Introgressing White Mold Resistance from Phaseolus coccineus PI 439534 to Common Pinto Bean

White mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] is a devastating disease of common bean (Phaseolus vulgaris L.) in cool-to moderate-temperature and wet-production regions worldwide. Use of resistant cultivars is crucial for effective and economical white mold control. Partial resistance exists in cultivated and wild common bean and Phaseolus species of the secondary gene pool. The objectives were to (i) develop highly resistant breeding lines (BL) from a recurrent interspecific backcross of common pinto bean 'UI 320' with P. coccineus PI 439534, and (ii) compare their response with known sources of resistance. Five pinto BL derived from UI 320 x 2/PI 439534 interspecific backcross population, the two parents, nine known sources of resistance, and susceptible pinto 'Othello' were screened in the greenhouse. Sclerotinia sclerotiorum isolates ARS12D and ND710 were used at the University of Idaho, Kimberly, in 2012 and isolates CO467 and NY133 at Colorado State University, Fort Collins, in 2013. All five interspecific pinto BL (VC13-1, VC13-3, VC13-4, VC13-5, VC13-6) in Idaho and three (VC13-4, VC13-5, VC13-6) in Colorado exhibited significantly (P <= 0.05) higher levels of resistance than PI 439534. Their resistance was either similar to (in Colorado) or higher (in Idaho) than the highest levels available in other interspecific BL (92BG-7, I9365-31, VCW 54, VRW 32) derived from the secondary gene pool thus far, as well as medium-(USPT-WM-1) and small-('ICA Bunsi') seeded Middle American and large-seeded Andean dry (G 122) and green (NY 6020-4) beans. The effectiveness of the five interspecific pinto BL for controlling white mold with and without fungicides and other disease management strategies should be performed. Genetics of resistance and tagging and mapping of new resistance genes and/or quantitative trait loci should be performed. Also, high levels of resistance from the five interspecific pinto BL should be pyramided across Phaseolus species and/or transferred into cultivars.