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Yuanfu Ji and John W. Scott

Resistance to begomoviruses tomato mottle virus (ToMoV) and tomato yellow leaf curl virus (TYLCV) has been introgressed to tomato (Lycopersicon esculentum) from L. chilense accessions LA 1932, LA 2779, and LA 1938. Resistance genes have been mapped to three regions on chromosome 6 using randomly amplified polymorphic DNA (RAPD) markers. We call these regions 1, 2, and 3. To facilitate breeding by marker assisted selection, advanced breeding lines with resistance from the above sources were assayed for the presence of RAPD markers to determine which were most tightly linked to begomovirus resistance. The best RAPD markers were then converted to sequence characterized amplified region (SCAR) markers or cleaved amplified polymorphic sequence (CAPS) markers. In addition, selected restriction fragment length polymorphism (RFLP) markers near the three regions were converted into CAPS markers, which were tested for association with the advanced breeding lines. Only LA 2779 derivatives have the L. chilense introgression in region 1, which is near the location of the Ty-1 gene and spans across CAPS markers 32.5Cla and TG118. Two region 1 RAPD markers UBC197 and UBC621 were converted co-dominant SCAR or CAPS markers, which were present in all 16 resistant breeding lines tested. Derivatives from all three accessions have introgressions in region 2. Further assays with more markers in this region are under way to determine the lengths and locations of the introgressions. No tightly linked RAPD markers have been found for the resistance gene from LA 1932 in region 3. RFLP and CAPS markers are being used to more precisely locate the region 3 gene.

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Mirosława Staniaszek, Katarzyna Szajko, Zbigniew Uliński, Magdalena Szczech and Waldemar Marczewski

Green mold is a serious disease of the cultivated mushroom causing losses in production of economical importance. In the present study, digestion of a Th444 amplicon with endonuclease BseGI was useful to discriminate Trichoderma aggressivum f. aggressivum (T.a.f.a) from the T. aggressivum f. europeanum (T.a.f.e.). The informative restriction fragments of 260 and 300 bp were revealed in the corresponding reference strains T.a.f.a. and T.a.f.e. The 300-bp marker was found in all 28 Polish mushroom isolates tested.

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Taifeng Zhang, Jiajun Liu, Shi Liu, Zhuo Ding, Feishi Luan and Peng Gao

represent the depth of the bb population derived from X and M, respectively. The stronger the correlations between SNPs and dwarf traits, the closer Δ(SNP index) is to one. Δ(SNP index) = 0 represents no association of SNP with dwarf trait. CAPS marker

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Anne M. Gillen and Fred A. Bliss

Tagging Genes for Nematode Resistance and Tree Growth in Peach.” Provision of the F 2 population HB × Oki by Craig Ledbetter, USDA-ARS, is gratefully acknowledged. Information regarding microsatellite pchgms1 and the L×N CAPs marker was provided by Albert

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Haejeen Bang, Angela R. Davis, Sunggil Kim, Daniel I. Leskovar and Stephen R. King

yellow and a cleaved amplified polymorphic sequence (CAPS) marker was developed based on a single-nucleotide polymorphism (SNP) within the LCYB gene; the resultant CAPS marker has been used to reliably distinguish canary yellow from red flesh in numerous

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Anne M. Gillen and Fredrick A. Bliss

Peach rootstock breeding may be accelerated by utilization of molecular markers linked to the root-knot nematode resistance locus (Mi) to screen segregating populations. A genetic linkage map was constructed using RFLP markers in an F2 population (PMP2) that is segregating for this locus. PMP2 is derived from a controlled cross of the relatively diverse peach rootstocks Harrow Blood (susceptible) and Okinawa (homozygous resistant). Bulked Segregant Analysis was applied using RAPD markers. A single small (227 base pairs) RAPD marker was found to be linked to the dominant resistant allele of Mi at a distance of 10 cM. This new marker joined the Mi locus to the RFLP linkage map and showed that two dominant RFLP markers are located between the RAPD marker and Mi. RFLPS are expensive, time-consuming and RAPD markers are unreliable, and therefore both are unsuitable for screening breeding populations. We attempted to convert the RAPD marker to a more breeder-friendly CAPS marker. The converted CAP marker was dominant. Attempts to convert the CAP marker to a co-dominant marker were not successful. The utility of the CAP marker was tested in an open pollinated F2 population derived from the F1 parent of PMP2 and in several rootstocks. The genetic linkage map was compared to other Prunus maps. The PMP2 linkage group containing the Mi locus can be related to the peach × almond linkage group which contains the phosphoglucomutase Pgm-1 locus.

