Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: August 1, 2009
Publication Date: August 5, 2009
Citation: Bell, A.A., Liu, J., Stipanovic, R.D. 2009. Secondary metabolites and toxins of Fusarium - what is causing disease symptoms. 2009 American Phyopathological Society Annual Meeting, August 1-5, 2009, Portland, Oregon. p.55. Technical Abstract: Fusarium species produce a plethora of phytotoxic secondary metabolites. In the case of various races of Fusarium oxysporum f. sp. vasinfectum (F.o.v.) that attacks cotton, alfalfa, okra and other crops, many of these metabolites are derived from the polyketide biosynthetic pathway. The recent discovery of races and pathotypes that had not previously been found in the U.S. is of particular concern to the cotton industry. In addition, a uniquely different and particularly virulent pathotype was identified in Australia in the 1992/1993 growing season. This F.o.v. is now widespread in Southern Queensland and under severe infestation plant mortality exceeds 60%. Spores of this F.o.v. pathotype were inadvertently introduced into the U.S. on at least one shipload of cottonseed imported into the U.S. as feed for dairy cows. This pathotype has not yet been observed in U.S. fields. The newly discovered F.o.v. race 4, however, is of increasing concern due to losses of Pima cotton in California. Both race 4 and the Australian isolates attack the plant at the seedling stage. In our studies of race 4 and the Australian isolates we found both produce prodigious quantities of fusaric acid when grown on Czapek media. Others have reported that fusaric acid is derived in part via a polyketide synthase (PKS). We have now confirmed the origin of fusaric acid via the PKS pathway using 13C-labelled compounds and have begun a search for the corresponding PKS genes involved in its biosynthesis. We are currently investigating the role of fusaric acid in the pathogenicity of these F.o.v. isolates. Our results on the biosynthesis of fusaric acid, identification of associated PKS genes and their knockouts will be presented.