Puccinia striiformis (Wheat Stripe Rust) Yuan Chai1, Darren J. Kriticos1,2, Jason M. Beddow1,2, Etienne Duveiller3, Will Cuddy4, Tania Yonow1,2, and Robert W. Sutherst5 1 HarvestChoice, InSTePP, University of Minnesota, St. Paul, MN, USA 2 CSIRO, Biosecurity and Agriculture Flagships, Canberra, Australia 3 CIMMYT, Global Wheat Program, El Batá n, Mexico 4 New South Wales Dept. of Primary Industries, Menangle, NSW, Australia 5 University of Queensland, Brisbane, QLD, Australia (deceased)
Common Names: Stripe rust; yellow rust
Wheat stripe rust disease, caused by Puccinia striiformis f. sp. tritici, is one of the most important fungal diseases of wheat worldwide. Infection can occur anytime during the wheat lifecycle from the one‐leaf stage to plant maturity. The pathogen infects the green tissues of the plant, forming linear rows of small yellowish rust pustules on the leaf or in the spike (Figure 1). Infected plants develop symptoms about one week after infection and sporulation starts about two weeks after infection (Chen 2005). Infection can result in characteristic necrotic stripes or elongated spots along the length of the leaf, weakening the plants by diverting water and nutrients from the host (Chen 2005).
Scienti ic Name: Puccinia striiformis f. sp. tritici Synonyms: Dicaeoma glumarum, Puccinia glumarum, Puccinia rubigo‐vera, Puccinia straminis, Puccinia striiformis, Trichobasis glumarum, Uredo glumarum Taxonomy: Kingdom: Fungi; Phylum: Basidiomycota; Class: Urediniomycettes; Order: Uridenales; Family: Pucciniastraceae Crop Hosts: Wheat (Triticum aestivum), Barley (Hordeum vulgare L.)
Figure 1. Wheat Strip Rust Infection. Source: USDA‐ARS Cereal rust image gallery http://www.ars.usda.gov/SP2UserFiles/ad_hoc/36400500Cerealrusts/stripe_rust.jpg
©2015 InSTePP‐HarvestChoice, Chai, Kriticos, Beddow, Duveiller, Cuddy, Yonow, and Sutherst
Known Distribution Stripe rust occurs throughout wheat production areas on all continents except Antarctica (Figure 2). In North America stripe rust is a major problem in the United States and Canada (Chen 2005). Prior to 2000, stripe rust epidemics mainly occurred in western Canada and the Paci ic Northwest region of the United States; after 2000, stripe rust became prevalent in eastern Canada and the central United States (Chen 2005) (Figure 3). The reasons for this change in spatial distribution are unclear. Some have proposed that the rust underwent rapid evolution before it could invade the warmer south‐ ern states (Chen 2005; Milus and Seyran 2006; Wellings et al. 2009). However, the climatic conditions in the southern United States closely match those of areas with‐ in P. striiformis’ native range in Eurasia. An alternative explanation for the invasion lag is that during the early phase of the invasion the rust spores had to disperse against the dominant wind systems. In South America, stripe rust causes frequent yield losses in Chile (Germá n et al. 2007). In Europe, stripe rust has been the most common wheat rust throughout France, the Netherlands, Germany, Denmark and the United Kingdom; in the central and western Asia and northern Africa (CWANA) region, at least three widespread epi‐ demics have occurred since the 1970s; and in east and south Asia, stripe rust is a serious problem in India, Paki‐ Suggested citation: Chai, Y., Kriticos, D.J., Beddow, J.M., Duveiller, E., Cuddy, W., Yonow, T. and Sutherst, R.W. (2015). Puccinia striiformis HarvestChoice Pest Geography. St. Paul, MN: InSTePP‐HarvestChoice.
stan and China (Solh et al. 2012). Stripe rust was irst introduced into Australia in 1979 (O’Brien et al. 1980; Wellings 2007) and then spread into New Zealand in 1980, presumably dispersed by winds from south‐ eastern Australia (Wellings and McIntosh 1990; Viljanen‐ Rollinson et al. 2002).
years for it to be reported in South Africa. It is now wide‐ spread throughout South Africa and the areas of northern Africa where the climate is Mediterranean, and the high elevation areas of eastern Africa experiencing a warm temperate climate (rusttracker.cimmyt.org).
