No abstract

We have isolated and sequenced 52 microsatellites or simple sequence repeats (SSRs) from nearly 60 positive clones obtained from two 'Frantoio' olive genomic libraries enriched in (AC/GT) and (AG/CT) repeats, respectively. The repeat-containing fragments obtained from genomic DNA restricted with Tsp509I were separated using a biotinylated probe bound to streptavidin-coated paramagnetic beads. Fragments were then cloned into lambda ZAPII vector and sequenced. Thirty of the 36 primer pairs which gave correct re-amplification in the source genome were used to assay the polymorphism of 12 olive cultivars, namely four well-known cultivars ('Coratina', 'Frantoio', 'Leccino', 'Pendolino') and eight ancient cultivars grown locally near Lake Garda ('Casaliva', 'Favarol', 'Fort', 'Grignan', 'Less', 'Raza', 'Rossanel', 'Trep'). The local cultivars were each re- presented by two to four long-lived individuals. The analysis was carried out using (33)P-labelled primers and 6% polyacrylamide sequencing gels. All except two microsatellites showed polymorphism, the number of alleles varying from 1 to 5. The average genetic diversity ( H) was 0.55. The power of discrimination ( PD) was 0.60. All cultivars, including the local ones, were easily separated from each other. Variations in the SSR pattern were observed among individual plants of the same cultivar in four out of the eight local cultivars analysed. Several primer pairs (17%) amplified more than one locus.

Background: Individual fingerprinting based on molecular markers has become a popular tool for studies of population genetics and analysis of genetic diversity in germplasm collections, including the solution of synonymy/homonymy and analysis of paternity and kinship.

We report 99 simple sequence repeats (SSRs) newly isolated from an apricot (Prunus armeniaca L.) genomic library enriched for AG/CT repeats. Twenty SSRs were screened for their polymorphism in 16 apricot cultivars. The number of alleles ranged from two to nine, whereas the expected heterozygosity (HE) ranged from 0.26 to 0.82. The same SSRs showed also an appreciable transportability across different Prunus species, such as peach, nectarine, almond, European plum, Japanese plum, sweet cherry and sour cherry, with 20% of primers giving successful amplifications in all Prunus species assayed. None gave amplification in apple.

Primers were developed for 118 microsatellites isolated from grape (Vitis vinifera) genomic libraries enriched for (AC)n repeats. Only one microsatellite sequence matched other grape SSR-sequences in the GeneBank database. Genotyping was carried out in the parental lines and four offspring of two pseudo-test-cross populations, 'Cabernet Sauvignon' x 'Seyval' and 'Chardonnay' x 'Bianca', and a further six other grape genotypes (V vinifera 'Sultanina', 'Merlot', 'Syrah', 'Muller-Thurgau', Vitis 'Regent' and V. riparia 'Gloire de Montpellier'). A total of 108 microsatellites showed easily scorable alleles and 100 of them segregated according to a configuration suitable for mapping in either cross. A further 8 SSRs, although unsuitable for mapping in those crosses, showed polymorphism in the other genotypes tested. This set of markers was used, along with 75 microsatellites of other repeat-types, to fingerprint 46 offspring of the cross 'Chardonnay' x 'Bianca'. For each full-sib, individual heterozygosity and distance in repeat units between pairs of alleles at each locus (mean d(2)) were calculated as a tool for predicting 'highly outbred' recombinant individuals. Six microsatellites with segregation ratios significantly distorted towards the lack of homozygous sibs were identified and mapped to linkage groups LG 3 and LG 5. Estimation of heterozygosity at genome-wide level and genotyping at loci for which homozygous sibs are discriminated against are discussed for marker-assisted background selection in outcrossing grapevines