Wheat yellow rust (Puccina striiformis f. sp. tritici) is currently the most damaging disease of wheat on the global scale. Under suitable conditions, yield losses of 60% or more are possible. Since 2000 two new aggressive strains of yellow rust have been identified and these have spread across continents at a rapid rate. Virulence to important resistance genes like Yr27 has appeared and has been one factor in major disease epidemics that have occurred from North Africa to South Asia.
Regularly updated situation reports on cereal rusts are given based on information provided by a global network of rust workers.
Currently, most of the global surveillance and monitoring efforts reported in RustTracker.org have focused on stem rust, but it is hoped to expand the information on yellow rust in the near future
Unusual and severe epidemics of yellow rust were observed on several continents in 2017. In a number of cases, epidemic sites at different continents were inter-related by prevalence of genetically identical yellow rust genotypes and races.
- South America: Three distinct genotypes were detected in severe yellow rust epidemics in Argentina in 2017. These genotypes have been associated with recent rust epidemics in Europe/northern Africa.
- Central Asia/East Africa: Region specific genotypes were prevalent in Central Asia. One of these (PstS11) was also detected in East Africa in 2016, prevalent in severe yellow rust epidemics in Ethiopia. The spread of PstS11 was confirmed by the presence of identical races in Central Asia and Africa.
- Europe: Warrior(-) was the most prevalent race in Europe (lineage PstS10). Original Warrior (PstS7) and Kranich (PstS8) races were less prevalent, but spreading to new areas.
- North Africa/South Europe: A distinct race of lineage PstS14, first detected in 2016, became widespread and caused severe yellow rust epidemics in Morocco 2017. Another distinct race of PstS13, first detected in 2015, caused epidemics on both bread wheat and durum wheat in Italy.
- SSR genotyping was successfully implemented as part of the Pst race surveys, expanding testing capacity significantly, and providing results for both recovered and non-recovered samples.
- Summary of SSR genotyping and race phenotyping results from GRRC (2008-2017), is available online (http://www. wheatrust.org/), including a new page with documentation of relationship between races and genetic lineages.
The number of incoming samples of rust infected plant material has increased in recent years. At the same time, the testing capacity has increased by the implementation of rapid and robust SSR (DNA) genotyping procedures, which does not require prior recovery and multiplication of alive spore samples.
It has been possible to establish a unique relationship between SSR genotyping and race typing results from huge datasets based on extensive yellow rust sampling across many years and multiple locations at six continents. In a number of cases of recent emerged genetic lineages, only a single race was present within a single lineage. In other cases, several races were present within individual lineages, reflecting the rapid evolution of virulence in the yellow rust fungus.
The naming system and relationships between genetic lineages and race phenotypes are documented here
New facilities in the Wheat Rust Toolbox
The Wheat Rust Toolbox is a data management system holding all data, tools and services from GRRC. The toolbox also generates the maps and charts with results of the SSR genotype and race phenotype test. These maps can be embedded into relevant web portals and information systems e.g. wheatrust.org and RustTracker – to be integrated with additional information and visualised in different contexts.
New maps and charts have been developed to descriminate the results based on SSR genotyping and race phenotyping. All samples reveived by GRRC are now genotyped using 19 SSR markers. Based on the results from this analysis only a subset of isolates are race phenotyped. Therefore, some results for a single isolate appears on both race phenotype maps and charts and the maps for genetic lineages.
A similar discrimination of results from SSR or SNP genotyping based on D-samples (dead) and race phenotyping from live samples is under development for stem rust data. Until this new system for SR is agreed upon and data have been organised accordingly, we have unhided maps and charts for SR at the GRRC web site.
This post by Jens Grønbech Hansen on 21st Feb 2017 originally appeared on the Global Rust Reference Center website
In 2016 surveys were carried out in all the four key wheat growing regions: South Rift (June, July), Mount Kenya region (July), and North Rift (September) and Central Rift (part of August and September). A total of 304 farms were sampled. Stem rust was detected in 235(78.3%), yellow rust in twenty-eight (9.3%) and leaf rust in fourteen (4.7%) of the farms. The disease severity was ranging from trace to 90S; trace to 60S and trace to 50S for stem rust, yellow rust and leaf rust respectively. Stem and yellow rusts were detected in all the wheat growing regions while leaf was detected in South, North and Central Rift. Stem rust infection ranged from TR to 90S with maximum infection in Central Rift( 88.3%), Mt. Kenya region (80.3%); South Rift(76.5%) and North Rift (72.4%). Yellow rust infection ranged TR to 60S with maximum infection in Central Rift (16.7%); North Rift(13.3 %) and minimum infection in South Rift( 4.9%),) and Mt. Kenya region ( 1.7%). Leaf rust infection ranged from trace to 50S with maximum infection in North Rift (10.2%) minimum infection in Central Rift (3.3 %) and South Rift (1.2%). Continue reading
