Published online 16 January 2008
Published in Crop Sci 48:357-363 (2008)
© 2008 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
Development of a Coupling-Phase SCAR Marker Linked to the Ur-7 Rust Resistance Gene and Its Occurrence in Diverse Common Bean Lines
S. O. Parka,
J. R. Steadmanb,*,
D. P. Coynec and
K. M. Crosbya
a Dep. of Horticultural Sciences, Texas A&M Univ., Weslaco, TX 78596
b Dep. of Plant Pathology, Univ. of Nebraska, Lincoln, NE 68583
c Dep. of Agronomy & Horticulture, Univ. of Nebraska, Lincoln, NE 68583. This paper was published as paper no. 14593 Journal Series, Nebraska Agricultural Research Division. Research was conducted under Projects 20-036 and 20-042
* Corresponding author (jsteadman1{at}unl.edu).
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ABSTRACT
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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 F2 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 Urc, 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.
Abbreviations: GN, great northern • LG, linkage group • MA, Middle American • PCR, polymerase chain reaction • RAPD, random amplified polymorphic DNA • RIL, recombinant inbred line • SCAR, sequence characterized amplified region
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ACKNOWLEDGMENTS
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We acknowledge financial support from the Title XII Bean/Cowpea CRSP (AID Contract No. DNA-1310-G-SS-6008-00). We also appreciate the constructive criticism of two reviewers, Drs. Don Lee and Ismail Dweikat, University of Nebraska-Lincoln, to improve the manuscript and thank Janelle Counsell, Lindsey Otto-Hanson, and Lisa Sutton, University of Nebraska-Lincoln, for their technical assistance.
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NOTES
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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication June 27, 2007.
Development of a Coupling-Phase SCAR Marker Linked to the Ur-7 Rust Resistance Gene and Its Occurrence in Diverse Common Bean Lines
S. O. Parka,
J. R. Steadmanb,*,
D. P. Coynec and
K. M. Crosbya
a Dep. of Horticultural Sciences, Texas A&M Univ., Weslaco, TX 78596
b Dep. of Plant Pathology, Univ. of Nebraska, Lincoln, NE 68583
c Dep. of Agronomy & Horticulture, Univ. of Nebraska, Lincoln, NE 68583. This paper was published as paper no. 14593 Journal Series, Nebraska Agricultural Research Division. Research was conducted under Projects 20-036 and 20-042
* Corresponding author (jsteadman1{at}unl.edu).
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 F2 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 Urc, 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.
Abbreviations: GN, great northern • LG, linkage group • MA, Middle American • PCR, polymerase chain reaction • RAPD, random amplified polymorphic DNA • RIL, recombinant inbred line • SCAR, sequence characterized amplified region
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INTRODUCTION
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BEAN RUST, caused by Uromyces appendiculatus (Pers.:Pers.) Unger, is a major disease resulting in reduced bean yield and quality in many parts of the world (Stavely and Pastor-Corrales, 1989). It consistently causes yield reductions ranging from 18 to 100% in dry and snap beans (Stavely and Pastor-Corrales, 1989; Lindgren et al., 1995). The pathogenic variability of the fungus is broad with over 300 races/pathotypes recognized (Stavely and Pastor-Corrales, 1989; Mmbaga et al., 1996a). Cultural practices such as crop rotation, elimination of plant debris, and adjustment of planting dates can reduce the disease severity (Stavely and Pastor-Corrales, 1989). However, the use of host resistance is the most economic and environmentally sustainable method for controlling bean rust (Mmbaga et al., 1996b).
More than 10 different sources of resistance to bean rust have been identified (Kelly et al., 1996; Miklas et al., 2002). Pyramiding monogenic resistance genes into a bean cultivar is a strategy recommended to obtain durable rust resistance (Mmbaga et al., 1996b). Because of host gene pool specificity of some U. appendiculatus pathotypes (Araya et al., 2004), combining resistance genes from both Andean and Middle American (MA) gene pools should provide more durable resistance to rust (Park et al., 1999).