In Africa, stripe rust was irst reported in Zambia in 1958 (Angus 1965, cited in Chen 2005), taking another thirty
Figure 2. Wheat areas of the world where stripe rust has been a problem (reproduced based on Roelfs et al. 1992 and rusttracker.cimmyt.org).
Figure 3. Wheat stripe rust losses in the United States (selected years 1960‐2010, produced by authors based on USDA CDL small grain rust losses data from http://www.ars.usda.gov/main/docs.htm?docid=10123).
Description and Biology
Puccinia striiformis has a complex lifecycle, requiring both a primary host and an alternate host for completion (Figure 4). The asexual (uredinial) stage of the disease occurs on the primary hosts (wheat, barley and some other grasses), causing epidemics through the cycling and spreading of urediniospores when conditions are favourable. The completion of the sexual (aecial) stage of the pathogen’s lifecycle occurs on the alternate barberry (Berberis spp.) hosts (Jin et al. 2010).
A CLIMEX model was developed for Puccinia striiformis using the CliMond 1975H historical climate dataset (Kriticos et al. 2012; Sutherst et al. 2007). The Ecocli‐ matic Index (EI) describes the relative climatic suitability of areas for year‐round persistence of the pathogen (i.e., establishment); the Annual Growth Index (GIA) indicates the relative climatic suitability for population growth (i.e., infection/outbreak). The CLIMEX parameters (Table 1) were itted based on the biology of stripe rust patho‐ gen and its known distributions in the USA, the Middle‐ East, India and Pakistan, taking into account the spatial distribution of irrigated and non‐irrigated wheat produc‐ tion. The distribution elsewhere was used to validate the goodness of it of the model. The general methodology used to it the model, along with an accessible guide to interpretation of CLIMEX models is provided by Beddow et al. (2010). Table 1. CLIMEX Parameter Values for Puccinia striiformis
Figure 4. Wheat stripe rust life cycle (reproduced based on Jin et al. 2010)
Disease epidemics are mostly affected by moisture, tem‐ perature, and wind. Moisture affects spore germination, infection, and survival (Chen 2005), and a dew period of at least three hours is required for germination and infec‐ tion (Rapilly 1979). Temperature affects spore germina‐ tion and infection, latent period, sporulation, spore sur‐ vival, and host resistance (Chen 2005). Puccinia strii‐ formis thrives in cool climates, so stripe rust mainly oc‐ curs throughout wheat production areas in temperate regions and areas of high elevations in tropical regions. The primary method of long‐distance dispersal is via windblown urediniospores (Rapilly 1979); although dis‐ persal across oceans is unlikely as stripe rust spores are sensitive to UV radiation (Roelfs et al. 1992). Stripe rust infections can occur at any point in the host plant’s lifecycle, from the end of the heading stage to the late milk stage, causing stunting of plants and thereby reducing yield. The most critical infection stage for yield losses is the early milk stage (Murray et al. 1994). If a severe infection occurs very early in the host’s lifecycle, stripe rust can cause 100 percent yield losses (Chen 2005). Because cool temperatures are more conducive to stripe rust development, higher temperatures during grain development decrease yield losses to the disease (Murray et al. 1994).
Host Crops and Other Plants The primary crop hosts of stripe rust are wheat (Triticum spp.), a few barley cultivars (Hordeum vulgare) and triticale (X Tritocosecale). Berberis species were recently discovered to be suitable hosts (Jin at al. 2010).
lower soil moisture threshold
lower optimum soil moisture
upper optimum soil moisture
upper soil moisture threshold
lower optimum temperature
upper optimum temperature
cold stress temperature threshold
temperature threshold stress accumulation rate ‐0.01 week‐1
Heat Stress TTHS
heat stress temperature threshold
stress accumulation rate
soil moisture dry stress threshold
stress accumulation rate
30 °C 0.01 week‐1 0.2 ‐0.005 week‐1
Hot‐Wet Threshold Temperature
Hot‐Wet Stress rate
Threshold Heat Sum PDD
number of degree days above DV0 needed to complete one generation
2.5 mm day‐1 as top‐up throughout the year
200 °C days *
* The Annual Threshold Heat Sum (PDD) was calculated using the minimum survival temperature of ‐4 °C, the optimal temperature 16 °C and a period of 10 days for one generation: (16 °C‐(‐4 °C))×10 days = 200 degree days.
