Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: January 15, 2008
Publication Date: January 15, 2008
Citation: Stipanovic, R.D., Wheeler, M.H., Puckhaber, L.S., Bell, A.A., Liu, J. 2008. NMR structural studies on the biosynthesis of fusaric acid from Fusarium oxysporum f. sp. vasinfectum [abstract]. Proceedings of Beltwide Cotton Conferences, January 8-12, 2008, Nashville, Tennessee. 2008 CDROM. Technical Abstract: Fusarium wilt of cotton is caused by Fusarium oxysporum Sclecht f. sp. vasinfectum (Atk.) Sny. and Hans (F.o.v.). F.o.v. occurs in most countries where cotton is grown. Losses in cotton yield can be especially devastating on farms where soil conditions, nematode populations, and indigenous populations of the pathogen favor the disease. Cotton producers lost >$24M in the U.S. as a result of infections by F.o.v. race 1 in 2005. A genetically unique biotype of the Fusarium wilt pathogen was first recognized in wilted and dead Upland cotton seedlings in Australia in 1993. Since that time, the disease has spread rapidly despite strict containment practices. On some Australian farms where it was first discovered, losses above 90% have forced cotton production to be abandoned. Australian biotypes have been inadvertently introduced into the U.S. in at least two shiploads of cottonseed imported into California for dairy feed. Specifically, 17 F.o.v. isolates per 10,000 seed were identified, twelve of which show a molecular relationship to race 3 of F.o.v., and one of these was vegetatively compatible with the Australian biotype. The Australian F.o.v. strain is favored by heavy clay soils and does not require nematodes for severe disease. As such, it is a threat to 4-6 million acres of cotton grown on heavy alkaline soils in the U.S. (i.e., Texas to California). There is limited resistance to the Australian 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 the U.S. (California) in 2000, and races 3 and 8 were recently identified in both California and Louisiana. Race 4 causes severe Fusarium wilt in Pima cultivars (G. barbadense). No resistance against race 4 has yet been found in Pima cultivars, although tolerance has been found in a few lines. The phytotoxin fusaric acid (FA) has been identified within cotton infected with F.o.v. Both the Australian F.o.v. biotype and race 4 produce prodigious quantities of the phytotoxin FA in culture. To investigate the importance of this phytotoxin to pathogenicity, we investigated the biosynthesis of FA using 13C- labelled acetate (1-13C-, 2-13C- and 1,2-13C-acetate). 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.