Puccinia striiformis Biology
Stripe or yellow rust of wheat caused by P. striiformis f. sp. tritici can be as damaging as stem rust. However, stripe rust has a lower optimum temperature for development that limits it as a major disease in many areas of the world. Stripe rust is principally an important disease of wheat during the winter or early spring or at high elevations. Table 13.3 shows regions of the world where stripe rust has been a major or local problem.
Stripe rust of wheat may be the cause of stripe rust on barley (Stubbs, 1985). In Europe, a forma specialis of P. striiformis has evolved that is commonly found on barley and seldom on any but the most susceptible wheats (Zadoks, 1961). Puccinia striiformis f. sp. hordei was introduced into South America where it spread across the continent (Dubin and Stubbs, 1986) and was later identified in Mexico and United States (Roelfs et al., 1992).
Puccinia striiformis has the lowest temperature requirements of the three wheat rust pathogens. Minimum, optimum and maximum temperatures for stripe rust infection are 0°, 11° and 23°C, respectively (Hogg et al., 1969). Puccinia striiformis frequently can actively overwinter on autumn-sown wheat. Most of the epidemiology work has been done in Europe and recently reviewed by Zadoks and Bouwman (1985) and Rapilly (1979).
In Europe, P. striiformis oversummers on wheat (Zadoks, 1961). The amount of over-summering rust depends on the amount of volunteer wheat, which, in turn, is a function of moisture in the off-season. The ured-iniospores are then blown to autumn-sown wheat. In northwestern Europe, overwintering is limited to urediniomycelia in living leaf tissues as temperatures of -4°C will kill exposed sporulating lesions. Latent lesions can survive if the leaf survives. In other areas of the world, snow can insulate the sporulating lesions from the cold temperatures so air temperatures below -4°C fail to eliminate the rust lesions. The latent period for stripe rust during the winter can be up to 118 days and is suspected to be as many as 150 days under a snow cover (Zadoks, 1961).
In areas near the equator, stripe rust tends to cycle endemically from lower to higher altitudes and return following the crop phenology (Saari and Prescott, 1985). In more northern latitudes, the cycle becomes longer in distance with stripe rust moving from mountain areas to the foothills and plains.
Due to their susceptibility to ultraviolet light, urediniospores of stripe rust probably are not transported in a viable state as far as those of leaf and stem rusts. Maddison and Manners (1972) found stripe rust urediniospores three times more sensitive to ultraviolet light than those of stem rust. Still, Zadoks (1961) reports stripe rust was wind-transported in a viable state more than 800 km. The introductions of wheat stripe rust into Australia and South Africa and barley stripe rust into Colombia were probably aided by humans through jet travel (Dubin and Stubbs, 1986; O’Brien? et al., 1980). However, the spread of stripe rust from Australia to New Zealand, a distance of 2 000 km, was probably through airborne urediniospores (Beresford, 1982). Perhaps an average spore of stripe rust has a lower likelihood of being airborne in a viable state over long distances than that of the other wheat rusts, but certainly some spores must be able to survive long-distance transport under special and favourable conditions. There are several examples of the sequential migration of stripe rust. Virulence for gene Yr2 (cultivars Siete Cerros, Kalyansona and Mexipak) was first recorded in Turkey and over a period of time was traced to the subcontinent of India and Pakistan (Saari and Prescott, 1985) and may be associated with the weather systems called the ‘Western Disturbance’. As mentioned, barley stripe rust in South America migrated from its introduction point in Colombia to Chile over a period of a few years (Dubin and Stubbs, 1986).
Most areas of the world studied seem to have a local or nearby source of inoculum from volunteer wheat (Line, 1976; Stubbs, 1985; Zadoks and Bouwman, 1985). However, some evidence points to inoculum coming from non-cereal grasses (Hendrix et al., 1965; Tollenaar and Houston, 1967). Future studies of stripe rust epidemiology need to take into account not only the presence of rust on nearby grasses, but also the fact that the rust must occur on the grasses prior to its appearance on cereals. The virulence phenotype must be shown to be the same on both hosts and that it moves from the grass to wheat during the crop season.
Stripe rust epidemics in the Netherlands can be generated by just a single uredinium per hectare surviving the winter if the spring season is favourable for rust development (Zadoks and Bouwman, 1985). Visual detection of a single uredinium per hectare is unlikely, however, as foci develop around the initial uredinium, it becomes progressively easier to detect.
Puccinia striiformis is a pathogen of grasses and cereal crops: wheat, barley, triticale and rye. Stripe rust is the only rust of wheat that consistently spreads beyond the initial infection point within the plant.
Only the telial and uredinial stages of stripe rust are known. Eriksson and Henning (1894) looked for the alternate host among species of the Boraginaceae. Tranzschel (1934) suggested that Aecidium valerianella, a rust of valerianella, might be related to P. striiformis. Mains (1933) thought that P. koeleriae Arth., P. arrhenatheri Eriks. and P. montanensis Ellis, which have aecidial states on Berberis and Mahonia spp., might be related to P. striiformis.
Straib (1937) and Hart and Becker (1939) were unsuccessful in attempts to infect Berberis, Mahonia and Valerianella spp. The alternate host of the rust, P. agropyri Ell. & Ev., is Clematis vitalba. This rust closely resembles P. striiformis thus Viennot-Bourgin? (1934) suggested that the alternate host of stripe rust might occur in the Clematis family. Teliospores readily germinate immediately to produce basidiospores (Wright and Lennard, 1980), and the teliospores probably do not assist the fungus as a winter survival mechanism. An epidemiological factor to consider is the possibility of infection of the alternate host late in the summer so aeciospores could infect the newly sown wheat or late cool season grasses. In some high-altitude areas of West Asia, the wheat crop may take 13 months to mature. In such cases, early spring season infections of the alternate host would be possible.
Puccinia striiformis is most likely a hemiform rust in that the life cycle seems only to consist of the uredinial and telial stages. Uredia develop in narrow, yellow, linear stripes mainly on leaves and spikelets (Plate 20). When the heads are infected, the pustules appear on the inner surfaces of glumes and lemmas (Plate 21). The urediniospores are yellow to orange in colour, more or less spherical, echinulate and 28 to 34 µm in diameter (Plate 22). Narrow black stripes are formed on leaves during telial development. Teliospores are dark brown, two-celled and similar in size and shape to those of P. triticina (Plate 23). Stripe rust populations can exist, change in virulence and result in epidemics independent of an alternate host. Urediniospores are the only known source of inoculum for wheat, and they germinate and infect at cooler temperatures.
Source: The wheat rusts: R.P. Singh, J. Huerta-Espino, A.P. Roelfs