Pathogen oomycetes

ROS production by an extracellular agar oligosaccharide oxidase Appressoria formation in the specific pathogenic oomycete Pythium porpyrae... 

Specific sensitivity of zoospores to the host-derived compounds has also been found in other pathogenic oomycetes. Kerwin et al. (1992) observed that Py. marinum exhibited encystment on the surfaces of red algae (its hosts) but not on green or brown algae (non-host) [58], Galactose or anhydrogalactose contents in the surface of red algae were found to be responsible for such a specific response. Similarly, fish and mosquito larval parasites showed positive chemotaxis toward their host surface chemical constituents [59-62]. 

Unlike fungal saponinases, little is known about hydrolytic enzymes secreted by phytopathogenic oomycetes or their role in pathogenicity [75, 76]. Although innate resistance is believed to be the main mechanism by which oomycetes avoid the toxicity of saponins (see above), some oomycetes have been found to produce saponin hydrolases [77], as well as other glycosyl hydrolases [76]. 

Novel cyclohexenones, acremines A-F (109-114), were isolated from a mycoparasitic Acremonium sp. from the oomycete pathogen Plasmopara viticola on Vitis vinifera cv. Regina blanca. Compounds 109-112 inhibited germination of the pathogen, and the most activity was shown by acremine C (111). This work may lead to a mechanism for the mycocidal activity of mycoparasitic fungi. 

Until about ten years ago, protectant foliar fungicides (such as ethylene bis-dithiocarbamates and phthalimides) and soil sterilants (such as vapam or methylbromide) were the only chemical means of controlling diseases caused by Oomycetes. These compounds are nonspecific biocides affecting many vital cell processes of both the pathogen and the host plant. This means that they are non-selective,... 

Table I. Major Plant Pathogens In the Class Oomycetes (29)...

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