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Paul Skroth, Jim Nienhuis, Geunhwa Jung and Dermont Coyne

Knowledge of genetic relationships and genetic diversity among accessions is essential for the efficient construction, maintainance and utilization of large ex-situ germplasm collections. Furthermore, streamlining of large collections into care collections necessitates validation of germplasm sampling techniques. DNA molecular markers provide potentially unbiased estimators of genome diversity end may facilitate organization, maintainance, and sampling of plant genetic resources. Our data suggests that RAPD markers will be o good tool for testing tore collection concepts and organizing genetic diversity in common bean. However, the genomic distribution of markers is unknown. Currently we are using recombinant inbred (RI) populations to place RAPD markers in the context of the bean genetic map. We hove evaluated the the distribution of RAPD markers in three RI populations: Bat93 × Jalo EEP558, PC50 × Xan159, and BAC6 × HT7719. Cultivated P.vulgaris has two primary renters of diversity Mesoamerican and Andean, the RI populations used for mapping RAPD markers ore Meso × Andean, Andean × Andean, and Meso × Meso crosses respectively. In the Bat93 × Jalo EEP558 population 383 markers have been mapped for a map length of 735 cM. However, approximately 150 of these markers ore members of 9 dusters which span only 90 cM. This inter gone pool mop is being integrated with linkage mops constructed in the other two populations to compare within and between gene pool marker distributions and to evaluate clustering of markers on the different mops. Implications for the application of RAPD markers will be discussed.

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Gino Beltran, Geunhwa Jung, Mark Bassett and James Nienhuis

The development of a complete linkage map including both morphological and molecular markers is important to understand the genetic relationships among quantitatively and qualitatively inherited traits in common bean. The objective of this study was to identify RAPD markers linked to genes for four morphological traits using bulked segregant analysis and to map the markers to a molecular linkage map previously constructed in common bean. Three segregating populations were evaluated. Two BC2F2 populations with dgs (dark green savoy leaf) and blu (blue flower) induced mutant was developed with a Florida breeding line 7-1404 and 5-593 as the recurrent parent. In addition, a BC3F2 population with the y (yellow wax pod) and the arg (silvery green pod) mutants was developed from the Lamprecht line PI 527858 and 5-593 as the recurrent parent. RAPD markers linked in coupling to the morphological traits were detected to be 4.1 cM, 4.3 cM, 7.3 cM, and 12.3 cM distant from the dgs, blu, y, and arg genes, respectively. The linked RAPD markers were mapped in the molecular linkage map previously constructed using recombinant inbred population of the cross PC-50 × XAN-159. In this linkage map, we observed a linkage between the C locus and blu gene whose location was not previously known. In addition, a linkage between an abaxial leaf pubescent gene and dgs gene was observed. These results indicate that integrating morphological markers and molecular markers can result in a more complete genetic linkage map in common bean.

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Geunhwa Jung, Paul Skroch, James Nienhuis and Dermot Coyne

One of the highest levels of common bacterial blight (CBB) resistance identified in Phaseolus vulgaris is found in XAN-159, which was developed for leaf resistance to CBB through six generations of pedigree selection of progenies derived from the interspecific cross [(`Pinto UI 114' × PI 319441) × P. acutifolius PI 319443] × `Masterpiece'. A RAPD genetic linkage map was previously constructed in a recombinant inbred population derived from the common bean cross PC-50 × XAN-159 for identification of genomic regions associated with bacterial disease resistance in XAN-159. To confirm that chromosomal regions associated with CBB resistance in XAN-159 were introgressed from tepary bean, we investigated the parentage of each genomic interval in XAN-159 by studying the genomic constitutions of the four different parents involved in the pedigree. The results indicate that all genomic regions associated with CBB resistance contain intervals derived exclusively from tepary bean. The uniqueness of marker polymorphisms associated with resistance to CBB in XAN-159 will allow the application of marker assisted selection for these resistance genes in most populations of common bean.

