Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Trade Journal
Publication Acceptance Date: December 30, 2007
Publication Date: December 30, 2007
Citation: Bellato, C.M., Frederick, R.D., Bowers, J., Zhang, D., Pastor Corrales, M.A. 2007. Identification of Candidate Gene Markers in Common Bean for Resistance to the Soybean Rust Pathogen. Bean Improvement Cooperative Annual Report. 50:121-122.
Phakopsora pachyrhizi, the fungus that causes the Asian soybean rust (ASR) is a very aggressive pathogen that can significantly reduce soybean yield (up to 80%). Since no commercial soybean cultivars are resistant to P. pachyrhizi, ASR poses a major threat to North American soybean production. Moreover, P. pachyrhizi can infect a broad range of leguminous crops including dry and snap beans (Phaseolus vulgaris L.). We have evaluated the reaction of selected dry bean cultivars to six isolates of P. pachyrhizi from three different continents and identified some cultivars that were resistant to all six rust isolates. These cultivars had lower disease severity, less sporulation and consistent reddish-brown lesions associated with resistance. These findings suggest these cultivars have genes for resistance to P. pachyrhizi that could protect common bean and soybean against the soybean rust pathogen. The objective of this study was to determine the inheritance of resistance of the putative resistance genes and to identify molecular markers linked to them. Bean cultivars Mexico 309 and CNC that are susceptible and resistant to P. pachyrhizi, respectively, were crossed to produce the F2 population used for this study. The F2 progeny and the parents were inoculated with P. pachyrhizi isolate BZ01-1 in the Biosafety Level 3 Plant Pathogen Containment Greenhouse at Fort Detrick, MD. The phenotypic F2 results were 69 resistant and 48 susceptible plants, suggesting that rust resistance was controlled by two-putative genes CNC. PCR was conducted with several primers (17 to 26 bp long) designed from simple sequence repeats (SSR), plant defense-related genes and conserved regions associated with resistance genes. Polymorphic fragments were obtained with primers #13 (CNC had a 664-bp fragment not found in Mexico 309), primer # 14 (CNC had a 694-bp fragment not found in Mexico309), and primer # 27 (Mexico 309 had 272-bp fragment not found in CNC). These three primers were tested in 117 F2 plants. The results for primers #13 were 86 plants with a 664-bp fragment and 31 without, and primer # 14 were 82 plants with a 694-bp fragment and 34 without it. The segregation of both these primers indicates a 3:1 monogenic ratio. The data for primer # 27 were 72 plants with a 272-bp fragment and 44 without it and revealed a 9:7 segregation ratio. Approximately 150 additional F2 plants will be tested to confirm these findings.