Parasexuality is the fusion and intermixing of nuclei and mitochondria of different fungal isolates without meiosis or formation of specialized sexual structures. Parasexuality is well defined for some fungi, but not for the phytopathogenic fungal genus, Phytophthora. The vast differences in Phytophthora host range, large number of pathogenic species available, and history of epidemics make this genus an excellent system in which to study the genetics that define host range and pathogenicity. New pathogenic races of Phytophthora are constantly appearing, but the source of these new races is unknown. As most species either do not undergo a sexual cycle or do not outcross, parasexuality may supply a recombination mechanism that generates new pathogenic races. We propose to develop isolate-specific hybridization probes to follow the nuclear and cytoplasmic genomes of phytophthora through fusion and into the asexual spores that are the main disease vector. To design these probes, we will first amplify by the polymerase chain reaction the nuclear and mitochondrial ribosomal genes of the fungi to be fused. We will screen for restriction fragment length polymorphisms in the amplified genes. The polymorphic fragments will be sequenced and isolate-specific probes synthesized from these sequences. The molecular diagnostic techniques we develop while training students to handle a fungal pathogen, as well as information on the effect of parasexuality on pathogenicity, may be applied to fungal pathogens of humans, such as Candida and Cryptococcus species. The research has been organized into one semester modules to provide a successful and meaningful research experience along with training in modern techniques of molecular biology. Such experiences will encourage and enable these students to pursue a research career in a biomedical discipline.
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