Biological activity of the isomeric forms of Helminthosporium sacchari toxin and of homologs produced in culture.
In further studies [RPP 61, 2318] with H. [Drechslera] sacchari toxin, which consists of 3 isomeric bis-5-O-(β-galactofuranosyl)-β-galactofuranosides (A, B and C) differing in the position of 1 double bond in the sesquiterpene aglycone, max. inhibition of dark CO2 fixation in susceptible sugarcane (CP52-68) occurred within 30-40 min. Amounts necessary for 50% inhibition values typically were c. 1.7 µsmallcap˜M for natural toxin mixture (c. 2:3:5 for A:B:C) and 4, 6 and 0.7 µsmallcap˜M for A, B and C respectively. Other fractions from pathogen cultures are described. Lower toxin homologues were not toxic to clone CP52-68 but protected sugarcane from the effects of the toxin. The results are discussed, in relation to the mode of action of the toxin.