| Puccinia triticina | |
|---|---|
| Symptoms of wheat leaf rust | |
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Basidiomycota |
| Class: | Pucciniomycetes |
| Order: | Pucciniales |
| Family: | Pucciniaceae |
| Genus: | Puccinia |
| Species: | P. triticina |
| Binomial name | |
| Puccinia triticina Erikss. (1899) |
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| Synonyms | |
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Puccinia dispersa f. sp. tritici Erikss. & E.Henn. 1894 |
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Wheat leaf rust, is fungal disease that effects wheat, barley and rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen overwinters. Infections can lead up to 20% yield loss - exacerbated by dying leaves which fertilize the fungus. The pathogen is Puccinia rust fungus. Puccinia triticina causes 'black rust', P.recondita causes 'brown rust' and P.sriiformis causes 'Yellow rust'. It is the most prevalent of all the wheat rust diseases, occurring in most wheat growing regions. It causes serious epidemics in North America, Mexico and South America and is a devastating seasonal disease in India. All three types of Puccinia are heteroecious requiring two distinct and distantly related hosts (alternate hosts). Rust and the similar smut are members of the class Teliomycetes but rust is not normally a black powdery mass.
Contents |
Wheat leaf rust is spreads via airborne spores. Five types of spores are formed in the life cycle. Uredospores, teleutospores and basidiospores develop on wheat plants and pycnidiospores and aeciospores develop on the alternate hosts.[1] The germination process requires moisture, and works best at 100% humidity. Optimum temperature for germination is between 15-20 C. Before sporulation, wheat plants appear completely asymptomatic. In the Asian Subcontinent, the spores cannot survive the hot dry weather but are re-introduced every year from the Himalayas or surrounding hills, possibly coming from Berberis spp, Thalictrum flavum and Muehlenbergia huglet or even some grasses. Wheat rust pathogens are biotrophic and require living plant cells to survive.
P. triticina has an asexual and sexual life cycle. In order to complete its sexual life cycle P. triticina requires a second host Thalictrum spp. which it will overwinter on. In places where Thalictrum does not grow, such as Australia, the pathogen will only undergo its asexual life cycle and will overwinter as mycelium or uredinia. The germination process requires moisture and temperatures between 15 – 20 °C. After around 10 – 14 days of infection, the fungi will begin to sporulate and the symptoms will become visible on the wheat leaves.[2]
The pathogen has an asexual and sexual cycle. In North America, South America and Australia the pathogen only undergoes its asexual cycle. However this does not seem to be a disadvantage to it, and wheat leaf rust has many races with different virulence. The sexual life cycle of wheat leaf rust requires a different host species, Thalictrumn spp.
Small brown pustules develop on the leaf blades in a random scatter distribution. They may group into patches in serious cases. Infectious spores are transmitted via the soil. Onset of the disease is slow but accelerated in temperatures above 15°C, making it a disease of the mature cereal plant in summer, usually too late to cause significant damage in temperate areas. Losses of between 5 and 20% are normal but may reach 50% in severe cases.
Varietal resistance is important. Chemical control with triazole fungicides may be useful for control of infections up to ear emergence but is difficult to justify economically in attacks after this stage