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Research has linked chlorothalonil exposure to declines in pollinator health due to an increased likelihood of Nosema ceranae infection, altered gut microbial community, and a reduction in colony fitness and survival of honey bees (Apis mellifera). Therefore, a reduction in use of chlorothalonil, a large component of cucurbit disease management, may be needed. Without chlorothalonil, a widely used, broad-spectrum fungicide, the fungal and oomycete pathogens in cucurbit cropping systems can more quickly evolve resistance to targeted fungicides due to a limited number of efficacious modes of action and frequent sprays. Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, for example, has a short life cycle, experiences repeated applications of fungicides, and has a wide host range making it a high risk for fungicide resistance development. Our research focused on the development of an alternative fungicide spray program in melons to reduce the use of chlorothalonil, identifying the fungicide insensitivities of local P. cubensis populations and determining the efficacy of fungicides used to manage cucurbit downy mildew, and investigating the clade-host relationship and formation of oospores in regional P. cubensis samples. Efficacy on two important diseases in melon, powdery mildew and gummy stem blight, can be largely maintained without chlorothalonil but anthracnose control was not adequate without the inclusion of chlorothalonil. Currently, there are a number of highly effective targeted fungicides available to growers for management of cucurbit downy mildew including oxathiapiprolin, zoxamide + chlorothalonil, chlorothalonil, and cyazofamid. Our research shows evidence of P. cubensis clade-host associations, with clade 1 preferentially infecting acorn and summer squash (Cucurbita pepo), butternut squash (Cucurbita moschata), and watermelon (Citrullus lanatus), while clade 2 preferentially infects cucumber (Cucumis sativus). Melons (Cucumis melo) a

The mycoparasitic oomycete Pythium oligandrum is homothallic, producing an abundance of thick-walled spiny oospores in culture. After mining a cDNA sequence dataset, we identified a family of genes that code for small tyrosine rich (Pythium oligandrum small tyrosine rich (PoStr)) proteins. Sequence analysis identified similarity between the PoStr proteins and putative glycine-rich cell wall proteins from the related plant pathogenic oomycete Pythium ultimum, and mating-induced genes from the oomycete Phytophthora infestans. Expression analysis showed that PoStr transcripts accumulate during oospore production in culture and immunolocalisation indicates the presence of these proteins in oogonial and oospore cell walls. PoStr protein abundance correlated positively with production of oogonia as determined by antibiotic-mediated oogonia suppression. To further characterise the role of PoStr proteins in P. oligandrum oospore production, we silenced this gene family using homology-dependent gene silencing. This represents the first characterisation of genes using gene silencing in a Pythium species. Oospores from silenced strains displayed major ultrastructural changes and were sensitive to degradative enzyme treatment. Oogonia of silenced strains either appeared to be arrested at the mature oosphere stage of development or in around 40 % of the structures, showed a complete suppression of oospore formation. Suppressed oogonia were highly vacuolated and the oogonium wall was thickened by a new inner wall layer. Our data suggest PoStr proteins are probably integral structural components of the normal oospore cell wall and play a key role in oospore formation., QC 20130524