The investigation grew out of concern about the performance of the commercial hybrid strain dN001, which had been maintained in subculture in the researchers’ laboratory for about 20 years. Its descendants divided into fast- and slow-growing phenotypes. Earlier work associated the slow descendants with degeneration, oxidative stress and altered expression of genes involved in mitochondrial respiration, hypoxia responses, antioxidant defence and cell death.

The new study tested the possibility that repeated mating and subculture had separated nuclear and mitochondrial components that had previously evolved together, producing incompatibilities associated with hybrid breakdown. To create parental lines with contrasting growth rates, the team intercrossed full-sib monokaryons descended from dN001 and sharing its mitochondrial type. Intercrossing fast descendants and, separately, slow descendants generated fourth-generation fast and slow lines.

The resulting lines had mean radial growth rates of 4.07 and 1.12 millimetres per day. The fast line increased the growth rate by about 50% relative to the earlier generation, while the slow line declined by only 1.8%. Nuclear and mitochondrial molecular markers were then used to confirm the construction of eight hybrids: crosses involving two fast parental lines and two slow parental lines, each represented with either the “n” mitochondrial genome inherited from dN001 or the “t” mitochondrial genome inherited from the compatible wild-derived tester strain mT1.

Each pair shared the same nuclear background but differed in mitochondrial type. Mitochondrial inheritance was uniparental, as each hybrid carried only one detected mitochondrial genotype. Under standard laboratory conditions of 24 degrees Celsius, the mitochondrial background made little consistent difference among hybrids made with fast-growing parents.

The clearest contrast instead appeared within the slow-parent set. Under the tested temperatures of 15, 24 and 32 degrees Celsius, d(NS423 × T1, t) consistently grew faster than d(NS423 × T1, n). Relative to the parental average, the “t” hybrid exhibited mid-parent heterosis ranging from 40% to 76% across the temperature conditions.

The second slow-line cross, d(NS426 × T1), showed no detected mitochondrial effect on growth rate, although both versions grew more slowly at 15 degrees Celsius. These divergent outcomes show that a mitochondrial genome did not have a uniform effect across nuclear backgrounds; its influence depended on which nuclear genome accompanied it. Carbon sources altered the picture again.

The fast and slow parental lines generally grew well with glucose, sucrose or glycerol, although glycerol reduced growth in most strains and by about 60% in the tester mT1. The d(NS423 × T1, t) hybrid grew faster than its “n” counterpart across the tested carbon sources, with mid-parent heterosis values from 32% to 100%, depending on the condition and mitochondrial background. By contrast, mitochondrial type did not consistently affect growth in the fast hybrids or the d(NS426 × T1) pair, apart from some differences involving glycerol.

One slow parental strain, mNS423, maintained similar growth across all three carbon sources, indicating that its nuclear background also contributed to metabolic flexibility. The measurements therefore supported genotype-by-environment interactions rather than a simple rule that hybridisation always improves growth. Mitochondrial differences were accompanied by distinct patterns of gene expression and reactive oxygen species, but these observations did not by themselves establish a causal molecular mechanism.

Using reverse-transcription quantitative PCR, the researchers measured the mitochondrial nd1 gene and nuclear bcs1, rip1, cox4 and cox5b genes associated with electron transport chain complexes I, III and IV. They also examined sod1, cat and gpx, encoding superoxide dismutase, catalase and glutathione peroxidase. Several hybrids expressed genes beyond the range of their parents, a pattern the researchers termed transgressive inheritance and classified as overdominance, underdominance or partial dominance depending on the gene and cross.

Slow-growing lines generally showed higher expression of genes connected with respiration, hypoxia and oxidative-stress responses, although the pattern was not identical for every gene. Fluorescent probes supplied a parallel physiological measurement. Slow lines and many of their hybrids accumulated more superoxide and hydrogen peroxide than fast lines.

In d(NS423 × T1, t), however, reactive oxygen levels fell to levels comparable to those of fast hybrids. This strain also showed elevated expression of nd1, bcs1 and rip1, while cox4 and cox5b expression was reduced to levels resembling those in fast-growing hybrids. The authors interpreted these associated patterns as consistent with improved mitochondrial function and lower oxidative stress in the successful hybrid.

They also noted two possible explanations for the hybrid vigour: masking of harmful parental mutations and disruption of regulatory safeguards that normally limit growth. The experiments did not distinguish these alternatives conclusively. The mitochondrial contrast persisted under cultivation designed to resemble mushroom production.

