Puccinia triticina (formerly known as Puccinia recondite f. sp. Tritici) - Wheat
Puccinia hordei - Barley
Puccinia recondite - Rye, Triticale
Puccinia tritici is specific to wheat, other Puccinia spp. and pathotypes can affect barley, rye and triticale but do not cross-infect.
Symptoms of brown rust infection are often seen in the autumn on early-sown crops as individual orange to brown pustules. With early autumn infection individual pustules are frequently confused with yellow rust, being orange to brown and about 0.5 - 1.0 mm in diameter. Later in the season diagnosis is much easier as the brown pustules tend to be scattered at random compared with the more stripped symptoms of yellow rust (Puccinia striiformis). Symptoms are usually seen on the leaves although in severe attacks symptoms can be seen on the stem and glumes. When leaves begin to senesce, a 'green island' develops around individual pustules. Towards the end of the season dark teliospores are sometimes produced.
The fungus overwinters primarily on volunteers and early-drilled crops. The alternate hosts for P. triticina include species of Thailctrum, Isopyrum and Clematis, although their role in the life cycle in the UK is not thought to be significant.
Until recently the disease was rarely important in the spring as temperatures between 15oC and 22oC, accompanied by 100% relative humidity are needed for sporulation and spore germination. Consequently, brown rust epidemics have normally occurred during mid to late summer in the UK with dry windy days which disperse spores, and cool nights with dew, favouring the build-up of the disease. However, with mild winters, brown rust can often be found at high levels in the spring. With climate change, mild winters and warm springs are likely to become a more common problem earlier in the season.
Until recently brown rust was not considered to be a major problem despite early-sown crops generally carrying high levels of brown rust through the winter. However, the occurrence of new virulent strains overcoming varietal resistance in a few key wheat varieties has moved brown rust up the league table of importance. Severe attacks result in a significant loss of green leaf area and hence yield, infection of the ears will also result in loss of grain quality. It is too soon to predict epidemic levels of brown rust in future seasons but it is now a disease that cannot be ignored.
Destruction of volunteers will help to prevent carry-over of the disease. Varieties with good disease resistance are available.