Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

211
Pathotype and molecular variability of yellow rust in
Western and Central Asia, in a global context
Mogens S. Hovmøller and Annemarie F. Justesen
Department of Integrated Pest Management, Danish Institute of Agricultural Sciences
(DIAS), Slagelse, Denmark.
Genetic diversity is often low at a both field and regional scales in populations
of Puccinia striiformis f.sp. tritici. The diversity is higher when taking into
account the changes that may occur over time (years) and among samples
representing larger geographical areas. Information about diversity and the
dynamics of the pathogen population is vital due to its impact on the expected
control of yellow rust by host resistance, either leading to a decrease or an
increase in the ability of specific sources of resistance to control yellow rust in
specific areas.
Almost 100 Pst samples were collected from 2003 to 2005 from Central Asia,
Pakistan, Nepal, Azerbaijan and Iran. The samples have been multiplied and
pathotyped in spore-proof and controlled environmental conditions at DIAS,
Denmark. In addition, selected samples chosen according to pathotype and
origin were analysed using Amplified Fragment Length Polymorphism
(AFLP). In general, the samples were collected from a wide range of host
varieties, locations, field trials and farmers’ fields in these regions.
A total of 16 pathotypes were observed when all samples were taken into
account. All isolates carried virulence for Yr6, Yr7 and Yr8, despite some
isolates giving intermediate to low infection type (IT) on Compair (Yr8) and
high IT on the Avocet S (Yr8) NIL. Virulence for Yr3, Yr5, Yr15, Yr17 and Yr32
was not detected, whereas virulence for Yr1, Yr2, Yr9 and Yr27 varied in
frequency. Virulence for Yr4 was observed as an (unusual) intermediate IT on
Hybrid 46 in samples from Nepal, but was otherwise absent. In Iran, we
observed wheat isolates showing incompatibility on Avocet S and all NILs
(IT 1 on a 0–9 scale). Isolates from durum wheat showed virulence for Yr10
and Yr24, whereas isolates from barley gave low IT on all differentials except
the susceptible control, wheat cv. Cartago.
Diversity in terms of number of clones (defined by AFLP phenotypes) was
generally low within geographically separated populations, but in contrast to
samples from many other regions, these AFLP phenotypes were often quite
different based on their AFLP phenotype. In particular, yellow rust from Nepal
and Pakistan was highly divergent from Central Asian Pst samples, even more
distant than samples originating from barley and durum wheat. The coexistence
of highly divergent individuals within the region may suggest a