Characteristics of a Rust Fungus

Types

• Almost 100,000 different types of plant rust fungi are in existence throughout the world. This makes rust-causing fungi the most diverse group of parasitic plants that have a wider host range than any other. This is also because the majority of rust fungi are host specific where they only attack certain kinds of plants. For instance, Puccinia graminis causes stem rust on wheat, Puccinia pelargonii-zonalis causes geranium rust, chrysanthemum white rust is caused by Puccinia horiana and Phragmidium mucronatum causes rust on roses.

Hosts

• Rust causes severe diseases in a great number of vascular plants including all ferns, gymnosperms, dicots and monocots. The only plants on which rust has not been found are mosses and liverworts. Rust infection in crops leads to heavy losses. The rust appears on corn, wheat, forage grasses, legumes, vegetables and forest plantations. It is a parasite that starts to grow on plants where the conditions are favorable for the germination of rust spores. The disease is more common on weak and poorly growing plants than vigorous, healthy ones.

Special Features

• The specialized composition of rust fungi give them a number of unique features such as the ability to have five spore-producing structures. Spores are the reproductive bodies of a fungus. These structures allow the fungi to spread rapidly once a plant is infected. Though the spores are produced at different times, one plant often has all five spores simultaneously. They also seek healthy, vigorous plants as hosts, unlike other plant pathogens that attack stressed and poorly growing plants.

Symptoms

• Rust infections are very hard to detect in the early stages of growth. Systemic infections lead to galls, cankers or abnormal growth from twigs referred to as witches brooms. Severely infected plants start to yellow from chlorosis. The presence of yellow- or orange-colored fruiting bodies gives the infected plant an orange appearance. Rust diseases are most commonly seen in temperate regions during spring.