Random amplified polymorphic DNA (RAPD) markers linked to five MA rust resistance genes (Ur-3, Ur-5, Ur-7, Ur-11, and Ur-Ouro Negro) and three Andean genes (Ur-4, Ur-6, and Ur-9) have been identified using bulked segregant analysis in beans (Haley et al., 1993, 1994; Miklas et al., 1993; Johnson et al., 1995; Park et al., 1999, 2003, 2004; Correa et al., 2000). Miklas et al. (2002) reported integration of identified rust resistance genes in the bean map. Rust resistance genes Ur-3, Ur-6, Ur-7, Ur-11, and Ur-BAC 6 are located on linkage group (LG) 11 (Miklas et al., 2002; Park et al., 2003, 2004), while other genes Ur-9, Ur-5, Ur-Ouro Negro and Ur-4 are located on LGs 1, 4, 4, and 6, respectively (Miklas et al., 2002). Reproducibility and simplicity of these linked RAPD markers to rust resistance genes can be enhanced by the use of sequence characterized amplified region (SCAR) markers (Paran and Michelmore, 1993). Actually, RAPD markers linked to Ur-3, Ur-5, Ur-6, Ur-11, and Ur-Ouro Negro have been converted into SCAR markers (Correa et al., 2000; Miklas et al., 2002; Park et al., 2004) for use as marker-assisted selection tools. Those RAPD and SCAR markers linked to rust resistance genes have been utilized to pyramid combinations of these genes into single bean cultivars, as suggested by Kelly (1995).
Augustin et al. (1972) reported a single dominant rust resistance gene of MA origin present in Great Northern (GN) 1140. This rust resistance gene (later identified as Ur-7) has been shown to have some valuable resistance against races 41, 44, 47, 49, 67, and 108 [M.A. Pastor-Corrales, United States Department of Agriculture (USDA)-Beltsville, personal communication]. This MA gene, along with other sources, was utilized to develop resistant GN and pinto breeding lines (Stavely et al., 1989; Brick et al., 2001). Park et al. (2003) reported six coupling-phase and three repulsion-phase RAPD markers linked to Ur-7 for specific rust resistance in an F2 population from the MA common bean cross of GN1140 x GN Nebr. #1. A coupling-phase RAPD marker OAD12.550 was found with no recombination with Ur-7. However, a SCAR marker for the MA gene present in GN1140 has not been reported. Thus, a study was designed to convert the RAPD marker OAD12.550 most tightly linked to Ur-7 to a SCAR marker on the basis of a specific forward and reverse 20-mer primer pair. We then surveyed the presence or absence of this newly developed SCAR marker in 90 MA and Andean bean cultivars/lines with or without Ur-7 and Ur-6 for determining their genetic relationship.
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MATERIALS AND METHODS
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Plant Materials
Eighty-nine F2 plants were previously derived from the MA common bean cross of GN1140 (genotype = Ur-7Ur-7) x GN Nebr. #1 (genotype = ur-7ur-7) for identification of Ur-7 (Park et al., 2003). Seventy-eight recombinant inbred lines (RILs) derived using single-seed-descent from the MA common bean cross GN BelNeb-RR-1 (possessing the three rust resistance genes Ur-5, Ur-6, and Ur-7) x A 55 were developed by Ariyarathne et al. (1999) and used by Park et al. (2003) for mapping of Ur-7. We used these F2 and RIL populations to score the SCAR marker segregation. Ninety MA and Andean common bean cultivars/breeding lines previously used by Park et al. (2004) were also utilized in this study for survey of the SCAR marker linked to Ur-7.
