F. Capettini1, H. Vivar2, L. Gilchrist,3 and M. Henry3 1ICARDA/CIMMYT Barley Breeding Program; 2CIMMYT Wheat Program Consultant; 3CIMMYT Wheat Program

Picture 1. Genotypes with different reactions to stripe rust at Toluca

Picture 2. Genotype susceptible to leaf rust at Ciudad Obregon

Picture 2. Genotype susceptible to leaf rust at Ciudad Obregon

Picture 4. BYDV screening nursery at Toluca

Picture 5. FHB screening nursery at Toluca

Picture 6. FHB Type II resistance in two-row barleys

Breeding to incorporate multiple disease resistance has been one of the main goals of the ICARDA/CIMMYT Barley Breeding Program. Among other things, participants developed an enhanced gene pool and varieties possessing resistance to the main barley diseases, in an agronomically improved genetic background. Selection in environments that ensured higher heritability of resistance was a major reason for success. Results for the most prevalent diseases in the Americas are presented here.

The Diseases

Stripe rust (Puccinia striiformis)
Selection for stripe rust resistance has been carried out since its appearance in the region in 1984. Sources of resistance were obtained after screening approximately 20,000 samples in Colombia and Mexico. Inoculation is conducted at the Toluca Experiment Station through the creation of infection borders and hills planted with susceptible genotypes. Partial stripe rust resistance was found, and cultivars with contrasting differences in the latent period of infection were characterized, obtaining a more durable type of resistance.

Leaf rust (Puccinia hordei)
Results of leaf rust research in Montana and Holland helped to identify parents for use in breeding. Every year 10-12 ha of segregating populations and yield experiments in the Yaqui Valley are artificially inoculated through infection borders using fresh pathogen spores. Epidemics are almost always present and selection is efficient.

Scald (Rhyncosporium secalis)
In the 1980s, a sample of entries from the world collection showing resistance after being screened in California was introduced to Mexico. Environmental conditions at Toluca are usually optimal for the development of this important barley disease. Every year 7-10 ha of experiments and segregating populations are artificially inoculated, creating relatively high epidemics that easily differentiate genotypes with different levels of resistance. Previous research found that disease development in resistant genotypes had small AUDPC values as compared to susceptible ones. This slow-scalding gene pool is frequently used in the program.

Fusarium head blight (Fusarium graminearum)
Selection for this devastating disease started in 1995 in response to its rapid rise in importance in North and South America. Twenty-three lines with different degrees of resistance after screening in Japan and Mexico were used as initial sources for the resistance program. Genotypes are screened under artificial epidemics at Toluca. The ICARDA/CIMMYT program was among the pioneers in screening and describing the independently inherited Type I (initial infection) and Type II (fungus spreading) types of resistance in barley, which had been previously described in wheat. Genotypes having both types of resistance were identified and confirmed through several years of testing and are widely used as resistance sources.

Barley yellow dwarf virus

Research on BYDV aims to characterize genotypes for their individual reaction to three biotypes: MAV, PAV, and RPV. BYDV symptoms are frequent under natural conditions at Toluca and selection against susceptible genotypes is usually carried out, but artificial inoculation with greenhouse-reared aphids is done in screening nurseries under field conditions to ensure uniform infection, differentiate biotype reaction, and reduce the risk of escapes. Four plots are planted with each genotype and three of them are inoculated with one biotype each. The fourth plot is a check kept free of aphids by insecticide applications.

Assembling resistant genotypes

We created "templates" to incorporate resistance to all diseases into a high yielding genetic background. At the first stage, resistance to scald and leaf rust was incorporated, followed by templates where resistance to stripe rust and to other diseases was added. This process continued for 20 years, with two generations per year, to pyramid resistance to the diseases described above and to net blotch, spot blotch, and stem rust.

An example of success is the variety Shyri, released in Ecuador in 1989. The disease resistance present in Shyri was studied in detail at Oregon State University (OSU) using molecular markers. QTLs for resistance to scald, net blotch, BYDV, stripe rust, and leaf rust were found. Shyri was also found to be resistant to fusarium head blight and partially resistant to leaf rust.

Another success story is China, where an estimated 400,000 ha of the country's 1 million ha barley area is sown to ICARDA/CIMMYT varieties, largely due to their high yield potential and resistance to both fusarium head blight and barley yellow mosaic virus. In several provinces the variety Zhenmai-1 (Gobernadora) yielded 20-25% more than the local varieties. In a genetic study carried out by OSU, a large effect QTL was found for FHB Type II resistance near the centromeric region of chromosome 2.

Besides the impact evidenced by the release of cultivars in different countries, the success of the program can be also measured by the large germplasm pool with resistance to different diseases in an improved agronomic background that is available to breeding programs worldwide.

Published on June 2001

August, 2004