Abundance and length polymorphism of microsatellite repeats in Beta vulgaris L
Résumé
Simple sequence repeats (SSRs) are known to exhibit high degrees of variability even among closely related individuals. Their usage as nuclear genetic markers requires their conversion into sequence-tagged sites (STSs). In this paper we present the development of simple sequences as STSs for Beta vulgaris. This species comprises wild, cultivated, and weedy forms; the latter are thought to originate from accidental hybridisation between the other two. Two partial genomic libraries were screened with simple sequence motifs (AT, CA, CT, ATT, GTG, and CA, CT, respectively). Clones of 22 CA, nine CT, eight ATT, and one GTG sequence were obtained. AT microsatellites were present in compound motifs, not recognised by the probe. Sequence comparisons revealed that 20 CA clones containing short motifs (< 16 bp) were variants of a previously described approximately 320-bp satellite DNA (Schmidt et al. 1991), and hence did not correspond to unique loci. Polymor-phism of one (ATT)I s and three (CT)n , with n = 15, 17 and 26, was detected by PCR on a sample of 64 plants from the different forms orB. vulgaris. 13 (ATT), 13 (CT), nine (CT) alleles and one (CT) allele were detected. One of the ATT alleles was much larger than the others (> 800 bp). Genetic variability was high among wild beets, lower among cultivated beets, and intermediate Communicated by G. Wenzel M. M6rchen 9 J. Cuguen 9 P. Saumitou-Laprade ([~) Laboratoire de G6n&ique et Evolution des Populations V~gStales,