Submitted to: International Congress of Plant Pathology Abstracts and Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 10, 1998
Publication Date: N/A
Technical Abstract: Plants employ a number of strategies to protect themselves from pathogens. These include anatomical structures, antimicrobial enzymes, polymers, and low molecular weight antibiotics (either preformed or induced [i.e., phytoalexins]). In the case of cotton, the latter are sesquiterpenoids aldehydes and naphthofurans. These terpenoids appear to be particularly important in protecting the plant from soilborne pathogens. These phytoalexins are synthesized in diseased tissues as part of an active defense reaction. Resistant cotton cultivars respond quicker and produce higher concentrations of the phytoalexins after infection with Verticullium dahliae as compared to susceptible cultivars. The phytoalexins desoxyhemigossypol (dHG), desoxyhemigossypol-6-methyl ether (dMHG), hemigossypol (HG), and hemigossypol-6-methyl ether (MHG) are synthesized as an active defense response by the paravascular cells appressed to the xylem mvessel. Recognition of the pathogen appears to be at or near its full potential in resistant cultivars. We believe increasing the potency of the phytoalexins offers a plausible avenue of research to further increase resistance. From studies on the toxicity of these compounds to these pathogens, the following conclusions can be deduced: 1)dHG is the most toxi against all of these pathogens, and 2)Methylation of the phenolic group in the C-6 position inevitably reduces the toxicity to the pathogens to one- half or less. We are attempting to sequence and clone the dHG-O- methyltransferase (dHG-OMT) enzyme. Since methylation of the phytoalexins reduces toxicity, expression of antisense constructs derived from dHG-OMT clones should provide a more potent mixture of the phytoalexins and lead to an increase in resistance.