Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Surveys of yellow rust populations and evaluation of trap nurseries
indicated the presence of many virulence types in CWANA. A wide range of
virulent pathotypes (132E136, 230E222, 255E112, etc.) is evolving in this region,
causing the breakdown of widely utilized sources of stripe [yellow] rust
resistance in wheat. Cereal Rust Trap Nurseries (CRTNs) have been a valuable
tool in monitoring air-borne rust pathogens; the nurseries include differential
sets harbouring known resistance genes for each of the three rusts, commercial
cultivars that cover large areas in the region, and selected new elite breeding
lines. The availability of comprehensive information on pathogen virulence
and variation, and epidemiological information on pathogen movements,
should provide the basis for the development of an early warning system to
alert farmers growing potentially susceptible cultivars.
Introduction
Wheat is the most important food crop in the Central and West Asia and North
Africa (CWANA) region. It provides a substantial component of the human
diet, and farming systems of the region revolve around wheat production.
Wheat occupies a third of the arable area in the region. However, the average
productivity of wheat in CWANA countries is low due to both biotic and
abiotic stresses. Despite the fact that 23% of the world’s wheat area is in
CWANA, the region accounts for only 14% of world production, due to low
yields; the average yield for the region is less than 1500 kg/ha, almost one-half
of the world average. Yields are particularly low in the recently independent
republics of Central Asia. In North Africa, wheat is characterized by high
levels of production in the high and moderate rainfall agro-ecological areas.
Monoculture of high yielding varieties is rapidly replacing the traditional,
lower yielding, landrace cultivars. Nonetheless, most of the available high
yielding varieties are susceptible to one or more foliar diseases, with resultant
losses in yield and quality that vary from year to year depending mainly on
the prevailing climatic conditions. In Algeria, Morocco and Tunisia, wheat leaf
rust is among the diseases that present a clear danger to cereal production in
the high to moderate rainfall areas.
Yield losses caused by air-borne rust diseases are common and represent an
important production constraint. Crop losses of 10–60% have been recorded in
many countries. During the last decade, several yellow rust epidemics have
occurred in most countries in the region and resulted in severe losses in wheat
production. These epidemics occurred in crops seeded both off-season and
during the main growing season. In the 1991/92 wheat-cropping season,
yellow rust spread into the Baluchistan region of Pakistan for the third
consecutive year and caused significant losses in the common cultivar Local
White. In 1990, the gross revenue in three of the Baluchistan districts was
reduced by an estimated US$ 8 million due to the yellow rust epidemic