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What are rusts?
On seedling leaves, however, stripes do not form and pustules are scattered at random. In severe infections, pustules may also be found inside the glumes of the ears and on the awns.Brown rust is distinguished by its brown pustules.
Normally circular in shape, they are somewhat larger than yellow rust pustules, and are scattered at random on the leaf. A pale green halo can often be seen around each pustule. In severe infections, pustules may appear on the leaf sheaths. Oat crown rust produces bright orange pustules.
Rusts feed on the living cells of their hosts, meaning they are dependent on living green plant tissue for their survival. They obtain nutrients from living cells of the host plant by producing specialised nutrient-absorbing structures called haustoria.
Rusts in the UK have greatly simplified life cycles, compared with many worldwide rust fungi. For example, wheat yellow rust, unlike many other rusts, has only one host plant species, and the survival and success of the fungi is entirely dependent on infection by airborne asexual spores (uredospores). Cereal rust fungi survive the post-harvest period on volunteer seedlings infected by uredospores. Infection then spreads to early-sown autumn crops and from these to later-sown crops. This ‘green bridge’ is critical for survival. Rusts over-winter either in the leaf or on the leaf surface. During the spring and early summer, uredospores are produced, which re-infect the plant and are responsible for the epidemic rapidly cycling.
Factors affecting rusts