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.

Key highlights

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.

) was also detected in East Africa in 2016, prevalent in severe yellow rust epidemics in Ethiopia. The spread of 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.

was the most prevalent race in Europe (lineage ). Original ( ) and ( ) 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.

, first detected in 2016, became widespread and caused severe yellow rust epidemics in Morocco 2017. Another distinct race of , 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.

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.

Increased capacity

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.

GRRC annual report on wheat yellow rust 2017

This post originally appeared on the Global Rust Reference Center website