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Lisa J. Rowland, Smriti Mehra, Anik L. Dhanaraj, Elizabeth L. Ogden, Janet P. Slovin and Mark K. Ehlenfeldt

Because randomly amplified polymorphic DNA (RAPD) is the only type of molecular marker that has been used extensively in blueberry (Vaccinium spp.) for mapping and DNA fingerprinting of cultivars, there is a need to develop a new, robust marker system. Expressed sequence tags (ESTs) produced from a cDNA library, derived from RNA from floral buds of cold acclimated plants, were used to develop EST-PCR markers for blueberry. Thirty clones, picked at random from the cDNA library, were single-pass sequenced from the 5' and 3' ends. Thirty PCR primer pairs were designed from the ends of the best quality sequences that were generated and were tested in amplification reactions with genomic DNA from 19 blueberry genotypes, including two wild selections (the original parents of a mapping population), and 17 cultivars. Fifteen of the 30 primer pairs resulted in amplification of polymorphic fragments that were detectable directly after ethidium bromide staining of agarose gels. Several of the monomorphic amplification products were digested with the restriction enzyme AluI and approximately half resulted in polymorphic-sized fragments (cleaved amplified polymorphic sequences or CAPS markers). The polymorphic EST-PCR and CAPS markers developed in this study distinguished all the genotypes indicating that these markers should have general utility for DNA fingerprinting and examination of genetic relationships in blueberry. Similarity values were calculated based on the molecular marker data, and a dendrogram was constructed based on the similarity matrix. Coefficients of coancestry were calculated for each pair of genotypes from complete pedigree information. A fair correlation between similarity coefficients calculated from marker data and coefficients of coancestry was found.

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James M. Bradeen, S. Kristine Ness, Geraldine T. Haberlach, Susan M. Wielgus and John P. Helgeson

Late blight of potato, caused by the fungal pathogen Phytophthora infestans, is of great economic significance and no important U.S. potato cultivars are reliably resistant. The diploid species Solanum bulbocastanum is highly resistant to late blight, even under extreme conditions, but is sexually incompatible with potato. We have generated potato + S. bulbocastanum somatic hybrids. These hexaploid hybrids are highly resistant to late blight and progeny from two successive backcrosses to cultivated potato are either fully resistant or susceptible. The advanced generations are morphologically similar to potato. We have initiated mapping efforts to identify bulbocastanum chromosomal regions responsible for late blight resistance. Using RFLPs, RAPDs, and AFLPs, we identified a single chromosomal region (i.e., single gene or group of linked genes) on chromosome 8 that accounts for 62.2% of the observed resistance. The tomato cDNA clone CT88 cosegregates with late blight resistance in our material and was used to isolate a homeologous BAC clone from a S. bulbocastanum library. Our current efforts include mapping resistance in both fusion-derived and diploid S. bulbocastanum materials via map merging. As markers linked to late blight resistance are identified, we will attempt to convert them to marker forms useful for large-scale breeding efforts. To date, we have successfully converted RAPD and RFLP markers to SCAR and CAPS marker forms. Finally, continued fine mapping and BAC clone characterization will enable future map-based cloning efforts.

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Akihiro Itai and Naoko Fujita

)-based CAPS markers (A: 1.57 kb and 0.63 kb of the PPACS1 fragment; B, 0.83 kb and 0.35 kb of PPACS2 fragment) ( Itai et al., 2003b ). These markers are useful for predicting the ethylene levels of Asian pear cultivars and they enable identification of

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Yuanfu Ji, John W. Scott and David J. Schuster

trays as described previously ( Fulton et al., 1995 ). All markers used in this study are PCR-based, including sequence-characterized amplified region (SCAR) markers and cleaved amplified polymorphic sequence (CAPS) markers taken from either the public