Hendrickx, P. | Search bioRxiv

bioRxiv2025

Genetic mapping and nuclear interactions of an incompatibility response in Agaricus bisporus

During cultivation, mixing of different heterokaryotic individuals of the button mushroom, Agaricus bisporus, generally reduces yield. This phenomenon could be caused by direct antagonistic responses and/or reduced synchronization by not forming a chimeric hyphal network. In other fungi, highly divergent alleles for a set of genes affect successful network formation between individuals either by preventing fusion or, more commonly, triggering cell death post-fusion. To understand this process in A. bisporus, it is important to identify the allelic variants allowing these fungi to discriminate self from nonself. We leverage a recently described cell death staining method utilizing Evans Blue to visualize mycelial compatibility. Here, we provide results of a first genetic mapping of incompatibility alleles in A. bisporus. Crossing strains between A. bisporus var. bisporus and A. bisporus var. burnetti we find segregation ratios of compatible progeny generally consistent with three nuclear loci. To identify these regions, we first use a set of single Chromosome Substitution Lines (CSLs), produced by genotyping progeny with recombination skewed to the very chromosome ends. We localize the main effect to be between two and three chromosomes, depending on the common nucleus of interacting heterokaryons. Using genome-wide markers for 167 sexual progeny, we identify loci controlling mycelial compatibility on chromosomes 4, 6 and 7, the same chromosomes as indicated by chromosome substitution lines. Notably, while the choice of a common nucleus seemed to affect the compatibility of CSLs, it did not seem to affect the loci identified in the sexual progeny. The ability to mix different strains of this mushroom-forming fungus could allow additional cultivation approaches, combining strains with complementary characteristics. These results provide a starting point towards understanding the molecular mechanisms underlying this fundamental property of hyphal networks in basidiomycetes.

genetics↗

bioRxiv2022

Feeding Growing Mushrooms

A number of experiments were done to further our understanding of the substrate utilization in button mushroom crops (Agaricus bisporus). An analysis of the degradation of dry matter of the substrate during a crop cycle revealed that for pin formation the upper layer is used, for the production of flush one all layers are involved and for flush two mainly the lower layer is used. A reduction in substrate depth leads to a decrease in yield/m2 but an apparent increase in yield per ton of substrate but with a lower mushroom quality. A short daily interruption of the connection between the casing soil with all the substrate results in a delay of the first flush. Repetitive interruption of the connection with all or only part of the substrate leads to a shift in yield from flush one to flush two but the total yield remains unchanged. The mycelial biomass in the substrate increases from filling up to pinning, a steeper increase during flush one, levelling off during flush two, indicating that in the period of venting and up to/including flush one, enzymes are secreted by growing hyphae generating nutrients to feed a fixed amount of mushroom biomass for two flushes. A sidewise extension of the substrate (without casing soil, thus not producing mushrooms) showed that the substrate at a distance more than 20-50 cm away from the casing soil does not contribute to feeding mushrooms in the first two flushes. The observations are discussed with respect to relevant previous research. ImportanceButton mushrooms (Agaricus bisporus) are cultivated on a substrate prepared of composted wheat straw, chicken and/or horst manure and gypsum. This manuscript describes a number of experiments indicating that in a harvesting strategy towards quality mushrooms there is a fixed amount of nutrients prepared/available to feed two flushes. The increase of mycelial biomass in the substrate after venting and especially during the development of flush one indicates that likely a branching of mycelium occurs during this period, leading to a substantial number of growing hyphal tips excreting lignocellulolytic enzymes that degrade substrate and make nutrients available during flush one which are utilised in flush one and two. The presently used substrate seems to have reached its limits and there are hardly opportunities for further improvement. Research on alternative, more energy dense, substrates are needed to improve the efficiency of the present production system.

microbiology↗