Spawn made from each hybrid was mixed with pasteurised wheat straw at a 2% weight-to-weight ratio and packed into 2-kilogram micro-perforated bags before fruiting at 18 degrees Celsius and 90% relative humidity. Spawn colonisation did not differ significantly between mitochondrial versions of the fast hybrids or the d(NS426 × T1) pair. The d(NS423 × T1, t) hybrid, however, colonised grain at a rate comparable to the fast hybrids, and its substrate weight loss matched that group.

Its mitochondrial background was associated with greater straw degradation in this cross, while the other slow hybrid pair remained low-performing regardless of mitochondrial type. The “n” hybrid produced a total yield of 29.2 ± 5.0 grams, fruited after 38 ± 3 days and formed one flush, with values reported as means of three replicates plus or minus standard deviation. The “t” hybrid produced 148.2 ± 11.6 grams, fruited after 26 ± 1 days and formed three flushes.

Total yields among the fast hybrids ranged from 199.7 ± 15.1 to 299.2 ± 77.2 grams, so the improved slow-line hybrid remained below that group in yield even though it behaved more like them in several other traits. Its earlier production and greater number of flushes nevertheless represented a marked improvement over its mitochondrial counterpart. Expression patterns for genes connected with substrate colonisation, iron handling and mitochondrial structure were consistent with additional physiological differences, without proving their role in the yield advantage.

The fast lines expressed more lacc4, whereas slow lines generally showed higher fet3 expression. The successful “t” hybrid stood out through increased fet3 expression and a yfh1 pattern that the authors interpreted as partial restoration of iron availability. It also showed increased expression of fzo1, associated with mitochondrial fusion, and cld1, involved in cardiolipin and mitochondrial membrane functions.

Antioxidant compounds detected by thin-layer chromatography also varied among hybrids, including a DPPH-reactive band at an Rf value of 0.80 restricted to fast hybrids carrying the “n” mitochondrial type. These findings broaden the phenotypic differences associated with mitonuclear background, but their individual contributions to growth or yield remain unresolved. The findings suggest two practical implications for breeding P. ostreatus, both of which remain proposals for further testing rather than outcomes established by this study.

The researchers advocate retaining compatible parental strains in long-term storage and remaking hybrids shortly before commercial use instead of repeatedly subculturing a hybrid, because degeneration may emerge across generations. They are also screening potential bred lines for new heterotic combinations. Candidate parents would need genomic and transcriptomic information, evidence of general and specific combining ability, and tolerance across substrates and temperatures.

For now, the study’s bounded conclusion is clear: in the tested oyster-mushroom crosses, mitochondrial type could reshape transgressive gene expression, reactive oxygen levels, growth, substrate degradation and fruiting performance, with the size and direction of the effect depending on the nuclear background and environment.

Subject of Research: How mitochondrial background affects hybrid growth, oxidative stress and mushroom yield in Pleurotus ostreatus

Article Title: Asymmetric mitonuclear interactions trigger transgressive inheritance and mitochondria-dependent heterosis in hybrids of the model system Pleurotus ostreatus

Article References: Garde, E., Pérez, G., Jiménez, I., Calvo, M. I., Pisabarro, A. G., & Ramírez, L. (2025). Asymmetric mitonuclear interactions trigger transgressive inheritance and mitochondria-dependent heterosis in hybrids of the model system Pleurotus ostreatus. IMA Fungus, 16, Article e165520. https://doi.org/10.3897/imafungus.16.165520

Image Credits: AI Generated

DOI: 10.3897/imafungus.16.165520

Keywords: Pleurotus ostreatus, mitochondrial inheritance, mitonuclear compatibility, hybrid vigour, heterosis, oxidative stress, mushroom breeding, fungal genomics, electron transport chain, mushroom yield, Asymmetric, mitonuclear

The new materials belong to a class known as mycelium biocomposites, in which the vegetative root-like networks of fungi are grown through organic substrates such as agricultural residues. The fungal hyphae bind the loose lignocellulosic particles into a solid, relatively lightweight structure that is biodegradable and recyclable. Historically an experimental biomaterial, mycelium composites have attracted growing attention because of their promising combination of low weight, thermal insulation capacity, and reasonable strength and durability. Their production also offers a route to valorizing by-products, storing atmospheric carbon dioxide, and reducing dependence on petrochemicals, all while embodying circular economy principles in which materials can be disassembled, reused, and ultimately returned to natural systems.

