The growing threat of stripe rust worldwide

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Borlaug Global Rust Initiative
M. Solh et al • BGRI 2012 Technical Workshop • 1–4 September 2012, Beijing, China
The growing threat of stripe rust worldwide
M. Solh1, K. Nazari1, W. Tadesse1 and C.R. Wellings2
1International Center for Agricultural Research in the Dry Areas (ICARDA), P.O. Box 5466, Aleppo, Syria; 2The
University of Sydney, Plant Breeding Institute, Private Bag 4011, Narellan NSW 2567, Australia. Email:
k.nazari@cgiar.org
Keywords: breeding, mitigation, resistance, rusts, strategy, surveillance, wheat
Abstract
Stripe rust of wheat (yellow rust) is a recurring production constraint in the majority of wheat growing areas
of the world. The transboundary nature of the pathogen coupled with its current virulence capabilities,
favorable environmental conditions, sometimes overlapping and/or continuous cultivation of susceptible
varieties in stripe rust-prone zones, and genetic uniformity of certain recent ‘mega-cultivars’ were major
driving forces in stripe rust epidemics worldwide. Breeding for resistance must continue be the central
pillar of stripe rust control, and for this to be effective there must be adequate pathogen monitoring
combined with commitment to identify and incorporate diverse sources of resistance, preferably of the
durable type. Deployment of resistance will only be successful if it is combined with high yield and
appropriate end-use quality to meet the needs of farmers and consumers. Suitable seed systems need to be
in place for timely distribution of varieties. This paper deals with the historical impacts and current status of
stripe rust epidemics and highlights the need for regional and global collaboration in mitigating the global
impact of this disease.
Introduction
Wheat was among the first of the domesticated food crops and for more than 10,000 years has been the basic
staple food for most of the world. It is the most widely grown cereal crop in the world and one of the central
pillars of global food security. About 650 million tonnes of wheat was produced worldwide on 217 million
hectares in 2010 with a productivity level of about 3 t/ha-1 (FAO 2012). After the quantum leap of the Green
Revolution, wheat yields have been rising by only 1.1% per year, a level that falls far short of the demand of a
population that is growing 1.5% or more annually. According to some estimates, global wheat production must
increase by at least 1.6% annually to meet a projected wheat demand of 760 million tonnes by 2020 (Dixon et al.
2007). This is however, very challenging with the current scenario of climate change, increasing drought/water
shortage, soil degradation, declining supply and increasing cost of fertilizers, increasing demand for bio-fuel, and
new virulent pathogen and pest strains.
Stripe rust epidemics have frequently occurred in the USA (particularly the Pacific Northwest region of North
America), South America (central and southern wheat production areas), North Africa (Morocco, Algeria and
Tunisia), East Africa (Ethiopia and Kenya), East Asia (northwest and southwest China), South Asia (India, Pakistan,
and Nepal), Australasia (Australia and New Zealand), the Nile Valley and Red Sea (Egypt and Yemen), West Asia
(Lebanon, Syria, Turkey, Iran, Iraq, and Afghanistan,), Central Asia (Kyrgyzstan, Uzbekistan, Tajikistan, and
Turkmenistan), Caucasus (Georgia, Armenia and Azerbaijan), and Europe (UK, northern and southern France, the
Netherlands, northern Germany, Denmark, Spain, and Sweden). Regular regional crop losses in the range 0.1–5%
and sometimes up to 25% have been recorded due to stripe rust. However, individual crop losses of up to 80%
were reported in the widespread epidemic in the Middle East and North Africa in 2010, when initial infection
occurred on susceptible wheat varieties at early growth stages. Considering the epidemiological factors and the
history of recurrent epidemics, the wheat areas in Africa (eastern and northern countries), the Middle East, the
Caucasus region, and West and South Asia now appear to comprise a single epidemiological zone – hence any
new pathotype that evolves in one country in the region is likely to disperse to the entire region.
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Borlaug Global Rust Initiative
M. Solh et al • BGRI 2012 Technical Workshop • 1–4 September 2012, Beijing, China
Although stripe rust is historically considered a disease of lower temperature regions, its relatively recent
introduction and establishment in Australia and South Africa suggest a wider level of adaptation. The more
recent spread of two new pathotypes/pathotype groups that largely replaced and expanded the range of stripe
rust in Australia, central USA, and across CWANA and Europe have exacerbated the situation. These pathotypes
appear not only to have the ability to adapt to higher temperatures (and therefore the potential to adapt to
climate change), but have undergone rapid mutational changes in Australia, North America and northern
Europe to overcome a number of specific resistance genes deployed in wheat and triticale. With current climate
change predictions, winters are likely to become warmer and the likely consequence is earlier stripe rust
infection and spread and hence more damaging epidemics throughout all wheat growing areas.
