heterothallism

Heterothallism refers to a reproductive characteristic in some fungi where individuals from the same mating type are sterile, but individuals from different mating types can cross-fertilize. This is in contrast to homothallic fungi, where a single individual's sex organs are self-compatible, and no second individual is needed for sexual reproduction.12

In fungi, sexual reproduction involves the fusion of two compatible haploid nuclei, which is essential for genetic variability and adaptation. This process typically includes plasmogamy (fusion of protoplasts), karyogamy (fusion of nuclei to form a zygote), and meiosis (reduction of chromosome number). Heterothallic fungi require the presence of thalli of different mating types for sexual fusion to occur, often designated as + and − or A and a.2