Developments in breeding of Agaricus bisporus var. bisporus : progress made and technical and legal hurdles to take

True breeding of button mushrooms has hardly been done in the last decades, despite this species being one of the most cultivated mushrooms worldwide. Research done in the last 20 years has identified and characterised new germplasm and improved our understanding of the genetic base for some traits. A substantial collection of wild-collected strains is now available and partly characterised for a number of important traits such as disease resistance and yield. Most of the variations found in a number of important agronomic traits have a considerable heritability and are thus useful for breeding. Genetic marker technology has also developed considerably for this mushrooms in the last decade and used to identify quantitative trait loci (QTL) for important agronomic traits. This progress has, except for one example, not resulted so far into new commercially varieties. One of the reasons lies in the typical life cycle of the button mushroom Agaricus bisporus var. bisporus which hampers breeding. Joint investment is needed to solve technical problems in breeding. Special attention is needed for the protection of new varieties. Due to its typical life cycle, it is very easy to generate so called “look-a-likes” from protected cultivars by screening fertile single spore cultures. A consensus has been reached within the mushroom (breeding) industry to consider this method as the generation of essentially derived varieties as defined in plant breeding

Critical factors involved in primordia building in agaricus bisporus : A review

The button mushroom Agaricus bisporus is an economically important crop worldwide. Many aspects of its cultivation are well known, except for the precise biological triggers for its fructification. By and large, for most basidiomycete species, nutrient availability, light and a drop in temperature are critical factors for fructification. A. bisporus deviates from this pattern in the sense that it does not require light for fructification. Furthermore its fructification seems to be inhibited by a self-generated factor which needs to be removed by microorganisms in order to initiate fruiting. This review explores what is known about the morphogenesis of fruiting initiation in A. bisporus, the microflora, the self-inhibitors for fruiting initiation and transcription factors involved. This information is subsequently contrasted with an overall model of the regulatory system involved in the initiation of the formation of primordia in basidiomycetes. The comparison reveals a number of the blank spots in our understanding of the fruiting process in A. bisporus.</p

Wheat bran addition improves Ceriporiopsis subvermispora and Lentinula edodes growth on wheat straw, but not delignification

A rapid and complete colonization of lignocellulosic biomass by white-rot fungi is a prerequisite for an efficient and contamination free delignification. To improve the colonization, mycelium growth and delignification by Ceriporiopsis subvermispora and Lentinula edodes of wheat straw, with addition of 2, 4, 6 and 10% of wheat bran for 0, 2, 4, 8 and 12 weeks, was evaluated. The ergosterol content, chemical composition and in vitro gas production (IVGP) by ruminal microorganisms were determined. The fungal biomass and starch amount was significantly (P 0.05) the amount of hemicellulose and lignin at the end of the incubation. There was no significant effect of wheat bran addition on the IVGP for the two fungal treatments. Supplementation of wheat straw with wheat bran resulted in a quicker fungal colonization, which is useful for C. subvermispora, a fungus that forms only thin mycelium and is more prone to contamination than L. edodes.</p

Preservation of Ceriporiopsis subvermispora and Lentinula edodes treated wheat straw under anaerobic conditions

BACKGROUND: No attention has been paid so far to the preservation of fungal-treated lignocellulose for longer periods. In the present study, we treated wheat straw (WS) with the white-rot fungi Ceriporiopsis subvermispora and Lentinula edodes for 8weeks and assessed changes in pH, chemical composition and in vitro gas production (IVGP) weekly. Fungal-treated WS was also stored for 64days 'as is', with the addition of lactic acid bacteria (LAB) or with a combination of LAB and molasses in airtight glass jars mimicking ensiling conditions. RESULTS: Both fungi significantly reduced the lignin and hemicellulose content of WS, and increased the cellulose content. The IVGP increased with increasing time of incubation, indicating the increase in digestibility. Both fungi lowered the pH of WS under 4.3, which guarantees an initial and stable low pH during anaerobic storage. Minor changes in fibre composition and IVGP were observed for stored L. edodes treated WS, whereas no change occurred for C. subvermispora. CONCLUSION: It is possible to conserve C. subvermispora and L. edodes treated straw under anaerobic condition without additives up to 64days. This finding is important for practical application to supply fungi-treated feed to ruminant animals for a prolonged period

Prospects and feasibility of fungal pretreatment of agricultural biomass for ruminant feeding

In recent years, the use of white-rot fungi as a pretreatment method to improve the nutritive value of agricultural biomass as ruminant feed, has received a substantial attention. However, there are several issues that need to be addressed for a successful application of this method. One of the issues is the inevitable variation in the nutritive values of the fungal-treated biomass. This paper reviews our recent works on validating the variation in the nutritive values of biomass treated with different fungal species. The general aims of these studies are: (1) to study the variability among different fungal species (and strains) in improving the nutritive value of the same batch of wheat straw; and (2) to assess the capabilities of selected fungi to improve different batches and types of wheat straw. A large variation of ruminal degradability – measured as in vitro gas production, IVGP), was observed, even for different strains of the same fungal species. The IVGP for different strains of Ceriporiopsis subvermispora ranged from 205.5 to 317.8 mL/g organic matter (OM), while the IVGP ranges for the strains of Lentinula edodes and Pleurotus eryngii were 183.5–306.6 ml/g OM) and 206.6–267.0 ml/g OM, respectively. A high potential fungus, strain CS1 of C. subvermispora consistently improved the IVGP of different batches and types of wheat straw by 27.7–47.6%. The variation in the nutritive value of fungal-treated biomass is evident. However, this issue can be overcome by using the right fungal strains with an optimal culture and growth conditions. More research needs to be done to make it an attractive substitute to physico-chemical methods. Here, we also put forward our manifestation on the future prospects of fungal pretreatment for ruminant feeding.</p