Regional impacts of stripe rust
Several worldwide stripe rust epidemics have occurred in recent decades with potential to inflict regular
regional crop losses in the range of 0.1–5%, with rare events giving losses of 5–25% (Wellings 2011). Stripe rust
can cause 100% yield loss in susceptible cultivars if infection occurs in early growth stages (Chen 2005), and this
is likely to be exacerbated in regions with mild winter periods and significant levels of pathogen survival
between cropping seasons.
North America
Stripe rust has been historically considered a common disease of wheat in North America since its first detection
in 1915 but was not considered a destructive disease in the US from the 1930s until the late 1950s (Line 2002).
However, it became increasingly important from the late 1950s and early 1960s (Chen et al. 2002). Since then,
stripe rust has been considered the most significant disease of wheat in western North America, and from the
1980s became increasingly important in the south-central USA and the central Great Plains in certain seasons.
Comprehensive reviews have dealt with the distribution of stripe rust, yield losses, status of resistance of
commercial wheat varieties, and fungicide application in the USA (Line 2002; Chen 2005). During 2000–2007,
stripe rust occurred in at least 15 US states each year with yield losses estimated at more than 6.5 million tonnes
(Chen et al. 2010). However, yield loss was estimated at 2.2 million Mt (87 million bushels) in the severe 2010
epidemic, and the additional cost of fungicide application was estimated at $30 million in Washington State
alone (X.M. Chen pers comm). In 2011, stripe rust was not a large problem in the Great Plains due to widespread
drought, although the Pacific Northwest was even more affected by the disease than in 2010. Based on the stripe
rust level in experimental fields and on crop growth stage, the potential yield loss on susceptible varieties was
estimated to exceed 70%. For the 2012 crop, yield losses were predicted to reach 50% in highly susceptible
wheat varieties.
Europe
Stripe rust has been considered one of the most damaging diseases of wheat in Europe for more than a century
(Hovmøller and Justesen 2007). It is the most common wheat rust in a region spanning northern France, the
Netherlands, northern Germany, Denmark, and the UK (Bayles et al. 2000). Northwestern Europe is considered a
source of new pathotype variability due to intensive breeding for resistance that led to the use of major genes
(Stubbs 1988). Epidemics have also occurred in southern Europe, but less frequently. Virulence for almost all
seedling resistance genes, either present singly or in various combinations, has generally been found following
their deployment in commercial cultivars (Stubbs 1985; Johnson 1988). A comprehensive survey conducted
during the 1960s and 1970s estimated average annual grain yield losses of 10% in Europe (Zadoks and Rijsdijk
1984). Despite favorable environmental conditions in Europe, stripe rust has been broadly under control since
the epidemics of the late 1980s and early 1990s, possibly due to successful deployment of resistance in modern
European cultivars, as well as the widespread use of fungicides (Schmits 2003, cited in Hovmøller and Justesen
2007). Nevertheless, failure of resistance genes continues to be observed as consequence of mutation. Virulence
for Yr17 (widely introduced into European cultivars in the early 1990s) was first detected as a single pathotype in
the UK in 1994 and this pathotype was subsequently detected in Denmark in 1997 (Justesen et al. 2002), then in
France and Denmark in 1997 and 1998, respectively (Hovmøller et al. 2002). This observation indicated that
northern Europe remained a single stripe rust epidemiological zone (Hovmøller and Justesen 2007). In France,
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Borlaug Global Rust Initiative
M. Solh et al • BGRI 2012 Technical Workshop • 1–4 September 2012, Beijing, China
stripe rust occurs most frequently in the north, with the most devastating epidemics occurring in the 1980s
(Mboup et al. 2012; de Vallavieille-Pope et al. 2011).
In 2009, stripe rust spread rapidly and overcame resistance in triticale cultivars in Denmark. This resulted from a
new pathotype, different from previously characterized Pst pathotypes in Denmark, and caused a 7.5 t/ha grain
loss. A recent epidemic of wheat stripe rust in Spain is being investigated as a likely introduction (M. S.
