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Orange-colored rust pustules on the abaxial surface of a Plumeria leaf. The rust fungus is the plant pathogen, Coleosporium domingense syn. C. plumeria.

Symptoms of rust disease on the adaxial surface of a Plumeria leaf are chlorotic specks. The rust fungus is the plant pathogen, Coleosporium domingense syn. C. plumeria.

Brightly colored rust disease on Oxalis sp. (wood sorrell) leaves, caused by the plant-pathogenic rust fungus,Puccinia oxalidis.

Erumpent rust (Uromyces tairae) pustules on a leaf of tree heliotrope (Tournefortia argentea).

Conspicuous rust pustules and spores (Puccinia psidii) on leaves of ohia (Metrosideros polymorpha).

Rust of lemongrass (Cymbopogon flexuosus), caused by the plant-pathognic fungus, Puccinia nakanishikii.

Definition

A rust is a disease caused by a specialized group of basidiomycetes that often produces spores of a rusty color.

Etymology. O.E. rust, related to rudu "redness," from P.Gmc. *rusta- (cf. Fris. rust, O.H.G., Ger. rost, M.Du. ro(e)st), from PIE *reudh-s-to- (cf. Lith. rustas "brownish," rudeti "to rust;" L. robigo, O.C.S. ruzda "rust"), from base *reudh- "red." The verb is attested from c.1225. As a plant disease, attested from c.1340. Rust Belt "dacayed urban industrial areas of mid-central U.S." (1984) was popularized, if not coined, by Walter Mondale's presidential campaign.