Converting RAPD to SCAR Markers
To develop a SCAR marker for the RAPD marker OAD12.550, the DNA fragment of the RAPD marker was excised and purified using the GENECLEAN II Kit (Q-BIO gene, Carlsbad, CA). Insertion of the purified RAPD fragment into the pCR 2.1-TOPO and cloning of the transformed plasmid were conducted using the TOPO TA Cloning Kit (Invitrogen, Carlsbad, CA). The cloned plasmid was harvested using the GenElute Plasmid Miniprep Kit (Sigma, St. Louis, MO). The RAPD fragment was sequenced using the M13 reverse and forward primers at the DNA sequencing and synthesis facility of the Iowa State University Office of Biotechnology (Ames, IA). A specific forward and reverse 20-mer primer pair was designed on the basis of the forward and reverse sequences of the RAPD fragment. The forward and reverse primer pair was synthesized by Operon Technologies (Alameda, California). Polymerase chain reactions (PCR) were performed on 96-well plates in an MJ Research thermalcycler (model PTC-0100; MJ Research, Waltham, MA). Protocols for PCR and the composition of the final volume of reactants were similar to those described by Rubio et al. (2001) with an annealing temperature of 66°C. A 100-base pair (bp) DNA ladder (Life Technologies, Grand Island, NY) was used to estimate the length of the SCAR marker. The name of the SCAR marker is derived from an ‘S’ prefix for SCAR, the original RAPD marker name without the approximate length, and the exact marker length (Park et al., 2004). The specific forward and reverse 20-mer primer pair was tested in two DNA bulks previously prepared from eight homozygous resistant and eight homozygous susceptible F2 plants, respectively, of the GN1140 x Nebr. #1 cross. The primer pair was also tested in 89 individual plants of the same population, the RIL population of the BelNeb-RR-1 x A 55 cross, and 90 common bean genotypes to determine the presence or absence of the SCAR marker linked to Ur-7.
Linkage Analysis
To detect segregation distortion of the SCAR marker, F2 and RIL population marker data were tested for goodness-of-fit to a 3:1 or 1:1 ratio using the chi-square test. We performed the linkage analysis of six RAPD markers and Ur-7 formerly identified by Park et al. (2003) with the new SCAR marker developed in our study on the data for 89 F2 plants of the GN1140 x Nebr. #1 cross using MAPMAKER version 3.0 (Lander et al., 1987). We also executed the linkage analysis of 99 markers previously mapped by Ariyarathne et al. (1999) and Park et al. (2003) with the new SCAR marker developed in this study on the data for the RIL population of the BelNeb-RR-1 x A 55 cross. On the basis of a logarithm of odds (LOD) score of 3.0 and a linkage threshold of 0.4, LGs were displayed using the Group command. Map distances (centiMorgan, cM) between ordered loci of marker and gene were calculated using recombination fractions and the Kosambi mapping function (Kosambi, 1944).
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RESULTS AND DISCUSSION
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Development of a SCAR Marker Linked to Ur-7
The most tightly linked coupling-phase RAPD marker OAD12.550 (Fig. 1a
) to Ur-7 identified in the F2 population from the GN1140 x Nebr. #1 cross (Park et al., 2003) was converted into a SCAR marker on the basis of the specific forward and reverse 20-mer primer pair. The exact length of the RAPD fragment OAD12.550 was 537 bp based on the sequence data. The sequence of the forward 20-mer primer was 5'-AAGAGGGCGTGAGATCGTCG-3', while that of the reverse 20-mer primer was 5'-AAGAGGGCGTCTTGAAGGTT-3'. The underlined sequences were the original 10-mer sequence of the OAD12 primer. Melting temperatures of the forward and reverse primers were 65°C and 61°C, respectively. We used 66°C as a consensus annealing temperature.