Hovmøller pers comm).
Australasia
Australia produces 20-25 million tonnes of wheat annually. Wellings and McIntosh (1990) stated that a single Pst
pathotype was introduced into eastern Australia in 1979 and moved to New Zealand) in 1980. More than 20 new
closely related pathotype derivatives were subsequently detected over two decades. A new exotic pathotype
was reported in Western Australia for in 2002 (Wellings et al. 2003). This pathotype was virulent for Yr6, Yr7, Yr8,
Yr9, and YrA, and avirulent for Yr1, Yr2 (Heines VII), Yr3, Yr4, Yr5, Yr10, Yr15, Yr17, and several uncharacterized
resistances in the differential set. It was clearly exotic because it was pathogenically and molecularly distinctive
from the pathogen population in eastern Australia at that time. During 2003-2006, an estimated $40-90 million
was spent annually on fungicides by Australian farmers (Wellings 2007). Pathotypes virulent for Yr17 and Yr27
are currently considered a serious threat to wheat growing areas in Australia. Despite periodic epiphytotics and
occasional exotic pathotype introductions, the national breeding program for rust resistance in Australia is
considered a success in containing the worst effects of rust epidemics. Murray and Brennan (2009) estimated the
value of the national breeding effort for resistance at $AUS million 438, 431 and 152, respectively, for stem rust,
stripe and leaf rust.
Central and West Asia and Northern Africa (CWANA)
Reports indicate that at least three widespread stripe rust epidemics have occurred in this region since the
1970s. In each case the epidemics were considered a consequence of favorable environmental conditions,
emergence and subsequent wide distribution of new virulent pathotype/s, and most notably, deployment of a
narrow genetic base of resistance in recently released popular cultivars. Importantly, local susceptible cultivars in
all three epidemics made very significant contributions to disease development and crop loss.
A major factor in the epidemics of the 1970s was the widespread cultivation of susceptible local cultivars
together with improved varieties based on Yr2 resistance. Siete Cerros, Kalyansona, PV 18A, Indus 66, Mexipak,
Ouds and Mivhor 77 were planted across wide areas including North Africa, the Indian sub-continent, the Middle
East, the East African highlands, Iran and China (Saari and Prescott 1985).
The second classical example of stepwise regional dispersal of the stripe rust pathogen was the widespread
distribution of Yr9-virulent pathotypes during 1985–1997, following initial detection in the Horn of Africa. These
pathotypes subsequently migrated northwards into CWANA, and progressively in a west-east direction that
eventually included the Indian sub-continent. This caused severe crop losses in widely grown cultivars covering
more than 20 million hectares. In 1993 and 1995, stripe rust epidemics occurred in most wheat-growing areas in
Iran and caused in excess of 30% crop loss. Estimated grain losses were in the order of 1.5 million Mt in 1993 and
one million tons in 1995 (Torabi et al. 1995). In Turkey, the wheat cv Gerek 79 grown on more than one million
hectares endured losses of 26.5% due to the stripe rust epidemic of 1991 (Braun and Saari 1992).
In the southern region of West Asia, severe epidemics of stripe rust were also recorded. In Yemen losses in grain
yield were in the range 10-50% during 1991-1996 (Bahamish et al. 1997). These epiphytotics occurred in crops
seeded in both the main and off seasons. In Central Asia a stripe rust epidemic in Azerbaijan in 1996 caused
significant yield losses. In 1997, the wheat crop in Tajikistan incurred greater than 60% loss (Yahyaoui et al. 2002).
The facultative winter wheat regions of Uzbekistan and southern Kazakhstan frequently report stripe rust
incidence, with recent severe epidemics occurring in 2009 and 2010.
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Borlaug Global Rust Initiative
M. Solh et al • BGRI 2012 Technical Workshop • 1–4 September 2012, Beijing, China
In Ethiopia, epiphytotics occurred in 1977, 1980-1983, 1986, 1988, and 1990. Yield losses in 1988 were severe in
bread wheat, and as high as 58% on cv Dashen (Badebo and Bayu 1992). Ethiopia and Yemen form an ecological
unit in regard to rust epidemiology and may have an important role in inoculum spread and virulence changes
across the CWANA region.
