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Polyoxin was found in the culture broth of Streptomyces cacaoi var. asoensis by Suzuki et al. in 1965. It consists of several closely related components, A through O, and shows activity against phytopathogenic fungi by inhibition of cell-wall chitin synthesis. Polyoxin has been used in agriculture against fungal infections, especially Alternaria leaf spot in vegetables and fruits.

The fungicidal activities of polyoxins reported on many plant pathogens, including Alternaria spp. and Rhizoctonia zoctonia spp. (24,25).
Polyoxin B is used for control of Alternaria spp. and powdery mildews in apples and pears; Botrytis cinerea in vines and aubergines; powdery mildews in roses, chrysanthemums, and melons; blight of carnation; powdery mildew, brown spot, and gray mold in tobacco; powdery mildew and gray mold in strawberries; leaf mold, early blight, and gray mold in tomatoes; powdery mildew, gray mold, Sclerotinia erotinia spp. rot, and Corynespora melonis in cucumbers; Alternaria spp. blight in carrots; purple blotch in leeks. Patent: JP 493008 Formulation types: WP; EC; SG. Mixes with captan; oxine-copper; iminoctadine triacetate. Compatibility: Incompatible with alkaline materials. Tradename “Polyoxin AL.”
Polyoxin D zinc salt is used for control of sheath blight (Rhizoctonia solani) in rice; canker in apples and pears; Rhizoctonia solani, Drechslera spp., Bipolaris spp., Curvularia spp., and Helminthosporium spp. in lawn turf. Formulation types: WP; PA. Mixes with thiram; propiconazole. Compatibility: Incompatible with alkaline materials. Tradenames “Kakengel” (zinc salt); “Polyoxin Z” (zinc salt); “Stopit.”
Application of polyoxins can be made at any growth stage of rice plants without causing phytotoxicity even at 800-ppm application. Foliar sprays of 200 ppm of polyoxins have produced no phytotoxicity on all the other crops tested.

Polyoxin B causes a marked abnormal swelling on germ tubes of spores and hyphal tips in Alternaria spp., and this makes the pathogen noninfectious. In a cellfree system of Neurospora crassa, polyoxin D inhibits the incorporation of N-acetyl-glucosamine (GlcNAc) into chitin in a competitive manner between UDP-GlcNAc and polyoxin D; the pyrimidine nucleoside moiety of the antibiotics was shown to fit into the binding site of the enzyme protein, and the carbamoylpolyoxamic acid moiety of polyoxins stabilizes the polyoxin-enzyme complex (26).
Polyoxin-resistant strains of A. alternata were recognized in pear orchards after several years of intensive use of the antibiotics. The resistance was suggested to be caused by a lowered permeability of the antibiotic through the cell membrane into the site of chitin synthesis (27).

Acute oral LD₅₀ of polyoxin B for male rats 21, female rats 21.2, male mice 27.3, and femalemice 22.5 g/kg. Acute percutaneous LD₅₀ for rats >2 g/kg. Nonirritant to mucous membranes and skin (rats). Inhalation LD₅₀ (6 h) for rats 10 mg/L air. NOEL (2 y) for rats and mice >48-g/kg diet. Toxicity class EPA (formulation) IV.
Acute oral LD₅₀ of polyoxin D for male rats and female rats >9.6 g/kg. Acute percutaneous LD₅₀ for rats >750 mg/kg. Inhalation LD₅₀ (4 h) for male rats 2.44, female rats 2.17 mg/L air. NOEL (2 y) for rats >50, mice >40 g/kg diet. Toxicity class EPA (formulation) III (WP).