Gamete selection for resistance to common and halo bacterial blights in dry bean intergene pool populations

The common [caused by Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp) and X. campestris pv. phaseoli var. fuscans (Xcpf)] and halo bacterial blights [caused by Pseudomonas syringae pv. phaseolicola (Burkh.) Young et al. (Psp)] are seed-borne diseases that cause severe yield losses in dry and snap bean (Phaseolus vulgaris L.) worldwide. Use of cultivars resistant to these diseases is pivotal for their integrated control and to facilitate production and distribution of pathogen-free seed. Our objective was to use gamete selection for resistance to both bacterial blights. Two intergene pool four-way crosses, namely ZARA III = Wilkinson 2/'Montcalm'//'Casasola'/'Harris' and ZARA IV = 'Edmund'/Wilkinson 2//Casasola/BRB 131 were made. Selection for resistance to both bacterial blights was practiced from F1 to F4 in the greenhouse or field at Valladolid, Spain. The F4-derived F5 breeding lines resistant to both blights were screened for Bean common mosaic virus (BCMV), Bean common mosaic necrosis virus (BCMNV), and common bacterial blight in the greenhouse at Kimberly, ID, and for halo blight at Filer, ID, in 2001. They were also evaluated for the two bacterial blights, growth habit, seed color, and 100-seed weight in the field at Valladolid in 2002. The proportion of resistant, intermediate, and susceptible plants was similar in both F1, and selection was effective from the F1 to F4 for both bacterial blights. Nonetheless, population ZARA IV had relatively lower halo blight scores than ZARA III (1.8-4.1 vs. 2.6-6.5). The contrary occurred for common bacterial blight. Five breeding lines resistant or intermediate to both diseases were obtained from two of 147 F1 plants in ZARA III. ZARA IV produced nine breeding lines resistant to both bacterial blights that originated from four of 128 F1 plants. Some breeding lines had a higher resistance to both bacterial blights than their parents indicating transgressive segregation, and all carried the I allele for resistance to BCMV. We suggest using gamete selection for introgression and pyramiding of resistance to both bacterial blights with multiple-parent populations in dry bean.