Following the Yr9 virulence-driven epidemics, the Yr9-susceptible varieties were extensively replaced with
CIMMYT-derived germplasm (e.g. cvs Kauz, Atilla, Opata, Nacozari, Buckbuck, and Crow). The resistances in many
of the replacement cultivars, including the mega-cultivars PBW343 (in India), Inquilab 91 and Bakhtwar (in
Pakistan), Chamran and Shiroudi (in Iran), Kubsa (in Ethiopia), and Cham 8 (in Syria) were later reported to be
based on Yr27, an all-stage resistance gene effective against the Yr9-predominant pathotypes of that time. The
third episode of regional stripe rust epidemics developed when these resistant varieties showed increased rust
levels, mainly in Pakistan, India, and southern Iran. Loss of effectiveness of Yr27 resistance in cvs PBW343,
Inquilab 91 and Chamran (in India, Pakistan, and Iran, respectively) were reported during 2002-2004. Although
sporadic stripe rust outbreaks appeared in some areas, unfavorable environmental conditions possibly restricted
rapid increases of the Yr27-virulent pathotypes until 2009 when conducive conditions resulted in severe
epidemics in a number of CWANA countries (Pakistan, Morocco, Algeria, Tunisia, Uzbekistan, Turkey, Iran,
Yemen, Azerbaijan, Georgia, Uzbekistan and Afghanistan). Environmental conditions favoring rust development
continued into 2010, with a mild winter and adequate rainfall in several CWANA countries, resulting in early
stripe rust outbreaks. The consequence was the 2010 stripe rust pandemic throughout the major wheat-growing
areas in CWANA and Caucasus countries, causing very high yield losses, particularly in Syria where, for example,
cultivar Cham 8 (with Yr27) occupied over 70% of the wheat area. Despite favorable environmental conditions in
many areas in CWANA in 2011 and 2012, severe stripe rust epidemics did not eventuate, illustrating the year-to
year variability of plant disease and its consequences. In 2010, the absence of resistant varieties in Ethiopia led to
more than US$3.2 million expenditure on fungicides, and over 750,000 ha were sprayed against stripe rust in
Iran. All major wheat cultivars grown in Uzbekistan, Morocco, Iraq, Azerbaijan, Afghanistan, and Tajikistan were
susceptible. A devastating epidemic occurred across the Central Plateau in Turkey where the susceptible cv
Gerek 79 predominated.
India, Pakistan and China
Following the Green Revolution in the mid-1960s, wheat production in India incrementally increased to the
present level of 86 Mt in 2010-11 (Sharma and Saharan 2011). Stripe rust is an important disease in India,
particularly in northwestern regions and the northern hills. During the 2010-11 season, it was severe in several
areas, particularly where the majority of varieties was susceptible. However, timely fungicide intervention largely
averted major crop damage. Pathotypes with virulence for Yr9 and Yr27 currently predominate in India (Sharma
and Saharan 2011).
With 22.8 million ha of wheat and total wheat production exceeding 100 million Mt, China is the world’s largest
wheat producer (Wan et al. 2004). Stripe rust epidemics are major recurrent problems that can annually affect
more than 20 million ha resulting in inter-regional epidemics (Li and Zeng 2000) with reported yield losses
totaling 14.38 Mt in the severe epidemics in 1950, 1964, 1990, and 2002. China is considered a unique
epidemiological zone and is considered to have the largest independent epidemic region. Extensive surveys in
the last 60 years indicated very high pathogenic variability (Wan et al. 2004) and breeding has been the main
focus of mitigation. Despite successes, stripe rust remains the most destructive wheat disease in China (W. Q.
Chen pers comm).
Stripe rust is a serious threat to wheat production in northern and central-west areas of Pakistan. High
production losses were reported in 1995 when cv Pak 81 (synonym Veery#5, carrying Yr9) predominated. This
epidemic was attributed to Yr9-virulent Pst pathotypes. As elsewhere in the region, stripe rust epidemics in
Pakistan fall into three periods: before 1993 when Yr9 was effective; 1993-2002 when Yr9-virulence was
widespread in major wheat-growing areas; and after 2002 with the occurrence of virulence for Yr27. The two
mega-cultivars Pak 81/ Pirasabak 85, and Inquilab 91, became susceptible due to ineffectiveness of Yr9 in
1994/95 and of Yr27 in 2002, respectively, resulting in significant yield losses. Yield losses of 20% were estimated
as a consequence of Yr9 virulence. The high-yielding cultivar Seher 2006, which is resistant to Yr27-virulent
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pathotypes, was to replace Inquilab 91, but became susceptible to leaf rust –illustrating the seriousness of leaf
rust in Pakistan and the need for multiple rust resistances.
