Purification, chemical characterization, host-specificity, bioassay, mode of action, and herbicidal use of the toxin produced by Alternaria brassicae

A chromatographic procedure was developed to purify the toxin produced in culture by Alternaria brassicae. The procedure included gel filtration, adsorption on charcoal, silicic acid chromatography and high pressure liquid chromatography. Negative ninhydrin reaction of the toxin and the presence of amino acids in the toxin hydrolysate indicated that the toxin is a cyclic peptide. Molecular weight, ninhydrin reaction, amino acid composition, proton nuclear magnetic resonance spectrum, HPLC retention time, and symptomatology and activity of the toxin on hosts and nonhosts of A. brassicae were identical with those of destruxin B. The degrees of toxin sensitivity of all plants tested were correlated with their degrees of susceptibility to A. brassicae, suggesting that the activity of A. brassicae-toxin is host-specific. This is the first report on the host-specific nature of a toxin produced by A. brassicae.; Comparison of four toxin bioassay methods indicated that the pollen germination bioassay was the most sensitive, quantitative, fast, and simple method for destruxin B. Significant inhibition of both germination and pollen tube growth of Brassica campestris var. yellow sarson pollen was observed after only 30 min of incubation with 2.5 {dollar}mu{dollar}g/ml destruxin B, and complete inhibition of germination was observed at 7.5 {dollar}mu{dollar}g/ml of the toxin.; Absence of rapid electrolyte leakage suggested that the plasma membrane may not be the initial site of destruxin B action. Non-sensitivity of protoplasts from the susceptible host and sensitivity of leaves and pollen from the same host appear to indicate that the target site of destruxin B is in the region of the cell wall and/or the periplasmic space.; Differential germination response of pollen from susceptible and resistant plants indicated that in vitro microspore culture in the presence of destruxin B is likely to be an excellent system for in vitro selection for A. brassicae resistance.; Destruxin B severely affected all cruciferous weeds tested except peppergrass and shepherd's purse. Stinkweed and wild mustard developed severe chlorosis and necrosis that often resulted in the death of the plant. However, there was no affect of destruxin B on barley, oats, rye, and wheat. These results suggested that destruxin B can be used to control some cruciferous weeds in cereals.