|Zheng, Xiuting - Texas A&M University|
|Bell, Alois - Al|
|Stipanovic (ret), R - US Department Of Agriculture (USDA)|
|Nichols, Robert - Cotton, Inc|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2018
Publication Date: 11/1/2018
Citation: Puckhaber, L.S., Zheng, X., Bell, A.A., Stipanovic (Ret), R.D., Nichols, R.L., Liu, J., Duke, S.E. 2018. Differences in active defense responses of two Gossypium barbadense L. cultivars resistant to Fusarium oxysporum f. sp. vasinfectum Race 4. Journal of Agricultural and Food Chemistry. 66:12961-12966. https://doi.org/10.1021/acs.jafc.8b05381.
Interpretive Summary: A highly virulent fungal wilt pathogen of cotton [race 4 (VCG0114) genotype of Fusarium oxysporum f. sp. vasinfectum (CA Fov-4)] was identified for the first time in the western hemisphere in 2002 in cotton fields in the San Joaquin Valley of California, and in 2017 it appeared in West Texas. The virulent nature of this pathogen has raised concerns within the Cotton Industry and new sources of resistance are being pursued. The Gossypium barbadense L. cotton cultivar Seabrook Sea Island 12B2 (SBSI) is resistant to another wilt pathogen, Verticillium dahliae, and we showed it is also resistant to CA Fov-4. We earlier demonstrated that when SBSI is infected with V. dahliae, it produces a mixture of antifungal chemicals more rapidly than susceptible plants. We hypothesized that this rapid response may also be responsible for it resistance to CA Fov-4. To test this hypothesis we compared the concentration of these antifungal compounds in SBSI with that found in the CA Fov-4 resistant Pima-S6 and susceptible Pima-S7. After 24 hours the concentration of antifungal compounds increased more quickly in SBSI compared to Pima S-6 and Pima S-7. This indicated that a different resistance mechanism is operating in SBSI. To further substantiate our hypothesis, SBSI plants were crossed with Pima-S6. Segregation of F2 progeny from ‘SBSI’ x ‘Pima S-6’ crosses gave some highly susceptible plants. This supports our hypothesis that SBSI and Pima-S6 contain separate genes for resistance. In addition, a new antifungal chemical was identified for the first time in nature from the diseased plants.
Technical Abstract: A highly virulent race 4 genotype of Fusarium oxysporum f. sp. vasinfectum (Fov) was identified for the first time in the western hemisphere in 2002 in cotton fields in the San Joaquin Valley of California. The Gossypium barbadense L. cotton cultivars 'Seabrook Sea Island 12B2' ('SBSI') and 'Pima S-6' are resistant to Fov race 4. Active defense responses were quantitated by monitoring the accumulation of antimicrobial terpenoids (i.e., phytoalexins) in inoculated stem stele tissue in these cultivars. The increase in the concentration of the most toxic phytoalexins was statistically faster after 24 h in 'SBSI' compared to 'Pima S-6'. The sesquiterpenoid hemigossylic acid lactone, which was observed for the first time in nature, also accumulated in diseased plants. Neither hemigossylic acid lactone nor the disesquiterpenoids gossypol, gossypol-6-methyl ether, and gossypol-6,6'-dimethyl ether showed toxicity to Fov. Segregation of F2 progeny from 'SBSI' x 'Pima S-6' crosses gave a few highly susceptible plants and a few highly resistant plants, indicating separate genes for resistance in the two cultivars.