Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

327
Introduction
Wheat (Triticum aestivum L.) is the most important cereal in Uzbekistan,
occupying 1.3 ×10 6 ha. Both winter and facultative wheat varieties are
cultivated in Uzbekistan. Irrigated wheat occupies 1.1 ×10 6 ha with average
productivity of nearly 5 t/ha. This makes irrigated wheat very significant in
food security in the country. Among the biotic constraints to irrigated wheat
production, yellow rust caused by Puccinia striiformis f.sp. tritici is most
important. Yellow rust is a perennial problem in wheat cultivation. In order to
sustain irrigated wheat production in Uzbekistan, yellow rust must be
managed efficiently. At present, wheat yellow rust is managed through
fungicide sprays, which is a costly solution, besides being hazardous for the
environment. Yellow rust-resistant wheat varieties would offer a more
sustainable option to minimize the economic impact of the disease.
Since most of the leading wheat cultivars of Uzbekistan show susceptibility
to yellow rust, new sources of resistance must be identified for use in the
wheat breeding programmes to develop resistant varieties. This study was
therefore conducted to examine yellow rust resistance in a set of wheat
landraces, old and improved cultivars and advanced breeding lines adapted to
the irrigated wheat growing conditions in Uzbekistan.
Materials and methods
A set of 272 winter wheat accessions were included in this study. These were
primarily from Uzbekistan (59 entries); the International Winter Wheat
Improvement Programme (IWWIP), a cooperative breeding project between
the Ministry of Agriculture and Rural Affairs of Turkey, CIMMYT and
ICARDA (103 entries); Russia (82 entries); Italy (10 entries); Ukraine (10
entries); and USA (7 entries). Approximately 90% of the germplasm
represented wheat developed for irrigated conditions.
A field experiment was conducted with 1 m 2 plots planted in the research
plots of the Uzbek Scientific Research Institute of Crop Production at Kibray,
Tashkent, in the 2008/09 winter wheat growing season. The plots were
exposed to natural infection by yellow rust. Data collected in each plot were
percent severity of and host reaction type to yellow rust on three occasions
during the grain filling period; the highest yellow rust scores were calculated.
Data were also recorded on maturity, plant height and 1000-kernel weight.
Results and discussion
Since there was a severe epidemic of wheat yellow rust in Uzbekistan in 2009,
the experimental germplasm was indeed evaluated under heavy natural