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H.M. Ariyarathne, Dermot P. Coyne and Geunhwa Jung

Halo blight (HB), brown spot (BS), and rust incited by the bacterial pathogens Pseudomonas syringae pv. phaseolicola (Psp), Pseudomonas syringae pv. syringae (Pss) and the fungal pathogen Uromyces appendiculatus, respectively, are important diseases of common beans. The objectives were to construct a RAPD linkage map, and to locate HB and BS resistance genes and genes for some other traits. One-hundred-seventy RAPD markers were mapped in 78 RI lines of the cross BelNeb 1 and A 55. Eleven main and nine minor linkage groups were identified. MAPMAKER/QTL, interval mapping, was used to identify genomic regions involved in the genetic control of the traits. One region was found to control HB leaf reactions to strain HB16 while three regions controlled reactions to strain HB 83. These regions accounted for 22% and 18%, 17%, and 17% of phenotypic variation of resistance, respectively. Four putative QTLs were identified for resistance to BS, and accounted for 37%, 26%, 23%, and 19% of the phenotypic variation. Rust resistance was determined by a single major gene to both rust strains US85NP 5-1 and D82vc74fh. However, linked markers were not identified. The V gene controlling flower and stem color was tightly linked with the Operon marker O10.620.

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William A. Hoch, Geunhwa Jung and Brent H. McCown

A significant pest affecting commonly planted Betula spp. is the birch leafminer (Fenusa pusilla Lepeletier), an insect that can be present in large populations in the landscape and can greatly reduce the vigor and ornamental value of these trees. Twenty-two interspecific crosses were performed between leafminer resistant and susceptible Betula species in an attempt to create the novel combination of ornamental white bark and significant leafminer resistance. Of the nine successful crosses, two produced resistant offspring. Progeny of the diploid × hexaploid cross B. turkestanica Litvin (2x) × B. alleghaniensis Britt. (6x) displayed a broad range of resistance levels, likely the result of segregating alleles contributed by the hexaploid parent. All crosses involving highly resistant individuals of B. costata Trautv. (2x) yielded leafminer susceptible progeny. These results suggest that the larval antibiosis demonstrated by B. alleghaniensis and B. costata is inherited as a recessive trait, and exhibits a gene dosage effect as evidenced by the B. turkestanica × B. alleghaniensis offspring. While most progeny of the B. populifolia Marsh (2x) × B. maximowicziana Regal (2x) cross were susceptible, a single resistant offspring, which was found to be triploid (3x), displayed a mechanism of resistance similar to that of a hypersensitive response. No strong intersectional barriers to hybridization were observed and all interploidy crosses were successful. The chromosome numbers of B. costata (2n = 2x = 28) and B. turkestanica (2n = 2x = 28) are reported here for the first time. The results of this study indicate that the potential exists for the development of insect resistant, ornamental white-barked birch clones through the implementation of a planned, systematic breeding program.

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Soon O. Park, Dermot P. Coyne, Atilla Dursun and Geunhwa Jung

Common bacterial blight (CBB), incited by Xanthomonas campestris pv. phaseoli (Xcp), is an important seed-transmitted disease of common bean (Phaseolus vulgaris L.). Tepary bean (Phaseolus acutifolius A. Gray) has high resistance to Xcp. The objective of this study was to identify RAPD markers linked to genes controlling resistance to three isolates of Xcp using bulked segregant analysis in an F2 population from the tepary bean cross CIAT-G40005 (resistant to Xcp) × Nebr.#4B (susceptible to Xcp). Twelve RAPD markers were mapped in a coupling-phase linkage with three genes for resistance to Xcp. The linkage group spanned a distance of 19.2 cM. A marker L7750 was linked to the genes for resistance to Xcp strains EK-11 and LB-2 at 8.4 cM and 2.4 cM, respectively. Markers U10400 and Y14600 were detected as flanking markers for the resistance gene to Xcp strain SC-4A at 2.4 cM and 7.2 cM, respectively. The symbols Xcp-1, Xcp-2, and Xcp-3 were assigned for the genes for resistance to Xcp strains EK-11, LB-2, and SC-4A, respectively. RAPD markers linked to the genes for resistance to Xcp could be used for transferring all of the resistance genes from P. acutifolius to a susceptible P. vulgaris cultivar.

