Biosynthesis of fusaric acid by Fusarium oxysporum f. sp. vasinfectum

• Published in: Phytopathology Vol. 98; no. 6; p. S151
• Main Authors: Stipanovic, R D, Wheeler, M H, Liu, J, Puckhaber, L S, Bell, A A
• Format: Journal Article
• Language: English
• Published: 01.06.2008
• Subjects: Fusarium oxysporum; Gossypium hirsutum
• ISSN: 0031-949X

A genetically unique biotype of the Fusarium wilt pathogen was first recognized in wilted and dead Upland cotton (Gossypium hirsutum) seedlings in Australia in 1993. Since that time, the disease has spread rapidly with losses >90% in some Australian fields where it was first discovered. Australian biotypes have been inadvertently introduced into the U.S. in at least two shiploads of cottonseed imported into California for dairy feed. These biotypes are a threat to 4-6 million acres of cotton grown on heavy alkaline soils in the U.S. There is limited resistance to the Australian Fusarium oxysporum f. sp. vasinfectum (F.o.v.) biotype. The Australian biotypes have not yet been found in California cotton fields; however, F.o.v. race 4 was identified for the first time in California in 2000. Race 4 causes severe Fusarium wilt in Pima cultivars (G. barbadense). The phytotoxin fusaric acid has been identified within cotton infected with F.o.v. Both the Australian F.o.v. biotype and race 4 produce prodigious quantities of fusaric acid in culture. To determine the importance of this phytotoxin to pathogenicity, we investigated the biosynthesis of fusaric acid using single and doubled labelled 13C-acetate and DL-4-13C-aspartate. Our findings substantiate those of earlier investigators showing that three molecules of acetate are introduced into fusaric acid at carbon atoms 5, 6, 7, 8, 9 and 10, while those from carbons 2, 3, 4 and 11 are derived from aspartate or oxaloacetate.