Producing these composites is a multi-phase biological process rather than an industrial extrusion. Mycelium is first grown on a substrate over one to two weeks under carefully controlled conditions, typically at temperatures between 24 and 30 degrees Celsius and humidity levels of 60 to 75 percent. The material then develops for two to four weeks as the fungal network colonizes the substrate into a uniformly dense structure. A final drying stage, lasting from a few days to a week, halts fungal growth and provides the strength and dimensional stability that make the material usable in construction. Each of these steps, along with the choice of substrate and fungal strain, shapes the physicochemical characteristics of the finished composite.

In the new study, a research team prepared four experimental series of mycelium biocomposites, each with a different composition, production flow, and specimen geometry. Series I combined wheat straw with Ganoderma lucidum, Series II paired flax straw with Pleurotus ostreatus, Series III used hemp shives with Pleurotus ostreatus, and Series IV tested wheat straw, hemp shives, and flax straw, each inoculated with Ganoderma lucidum. All samples were produced by mixing 7.5 grams of colonized grain spawn into 300 grams of sterilized straw, a spawn-to-substrate ratio of 2.5 percent, with the sterilized substrate held at approximately 60 percent preparative moisture. The mixtures were compressed by hand into cardboard molds shaped as cubes, cylinders, or rectangular prisms, then cultivated and dried under formulation-specific conditions before testing.

The team evaluated four parameters most relevant to insulation performance: thermal conductivity, density, flexural strength, and compressive strength. Density was measured with a precision laboratory balance and manual dimensional measurements, while thermal conductivity was assessed with a portable Isomet 2114 heat transfer analyzer under controlled laboratory conditions of 20 degrees Celsius and 50 percent relative humidity. Each specimen was measured twice on adjacent surfaces, with the median value used for analysis. The researchers also computed a thermal conductivity-to-weight ratio, an inverse indicator that favors formulations combining low heat conduction with low bulk density, to compare the overall thermal-mass balance of the tested materials.

The results revealed striking differences among the formulations. Thermal conductivity ranged from 0.0385 to 0.0719 watts per meter-kelvin depending on substrate and fungal strain, while densities spanned from 80 to 227 kilograms per cubic meter. The standout performer was the hemp shive composite inoculated with Pleurotus ostreatus, which achieved the lowest density range of 80 to 120 kilograms per cubic meter and the most efficient thermal conductivity, from 0.0385 to 0.057 watts per meter-kelvin. This formulation recorded the highest thermal conductivity-to-weight ratio of 0.209, approximately 35.7 percent higher than the next best formulation in the study. By contrast, the multi-material Series IV showed the widest variability in both density and conductivity, reflecting the challenges of consistency in mixed compositions.

Mechanical testing of the optimal hemp shive and Pleurotus ostreatus composite produced equally notable results. Two independently molded prism specimens, each 40 by 40 by 160 millimeters, were subjected to three-point bending on a standardized flexure testing device with a 100-millimeter support span. The composite achieved an average flexural strength of 8.85 megapascals, with individual specimens reaching 8.58 and 9.11 megapascals. Compressive testing on the uncracked halves of the broken prisms yielded an average compressive strength of 4.25 megapascals. Both values exceed or match similar mycelium-based composites described in the literature, where flexural strengths have typically ranged from 0.44 to 4.23 megapascals depending on substrate, and many lignocellulosic formulations have shown compressive strengths below 1 megapascal.

To contextualize these findings, the researchers benchmarked their data against seven published studies of mycelium composites made from comparable plant-derived substrates, plotting thermal conductivity jointly with density because porosity and density strongly influence thermal performance. The literature dataset spans roughly 0.035 to 0.096 watts per meter-kelvin across a wide density range. The hemp shive composite’s minimum conductivity of 0.0385 watts per meter-kelvin compares favorably with values reported for birch sawdust composites and mycelium-bound fibers from invasive plants, and its combination of approximately 100 kilograms per cubic meter density with low conductivity places it firmly in the favorable low-density, low-conductivity region of the performance map. The authors caution, however, that differences in specimen geometry, moisture state, processing conditions, and measurement procedures mean such comparisons serve as performance benchmarking rather than a strictly standardized ranking.