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Federico L. Iñiguez-Luy, Michell E. Sass, Geunhwa Jung, Mitrick A. Johns and James Nienhuis

This research describes the development of robust molecular descriptors that are reliable and easy to use (PCR-based) for the proper classification of the six cultivated Brassica L. species and subspecies that make up the U triangle. Sequence characterized amplified regions (SCAR) were derived from DNA fragments generated by randomly amplified polymorphic DNA (RAPD) primers that distinguished the U-triangle Brassica species: B. rapa L. (A, n = 10), B. nigra (L.) Koch (B, n = 8), B. oleracea L. (C, n = 9), B. juncea (L.) Czern (AB, n = 18), B. napus L. (AC, n = 19), and B. carinata Braun (BC, n = 17). The SCAR descriptors developed in this study reveal the presence-absence of a DNA fragment and sequence length polymorphisms to distinguish the three genomes (A, B, and C) of the six cultivated Brassica species. These markers should prove to be useful in revealing misclassifications at the subspecies level. The amplification of a single DNA fragment and reduced sensitivity to reaction conditions make these SCAR descriptors ideal to accurately classify and organize large numbers of cultivated Brassica accessions typically present in large germplasm collections.

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Geunhwa Jung, Dermot P. Coyne, James Bokosi, James R. Steadman and James Nienhuis

Dry bean (Phaseolus vulgaris L.) production is limited by bean rust [Uromyces appendiculatus (Pers.) Unger var. appendiculatus]. An effective control strategy for this disease is to breed cultivars with durable resistance. Information on the inheritance, genetic relationships, and mapping of genes with molecular markers for specific resistance (SR), adult plant resistance (APR), and abaxial leaf pubescence (ALP) is needed to pyramid the desired genes for durable resistance. ALP was found to be associated previously with APR in Andean germplasm. The objective here was to identify and map RAPD markers for the genes controlling SR, APR, and ALP and to examine their relationships. Five rust pathotypes were inoculated on the unifoliate leaves of 68 recombinant inbred (RI) lines derived from `PC-50' (presence of SR, APR, and ALP) × XAN-159 (absence of SR, APR, and ALP). SR was determined by a single major gene (Ur-9) to the five rust pathotypes with no detection of recombinants. The fourth trifoliolate leaves were inoculated with one pathotype (A88T1-4b). A single major gene Ur-12 controlled APR to that pathotype. The Ur-9 gene (SR) was independent of and epistatic to the Ur-12 gene (APR). Because of the low number of APR lines in the RI population resulting from the elimination of RI lines with SR, an F2 population was developed from a cross of two homozygous RI lines selected for unifoliate susceptibility to pathotype A88T1-4b and for resistance and susceptibility of the fourth trifoliolate leaves to tag RAPD markers linked to the Ur-12 gene (APR). The single major gene Pu-a determinated ALP and was not linked to Ur-9 (SR) and Ur-12 (ALP). The gene Ur-9 (SR) was linked to RAPD marker J13-1100 at 5 cM and was not assigned to any linkage group or other markers. The gene Pu-a (ALP) was mapped at 20.2 cM from 116.500 and 3.9 cM from marker G3.1150 in linkage group 3. The Ur-12 gene (APR) was mapped at 34.6 cM from marker O13.1350 in linkage group 4b. This is the first report of mapping a gene for APR in common bean.

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

Common bacterial blight, incited by Xanthomonas campestris pv. phaseoli (Xcp) is a serious disease of common bean (Phaseolus vulgaris L.). Randomly amplified polymorphic DNA (RAPD) markers and flower color (V gene) previously were reported to be associated with six quantitative trait loci (QTL) affecting leaf and pod resistance to Xcp. However, the markers for the QTL were not confirmed in different populations and environments to indicate their merit in breeding. The objective was to determine if the associations of RAPD markers and the V gene with QTL for leaf and pod resistance to Xcp in a recombinant inbred (RI) backcross population from the cross BC2F6 `PC-50' × XAN-159 and for leaf resistance to Xcp in an F2 population from a different cross pinto `Chase' × XAN-159 could be confirmed. One or two genes from XAN-159 controlled leaf and pod resistance to Xcp. Among six QTL previously detected, five in the RI backcross population and three in the F2 population were confirmed to be associated with resistance to Xcp. The V gene and RAPD marker BC437.1050 on linkage group 5 were most consistently associated with leaf and pod resistance to two to five Xcp strains in the RI backcross population and with leaf resistance to two Xcp strains in the F2 population. One to three QTL affecting leaf and pod resistance to Xcp accounted for 22% to 61% of the phenotypic variation. Gene number (one to two) estimations and number of QTL (one to three) detected for leaf and pod resistance to Xcp in the RI backcross population were generally in agreement. The marker BC437.1050 and V gene, along with other resistance genes from other germplasm, could be utilized to pyramid the different genes into a susceptible or partially resistant bean line or cultivar to enhance the level of resistance to Xcp.