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Soon O. Park, Dermot P. Coyne, James R. Steadman, and Geunhwa Jung

White mold, incited by Sclerotinia sclerotiorum (Ss), is an important disease of common bean (Phaseolus vulgaris). Our objective was to identify RAPD markers and seedcoat pattern associated with QTL affecting resistance to Ss isolates 152 and 279 in a molecular marker-based linkage map previously constructed using a recombinant inbred (RI) population from the common bean cross `PC-50' (resistant to Ss) x XAN-159 (susceptible to Ss). White mold reactions were derived from a greenhouse straw test. Continuous distributions for the reactions to Ss isolates 152 and 279 were observed for RI lines, indicating quantitative inheritance. An intermediate (+0.67) Pearson correlation was observed between the reactions to Ss isolates 152 and 279. Low (0.24 and 0.23) narrow-sense heritabilities were found for the reactions to Ss isolates 152 and 279. Three QTL affecting resistance to Ss isolate 152 explained 33% of the phenotypic variation. Four QTL affecting resistance to Ss isolate 279 explained 54% of the phenotypic variation. The seedcoat pattern marker (C) on linkage group I was most consistently associated with resistance to Ss isolates 152 and 279, and explained 10% and 24% of the phenotypic variation for the traits, respectively. This is the first report on detection of QTL for white mold resistance in common bean. The RAPD markers and seedcoat pattern could be useful in breeding for white mold resistance.

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Rebecca C. Lough and R.G. Gardner

During the last century Phytophthora infestans (Mont.) de Bary, which causes the devastating disease late blight of tomato and potato, has been controlled with pesticides. Recently, the difficulty of controlling late blight has increased due to the appearance of new strains of P. infestans that are more virulent and are resistant to metalaxyl. Numerous P. infestans resistance genes exist within the Solanaceae; however, most of these are race-specific and have the potential of being overcome. To achieve durable resistance, it may be necessary to utilize multigenic resistance or gene pyramiding. The Lycopersicon hirsutum Kunth accession LA1033 is highly resistant to P. infestans. To incorporate resistance into a useful background, the L. esculentum Miller inbred line NC215E was used as a recurrent parent in backcrossing with L. hirsutum LA1033. A population of 264 BC3F1 plants derived from 11 BC2F2 families was planted at Fletcher and Waynesville, N.C., in July 1998 in a replicated field trial. BC3F2 seed were collected from a single highly resistant BC3F1 plant. The BC3F2 population was tested for resistance using a detached leaf screen. To verify growth chamber test results, BC3F3 seeds were collected from the BC3F2 individuals and were planted in a field trial at Fletcher in July 1999. The ratio of resistant to susceptible progeny fit the expected ratio for an incompletely dominant trait controlled by two loci. To identify molecular markers linked to the resistance loci, DNA was extracted from the highly resistant and susceptible BC3F2 individuals, and bulks of DNA were constructed. The resistant and susceptible bulks were screened with AFLP (amplified fragment length polymorphism) markers. Results of the AFLP study indicate marker linkage to resistance.

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Geunhwa Jung, Paul W. Skroch, Dermot P. Coyne, James Nienhuis, E. Arnaud-Santana, H.M. Ariyarathne, Shawn M. Kaeppler, and Mark J. Bassett

Randomly amplified polymorphic DNA (RAPD) molecular markers were used to construct a partial genetic linkage map in a recombinant inbred population derived from the common bean (Phaseolus vulgaris L.) cross PC-50 × XAN-159 for studying the genetics of bacterial disease resistance in common bean. The linkage map spanned 426 cM and included 168 RAPD markers and 2 classical markers with 11 unassigned markers. The seventy recombinant inbred lines were evaluated for resistance to two strains of common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye] (Xcp). Common bacterial blight (CBB) resistance was evaluated for Xcp strain EK-11 in later-developed trifoliolate leaves and for Xcp strains, DR-7 and EK-11, in first trifoliolate leaves, seeds, and pods. One to four quantitative trait loci (QTLs) accounted for 18% to 53% of the phenotypic variation for traits. Most significant effects for CBB resistance were associated with one chromosomal region on linkage group 5 and with two regions on linkage group 1, of the partial linkage map. The chromosomal region (a 13-cM interval) in linkage group 5 was significantly associated with resistance to Xcp strains DR-7 and EK-11 in leaves, pods, and seeds. The regions in linkage group 1 were also significantly associated with resistance to both Xcp strains in more than one plant organ. In addition, a seedcoat pattern gene (C) and a flower color gene (vlae) were mapped in linkage groups 1 and 5, respectively, of the partial linkage map. The V locus was found to be linked to a QTL with a major effect on CBB resistance.

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Milica Ćalović, Chunxian Chen, Qibin Yu, Vladimir Orbović, Frederick G. Gmitter Jr, and Jude W. Grosser

histogram produced by the ploidy analyzer. EST-SSR molecular analysis. Selected somatic tetraploid plants were further tested with molecular markers using EST-SSR method to determine whether they were auto- or allotetraploids. Genomic DNA of recovered

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Michael J. Havey and Yul-Kyun Ahn

polymorphisms in expressed regions of larger genomes useful for diversity analyses and development of genetic maps ( Duangjit et al., 2013 ; Gore et al., 2009 ; Ipek et al., 2015 ; Kuhl et al., 2004 ; Martin et al., 2005 ). Molecular markers, such as

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Christopher S. Cramer and Michael J. Havey

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Melinda A. Miller-Butler, Barbara J. Smith, Brian R. Kreiser, and Eugene K. Blythe

; Lerceteau-Köhler et al., 2003 ), which allows breeders to identify dominant and recessive alleles for these loci. The advent of molecular genetics provided plant breeders with molecular markers to use for identification of alleles linked to disease

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Innocenzo Muzzalupo, Francesca Stefanizzi, and Enzo Perri

/or developmental stages ( Martins-Lopes et al., 2007 ). An ideal molecular marker technique should have the following criteria: 1) to be polymorphic and evenly distributed throughout the genome; 2) to provide adequate resolution of genetic differences; 3) to be

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Carlos Calderón-Vázquez, Mary L. Durbin, Vanessa E.T.M. Ashworth, Livia Tommasini, Kapua K.T. Meyer, and Michael T. Clegg

, 2010 ). Selection on molecular markers such as simple sequence repeats (SSRs) or single nucleotide polymorphisms (SNPs) associated with traits of economic value promise to increase breeding efficiency for beneficial traits, especially in long-lived tree

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Minou Hemmat, Norman F. Weeden, Herb S. Aldwinckle, and Susan K. Brown

Bulked segregant analysis was used to identify RAPD markers that display tight linkage to the Vf gene in apple (Malus sp.) that confers resistance to five races of apple scab [Venturia inaequalis (Cke.) Wint.]. We identified several new RAPD markers linked to Vf. The most tightly linked marker in the test population, S52500, was cloned and sequenced. A linkage map of the Vf region was developed using these markers, RAPD markers previously described by other laboratories, and the isozyme locus Pgm-1. An assay was developed for Vf by multiplexing the two markers closely flanking the Vf locus. This assay has a theoretical `escape' value (discarding a resistant plant) of 3% and an error rate (selection of a susceptible plant) of 0.02%.