The Temperature Index parameters were based primari‐ ly on the environmental conditions described by Roelfs et al. (1992) (Table 2), with the optimum temperature pa‐ rameters ranging from 12 °C to 16 °C, and the lower and upper thresholds for growth at 3 °C and 30 °C, respec‐ tively. The optimum temperatures concur with the re‐ port of Ellison and Murray (1992) where infection rates are positively correlated with mean temperature for the range of 12.9 °C to 16.2 °C. The claim of Roelfs et al. (1992) of an upper threshold for growth of P. striiformis of approximately 20 to 23 °C is at odds with observations of other authors. Coakley (1988) stated that tempera‐ tures above 25 °C reduced disease severity and Georgievskaja (1966, cited by Rapilly 1979) noted that P. striiformis can tolerate 38 °C peak temperatures for a very short period of time. Daily maximum temperatures ≥32.4 °C were found to be lethal for P. striiformis survival over 10 days (Tollenaar and Houston 1967) and temper‐ atures above 33 °C stop sporulation (Rapilly 1979). Den‐ nis (1987) investigated the heat tolerance of spores and latent and sporulating infections, noting that spores could survive for up to 5 d at a constant 40 °C, but infec‐ tions could only survive for 5 hours at 40 °C. According‐ ly, DV3 was set at 30 °C, reasoning that reduced popula‐ tion growth rates are still achievable somewhat above Coakley’s 25 °C, but population processes start shutting down at higher temperatures. This parameter should be treated as being approximate. Table 2. Temperature and moisture requirements for P. striiformis Stage
Temperature (°C) Minimum Optimum
Light Free water
Source: Roelfs, A.P., Singh, R.P. and Saari, E.E. Rust diseases of wheat: Concepts and methods of disease management. CIMMYT: Mexico, 1992. p.3.
Cold Stress parameters were included to restrict the over ‐wintering survival, with ‐4 °C as the threshold. This is in broad agreement with Rapilly (1979) who considered that temperatures below ‐10 °C might limit the pathogen. Heat stress was added to limit the potential distribution of stripe rust in India where the growing season appears too hot for stripe rust development (A. Joshi, pers. comm.). Whilst relatively high temperatures (and dry conditions) have been reported to favor dormant surviv‐ al (Chen 2005), P. striiformis apparently cannot persist where temperatures exceed 30 °C for some time. Warm wet conditions reduce spore viability in P. striiformis (Chen 2005), and Hot‐Wet Stress appears to limit the range of P. striiformis into the tropics. This may re lect biotic stress due to hemi‐parasitism, but is more likely due to inclement conditions for wheat under warm hu‐ mid conditions. The temperature threshold of 30 °C is at
the upper limit of growth. The soil moisture limit (MTHW) is just above the lower limit for growth of this species. The Hot‐Wet Stress accumulation rate (PHW 0.005 week‐1) indicates the need for prolonged warm wet conditions to preclude persistence of P. striiformis. This set of parameters precludes P. striiformis from per‐ sisting in the coastal south‐eastern USA. In the absence of growth response experiments, the Moisture Index parameters were set to biologically rea‐ sonable values. The lower limit for population growth, SM0 was set to 0.2; well above permanent wilting point, re lecting the need for active host plant turgor and growth to support growth of the fungus. In accordance with the high SM0 value, The lower and upper range for optimal growth (SM1 and SM2) were set relatively high at 0.7 and 1.5 respectively. The upper limit for optimal growth (SM3) was set to 2.5 to preclude growth under very high soil moisture conditions. The Dry Stress Threshold (SMDS) of 0.2 is equal to the lower limit for growth (SM0). The Dry Stress Accumula‐ tion Rate (HDS) of ‐0.005 is a relatively slow accumula‐ tion rate. These parameters preclude P. striiformis from persisting in the xeric regions in the USA and India from which it has not been observed, except where irrigation is practiced during the growing season. In the United States, the EI map shows that stripe rust can persist year round