Within Phaseolus, the scarlet runner bean (P. coccineus) has highest levels of white mold resistance. This species is in the secondary gene pool for common bean, and it is possible to introgress genes without using extraordinary measures. Previous researchers have partially transferred resistance, but the resulting germplasm appears not to have been widely used to develop elite common bean cultivars. There are several possible reasons: accessions used were not the most resistant, resistance is quantitatively controlled and not all resistance factors were transferred, and linkage drag hindered transfer. Molecular tools integrated into a breeding program provide new avenues through which the genetic architecture of white mold resistance can be understood and transferred.
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