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Genyi Li and Carlos F. Quiros

DNA samples from 21 cultivars of celery (Apium graveolens L. var. dulce) were subjected to amplified fragment length polymorphism (AFLP) analysis. The most informative adapter combination was EcoRI-TaqI. All cultivars could be distinguished from each other by their unique fingerprints based on 73 markers. The program NTSYS grouped the cultivars in three main clusters according to their origin. The groupings observed agreed, with a few exceptions, with those expected by historical accounts and previous analyses based on biochemical and ramdomly amplified polymorphic DNA (RAPD) markers.

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Juan J. Ruiz, Belen Pico, Genyi Li, Vincent D'Antonio, Bryce Falk, and Carlos F. Quiros

Resistance to Celery mosaic virus (CeMV) in celery [Apium graveolens L. var. dulce (Mill.) Pers.] is recessive and determined by the single gene, cmv. We report discovery of two polymerase chain reaction-based dominant markers tightly linked to cmv in segregating F2 and BC1 populations. Marker me1em2 is associated to the dominant (susceptibility allele) and the second marker, me8em2, to the recessive (resistance allele). Simultaneous screening for both markers in segregating populations allows for identification of both homozygous and heterozygous genotypes for disease resistance. This marker system can be used for early seedling selection, which will simplify and speed development of celery cultivars resistant to CeMV.

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Feng Gao, Arvind H. Hirani, Jun Liu, Zheng Liu, Guohua Fu, Chunren Wu, Peter B.E. McVetty, and Genyi Li

There are various clubroot pathogen (Plasmodiophora brassicae) resistance genes within Brassica species with european turnip (B. rapa ssp. rapifera) being identified as potentially the best source of resistance for the development of clubroot-resistant cultivars in chinese cabbage (B. rapa ssp. pekinensis). To use clubroot resistance genes effectively, it is necessary to map these genes so that molecular markers inside or closely linked to these resistance genes can be developed. Using molecular marker-assisted selection, the clubroot resistance genes can be effectively transferred from cultivar to cultivar and from species to species. In this report, one clubroot resistance locus was mapped on linkage group A3 using five segregating populations developed from five chinese cabbage cultivars, suggesting that all the five cultivars shared the same clubroot resistance locus. Furthermore, one of these five chinese cabbage cultivars was used to develop a large segregating population to fine-map this clubroot resistance locus to a 187-kilobp chromosomal region. Molecular markers that are closely linked to the mapped clubroot resistance locus have been developed that can be used for marker-assisted selection in chinese cabbage and canola/rapeseed (B. rapa and B. napus) breeding programs.