in eastern Washington and Ore‐ gon (Figure 5). This accords with the observation that stripe rust can over‐summer and over‐winter in these regions and provide local inoculum each year (Chen 2005). Our model also indicates suitable climates for stripe rust persistence along the eastern states from Georgia to Pennsylvania, which has also been reported as potentially both oversummering and overwintering re‐ gions along the Appalachian Mountains (Sharma‐Poudyal et al. 2013). In its native range in the Middle East the P. striiformis model accords with known distribution data (rusttracker.cimmyt.org). The model also agrees with observations that stripe rust can persist year round in Europe (Roelfs et al. 1985) and China (Zeng et al. 2006). The modelled potential for year‐round survival of stripe rust along the northwest, southwest and southeast coasts of South America and parts of eastern and southern Afri‐ ca could be the sources of inoculum for stripe rust epi‐ demics that occur in those regions. The CLIMEX Growth Index (GIA) map shows how climati‐ cally suitable areas would be for stripe rust development if infection were to occur, typically via wind‐dispersed inoculum (Figure 6). In the United States, the CLIMEX GIA map agrees with the known distribution of stripe rust epidemics in south central states and the central plains. The CLIMEX GIA map shows that Europe is a suitable re‐ gion for stripe rust infections. Southeastern and south‐ western Australia are also projected to be suitable for stripe rust development, which agrees with the known
Figure 5. Modelled global climate suitability (EI) for Puccinia striiformis, as a composite of natural rainfall and irrigation based on the irrigation areas identi ied in Spatial Production Allocation Model (SPAM 2005).
occurrence data (Wellings 2007). In south Asia, the GIA map indicates suitable climate for stripe rust in Pakistan, where stripe rust has been reported (Afzal et al. 2007; Roelfs and Bushnell 1985). In the rainfed version of the CLIMEX model used to generate this GIA map (Figure 7), soil moisture is a limiting factor. However, there is a sub‐ stantial amount of irrigated wheat production in Paki‐ stan. Once we allow for 2.5 mm per day of top‐up irriga‐
tion throughout the year (Figure 6), the mapped GIA ac‐ cords closely with the reported occurrence of stripe rust in Pakistan. The model results provide a good it to the geographical distribution of stripe rust. In general, areas at risk of damage by P. striiformis include all regions in which wheat is grown under conditions with high soil moisture
Figure 6. Modelled global potential occurrences (GI) for Puccinia striiformis, as a composite of natural rainfall and irrigation based on the irrigation areas identi ied in Spatial Production Allocation Model (SPAM 2005).
or high natural dew formation. Stripe rust epidemics are related to both year‐round survival and long distance dispersal via wind. The CLIMEX model shows where stripe rust can persist year round (EI) versus where the disease can develop (GIA) if inoculum arrives via long distance dispersal. These spatially calibrated climate suitability and inter‐seasonal persistence data have value in guiding the development of stripe rust resistant wheat and the deployment of other strategies to mitigate the crop losses attributable to stripe rust.
Figure 7. CLIMEX GIA Map for Eurasia with only natural rainfall
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ACKNOWLEDGEMENTS HarvestChoice would like to acknowledge Noboru Ota for spa al data analysis and the produc on of all maps. This brief was prepared with support from the CGIAR Research Program on Wheat led by CIMMYT (Interna onal Maize and Wheat Improvement Center) and ICARDA (Interna onal Center for Agricultural Research in the Dry Areas), and the Bill and Melinda Gates Founda on by way of the Har‐ vestChoice project with addi onal support from the Commonwealth Scien fic and Industrial Research Organisa on (CSIRO) and The Interna onal Science and Technology Prac ce and Policy Center (InSTePP), University of Minnesota.
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