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Figure 1. (a) Coupling-phase RAPD marker OAD12.550 and (b) SCAR marker SOAD12.537 amplified with the specific primer pair designed from the sequence of the RAPD marker OAD12.550 expressing polymorphism between two DNA bulks from susceptible and resistant F2 plants, between the susceptible parent GN Nebr.#1 and the resistant parent GN1140, and between the susceptible line A 55 and the resistant line BelNeb-RR-1. 1 = a 100-bp DNA marker ladder, 2 = GN Nebr.#1, 3 = GN1140, 4 = DNA bulk from susceptible F2 plants, 5 = DNA bulk from resistant F2 plants, 6 = A 55, and 7 = BelNeb-RR-1.
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The resulting SCAR marker SOAD12.537, shown in Fig. 1b, was present in the resistant parent GN1140 and the DNA bulk from homozygous resistant F2 plants, whereas it was absent in the susceptible parent Nebr. #1 and the DNA bulk from homozygous susceptible F2 plants. The SCAR marker fragment segregated in the F2 population of the GN1140 x Nebr. #1 cross. A goodness-of-fit to a 3:1 ratio for band presence to band absence for the SOAD12.537 marker was observed in the F2 (Table 1
). The integrated location of the MA rust resistance locus and the loci of seven coupling-phase markers including the SCAR is shown in Fig. 2
. The marker SOAD12.537 showed no recombination with the RAPD marker OAD12.550 in the F2 population, and thus, the SCAR and RAPD markers were observed at the same locus on the LG. The marker SOAD12.537 also cosegregated with Ur-7. The results confirm that the coupling-phase SCAR marker SOAD12.537 was amplified from the same DNA as the RAPD marker OAD12.550. This is the first report on development of a cosegregating SCAR marker for Ur-7 rust resistance gene in common bean.
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Table 1. The chi-square test for segregation of the SCAR marker SOAD12.537 on linkage group 11 in an F2 population from the Middle American (MA) common bean cross GN1140 x Nebr.#1 (GN) and a recombinant inbred line (RIL) population from the MA bean cross BelNeb-RR-1 x A 55 (BA).
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Figure 2. Linkage group 11 including Ur-7 controlling specific rust resistance and seven coupling-phase RAPD and SCAR markers developed using an F2 population of the common bean cross GN1140 x Nebr.#1 (GN), and the RAPD and SCAR markers linked to Ur-7 developed using a recombinant inbred line population of the cross BelNeb-RR-1 x A 55 (BA). The gene and marker names are given on the right and the length in centiMorgans is indicated on the left of linkage group 11. The SCAR marker SOAD12.537 in linkage group 11 is connected between the F2 and recombinant inbred line populations by a line.
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The RAPD marker OAD12.550 was positioned on LG 11 in an existing RAPD marker-based linkage map constructed using RILs from the MA cross of BelNeb-RR-1 x A 55 (Park et al., 2003). The SCAR marker was also polymorphic between the parents BelNeb-RR-1 and A 55. The coupling-phase SCAR marker displayed an amplified DNA fragment in the BelNeb-RR-1 parent that was absent in the A 55 parent (Fig. 1b). The SCAR marker segregated in a 1:1 ratio for band presence to band absence in this RIL population (Table 1). Based on the linkage analysis of 99 formerly mapped markers with the new SCAR marker developed here, the SCAR marker and nine coupling- and repulsion-phase RAPD markers linked to Ur-7 were mapped into one LG (Fig. 2). The RAPD and SCAR markers also cosegregated in this RIL population.
SCAR and RAPD markers have been reported for disease resistance genes in common bean. Melotto et al. (1996) found a few recombinations between a RAPD marker (OW13.690) and a SCAR marker (SW13) linked to the I gene for resistance to bean common mosaic virus. We developed the dominant SCAR marker linked to Ur-7, while Adam-Blondon et al. (1994) reported a codominant SCAR marker linked to a resistance gene Are for anthracnose. Several SCAR markers have been reported for resistance to bean rust, including SK14 linked to Ur-3 on LG 11, S119 linked to Ur-5 on LG 4, SCARBA08 and SCARF10 linked to Ur-Ouro Negro on LG 4, SOBC06.308 linked to Ur-6 on LG 11, and GT02 linked to Ur-11 on LG 11 (Correa et al., 2000; Miklas et al., 2002; Park et al., 2004). The coupling-phase SCAR marker linked (no recombination) to Ur-7 of MA origin developed here, along with the markers linked to the above genes, could be utilized to develop a P. vulgaris cultivar or line with different genes pyramided for broad rust resistance and resistance to other bean diseases.