Minimizing the impacts of stripe rust epidemics
A. Coordinated pathogen monitoring
The rapid spread of highly virulent and aggressive Pst strains, and the genetic uniformity of mega-cultivars
across large areas, emphasizes the relevance of pathogen surveys covering larger areas (Hovmøller et al. 2011).
In response to the need for a global rust survey, an important step towards a unified and intensive Pst survey
was taken in 2008 when ICARDA, CIMMYT, and Aarhus University launched the Global Rust Reference Center
(GRRC) at Aarhus University, Flakkebjerg, Denmark (Hovmøller et al. 2010). The Center is accessible year-round
for rust samples from all countries. One purpose of the establishment of the GRRC, which has become part of
BGRI, is to complement existing stripe rust and stem rust surveillance efforts by ICARDA, CIMMYT, and the NARs,
particularly in developing countries. The principal objectives of the GRRC are:
1. Facilitating an early global warning system for transboundary spread of pathotypes through:
a. Pathogen fingerprinting for rapid detection of incursions on a global scale and on understanding
dispersal pathways
b. Assessment of pathogenic variability and aggressiveness to determine wheat varieties at immediate
risk
c. Risk analysis of rust pathogen adaptation to changing climates
2. Securing unique pathogen resources to assist breeding for rust resistance
3. Providing and facilitating specialized training in epidemiology, population genetics, and pathogen evolution
4. A global source of publically available information on the cereal rusts and rust pathogen virulence surveys
The success of the GRRC will depend on global communication networks that allow rapid and free exchange of
information to inform local advisory personnel in a timely and effective manner. National pathotyping capability
will nevertheless be crucial in managing the large sample volumes necessary for effective regional surveillance
of Pst populations. The GRRC will be a valuable reference for local pathology teams in gaining confidence in
pathotype identity and confirming the potential of newly identified variants.
B. Resistance gene monitoring in commercial cultivars
Unless a comprehensive understanding of resistance genes in major cultivars within and between regions is
established and updated, the outputs of the very best efforts to monitor Pst populations will remain largely
irrelevant. Characterized pathotype collections of Pst are frequently used for postulation of resistance genes in
multi-pathotype seedling tests (Perwaiz and Johnson 1986; Dubin et al. 1989; de Vallavieille-Pope et al. 1990;
Nazari et al. 2008).
The development of diagnostic molecular markers has allowed some genes to be routinely screened in
laboratories supporting breeding programs. The most important gene in this respect is the durable adult plant
resistance gene Yr18 which can now be conveniently monitored without the need for field disease nurseries. An
international effort is needed for collaboration in marker development and utilization of linked markers, and
especially in breeding for multiple gene resistance.
C. Effective resistance breeding
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Development and use of resistant cultivars is widely considered the most economically feasible and
environmentally appropriate way to combat wheat rusts. The international wheat breeding programs at CIMMYT
and ICARDA have been developing high yielding, widely adapted wheat germplasm with resistance/tolerance to
major biotic and abiotic stresses following the classical breeding approaches and strategies whereby crossing
blocks are assembled using hallmark cultivars and elite genotypes; the segregating generations are evaluated in
shuttle breeding and inoculated rust nurseries, followed by key location testing of fixed lines to identify stable
genotypes with appropriate combinations of desired traits. Distribution of elite material globally through the
international nursery and yield trial system has resulted in the release of many high yielding, rust resistant and
widely adapted wheat varieties in many countries. However, use of single resistance genes has repeatedly led
‘boom and bust cycles’ as the pathogens adapt and increase as evidenced above. The assembly of adult plant
minor gene resistances (APR) has been the dominant breeding approach for reducing the impacts of ‘boom and
bust’ by CIMMYT and ICARDA over the past decade. The development of molecular markers closely associated
with APR genes will enable the assembly of gene pyramids to combat the evolutionary capacity of Pst. However,
there is only one currently available marker (CsLv34 for selecting Lr34/Yr18) and more research and development
is required in this area. Future strategies may also involve genomic selection (GS) which allows prediction of
genotypic values, and thereby facilitate the selection of multiple minor QTLs associated with presumed non-race
specific APR genes. Conventional breeding approaches complimented with GS and doubled haploid production
systems would also enable the enhancement of breeding efficiency in developing high yielding, widely adapted
genotypes with durable resistance to rusts.
