Rhizopogon roseolus basidiospore germination decreases as the fruiting bodies mature and the spore wall becomes more complex

Abstract

Rhizopogon roseolus (Corda) Th. Fr. is a basidiomycete truffle that is considered edible. Its gleba changes color from white to beige to brown as it matures. Although ultrastructural changes in the spore wall have been linked to the maturation of the fruiting body, little is known regarding the relationship between spore germination success and the ultrastructure of the spore wall. We examined spore germination on agar plates and analyzed the spore wall ultrastructure using transmission electron microscopy (TEM). Fruiting bodies, collected from a pine forest, were classified into three developmental stages based on gleba color, and the germination success was evaluated at each stage. Variability in the spore germination rate was observed between individual fruiting bodies. The peak germination rate was recorded for the spores from the fruiting bodies in the beige glebal stage, and the rate was lower in the brown glebal stage. When spore wall structures were studied using TEM, the spore wall was found to be multilayered upon maturation of the fruiting body. The spores of the beige glebal stage showed three types of spore walls, namely two-layered, three-layered, and four-layered spore walls. On the other hand, the spores of the brown glebal stage showed predominantly four-layered spore walls. These results indicate that spore germination of R. roseolus decreases as the fruiting body matures and the spore wall becomes more complex.