A major QTL for common bacterial blight resistance derives from the common bean great northern landrace cultivar Montana No. 5

Knowledge of the evolutionary origin and sources of pest resistance genes will facilitate gene deployment and development of crop cultivars with durable resistance. Our objective was to determine the source of common bacterial blight (CBB) resistance in the common bean Great Northern Nebraska #1 (GN#1) and GN#1 Selection 27 (GN#1 Sel 27). Several great northern cultivars including GN#1, GN#1 Sel 27, and Montana No. 5 (the female parent of the common x tepary bean interspecific population from which GN #1 and GN # 1 Sel 27 were derived) and known susceptible checks were evaluated for CBB reaction in field and greenhouse environments. These genotypes and CBB resistant and susceptible tepary bean including Tepary #4, the male parent and presumed contributor of CBB resistance to GN#1 and GN#1 Sel 27, were assayed for presence or absence of three SCAR markers tightly linked with independent QTLs conditioning CBB resistance. The parents and F2 of Montana No. 5/GN #1 Sel 27 and Montana No. 5/Othello (CBB susceptible) were screened for CBB reaction and SCAR markers. CBB resistance in Montana No. 5 was comparable to that of GN#1 and GN#1 Sel 27. The SAP6 SCAR marker present in GN#1 and GN#1 Sel 27 was also present in Montana No. 5, and it co-segregated (R2 = 35%) with the CBB resistance in the Montana No. 5/Othello F2 population. Although a few CBB resistant and susceptible transgressive segregants were found in the F2 of Montana No. 5/GN #1 Sel 27 and later confirmed by F3 progeny tests, SAP6 SCAR marker was present in all progenies. None of the tepary bean specific CBB resistance-linked SCAR markers were present in GN#1, GN#1 Sel 27, or Montana No. 5. A cluster analysis of 169 polymorphic PCR-based markers across three common bean and Tepary #4 indicated that GN#1, GN#1 Sel 27, and Montana No. 5 were closely related, and not related at all with Tepary #4. Thus, these results clearly indicate Montana No. 5, not Tepary #4, as the source of CBB resistance in GN#1 and GN#1 Sel 27