Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: 8/10/1996
Publication Date: N/A
Technical Abstract: Each of 124 isolates of F.o.v. secreted polyketide naphthazarin quinones of which bikaverin and norbikaverin were identified. Most of 16 avirulent isolates of F. oxysporum failed to secrete the polyketides and synthesized lower concentrations. Thus, the polyketide toxins may have a role in virulence. The production of these toxins was highly regulated by pH, carbon/nitrogen ratios, and availability of minor elements, especially iron. The synthesis of polyketides increased progressively as pH was reduced from 7.0 and as carbon/nitrogen ratios were increased by reducing the amount of nitrogen normally added to media. Glutamine inhibited bikaverin synthesis, even at low nitrogen levels, indicating that it may be a key regulator of the bikaverin pathway. While bikaverin and norbikaverin are the major polyketides accumulated in synthetic media at pH 4.5 and below, these compounds apparently are converted at pH 5.0 and above to a family of quinones and tetralones that are more water soluble than bikaverin. These polyketides are the major natural products formed when F.o.v. isolates are grown on sterilized stems of susceptible cotton cultivars.