Difference between Rusts and Smuts

The rusts and smuts are perhaps the most economically important fungal plant pathogens.
Rusts: A plant disease caused by a fungus of the class uredinomycetes. The characteristic symptom is the development of spots or pustules bearing masses of powdery spores which are usually rust coloured, yellow, or brown. Infected plants may also show distortions or gall like also distortions or gall like swellings.
Smuts: A plant disease caused by a fungus of the order Ustilaginales. Many types of plant can be affected, but smuts are particularly important in cereals and other grasses. The symptoms include the formation of masses of lack soot like spores and infected plants often show some degrees of distortions.
Rusts vs Smuts
Stem rust (Puccinia graminis) on wheat stem and leaves
Bermuda grass smut (Ustilago cynodotis) on flowers
Common name given because of the “rusty” appearance caused by disease, in urediospore stage. Many species parasitic on grain crops. Characterized by lack of fruiting bodies, formation of basidia and basidiospores from germination of teliospores and having as many as five spore stages and two hosts, e.g., Puccinia graminis (=Wheat Rust) Common name given because of the black, powdery appearance of infected host plants, in teliospore stage. Many species parasitic on grain crops.
Wheat rusts are heteroecious and others are autoecious
All smuts are autoecious
The rusts are intecellular and obtain their nutrition by means of haustoria.
Clamp connections on the secondary mycelium are rare.
The smuts may be intercellular or intracellular (U.maydis). Haustoria are present.
Clamp connections are common.
The dikaryotic mycelium produces three kinds of binucleated spores; uredospores and teleutospores on the primary host and aeciospores on the alternate host.
It produces only one kind of binucleate spores called the smut pores which are comparable to the teleutospores of rusts.
The teleutospores are developed from the terminal cells of the mycelium.
Smut spores are formed from the intercalary cells.
The teleutospores are stalked, two celled and each cell is binuclate.
The brand spores (teleutospores) are uninuclear and binucleate.
Each cell of the two celled teleutospores produces an epibasidium which bears four basidiospores. They are borne on sterigmata and are discharged violently by the water drop method.
The single celled, brand spore which is equivalent to teleutospores, germinates to produce a single epibasidium which bears a varible number of basidiospores. They are not borne on the sterigmata nor are they discharges violently.

Aeciospore: One of five spore stages in some rusts fungi, e.g., Puccinia graminis. Spore stage produced on lower surface of Barberry leaves.
Spermatia: Element of spermogonium, in rust fungi. May be thought of as male portion of life cycle. Spore-like structures that is carried to receptive hyphae, by flies, in Wheat Rust. The mixing of the two different nuclei provides the continual genetic variation in the rusts that has made them difficult to with breeding of resistant varieties of Wheat.


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