Identification of Sources of Bacterial Wilt Resistance in Common Bean (Phaseolus vulgaris)

Over the last decade, bacterial wilt, caused by Curtobacterium flaccumfaciens pv. flaccumfaciens, has reemerged in the Central High Plains (Nebraska, Colorado, and Wyoming) and has been identified in almost 500 fields. Affected fields were planted with bean (Phaseolus vulgaris) from multiple market classes and seed sources, including yellow, great northern, pinto, kidney, cranberry, black, navy, pink, and small red, and incidence varied from trace levels to >90%. One wilt-resistant bean, 'Emerson', is available today but it is grown on a limited basis as a specialized cultivar for targeted markets in Europe and cannot be grown in all fields where the disease has recently been identified. Thus, we are faced with an emerging problem that must be addressed by utilizing newly developed resistant cultivars. This study was initiated to evaluate the Phaseolus National Plant Germplasm System (NPGS) bean collection for resistance to C. flaccumfaciens pv. flaccumfaciens in the ongoing effort to develop a new wilt-resistant cultivar adapted to this region. In total, 467 entries, including accessions from the NPGS, several commercial great northern and pinto cultivars, and University of Nebraska experimental lines, were screened with a highly virulent orange strain of C. flaccumfaciens pv. flaccumfaciens previously recovered from an infected great northern bean plant in Nebraska. Bacterial wilt severity ratings were 1.0 to 9.0 (0 to 90% incidence). Of the 427 accessions from the NPGS, only 1 showed resistance (0.23%), 19 showed intermediate resistances (4.45%), and the remainder were susceptible (95.34%). PI 325691 was identified as a source of bacterial wilt resistance. It was screened against six additional C. flaccumfaciens pv. flaccumfaciens strains and still produced resistant reactions. PI 325691 is a wild common bean (P. vulgaris) collected 8 miles South of Tzitzio, Michoacán, Mexico; however, it has a small seed size (5.3 g 100^-1 seeds) that is commercially unacceptable. It will take several backcrosses to transfer this resistance to bacterial wilt and recover the seed size into a cultivated bean.