The researchers supplemented their measurements with scanning electron microscopy of the wheat straw and Ganoderma lucidum formulation, which revealed an interconnected filamentous network bridging the lignocellulosic structural elements and numerous micrometer-scale voids. These images provide qualitative evidence of the porous microstructure that underpins the materials’ insulating behavior, although porosity was not quantitatively determined. The team also conducted a rigorous uncertainty analysis, estimating measurement-related uncertainties of roughly 0.6 to 1.3 percent for density, 6.4 to 7.6 percent for thermal conductivity, 3.0 percent for flexural strength, and 2.0 percent for compressive strength, ensuring the reported values rest on a transparent methodological foundation.

The implications extend beyond the laboratory. The hemp shive and Pleurotus ostreatus composite appears suitable for non-load-bearing panels, partition walls, insulation boards, and lightweight structural components, applications where its combination of insulation efficiency, mechanical cohesion, and biodegradability offers genuine advantages over conventional materials. The authors emphasize that their mechanical values rest on limited replication and that future work must address scalability, fire behavior, moisture resistance, biological durability, ageing, dimensional stability, and industrial-scale manufacturability before building-scale deployment. Nevertheless, the study provides practical guidance for future research, industrial pilot projects, and policy-driven adoption of eco-composites. As the construction sector confronts its outsized carbon footprint, materials grown from fungal networks and farm waste are moving from curiosity toward credible contender, proving that the walls of future buildings might one day be cultivated in a matter of weeks.

Subject of Research: Thermal and mechanical performance of mycelium-agricultural waste biocomposites for building insulation

Article Title: Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance

Article References: Babenko, M., Kononets, Y., Kunes, R., Makys, P., Spalek, F., Sramhauser, K., Hanzal, P., Majernik, J., Zoubek, T., & Bartos, P. (2026). Mycelium–Agriwaste Biocomposites for Cleaner Building Insulation: Thermal and Mechanical Performance. Cleaner Engineering and Technology, Article 101334. https://doi.org/10.1016/j.clet.2026.101334

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101334

Keywords: mycelium biocomposites, building insulation, hemp shives, Pleurotus ostreatus, Ganoderma lucidum, thermal conductivity, agricultural waste, sustainable construction, circular economy, flexural strength, compressive strength, lignocellulosic substrates

Mycelium-based composites are grown rather than manufactured in the conventional sense. Living fungal hyphae are inoculated onto lignocellulosic substrates, where they colonize the particles and weave them into a coherent, self-binding matrix. After the growth phase, the material is dried and heat-treated, killing the fungus and stabilizing the structure. The result is a foam-like solid that is predominantly organic, compostable, and produced at ambient temperatures, in contrast to the energy-intensive polymerization and molding processes behind expanded polystyrene. Despite a decade of enthusiasm, the field has lacked careful, statistically controlled comparisons of how substrate formulation controls performance—precisely the gap the new study set out to close.

The team, led by Diana S. Ocegueda-Vega, Nelly Flores-Ramirez, and Salomon R. Vasquez-Garcia of the Universidad Michoacana de San Nicolás de Hidalgo, together with colleagues at the Tecnológico Nacional de México in Aguascalientes, produced five P. ostreatus composites labeled S1 through S5. Formulations S1 through S4 varied the proportions and particle sizes of oak wood chips, sawdust, and corn cob, while S5 served as a 100 wt% corn-cob reference. Particle architecture proved to be a decisive variable: scanning electron microscopy showed that the geometry of the underlying particles shaped how the fungal hyphae organized, branched, and consolidated the matrix. Coarse wood chips yielded an open, loosely knit structure, whereas finer particles enabled denser hyphal packing and better mechanical integration.

That microstructural difference translated directly into bulk properties. The sawdust-based formulation, S3, achieved the highest apparent density at 178.0 kilograms per cubic meter and the highest compressive strength at 0.63 megapascals. In contrast, the coarse wood-chip formulation S1, with its more open skeleton, delivered the weakest mechanical performance. For context, these densities sit in the same low range as commercial foam packaging materials, but the strength values remain modest—confirming that current mycelium composites are best suited to low-load protective applications such as cushioning inserts, rather than structural load-bearing roles.

