Selecting Common Bean with Genes of Different Evolutionary Origins for Resistance to Xanthomonas campestris pv. phaseoli

Abstract

Common bacterial blight (CBB) is an important seed‐borne disease of common bean (Phaseolus vulgaris L.). Low levels of resistance occur in the common and scarlet runner bean (Phaseolus coccineus L.), with higher levels available in the tepary bean (Phaseolus acutifolius A. Gray). Germplasm lines with CBB resistance separately from each of the three Phaseolus species and pyramided resistance are available. The objectives of this study were to: (i) determine the main and interaction effects of two isolates of Xanthomonas campestris pv. phaseoli (Xcp), one from Colorado and one from Wisconsin, and their inoculum densities with CBB resistance from the three species separately and pyramided; and (ii) identify the most useful germplasm for breeding for resistance. Thirty‐one genotypes were evaluated at 14 and 21 d after inoculation (DAI) using two inoculum densities in 2005 and three in 2006 of each of the two Xcp isolates. Large differences in response to Colorado and Wisconsin Xcp isolates, densities, and evaluation time were observed. The resistance derived from the three species separately was not effective against the aggressive Wisconsin Xcp isolate at higher densities ≥108, especially at 21 DAI. Resistance pyramided with the tepary bean was the most effective. No crossover interactions were observed between the 31 common bean germplasm sources and the two Xcp isolates at any density and evaluation date. Use of only pyramided resistance for breeding is advised.