a homothallic entity while the other was heterokaryotic and possibly resulted from hybridization between a member of this entity and a classical bisporic strain. A third tetrasporic specimen recently was discovered in Greece. Morphological and genetic comparisons, using alloenzymatic markers, molecular markers and ITS polymorphisms, reveal that this third specimen is homokaryotic and belongs, with the homokaryotic specimen from France, to the same entity. Dissimilarity analysis confirms the hybrid origin of the heterokaryotic specimen. Varietal status is proposed for this homothallic, highly homogeneous entity, and A. bisporus var. eurotetrasporus is described. This novel variety clearly differs from var. bisporus by its tetrasporic basidia and from var. burnettii by its longer spores. It has a complex story because it can interbreed with var. bisporus and shares the same habitat; however, because of its homothallic life cycle and its partial intersterility, it is probably in the process of speciation.

Effect of Ozone Treatment and Storage Temperature on Physicochemical Properties of Mushrooms (Agaris bisporus)

The aim of this paper was to determine the effect of ozone, storage time and temperature on postharvest quality of mushroom ( Agaris bisporus var. Gurelan 55). Mushrooms, treated with ozone (100 mg/h) during 0, 15 or 25 minutes, were packed in polystyrene packs, overwrapped with PVC plastic film, and stored at 5, 15 or 25 °C for seven days. Internal and external lightness ( L*) texture properties, maturity index and weight loss were analyzed during storage. Ozone treatment on mushrooms prior to packaging caused an increase in external browning rate and a reduction of the internal browning rate. The ozone treatment exhibited no significant differences in terms of texture, maturity index and weight loss of mushrooms. Increased storage time and temperatures meant an increase in browning, senescence and weight loss, as well as a decrease in firmness, following, in all cases, a zero-order reaction kinetics. Temperature dependence of the reaction rates coule be described by Arrhenius equation. Among all the quality parameters assessed in this research, weight loss was the most affected by temperature increase ( Ea = 17.60 kcal/mol). The lowest storage temperature (5 °C) favored the best quality.