Genetic analysis and mapping of resistance in barley to non-adapted Puccinia graminis isolates

Haghdoust R, Singh D, Park RF and Dracatos PM

The University of Sydney, Plant Breeding Institute, Cobbitty, Private Bag 4011, Narellan, NSW, 2567, Australia.

Stem rust, caused by Puccinia graminis, is an important disease that affects many economically significant cereals and can cause great concern for global cereal production. Different formae speciales of P. graminis have co-evolved, which primarily infect specific hosts. This host specificity is not always complete and some genotypes of other closely related cereals can also be infected. Barley is a host to the wheat and cereal rye adapted formae speciales of P. graminis (Puccinia graminis f. sp. triticiand Puccinia graminis f. sp. secalis), and a near nonhost to the formae speciales adapted to rye grass [P. graminis f. sp. lolii(Pgl)] and oat [P. graminis f. sp. avenae (Pga)]. This study aimed to determine the genetic basis of resistance in barley to Pgland Pga, to map resistance to both pathogens, and to compare the histology of resistance in barley to Pgl with the common host (Lolium perenne L). We tested over 400 diverse barley accessions with Pgl and Pga and determined that less than 10% were fully compatible at the seedling stage, suggesting barley is a near nonhost to these two formae speciales. The Oregon Wolf Barley (OWB) doubled haploid (DH) population was used to characterize and map resistance to Pgl and Pga. The resistance observed at seedling stages to three diverse Pga isolates and to one isolate of Pgl was polygenically inherited and due to QTL on chromosomes 1H, 2H, 4H, 5H, 6H and 7H with both overlapping and distinct specificities. Microscopic examination 14 days post inoculation suggested that the immunity observed within resistant lines was most likely prehaustorial.