Cytological analysis of mycelial incompatibility in Helicobasidium mompa.

When the mycelia of Helicobasidium mompa encounter mycelia with a different genetic background, distinct demarcation lines form. The hyphae of H. mompa induce heterogenic incompatibility accompanied by active programmed cell death (PCD) process. In this study, we observed hyphal interaction between compatible and incompatible H. mompa pairs by means of light and electron microscopy. PCD started with one of the two approaching hyphae. Heterochromatin condensation and genomic DNA laddering were not observed. Moreover, cell damage began with the tonoplast and continued with the plasma membrane and nuclear membrane, suggesting that the PCD observed in heterogenic incompatibility of H. mompa is a vacuole-mediated process.