Two rust diseases, stem rust and leaf (or crown) rust, are often seen on oats. This includes wild oats that occur as weeds in crops and along roadsides, fence lines, and other disturbed areas. Susceptible varieties and the widespread occurrence of wild oats ensure the presence of rust whenever there is moisture (including dew) for infection.
The red spores that are blown from oat plant to oat plant do not infect other cereals. Stem rust is a major threat to quality grain production, whereas leaf rust is a greater threat in the grazing situation.
Staying a step ahead of the pathogens
Although oat breeders have worked hard to produce rust-resistant varieties, the rust parasites have changed just as fast. These changes are due to mutations that enable the parasite to neutralise the effects of the resistance genes.
The new pathotypes are very similar to the old ones except for the added ability to overcome a particular resistance gene. The outcome is that sources of leaf rust resistance in the world's oat collections are becoming difficult to find, and sources of stem rust resistance are virtually exhausted.
Challenges to controlling oat rusts
Control of rust in oats has for various reasons been more difficult to achieve than control in wheat. The parasites appear to be more variable than those on wheat; more frequent susceptible varieties and wild oats permit much more inoculum to be present; the global industry is relatively small, and therefore there are fewer resources for research.
Although resistance is present in wild relatives of cultivated oat, traditional hybridisation and selection procedures for successful transfer take more than 20 years. Hopefully, developments in plant biotechnology and transformation will shorten this process.