In this article we will discuss about the economic importance of rust fungi.
The order included a group of some 4,500 species of highly specialized and economically most important internal parasites which attack higher plants and sometimes the ferns.
They are economically important because majority of them cause disease of cereals and other crops resulting in enormous losses. In spite of the damage they cause, they seldom kill the host plant immediately.
These organisms receive the popular name rusts or rust fungi from the rusty colour of the spores (uredospores) which appear on the surface of the host. In nature the rust fungi appear to be obligate parasites.
Till recently all attempts to grow them in the laboratory apart from the host or hosts failed. However, a considerable success in culturing some of them on artificial media has been attained within recent years.
Wolf (1974) stated that so far 9 species belonging to 4 different genera of rust fungi have been grown on pure culture in the laboratory.
Hotson and Cutter (1951) and later Cutter (1951 and 1959) were the pioneers to meet success in their efforts to cultivate cedar apple rust fungus on an artificial medium.
Brown (1967) divided rust fungi into two categories namely, physiologically obligate parasites and ecologically obligate parasites. The former would not grow apart from the host or hosts.
The latter to which the wheat rusts belong fail to grow as saprobes in nature but can be grown in the laboratory on die artificial media. In the rusts the mycelium lacks the dolipore septal complex. It spreads intercellularly forming haustoria.
More than one type of spores are formed in the life cycle. The rusts are thus polymorphic. The basidia are transversely septate.
The basidiospores are produced on sterigmata and are discharged forcibly. The rusts like Smuts lack basidiocarps. Karyogamy takes place in the teliospore.
Rusts infect ferns, gymnosperms and angiosperms and are known since ancient times. According to Pliny (29-79 AD) Rust is the greatest enemy of cereals.
This statement holds true even today because the damage caused by rusts is severe but slow and prolonged. Rusts have attracted both the Mycologists and the plant pathologists.