Biological Pesticides - Xanthomonas L4 Toxin Product Development

Xanthomonas retroflexus, a new strain with high herbicidal activity, was isolated from the rhizosphere of redroot pigweed by our subject group. The toxins of Xanthomonas retroflexus were identified to be composed of Cyclo-(Phe-Pro), extracellular polysaccharide and six organic acids. And the action target of the toxins was on the chondriosome of weed leafs.In this paper, firstly the cyclo-(Phe-Pro) was synthesized by chemical method and the relationship among cyclo-(Phe-Pro), extracellular polysaccharide and organic acid were studied via EC50 method. The detective methods of cyclo-(Phe-Pro) and polysaccharide were also established. Then, the optimization of fermentation technique was carried out both in Erlenmeyer flasks and 15 L agitating fermentor, and the amplifying of fermentation technique was implemented in 50 L agitating fermentor. The result showed that suitable fermentation medium were corn steep liquor 7.5 g L^-1, sucrose 35 g L^-1, (NH₄)₂SO₄ 15 g L^-1, yeast powder 0.1 g L^-1, MgSO₄ 2 g L^-1 and NH₄H₂PO₄ 5 g L^-1, and the the optimal condition were 300 r min^-1, 1:1.00 vvm and 27 ℃. Furthermore, the formulation processing, field examination and toxicology of L4 toxin were studied in detail. The results demonstrated that the toxins of Xanthomonas retroflexus had low toxicity and well environmental compatibility and could been used on the lawn for controlling the mostly dicot weeds and the part of monocot weeds.