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The grapevine trunk is colonized by a diverse community of fungi, collectively referred to as the endophytic mycota. These communities are shaped by different factors, both biotic and abiotic, including diseases status. Pathogens and beneficial fungi play important roles in grapevines, and these endophytes are considered key players that enhance plant growth, reduce plant disease and can improve the ability to adapt to stress. Some pathogenic fungi are known to be the causal agents of grapevine trunk disease (GTD) and are considered latent pathogens. Studying variation in their disease expression in response to the endomycobiome can guide the identification of disease suppressive microbial antagonists against (or that interact with) GTDs pathogens. Understanding of the processes by which these endophytic fungi initiate, maintain, or modulate trunk diseases is lacking. This thesis focused on characterising the taxonomic diversity and the composition of the trunk endophytic mycota (endomycobiome) colonizing symptomatic and asymptomatic trunk tissues of old and young vines from different management systems, by using both culture- dependent and high-resolution culture-independent approaches. Samples were taken from nine vineyards in the Marlborough region. The samples encompassed 60 mature vines (>10 years old) and 30 young vines (

Gibberella zeae (anamorph Fusarium graminearum) is a homothallic ascomycete pathogen that is responsible for causing Fusarium head blight (FHB) of wheat and small grains. In addition to causing a reduction in yield, harvested grain is frequently contaminated with trichothecene mycotoxins that are harmful for human and animal health. Use of wheat varieties with resistance to FHB is an important strategy to lower its impact. In order to produce varieties with durable resistance, we must understand the origin and degree of genetic diversity present in the pathogen population. In my research, I focused my efforts on an investigation of the role of mating and sexual development in the generation of genotypic and phenotypic variability in G. zeae. The goal of one part of my work was to develop new genetic markers that can be used to monitor out-crossing and genetic diversity in the population. I also optimized gene deletion protocols for G. zeae so that I could produce mutant and control strains to address my research hypothesis that MAT genes play a direct role in pathogenicity. Application of novel repetitive RFLP probes to a group of G. zeae isolates originating from and near Kentucky revealed a surprisingly high degree of diversity in these local populations. Diversity between locations was greater than that within locations, suggesting the relative importance of local inoculum sources. The probes were also useful as genetic markers for segregation analysis. I crossed two genetically closely related, and commonly used, laboratory strains of G. zeae and found that this resulted in transgressive segregation for both aggressiveness and toxigenicity. I showed that the very high and very low levels of aggressiveness and toxigenicity in transgressive segregants are heritable. I also showed that selfing produced a higher degree of diversity in these traits among the progeny than was observed among conidial progeny. This suggests the presence of epigenetic factors that impact pathogenicity. Sexual behavior in G. zeae is under the control of MATing type genes. I deleted the complete MAT1 locus, and the MAT1-1-1, and MAT1-2-1 genes separately. Deletion of each of the targeted sequences produced the expected shifts in fertility phenotype. The mat1KO strains became asexual, while mat1-1-1KO and mat1-2-1KO strains shifted to obligate heterothallism. Deletion of the MAT1-1-1 and MAT1-2-1 genes had a negative effect on aggressiveness and mycotoxin production in planta, but deletion of the complete MAT1 locus had no effect. The set of mutant and ectopic control strains that I generated will be a useful asset that will be made available to the research community.

The gradual rewiring of transcriptional circuits over evolutionary timescales is a major source of the diversity of life on the planet. Studies in animals have shown how seemingly small changes in gene regulation can have large effects on morphology and physiology and how selective pressures can act on these changes. The underlying principle in these studies is that gene regulation is modular--changes can be made to the expression of a gene at one place and time, without affecting the expression of that gene at other places and times. Genome-wide studies in single cell yeasts, including those described here, have uncovered evidence of massive transcriptional rewiring, indicating that even closely related species regulate their genes using surprisingly different circuitries. The work described in this thesis begins to suggest some general principles guiding the evolution of transcription circuits. Mechanisms by which large sets of co-expressed genes can be rewired (without disrupting co-expression) are proposed and combinatorial regulation is implicated as a catalyst for change in transcriptional networks.

Se estudian 24 especies de Ascomycetes recolectados durante las primaveras de 1978 y 1979 en pinares de Pinus sylveatris L. repartidos por el NE navarro. Cada especie, en las localidades reseñadas, se acompaña de un breve comentario ecológico. Un estudio descriptivo e iconográfico se ha llevado a cabo para todos los taxa.