Abstract:
Hybridization is recognized as a notable driver of evolution and adaptation, which closely
related species may exploit in the form of incomplete reproductive barriers. Three closely related
species of Ceratocystis (i.e., C. fimbriata, C. manginecans and C. eucalypticola) have previously been
shown to hybridize. In such studies, naturally occurring self-sterile strains were mated with an
unusual laboratory-generated sterile isolate type, which could have impacted conclusions regarding
the prevalence of hybridization and inheritance of mitochondria. In the current study, we investigated
whether interspecific crosses between fertile isolates of these three species are possible and, if so,
how mitochondria are inherited by the progeny. For this purpose, a PCR-RFLP method and a mitochondrial
DNA-specific PCR technique were custom-made. These were applied in a novel approach
of typing complete ascospore drops collected from the fruiting bodies in each cross to distinguish
between self-fertilizations and potential hybridization. These markers showed hybridization between
C. fimbriata and C. eucalypticola and between C. fimbriata and C. manginecans, while no hybridization
was detected in the crosses involving C. manginecans and C. eucalypticola. In both sets of hybrid
progeny, we detected biparental inheritance of mitochondria. This study was the first to successfully
produce hybrids from a cross involving self-fertile isolates of Ceratocystis and also provided the first
direct evidence of biparental mitochondrial inheritance in the Ceratocystidaceae. This work lays the
foundation for further research focused on investigating the role of hybridization in the speciation of
Ceratocystis species and if mitochondrial conflict could have influenced the process.