D. Encouraging national action plans
An effective national strategy for combating wheat rusts has four key components: surveillance and rapid
reaction plans; information sharing within and between countries; capacity strengthening – for government
officials, extension services, and farmers; and participation in ongoing research programs to develop resistant
wheat cultivars. A multi-faceted approach is needed by countries to combat wheat rusts. The obvious immediate
response to combat rust outbreaks (whether new pathotypes or not) is fungicides wherever possible. Reducing
the cropping area of susceptible cultivars across large areas is perhaps the best insurance against widespread
rust damage. Countries can consider policies to plant a range of resistant wheat types in their farming systems –
greatly reducing the risk of widespread epidemics. A long-term plan includes participation in international
research efforts to continually monitor and develop wheat varieties that resist rust and other diseases.
One core issue for planners and policy makers is that stripe rust does not respect national borders. The rusts are
‘social diseases’ and can best be managed by shared agricultural practices and policies agreed across regions.
The fight against rust requires good neighbors, working together. The role of policy makers and global
leadership is crucial if we are to take a significant step forward in minimizing the impacts of this disease.
At the regional and international level there is a need to build a cooperative attitude for information sharing, the
mutual sharing of risk analyses, and trust. The information that needs to be collected and shared across regions
includes data on changing rust disease patterns, wheat variety distribution, changing agronomic practices, and
climate change and weather patterns. The use of ‘rust trap nurseries’ across affected regions is a good example
of an effective strategy for early detection and prevention of stripe rust. As rust moves across a region,
researchers and planners can see the effect of new pathotypes on wheat varieties, and organize for
dissemination of the most resistant varieties for the following season.
E. Accelerated seed delivery system to combat the threat of rusts
Seed is the most efficient mechanism for delivering rust-resistant wheat varieties to farmers. Availability and
access to quality seed is expected to accelerate the adoption and dissemination of new durable rust-resistant
varieties and associated production technologies. However, weaknesses in national seed systems threaten to
impede the diffusion and adoption of replacement varieties.
For an effective seed delivery system, it is important to develop and implement the following approaches:
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a. Fast-track variety testing and release (e.g. adaptation trials) systems by pursuing flexible policy/regulatory
options with partners.
b. Accelerate pre-release seed multiplication of promising lines and large-scale production of released
varieties for distribution through both formal and informal channels.
c. Popularize and promote rust-resistant varieties among farmers (including targeted small-pack seed
distribution) to initiate informal farmer-to-farmer seed sharing and diffusion.
d. Build capacity in technical aspects of seed production and in the provision of infrastructure (training and
critical equipment).
e. Develop methods to rapidly dis-adopt cultivars that are susceptible or whose resistance is at threat from
an emerging new pathotype.
Conclusions
The current challenges facing the global wheat production are complex, and addressing them requires an
understanding of the drivers of past trends and prediction of future changes. Designing an effective research
strategy with application of new breeding tools, such as genome-wide selection and resistance gene pyramids,
needs a matching effort in establishing communication net-works and collaborations. The concept of food
security involves the ability to improve and sustain production consistent with an array of economic and social
measures. NARS must provide a significant contribution to this goal by improving and securing production in
the long term.
Wheat cropping technologies, including varieties, are specifically important factors for controlling pest
outbreaks. Developing and disseminating cultivars with progressively improved rust resistances needs to be
strengthened with technological packages, such as integrated pest management (IPM). In addition to the
availability of resistant varieties that are known to, and accepted by, farmers, country preparedness for stripe
rust outbreaks necessitates the availability of sufficient seed in both quantity and quality. In most cases, the
bottleneck for getting resistant varieties into the field is lack of local and national capacity to rapidly multiply
seeds and deliver them to the market.
Improving national seed production capacity and delivery requires long-term planning and funding, and must
involve government, private enterprise and farmers. There are many complex organizational, procedural and
legal issues that differ between countries, but for success, coordination and timely information-sharing among
all stakeholders - including pathologists, plant protection officers, breeders, seed system and extension agents,
marketers and farmers - are paramount.
