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).
