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Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is an important disease of common bean (Phaseolus vulgaris L.). A coupling-phase random amplified polymorphic DNA (RAPD) marker OAD12.550 previously was identified to be linked (no recombination) to Ur-7 of Middle American (MA) origin for specific rust resistance in the common bean cross of Great Northern (GN) 1140 x GN Nebr. #1. However, a sequence characterized amplified region (SCAR) marker for Ur-7 present in GN1140 has not been reported. Our objectives were to convert the RAPD marker OAD12.550 most tightly linked to Ur-7 to a SCAR marker SOAD12.537 for use as a marker-assisted selection tool, and survey the presence or absence of the SCAR marker SOAD12.537 in 90 MA and Andean bean genotypes for determining the genetic relationship of Ur-7 with Ur-6. The coupling-phase SCAR marker SOAD12.537 based on a specific forward (5'-AAGAGGGCGTGAGATCGTCG-3') and reverse (5'-AAGAGGGCGTCTTGAAGGTT-3') primer pair showed no recombination with Ur-7 in an F 2 population of the GN1140 x Nebr. #1 cross. The SCAR marker was also present in pinto US-5 from which the rust resistance of GN1140 was derived and in the closely related pinto US-14. The cosegregating SCAR marker identified MA pinto bean cultivars/lines Olathe, Bill Z, Apache, Montrose, BelDak-RR-1 and-2, and CO 12783 that have rust resistance gene Ur-6 and also have Ur-7, identified in earlier literature as Ur c , due to presence of the marker. Other cultivars/lines with Ur-6 such as Weihing, Burke, Kodiak, Topaz, Golden Gate Wax, BelMiNeb 1-13, BelDakMi 1-23, and other Colorado breeding lines lack Ur-7 because of absence of the SCAR marker for the MA gene. This SCAR marker linked to Ur-7 on linkage group 11 of the core P. vulgaris linkage map can identify a phenotypically hidden resistance gene, and along with markers for other rust resistance genes, can be utilized to pyramid multiple genes for more durable rust resistance.

Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is a major disease of common bean (Phaseolus vulgaris L.). A recommended strategy to obtain durable rust resistance is to use molecular markers linked to rust resistance genes for pyramiding monogenic resistance genes into a single bean cultivar. However, markers tightly linked to Ur-6 of Andean origin conferring specific resistance (SR) to rust present in Olathe have not been reported. Our objectives were to identify random amplified polymorphic DNA (RAPD) markers linked to Ur-6 controlling SR to race 51 using bulked segregant analysis in an F 2 population from the Middle American (MA) common bean cross Olathe (resistant) × Nebr.#1 sel.27 (susceptible), and determine the presence or absence of these identified markers in 70 MA and Andean bean cultivars and breeding lines. A single dominant gene controlling SR to race 51 was found in the F 2 and confirmed in the F 3 . Six RAPD markers were detected in a coupling phase linkage with Ur-6. The gene was flanked by two coupling-phase markers OBC06.300 and OAG15.300 at 1.3 and 2.0 cM. Sequence characterized amplified region (SCAR) marker SOBC06.308 was developed based on the specific primer pair designed from the sequence of the RAPD marker OBC06.300. The RAPD and SCAR markers were also present in MA pinto bean germplasm having Ur-6 as well as Golden Gate Wax, another source of Ur-6. However, these markers were also present in six Andean cultivars without Ur-6, suggesting gene pool specificity. Among five repulsion-phase markers identified, OAY15.200 was the most closely linked to Ur-6 at 7.7 cM. We also confirm the Ur-6 location on linkage group 11 of the P. vulgaris map. These RAPD and SCAR markers linked to Ur-6 identified here, along with markers for other independent rust resistance genes, could be utilized to pyramid multiple genes into a bean cultivar for more durable rust resistance.

Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is a major disease of common bean (Phaseolus vulgaris L.). A recommended strategy to obtain durable rust resistance is to use molecular markers linked to rust resistance genes for pyramiding monogenic resistance genes into a single bean cultivar. However, markers linked to the Ur-7 gene for specific resistance (SR) to rust present in the cultivar Great Northern (GN) 1140 have not been reported. Our objectives were to identify random amplified polymorphic DNA (RAPD) markers linked to the Ur-7 gene for SR to rust race 59 using bulked segregant analysis in an F 2 population from the Middle American (MA) common bean cross 'GN1140' (resistant) × GN Nebr. #1 (susceptible) and to map the Ur-7 gene on an existing RAPD marker-based linkage map constructed by means of recombinant inbred lines (RILs) from the MA cross GN BelNeb-RR-1 × A 55. A single dominant gene controlling SR to race 59 was found in the F 2 and confirmed in the F 3 . Six RAPD markers were detected in a coupling phase linkage with the Ur-7 gene. Cosegregating coupling-phase markers OAD12.550 and OAF17.900 were found. These were also present in pinto US-5 from which the rust resistance of GN1140 was derived. Among the three repulsion-phase markers, marker OAB18.650 was the most closely linked to the Ur-7 gene at a distance of 7.6 centimorgans (cM). All linked markers detected in the F 2 population also segregated in the RILs and were located on linkage group 11 of the existing linkage map. These markers linked to the Ur-7 gene of MA origin identified here, along with other independent rust resistance genes from other germplasm, could be utilized to pyramid multiple genes into a bean cultivar for more durable rust resistance.

White mold (WM), incited by Sclerotinia sclerotiorum (Lib.) de Bary, is a serious disease of common bean (Phaseolus vulgaris L.). However, plant breeders have had very limited success in developing resistant (R) cultivars. Molecular markers linked to genes for R to WM may improve selection for R. The objective was to identify random amplified polymorphic DNA (RAPD) markers linked to quantitative trait loci (QTL) for partial physiological resistance (PPR), partial field resistance (PFR), porosity over the furrow (POF), and plant height (PH) in a linkage map by means of recombinant inbred lines (RILs) from the cross 'PC-50' (R) x XAN-159 (susceptible). The parents and RILs were inoculated in two separate greenhouse experiments for each isolate and were also infected naturally in the field. Significant correlations (0.39, 0.47) were found for the WM reactions in the greenhouse and field. Nine candidate QTL were found affecting PPR isolate 152 (comparison-wise P < 0.05) with strong evidence (genome-wise P < 0.01) for three QTL on linkage groups (LGs) 4, 7, and 8, based on composite interval mapping analysis. Candidate QTL affecting PPR to isolate 279 were found on LGs 2, 3, 4, 7, and 8 with very strong evidence (genome-wise P < 0.001) for a QTL linked to the C locus for seedcoat pattern. Seven candidate QTL for PFR were observed on LGs 4, 7, 8, and 11. Six of the seven candidate QTL for PFR were found in the same locations as QTL for PPR. However, two of the seven genomic regions were associated with PFR and POF that may contribute to disease avoidance.