An international forum to discuss the way forward in stripe rust R&D was held at ICARDA headquarters in
Aleppo, Syria, in April 2011. The following resolutions from that meeting continue to provide a framework for
the future:
1. Long-term investment is needed to reduce the threat of stripe rust
While a significant investment has been made over the past five years in surveillance and control of stem rust,
stripe rust remains the most significant endemic threat across a majority of the global wheat producing regions.
In spite of its preference for cooler environments, stripe rust is rapidly spreading to new areas where it was not
previously a problem. Aggressive new stripe rust pathotypes are adapting to warmer climates, causing recent
outbreaks at the global level. Comparatively, investments in stripe rust R&D are small and less coordinated
across countries. To reduce the current spread of stripe rust, more investment to support countries to improve
surveillance and in breeding of durable varieties that resist stripe rust.
2. Strategies to address wheat stripe rust disease
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M. Solh et al • BGRI 2012 Technical Workshop • 1–4 September 2012, Beijing, China
a. Surveillance and information exchange between countries.
b. Planning, awareness, and preparedness to rapidly deliver appropriate seeds and fungicides where they are
needed to arrest the spread of wheat rust diseases.
c. New capacity and skills in ministries, extension services, and at the farm level to develop effective strategies for
managing rust diseases.
d. Crop research for a continued, long-term effort in developing new varieties that are resistant to the emerging
pathotypes of wheat rust.
3. Approaching stripe rust as a social disease
One core issue for planners and policy makers is that stripe rust does not respect national borders. The rusts are
‘social diseases’ and can best be managed by shared agricultural practices and policies agreed across regions.
The fight against rust requires good neighbors, working together. The role of policy makers and global
leadership is crucial if we are to take a significant step forward in minimizing the impacts of Pst.
At the regional and international level there is a need to build a cooperative attitude for information sharing, the
mutual sharing of risk analyses, and trust. The datasets that need collecting and sharing across regions include
information on monitoring of changing rust disease patterns, wheat variety use per region, changing agronomic
practices, and observations of climate change and weather patterns. The use of ‘rust trap nurseries’ across
affected regions is a good example of an effective strategy for early detection and prevention of stripe rust. As
rust moves across a region, researchers and planners can immediately see the effect of new pathotypes of rust
on wheat varieties, and organize for dissemination of the most resistant varieties for the following season.
4. Encouraging the development of national action plans
An effective national strategy for combating wheat rust has four key components: surveillance and rapid
reaction plans; information sharing across countries; capacity strengthening – for government officials,
extension services, and farmers; and participation in ongoing research programs to develop resistant wheat
varieties. A multi-faceted approach is needed by countries to combat wheat rusts. Immediate action to combat
new rust pathotypes is often the use of fungicides. Reducing the cropping of susceptible mega-cultivars across
vast wheat growing areas is perhaps the best insurance policy against widespread rust damage. Countries can
consider policies to plant a range of resistant wheat types in their farming systems – greatly reducing the risk of
emerging virulent rust types spreading over the entire area. A long-term plan includes participation in
international research efforts to continually develop wheat varieties that resist rust and other diseases.
5. Reducing the impacts of narrow range variety dependence
Diversified cropping of wheat – avoiding the sowing of mega-cultivars across large cropped areas – is another
possible defense against wheat rust. In most areas of the Middle East, East Africa, and South Asia, farmers have
been planting the same varieties for 20–30 years. This practice is not advisable in a situation where stripe rust
pathotypes are mutating and new ones are emerging much more rapidly than in the past and overcoming
resistance in current varieties.
6. Developing a clear approach to seed multiplication and farmer engagement with new, diverse varieties
Efficient and effective seed delivery systems are critical for new crop varieties to reach farmers and bring impacts
in ensuring food security and improving livelihoods of farmers. However, most national seed systems operate
under heterogeneous environments in terms of agro-ecology, farming systems, crops and markets. They face a
broad range of constraints including policy and regulatory frameworks; inadequate institutional and
organizational arrangements; deficiencies in production, processing, and quality assurance infrastructure; and
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lack of trained personnel limiting technical and managerial capacities, compounded by farmers’ difficult socio-
economic circumstances. It is therefore important to assist and strengthen NARS in capacity development,
establish fast-track variety release systems, and participatory demonstration and accelerated seed multiplication
of newly released wheat varieties to ensure fast replacement of existing vulnerable commercial varieties.
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