Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1999
Publication Date: N/A
Interpretive Summary: Losses to US cotton producers from fungal wilt diseases were estimated to be in excess of 245,000 bales of cotton in 1998. Evidence suggests that compounds, called phytoalexins, that are produced by the plant when it is infected, are important in protecting the plant from these pathogens. In a time course investigation, we found phytoalexins are produced significantly yearlier in a resistant cultivar as compared to a susceptible cultivar. We also found that a critical enzyme involved in the biosynthesis of the phytoalexins is present earlier and in higher concentrations in the resistant cultivar. These findings are consistent with the hypothesis that the phytoalexins are an essential component in the cotton plant's response to infection by these wilt pathogens.
Technical Abstract: Phytoalexin biosynthesis is induced earlier in resistant cotton [Seabrook Sea Island 12B2 (SBSI), Gossypium barbadense] than in susceptible cotton (Rowden, G. hirsutum) after inoculation with a defoliating isolate of the pathogen Verticillium dahliae. This is demonstrated by significantly higher levels of phytoalexins in SBSI 12 hours after inoculation. Furthermore, by forty-eight hours after inoculation of SBSI, the phytoalexins hemigossypol and desoxyhemigossypol achieved levels (23.9 micrograms and 10.5 micrograms/mg fresh tissue, respectively) sufficient to completely inhibit conidia germination. Rowden required 96 hours to attain comparable levels. Similarly, the activity of delta-cadinene synthase (delta-CS), a key enzyme required for the biosynthesis of the phytoalexins, increased more rapidly in the resistant cotton than in the susceptible. The changes in phytoalexin concentrations and enzyme activity are consistent with the hypothesis that phytoalexins are an essential component in protecting the plant from V. dahlia.