Survey of the SCAR Marker in Diverse Bean Germplasm
We investigated the presence or absence of the SCAR marker SOAD12.537 in 77 MA and 13 Andean common bean cultivars/breeding lines (Table 2
). The presence of the SCAR marker was associated with four MA GN and pinto cultivars known to have Ur-7 based on previous information (genotype = Ur-7), while the absence of the marker was associated with other MA cultivars/lines known to lack Ur-7 (genotype = ur-7). Exceptions were Marquis and BAC 6, which lack Ur-7 but amplified the SCAR fragment. All Andean cultivars/lines lacked the SCAR marker fragment. This would be expected due to the MA origin of Ur-7 and the tight linkage of the marker with Ur-7. Thus, the SCAR marker would be useful for selecting the MA gene for rust resistance in MA bean germplasm.
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Table 2. Presence (+) or absence (–) of the coupling-phase SCAR marker SOAD12.537 linked (no recombination) to Ur-7 in Middle American (MA) or Andean (A) bean cultivars/lines.
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The SCAR marker was generally regarded as gene pool specific based on the analysis of our marker survey (Table 2). Miklas et al. (1993) and Park et al. (2004) reported a gene pool specificity and usefulness of their identified markers for Andean rust resistance genes Ur-4 and Ur-6 in MA bean germplasm. Pathogen race specificity has also been observed within the Andean gene pool (Haley et al., 1993). However, Haley et al. (1994) and Melotto et al. (1996) reported no gene pool or race specificity on the basis of marker surveys in a MA and Andean bean collection, and utility of their linked markers for Ur-3 and I across MA and Andean bean gene pools.
The rust resistant GN1140 was selected from progenies of the cross GN UI 123 (susceptible to rust) x pinto US-5 (resistant to rust). Pinto US-5, a parent of GN1140 and the closely related pinto US-14, possessed the coupling-phase SCAR marker linked to Ur-7 (Table 2).
The cosegregating coupling-phase SCAR marker SOAD12.537 developed here was positioned on LG 11 of the existing bean linkage map (Fig. 2). Park et al. (2004) developed the coupling-phase SCAR marker SOBC06.308 linked to Ur-6 at 1.3 cM in the Olathe (Ur-6) x Nebr. #1 sel. 27 cross, and confirmed the finding of Miklas et al. (2002) that Ur-6 mapped to LG 11 of the core bean linkage map. Because the SCAR marker SOBC06.308 linked to Ur-6 was absent in BelNeb-RR-1 (Park et al., 2004), we cannot calculate the genetic distance between Ur-7 and Ur-6 in the BelNeb-RR-1 x A55 RIL population using the two SCAR markers. However, a repulsion-phase RAPD marker OAB18.650 linked to Ur-7 and Ur-6 at distances of 7.6 and 38.7 cM, respectively (Park et al., 2003, 2004) that was also located on LG 11 of the RAPD bean linkage map (Fig. 2) constructed from the BelNeb-RR-1 x A55 population (Park et al., 2003, 2004). Based on the previous results of Park et al. (2003 and 2004) and our new data, Ur-7 and Ur-6 are distinct but loosely linked at a distance of more than 30 cM on LG 11 of the P. vulgaris map.