The typical life cycle of the button mushroom Agaricus bisporus var. bisporus: Implications for breeding and protection of new cultivars

International audienceThe button mushroom (Agaricus bisporus)is one of the world’s most cultivated mushroom species. In spite of its economic importance, new cultivars by outbreeding have been hardly produced in the last 40 years. One of the reasons for this lack of breeding effort is the difficulty to introduce new traits. This is caused by the atypical meiosis in button mushrooms. Recombination between homologous chromosomes is restricted to chromosome ends resulting in the inheritance of nearly parental type of chromosomes. In addition, instead of four spores, most basidia produce two spores in which non-sister nuclei are paired. As a result, these spores are fertile and each produce mushrooms that are genetically and phenotypically very similar to the parental line. Genetic analysis has shown that most present-day white commercial cultivars are derived in this way from the first hybrids released in 1980. These were generated by outcrossing and required a considerable investment. The selection of fertile single spore cultures from protected varieties and the use of these to generate new cultivars should be considered as the generation of essentially derived varieties (EDV) similar to how derived varieties in plant cultivars are defined. A working group of 4 spawn/breeding companies and two research groups has been formed to come to a consensus what should be considered as essentially derived varieties in cultivars of edible fungi. The initiative of this group is supported by the international organization of plant protection (UPOV), the European agency that manage the system of plant variety rights (CPVO) and the ISMS. Next generation sequencing technologies can support the identification of copied, derived and genially new cultivars

Fine Mapping and Functional Analysis of the Gene PcTYR, Involved in Control of Cap Color of Pleurotus cornucopiae

Oyster mushrooms have a high biological efficiency and are easy to cultivate, which is why they are produced all over the world. Cap color is an important commercial trait for oyster mushrooms. Little is known about the genetic mechanism of the cap color trait in oyster mushrooms, which limits molecular breeding for the improvement of cap color-type cultivars. In this study, a 0.8-Mb major quantitative trait locus (QTL) region controlling cap color in the oyster mushroom Pleurotus cornucopiae was mapped on chromosome 7 through bulked-segregant analysis sequencing (BSA-seq) and extreme-phenotype genome-wide association studies (XP-GWAS). Candidate genes were further selected by comparative transcriptome analysis, and a tyrosinase gene (PcTYR) was identified as the highest-confidence candidate gene. Overexpression of PcTYR resulted in a significantly darker cap color, while the cap color of RNA interference (RNAi) strains for this gene was significantly lighter than that of the wild-type (WT) strains, suggesting that PcTYR plays an essential role in cap color formation. This is the first report about fine mapping and functional verification of a gene controlling cap color in oyster mushrooms. This will enhance our understanding of the genetic basis for cap color formation in oyster mushrooms and will facilitate molecular breeding for cap color. IMPORTANCE Oyster mushrooms are widely cultivated and consumed over the world for their easy cultivation and high biological efficiency (mushroom fresh weight/substrate dry weight × 100%). Fruiting bodies with dark caps are more and more popular according to consumer preferences, but dark varieties are rarely seen on the market. Little is known about the genetic mechanism of the cap color trait in oyster mushrooms, which limits molecular breeding for the improvement of cap color-type cultivars. A major QTL of cap color in oyster mushroom P. cornucopiae was fine mapped by using bulked-segregant analysis (BSA) and extreme-phenotype genome-wide association study (XP-GWAS) analysis. A candidate gene PcTYR coding tyrosinase was further identified with the help of comparative transcriptome analysis. qPCR analysis and genetic transformation tests proved that PcTYR played an essential role in cap color formation. This study will contribute to revealing the genetic mechanism of cap color formation in mushrooms, thereby facilitating molecular breeding for cap color trait

Multi-trait QTL analysis for agronomic and quality characters of Agaricus bisporus (button mushrooms)

The demand for button mushrooms of high quality is increasing. Superior button mushroom varieties require the combination of multiple traits to maximize productivity and quality. Very often these traits are correlated and should, therefore, be evaluated together rather than as single traits. In order to unravel the genetic architecture of multiple traits of Agaricus bisporus and the genetic correlations among traits, we have investigated a total of six agronomic and quality traits through multi-trait QTL analyses in a mixed-model. Traits were evaluated in three heterokaryon sets. Significant phenotypic correlations were observed among traits. For instance, earliness (ER) correlated to firmness (FM), cap color, and compost colonization, and FM correlated to scales (SC). QTLs of different traits located on the same chromosomes genetically explains the phenotypic correlations. QTL detected on chromosome 10 mainly affects three traits, i.e., ER, FM and SC. It explained 31.4 % phenotypic variation of SC on mushroom cap (heterokaryon Set 1), 14.9 % that of the FM (heterokaryon Set 3), and 14.2 % that of ER (heterokaryon Set 3). High value alleles from the wild parental line showed beneficial effects for several traits, suggesting that the wild germplasm is a valuable donor in terms of those traits. Due to the limitations of recombination pattern, we only made a start at understanding the genetic base for several agronomic and quality traits in button mushrooms.</p