Moisture behavior, a long-standing Achilles heel of fungal materials, received detailed treatment. Static water contact angle measurements on the dried surfaces ranged from 107.7 to 110.7 degrees across all five formulations—values comfortably above 90 degrees that indicate hydrophobic character, likely aided by fungal hydrophobin proteins that coat aerial hyphae. Notably, these contact angles did not differ significantly between formulations, suggesting that surface wettability is largely dictated by the mycelium itself rather than the substrate. However, bulk water absorption after 24 hours told a different story: values spread from 30.6 to 46.6 percent, with statistically significant differences. Dunnett-adjusted comparisons against the corn-cob reference showed that S1 absorbed significantly less water while S3 absorbed significantly more, a finding the authors attribute to differences in pore connectivity and particle porosity.

Surface hardness, measured with a Shore D durometer, spanned 27.6 to 37.7 across the formulations. S1 and S2 fell significantly below the corn-cob reference, whereas S3 and S4 were statistically indistinguishable from it. This gradient again tracks the density trend: harder, more consolidated surfaces come from tighter particle packing and more thorough hyphal colonization. The result gives manufacturers a practical dial—adjusting particle size distribution can shift surface robustness without changing the organism or the growth protocol.

Flexural testing exposed one of the field’s persistent limitations. Three-point bending strengths ranged only from 0.07 to 0.10 megapascals, and Tukey’s all-pairwise comparison detected no statistically significant differences among the formulations. In other words, no substrate recipe in this study meaningfully improved bending resistance, which remains the weakest mechanical attribute of mycelium composites. Interestingly, S4 and S5 did post the highest mean compressive and flexural moduli, indicating that stiffness and strength respond differently to formulation—stiffness can be tuned through substrate choice even when ultimate bending strength cannot, at least not within the ranges explored here.

The statistical framework of the study deserves attention because it strengthens the practical value of the findings. Beyond one-way analysis of variance and Tukey’s honestly significant difference test for all pairwise comparisons, the authors applied Dunnett-adjusted comparisons to test each experimental formulation S1 through S4 specifically against the corn-cob reference S5. This design mirrors what an industrial formulator would actually ask: not which recipe wins overall, but whether a given blend of local residues performs as well as, or better than, a baseline single-substrate material. The answers were property-dependent—no single formulation dominated every metric, underscoring that composite design must be matched to the end-use requirements of the packaging component.

The broader significance lies in waste valorization. Quercus castanea wood residues and corn cobs are abundant, inexpensive, and locally available in many agricultural regions, including central Mexico where the research was conducted. Growing packaging from these streams couples two sustainability gains at once: it diverts lignocellulosic waste from open burning or landfilling, and it displaces petroleum-derived foams that persist for centuries and fragment into microplastics. Because mycelium composites are produced at ambient temperature and pressure and are fully biodegradable, their lifecycle emissions profile contrasts sharply with conventional expanded polystyrene, even before accounting for end-of-life benefits.

Realistic caveats remain, and the authors state them plainly. The composites are appropriate for low-load protective packaging only when shielded from direct or prolonged moisture exposure, since bulk water uptake above 30 percent would degrade cushioning performance over time in wet conditions. Mitigation strategies reported elsewhere in the literature—such as beeswax or natural oil coatings—could extend service envelopes, but were outside the scope of this study. Scaling from laboratory samples to mass production will also demand consistent control of colonization time, humidity, and sterilization. Nonetheless, by quantifying exactly how substrate composition and particle architecture govern density, moisture response, hardness, and mechanical performance, the Mexican team has converted a promising but diffuse concept into an engineerable material platform, bringing grown packaging one measurable step closer to the shipping box.

Subject of Research: Physicomechanical properties of Pleurotus ostreatus mycelium biocomposites made from agroforestry residues for sustainable packaging

Article Title: Physicomechanical properties of Pleurotus ostreatus mycelium biocomposites from agroforestry residues for sustainable packaging

Article References: Ocegueda-Vega, D. S., Flores-Ramirez, N., Vasquez-Garcia, S. R., Martínez-Flores, H. E., Velazquez-Becerra, C., & Meza-de Luna, A. (2026). Physicomechanical properties of Pleurotus ostreatus mycelium biocomposites from agroforestry residues for sustainable packaging. Polymer Bulletin, 83(11), Article 630. https://doi.org/10.1007/s00289-026-06683-0

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06683-0

Keywords: mycelium composites, Pleurotus ostreatus, sustainable packaging, agroforestry residues, biodegradable materials, lignocellulosic waste, water absorption, mechanical properties, biocomposites, waste valorization, circular economy, Polymer Bulletin