Lili Qi, Guojia Ma, Yunming Long, Li Gong, Brent Hulke, Sam Markell
Abstract: Rust (caused by Puccinia helianthi Schwein.) is a major disease of sunflower worldwide. Due to the frequent evolution of new pathogen races, the disease is a recurring threat to sunflower production especially in North America, Argentina, and Australia. The inbred line MC29 carries the rust resistance gene, R2, conferring resistance to numerous races of the rust fungus in the U.S., Canada, and Australia, and can be used as a broad-spectrum resistance resource. Based on phenotypic assessments and simple sequence repeat (SSR) analyses on the 117 F2 individuals derived from a cross of HA 89 with MC29 (USDA), R2 was mapped to linkage group (LG) 14 of the sunflower genome, and not to the previously reported location on LG9. The closest SSR marker HT567 was located at 4.3 cM distal to R2. Furthermore, 36 selected single nucleotide polymorphism (SNP) markers from LG14 were used to saturate the R2 region. Two SNP markers, NSA_002316 and SFW01272, flanked R2 at a genetic distance of 2.8 and 1.8 cM, respectively, delimiting R2 to an interval of 4.6 cM. Of the three closely linked markers, SFW00211 amplified an allele specific for the presence of R2 in a marker validation set of 46 breeding lines, and SFW01272 was also shown to be diagnostic for R2. These newly developed markers, together with the previously identified markers linked to the gene R13a, were used to screen 524 F2 individuals from a cross of a confection R2 line and HA-R6 carrying R13a. Eleven homozygous double-resistant F2 plants with the gene combination of R2 and R13a were obtained. This double-resistant line will be extremely useful in confection sunflower, where few rust R-genes are available and when R-genes are utilized they are typically incorporated singly, risking evolution of new virulence phenotypes and further disease epidemics.
Located in Sunflower and Plant Biology Research. To view article click here.