An additional rust resistance gene Urc present in Olathe was found by Grafton et al. (1985). Kelly et al. (1996) subsequently proposed that Urc present in Olathe was the same as Ur-7 present in GN1140. Park et al. (2004) reported that the coupling-phase SCAR marker SOBC06.308, amplified from Olathe and Golden Gate Wax (another source of Ur-6) and tightly linked to Ur-6 on LG 11, was absent in GN1140 carrying Ur-7 as well as US-5, the source of the rust resistance of GN1140. Our coupling-phase SCAR marker SOAD12.537 that cosegregated with Ur-7 on LG 11 was present in UI-111 (another source of Urc) (Grafton et al., 1985), as well as Olathe (Ur-6 and Urc), whereas it was absent in Golden Gate Wax (only Ur-6) (Table 2). This SOAD12.537 marker also segregated in the F2 population of the Olathe x Nebr. #1 sel. 27 cross but at a distance of 52.2 cM, the SCAR marker could not be linked to Ur-6 in the population. This marker information derived from survey of key cultivars including GN1140, Olathe, Golden Gate Wax, UI-111, and US-5 supports the hypothesis that the Urc and Ur-7 genes are the same. However, to prove this hypothesis, an allelism test is needed in an F2 population of the Olathe x GN1140 cross with the rust races used by Grafton et al. (1985).
Rust resistance in dry beans has been shown to originate in germplasm from both Andean and MA regions of P. vulgaris domestication. Combining resistance genes from both regions may improve resistance stability to this highly variable pathogen. Two genes, Ur-6 of Andean origin and Ur-7 of MA origin, cannot be phenotypically discriminated in MA bean germplasm having Ur-6. Ur-6 is resistant to more U. appendiculatus races than Ur-7, and thus, the MA gene is masked in the presence of the Andean gene in MA cultivars/breeding lines with both genes. We used the coupling-phase SCAR marker linked to Ur-7 to identify bean cultivars/lines with both genes (Table 2). In 90 bean genotypes, the linked SCAR marker identified MA pinto beans Olathe, Bill Z, Apache, Montrose, BelDak-RR-1 and-2, and CO 12783 that have Ur-6 and also have Ur-7 due to the presence of the coupling-phase marker for Ur-7. Other beans with Ur-6 such as Weihing, Burke, Kodiak, Topaz, Golden Gate Wax, BelMiNeb lines, BelDakMi lines, and other Colorado breeding lines lack Ur-7 because of the absence of the SCAR marker. Pinto beans Apache, Montrose, BelDak-RR-1, and -2 have Olathe in their lineages, while Bill Z and CO 12783 possess UI-111 in their lineages. UI-111 could have US-5 or -14 in its background. However, the lineages of Marquis (Rogers Seed) and BAC 6 (Brazilian), which amplified the SCAR fragment but lack Ur-7, are unknown.
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CONCLUSIONS
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A coupling-phase SCAR marker SOAD12.537 was developed for bean rust resistance gene Ur-7 of Middle American origin. This SCAR marker cosegregated with Ur-7 and was positioned on LG 11 of the core P. vulgaris linkage map. The SCAR marker facilitated identification of Ur-7 in pinto bean cultivars/lines Olathe, Bill Z, Apache, Montrose, BelDak-RR-1 and -2, and CO 12783 that also have rust resistance gene Ur-6 which precludes phenotypic recognition of Ur-7 due to its broad rust resistance. This SCAR marker linked (no recombination) to Ur-7, along with markers for other rust resistance genes, can be utilized to pyramid multiple genes for more durable resistance to bean rust.
We acknowledge financial support from the Title XII Bean/Cowpea CRSP (AID Contract No. DNA-1310-G-SS-6008-00). We also appreciate the constructive criticism of two reviewers, Drs. Don Lee and Ismail Dweikat, University of Nebraska-Lincoln, to improve the manuscript and thank Janelle Counsell, Lindsey Otto-Hanson, and Lisa Sutton, University of Nebraska-Lincoln, for their technical assistance.
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication June 27, 2007.
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ABSTRACT
INTRODUCTION
