Project Number: 6202-22000-026-00
Project Type: Appropriated

Start Date: Apr 09, 2007
End Date: Apr 08, 2012

Objective:
Develop control strategies that will minimize yield and fiber quality losses caused by nematodes and microbial pathogens that are emerging as significant impediments to sustained profitability by cotton producers. Of particular concern is the spread of the reniform nematode in the southern U.S. and south Texas, the emergence of a new disease called South Carolina seed rot in the southeast, the introduction of a particularly virulent isolate of Fusarium oxysporum f. sp. vasinfectum that was inadvertently imported from Australia on cottonseed and that could adversely affect 50% of U.S. cotton production, and the identification of race 4 of F.o.v. for the first time in the U.S. To address these emerging diseases we will: 1) Complete the introgression of reniform nematode (Rotylenchulus reniformis) resistance from Gossypium longicalyx and G. barbadense into Upland cotton (G. hirsutum) and develop markers for the trait suitable for marker-assisted selection; 2) Describe mechanisms of pathogenesis and identify virulence genes in the bacterial pathogen(s) causing the disease known as South Carolina seed and boll rot; and develop detection methods for the pathogen(s); and 3) Determine whether fusaric acid contributes to differences in virulence among races and biotypes of Fusarium oxysporum f. sp. vasinfectum to provide a basis for developing strategies for controlling Fusarium wilt of cotton.

Approach:
1) Introgression of Reniform Nematode Resistance: Standard procedures for cotton flower emasculation and pollen transfer will be followed for backcross breeding. After each cross, progeny will be bioassayed for resistance to the reniform nematode, and the most highly resistant progeny will be retained for subsequent crossing, self seed generation, and DNA extraction for marker development. Plants will be grown under field conditions and evaluated for agronomic performance. Standard techniques and commercially available technology will be used for cotton DNA extraction. PCR amplification, electrophoresis, and fragment size detection will be utilized to identify molecular markers. 2) South Carolina Seed and Boll Rot: A mutagenesis system will be used to identify genes involved in production, regulation, and/or secretion of factors that cause boll rot. Based on these results, a set of predicted gene sequences associated with pathogenicity will be used to develop a PCR based method for detecting seed and boll rotting bacteria in field samples. Bolls from greenhouse grown plants will be used in initial testing to determine the efficacy of the developed amplification system. 3) Relation of Fusaric Acid to Virulence of Fusarium oxysporum f. sp. vasinfectum (F.o.v.): Biotypes of F.o.v. will be monitored for their ability to produce high levels of phytotoxins, and virulence of biotypes will be determined. The biosynthesis of those phytotoxins that correlate with virulence will be determined by feeding labeled substrates to the pathogens. Genes involved in the biosynthesis of these phytotoxins will be identified. Knock-out mutants will be generated to assess the role of specific phytotoxins in virulence and pathogenicity.