Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 9, 2003
Publication Date: April 1, 2004
Citation: Larsen, R.C., Miklas, P.N. 2004. Generation and molecular mapping of a scar linked with the bct gene for resistance to beet curly top virus in common bean. Phytopathology. 94:320-325. Interpretive Summary: Beet curly top is an endemic disease in the Pacific Northwest that periodically causes severe crop loss in snap (garden bean) and dry edible bean fields. Losses in the Columbia Basin last year exceeded $1 million. The disease results from a Beet curly top virus (BCTV) and is vectored by the sugarbeet leafhooper. The same leafhopper-transmitted virus also devastates tomato, pepper, squash, sugarbeet, cucumber and other crop production. Genetic resistance within the bean host is the only effective control. Developing resistant bean cultivars is difficult because it is next to impossible to predict when field infections will occur, and laboratory and greenhouse screening methods are tedious, inadequate and time consuming. Using molecular biological protocols, we identified a natural gene for resistance that has been used for the last 50 years to breed resistant cultivars. We developed a DNA marker linked with the resistance gene that can be used to rapidly and reliably screen lines and cultivars for resistance to BCTV using the molecular biological technique known as marker-assisted selection (MAS). As a result of this highly efficient screening tool, MAS will dramatically reduce the time frame currently required for screening breeding lines that typically require extensive field trials or greenhouse methods, and expedite development of bean cultivars resistant to BCTV.
Technical Abstract: Beet curly top virus (BCTV) is a persistent problem of common bean (Phaseolus vulgaris) grown in semi-arid regions where the beet leafhopper Circulifer tenellus is present. Genetic resistance is the only effective control but identifying resistance is difficult using pathogen tests. A RAPD marker directly linked (0.0 cM) with resistance was identified in a recombinant inbred snap bean population (Moncayo/Primo) consisting of 94 F5:7 lines that had uniform segregation for disease reaction to BCTV across three field locations. Resistance was conditioned by a single dominant gene designated Ctv-1. Seven hundred and fifty decamer primers were screened to obtain the linked RAPD marker that was then converted to a dominant sequence characterized amplified region (SCAR) marker SAS8.1550. The SCAR mapped within a cluster of resistance genes on linkage group B7 of the core map. A survey of 112 BCTV resistant and susceptible snap bean and dry bean cultivars and advanced breeding lines was conducted using SAS8.1550. Results showed that the SCAR would be highly useful for marker-assisted selection of Ctv-1 in snap bean and dry bean originating from the Andean gene pool. Marker-assisted selection for Ctv-1 will expedite the development of BCTV-resistant cultivars and circumvent the need for unreliable and cumbersome pathogen tests.