Puccinia striiformis

Scientific Name Puccinia striiformis var. striiformis Westend, Puccinia striiformis f.sp. tritici
Synonyms Puccinia glumarum Erikss. & Henning
Common Names English: Stripe rust, yellow rust, glume rust; Spanish: Roya amarilla, Polvillo estriado de la hoja; German: Gelbrost; French: Rouille jaune
Description Puccinia striiformis, a basidiomycete belonging to the uredinales, is the cause of stripe rust on cereal crops and grasses. Several formae speciales of P. striiformis West. var. striiformis have been successively named on the basis of physiological specialization: P. striiformis f.sp. tritici collected from wheat. Like other cereal rusts, P. striiformis forms races which are usually identified with a differential set of wheat cultivars.

Biology

Damage

Symptoms occur on all aerial parts of the plant, but are most frequently seen on the leaves. They appear about 1 week after infection, and sporulation starts about 2 weeks after infection, under optimum temperature conditions. The pustules, which are tiny, yellow- to orange-colored, are often arranged into conspicuous stripes. Lines of bright yellow new urediospores give the typical striped appearance on the leaves from which the specific name striiformis and common name stripe rust are derived. In Europe the yellow color of the spores caused it to be given the common name yellow rust. During the summer, stripe rust infection of wheat spikes may occur, resulting in the formation of masses of spores between the glume and the lemma. At the end of the season, black telia may form in patches of tissue that have been killed by stripe rust uredia.

Lifecycle

P. striiformis survives mainly as dormant mycelium or uredia on volunteer plants and early autumn-sown wheat. In spring, particularly in cool moist weather, the fungus starts to grow again and more urediniospores are produced. Temperatures of 10-15°C and a relative humidity of 100% are optimal for spore germination, penetration and production of new, wind-dispersed spores (although races of different geographical origins may have higher optima for germination). The disease cycle may be repeated many times in one season.
Stripe rust epidemics tend to start from disease foci in the field and, at least initially, the pattern of spread may be related to wind direction. As well as local inoculum initiating disease epidemics there is also a possibility of urediniospores being blown for long distances and into a crop. Stripe rust epidemics tend to occur in spring and early summer. The fungus is inhibited by temperatures over 20°C. During late summer, telia may form which give rise to teliospores. The latter can form basidiospores, but no alternative host has been found and the teliospores therefore appear to have no function in the life cycle.

Cause

The pathogen spreads by means of airborne urediospores. After landing on wheat plants they germinate in high humidity, usually at temperatures of less than 15°C, and the germ tubes enter the leaves or other parts of the plant via the stomata. P. striiformis hyphae are thread-like and spread between intercellular spaces of their host. Hyphae are dikaryotic and often multinucleate. Once inside the leaf, haustoria are inserted into the mesophyll cells and the mycelium spreads along the leaf. In mature leaves it spreads longitudinally between the veins of the leaf. Two kinds of spores are produced by P. striiformis: urediniospores and teliospores. Urediniospores are 20-30 µm in diameter, yellow-orange and spherical. They have thick, spiny walls and 6-12 scattered germ pores. Teliospores are two-celled, ellipsoid to clavate, orange to brown, and 12-20 x 36-68 µm. The teliospores are flattened at their apex and have smooth, thick walls with a slight constriction at the septum. It is an obligate parasite and damage to plant is caused by extracting nutrients via the haustoria and by disruption of the epidermis, which reduces the water retention capacity of the leaves.

Occurrence

Additional Crop Information

Unlike many other cereal rusts the stripe rust pathogen does not have any known alternate hosts.

Agricultural Importance

The disease occurs on wheat crops in the cooler areas in which wheat is cultivated, especially in mountainous and upland areas. Stripe rust reduces the yield and quality of grain and forage. Seed produced from crops damaged by stripe rust have low vigour and thus poor emergence after germination. The recorded amounts of yield loss up to 100% depended on the timing and severity of the infection.

Control

Integrated Crop Management

The most effective, economic and practical means of control of stripe rust on wheat is through the use of varieties that are resistant to P. striiformis. To stabilize the pathogen population and decrease epidemic frequency, it is important to use different sources of variety resistance, including major-gene resistance, polygenic resistance, high-temperature resistance, and adult-plant resistance. Chemical control of P. striiformis can be attempted if resistant varieties are scarce. On very susceptible varieties, fungicides should be applied as soon as the disease appears. On less susceptible varieties, fungicides should be applied if weather conditions are favorable for disease development and there is evidence of the disease spreading in the crop. Since the 1990s expert systems combined information on management practices, use of fungicides and resistant cultivars into an integrated disease management program called MoreCrop.

Chemical Control

In regions where yellow rust is occurring regularly in autumn or early spring seed treatments containing a systemic triazole fungicide are considered an important strategy to protect plants against infection by P. striiformis. Bayer CropScience offers for this purpose seed treatment products containing the active ingredients triadimenol and fluquinconazole.
For spray treatment of foliar or ear infections broad-spectrum fungicides such as triazoles and strobilurins as well as amine fungicides controlling simultaneously other diseases are effective against Yellow Rust. Bayer CropScience products containing (triadimenol), tebuconazole, prothioconazole and trifloxystrobin as well as fluoxastrobin and spiroxamine are all suited to control yellow rust leaf and ear infections.

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