About usage of monopustule isolates of Puccinia helianthi Schwein. in breeding of sunflower for resistance to rust

A wide distribution of rust on sunflower in the different regions of the Russian Federation caused the necessity to identify races of this disease (Puccinia helianthi) and to conduct breeding on resistance to this obligate parasite. Two methods of inoculation of plants of the lines-differentiators of sunflower resistance were compared: 1) with a mixture of spores of the different uredinia collected on the leaves of an infected plant, and 2) with monopustule isolates (clones of spores from the separate isolated uredinia). The first method is shown to be more appropriate for identification of a racial origin of the field samples of infected sunflower leaves. As being simpler and economic, in a short time, it allows revealing the most common biotypes of a pathogen and identifying a spectrum of races occurring in the studying regions. The second method is necessary for revealing the resistant sunflower genotypes in breeding for resistance to rust. Therefore, it is necessary to create and maintain a working collection of spores of the different races of the pathogen of the various monopustule origin. Identifying monopustule isolates collected from the infected sunflower leaves in the Krasnodar and Saratov region, we determined new races, which were not detected earlier in field samples: 500, 503, 510, 516, and 546. Resistance of the lines HAR 266 and HAR 340 to races of the previous nomenclature (3, 4) was proved under inoculation with the monopustule isolates. However, the biotypes of a rust pathogen with a virulent codes 710 and 747 overcame the resistance of these lines.