| Resistance to common bacterial blight (CBB) in common bean is a quantitative trait. Although previous attempts to breed CBB resistant bean cultivars have had limited success, progress in marker-assisted selection (MAS) has created new opportunities for breeding programs. The potential of the marker SU91 in MAS for CBB resistance was evaluated in field experiments. SU91 was correlated with lower CBB leaf scores in East Lansing (r = −0.50), and Saginaw (r = −0.59), and correlated with pod resistance in Saginaw (r = −0.48). SU91 exhibited a negative correlation with yield (r = −0.20) and a positive correlation with maturity (r = 0.22) in East Lansing, but showed no association in Saginaw. Selections carrying SU91 were crossed with additional sources of resistance to CBB and anthracnose. F2 progeny were screened for the marker BC420, linked to a QTL for CBB resistance on bean linkage group 136. The effects of SU91 and BC420 were examined in two greenhouse studies. The presence of SU91 was negatively correlated with CBB disease ratings for leaves (r = −0.20) and pods (r = −0.27). Presence of BC420 was only correlated with pod ratings (r = −0.19) in experiment one, and CBB leaf resistance (r = −0.18) in experiment two. Presence of both markers resulted in lower levels of CBB resistance than provided by either marker alone. |
