Adaptations of Sporocarps of the Basidiomycete Flammulina velutipes (Agaricales) to Lower Humidity

Developing sporocarps are less likely to mature if the relative humidity is not near saturation. Sporocarps that do mature under dryer conditions usually produce fewer spores. For some genotypes this detrimental effect is much greater than for others. Isolates were collected from around the world and cultured. Spore production at 100% and 80% relative humidity was measured, and 10 populations, representing the variety of tolerances to dryer conditions, were chosen. Single mycelial isolates from each population were cultured under identical conditions to constitute 10 putatively distinct genotypes Genetically identical emerging sporocarps of each genotype were excised and desiccated in a 16 C chamber that held relative humidity at 80%. Surface area and weight were measured at excision and weight remeasured after 6, 12, and 24 h of desiccation. Dry weight was measured after 2 more d under silica gel. Water loss rates decreased with sporocarp surface area. The rate of water loss was proportional to about the 3/4 power of surface area However, surface area varies significantly among genotypes, and intrinsic resistance to water loss may also vary among genotypes. To separate these effects, a global surface area effect and average, genotype-specific intrinsic resistances to water loss were estimated simultaneously. Water loss was then proportional to about the 7/8 power of surface area. These proportionality constants (intrinsic water loss rates) were calculated for each sporocarp. They varied significantly among genotypes. Hydration (water content expressed in units of dry weight), with an initial average of about 10, varied significantly among genotypes. Genotypes with initially fastest intrinsic water loss rates tended to have smaller and less well hydrated sporocarps that dried out quickly. Because of these contrary trends, hydration was not correlated with water loss rate during the first 6 h. During the next 6 h, water loss rates remained uncorrelated with hydration for wetter sporocarps, but for dryer sporocarps decreased with decreasing hydration. Time from emergence until hydration of each sporocarp would fall to various thresholds below five (when critical drying might be presumed to have occurred) was estimated for each sporocarp and varied significantly among genotypes; those taking longer usually have slower intrinsic drying rates, larger size, higher initial hydration, and greater spore production in dryer environments.