Breeding for Resistance to Common Bacterial Blight and White Mold in Common Bean.

Common bacterial blight [CBB, caused by Xanthomonas campestris pv. phaseoli (Smith) Dye and Xanthomonas campestris pv. phaseoli var. fuscans] and white mold [WM, caused by Sclerotinia sclerotiorum (Lib.) de Bary] are among the most devastating diseases of common bean (Phaseolus vulgaris L.). CBB resistance has been introgressed into common bean from the tepary bean (P. acutifolius); however, no common bean cultivar has the high levels of resistance found in tepary bean. Additionally, there are no common bean cultivars with high levels of WM resistance. The objective of this research was to simultaneously introgress CBB and WM resistance into the large-seeded dark red kidney (DRK) bean, while maintaining yield, canning quality, and resistance to Bean common mosaic virus (BCMV) and fungal root rots. Using a large multiple-parent cross, 12 breeding lines were selected that combined some level of CBB and WM resistance with desirable seed quality and agronomic traits. These 12 breeding lines, the parents and checks were compared for resistance in the greenhouse and in nine field environments within a major DRK production region. All 12 breeding lines were significantly (P<0.05) more resistant to CBB in greenhouse and field tests. In greenhouse tests, these lines had intermediate WM resistance. In field tests, higher levels of resistance were observed; however, this was attributed to the combined effects of physiological resistance and plant architectural avoidance. Under high disease (CBB, WM and root rot) pressure, the breeding lines also yielded equal or better than the DRK parents. Finally, all breeding lines retained acceptable canning quality and remained resistant to BCMV. The implications of these results and breeding methodologies used will be discussed.