The latest version of the Mehtaensis newsletter (a 6 monthly newsletter named after Prof. K.C. Mehta) has just been published by the IIWBR, Regional Station, Flowerdale, Shimla. Compiled and edited by Dr. S.C. Bhardwaj, O.P. Gangwar, Pramod Prasad and Hanif Khan with technical assistance from S.B. Singh and Subodh Kumar. Mehtaensis contains a detailed summary of all the rust activities and race analysis results from India and neighbouring South Asian countries during the period July – Dec 2015. The executive summary is reproduced here:
“During offseason 135 samples of three rusts of wheat were received from Himachal Pradesh, Punjab, Tamil Nadu and Uttarakhand. 49 samples of all three rusts of wheat were analyzed, some of which were spill over of main season. Ug99 type of virulence was not identified anywhere in India. In brown rust pathotype77-5 (121R63-1) of brown rust, 46S119 and 110S119 of yellow rust and 40A (62G29) of black rust were found most frequently among the analyzed samples. Nucleus inocula of three rusts were also supplied to 38 Scientists/Research centres to facilitate research work elsewhere in India. More than 2850 lines of wheat and barley were evaluated against the pathotypes of different rusts. The tested material included the breeding lines provided by breeders from various parts of India, exotic wheat lines from CIMMYT and ICARDA. In addition 150 lines of AVT I and II are being evaluated against different pathotypes to identify rust resistant wheat lines. For monitoring the occurrence/spread of different diseases of wheat, Wheat Disease Monitoring Nursery (WDMN) and SAARC-WDMN were planted at 50 and 28 locations, respectively. Early occurrence of yellow rust was reported from Ropar, Anandpur Sahib and Hoshiarpur district of Punjab. Three Ug99 resistant genetic stocks namely FLW31, FLW32 and FLW33 have been developed. FLW31 and FLW33 are completely resistant against black and brown rusts while FLW32 has resistance to black rust and adult plant resistance against yellow and brown rusts. Work on standardization of doubled haploid production in wheat using maize pollination induced chromosome elimination was initiated. Offseason nursery was used for selection and generation advancement of 325 wheat lines. Under frontline demonstration of wheat variety, HS542 was planted in five adopted villages (12 farmers) of Tehsil Arki (Solan district of Himachal Pradesh).”
Stripe rust was detected on 18th Dec 2015 in Anandpur Sahib and Ropar districts, Punjab and subsequently in Hoshiarpur district. The variety affected was HD-2967. Following the first detection, the Indian Institute of Wheat and Barley Research (IIWBR) and other authorities are stepping up their efforts to curb the spread of the disease and urging farmers to be vigilant and take appropriate control measures. These first reports are slightly earlier than in previous years, but the locations are consistently the first places in India where stripe rust is detected. Several Indian media sources are reporting the first appearance of stripe rust in Punjab (see The Tribune, Business Standard, The Hindu, Times of India, The Tribune). As in previous years, Indian authorities are responding to these initial outbreaks in a rapid, effective and well organized way.
Favourable weather conditions for stripe rust are occurring across North Africa to South Asia. Cool, wet conditions across many parts of the region are producing a conducive environment for disease outbreaks. Aggressive races with virulence to Yr27 are known to be widely distributed in several countries and susceptible Yr27 carrying cultivars are still planted on large areas. In addition, the Warrior race (virulent on: Yr1,2,3,4,-,6,7,-,9,-,-,17,-,25,-,32,Sp,Avs,Amb) has spread into the region from Europe. Many of the resistant cultivars to the Yr27 race are likely to carry some of the genes defeated by the Warrior race, particularly in winter wheat material. After first detection in 2010, the Warrior race has spread rapidly across Europe. Most previously resistant cultivars became susceptible to this new race and widespread damage resulted in major European wheat growing areas. The Warrior race was confirmed in 2013 from Morocco, and subsequently in Algeria in 2014 (GRRC, Denmark) and Turkey in 2014 (Field Crops Research Institute, Ankara and Regional Cereal Rust Research Center, Izmir, Turkey). Under current conditions, this race is likely to spread in North Africa and the Middle East. The combined presence of the Yr27 aggressive race and the Warrior race may result in susceptibility of many existing spring and winter wheat cultivars. Although not recorded at present, acquisition of virulence for Yr27 by the Warrior race is not impossible and needs to be carefully monitored.
Serious stripe rust outbreaks are now being reported from Morocco (March 2015), and outbreaks have occurred in India (Feb 2015 http://www.tribuneindia.com/news/haryana/yellow-rust-hits-wheat-over-2000-acres-in-y-nagar/47843.html). First reports of stripe rust appearance have also been reported from south-west Iran at the end of Feb 2015. Other countries e.g., Yemen currently only have low levels of disease or are currently reported to be disease free.
Given the current and forecasted favourable weather conditions for disease development and the presence of the Yr27 aggressive race and the Warrior race, extreme caution and vigilance is advised with respect to stripe rust. Early detection, sampling, reporting and timely effective control of any outbreaks on susceptible cultivars is recommended.
Reporting of new outbreaks to Borlaug Global Rust Initiative (BGRI) staff, K. Nazari (ICARDA) email@example.com and D. Hodson (CIMMYT) firstname.lastname@example.org is encouraged. Pathotype analysis of representative samples of stripe rust would provide additional information about which sources of resistances in wheat may be at particular risk. The Global Rust Reference Centre in Denmark may undertake such analysis, but only on a limited number of samples. Please contact K Nazari or D. Hodson for essential sampling and dispatching procedures.