Graduate Thesis Or Dissertation
 

Testing the effectiveness of barley stripe rust resistance QTL detected in Mexico and the USA against a possible new race in Peru and mapping of genes conferring resistance to leaf rust and mildew in the same population

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  • Barley is the fourth most important cereal crop in the world because of its broad adaptation, its utility as a feedstock and for human food, and the superior properties of barley malt for brewing. Three of the most important foliar diseases of barley, on a worldwide level are: barley leaf rust caused by Puccinia hordei G. Otth, barley stripe rust (yellow rust) caused by Puccinia striformis Westend f sp. hordei and powdery mildew caused by Blumeria graminis f. sp. hordei. Although barley is an autogamous species, there is sufficient DNA-level diversity for efficient linkage map construction and this polymorphism has been used for extensive mapping and QTL detection efforts. The ICARDA/CIMMYT barley program is an important source of quantitative disease resistance genes. Oregon State University and the ICARDA/CIMMYT barley program have maintained a long-term collaborative effort to map and deploy stripe rust resistance genes. This germplasm has shown consistent and adequate levels of resistance over the past 18 years in repeated tests in Mexico and the USA. However, in the 1999-2000 season there were reports from Peru, Bolivia, and Ecuador that there was a new race of stripe rust that was causing high levels of disease on formerly resistant varieties and experimental materials. This was cause of concern because considerable effort had been invested in identifying stripe rust quantitative resistance genes, based on the assumption that they would prove durable. We therefore used a well-characterized barley QTL mapping population - the ORO population - which is derived from the cross of BCD47 x Baronesse, to determine if barley stripe resistance QTL mapped in Mexico and the USA were effective in Peru. The same resistances QTL were detected in Peru as in Mexico and the USA. If there is a new virulence in Peru, the mapped QTL are still effective and under field conditions do not show specificity to any race the population has been challenged with in the Americas. This finding is of importance to barley breeders interested in deploying effective resistance genes. Confirmation of a new race in Peru will require characterization against a standard set of differentials, an experiment that is planned. The increase in disease severity of C110587, a genotype with a mapped qualitative resistance gene, between Mexico and Peru suggests there is a new race in Peru. The highest levels of resistance in Peru were achieved in lines where the qualitative resistance gene was pyramided with quantitative resistance alleles. We also used the ORO population to map QTL for barley leaf rust and barley powdery mildew in the Andean region and for the latter disease identified resistance QTL in addition to the Mia resistance mapped using specific isolates under controlled conditions. The availability of this germplasm, with mapped genes conferring quantitative resistance to three diseases, will be a resource for the barley breeding community.
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