Characterization of hybridization events between three closely related species of Ceratocystis

Abstract

Hybridization stands out as a pivotal driver of evolution and genome adaptation, making it an important concept to study. Understanding the likelihood of hybridization in plant pathogens holds critical significance, as it related to the potential emergence of highly destructive novel plant pathogen species that may surpass their parental strains in competition or exploit previously unoccupied ecological niches. The review presented in this dissertation provides a comprehensive definition of hybridization and examines the phenotypic and genotypic traits characterizing hybrids. Examples of plant-pathogenic fungal hybrids that have caused significant economic damage are provided, underscoring the importance of these species as plant pathogens. The remainder of this dissertation is focussed on hybridization among Ceratocystis species. For the first time successful hybridization between fertile Ceratocystis species were demonstrated. This was accomplished using a novel PCR RFLP protocol that could discriminate between self-fertilization and outcrossing events among the species. Interestingly, evidence of biparental mitochondrial inheritance was found within some of these crosses although the importance of this on the biology of the hybrids has not been considered. This study lays the foundation for future work on the biology of Ceratocystis hybrids produced from self-fertile hybridization, and how these might be different from self-sterile hybridization events. An in-depth analysis uncovered segregation distortion and genome mosaicism in the genomes of interspecific hybrids produced in a previous study. This was studied using a SNP based approach that scored the presence of variation among the genomes of 69 hybrid progeny produced from self-sterile crosses. Some de novo mutations were also identified at a mutation rate comparable to other fungal species. This research contributes to the growing body of knowledge on hybridization. Ceratocystis species are capable of interspecific hybridization and serve as an excellent model for further research on the dynamics of this process in fungi also capable of self-fertilization. Although the genomes of Ceratocystis hybrids were investigated, further meticulous analyses are likely to provide further invaluable insights into the genetic and genomic characteristics of naturally occurring hybrids.