Plant Genome III Conference Plant Genome III Conference
The RAPD technique has been indicated as one of the most powerful methods to obtain a large number of genetic markers in a wide range of species. In conifers, the Mendelian inheritance of the RAPD bands may be verified analyzing a suitable number of (haploid) megagametaphytes from a single tree (Binelli & Bucci, 1994, Theor.Appl.Genet. 88:283-288). The availability of genetic linkage maps from different individuals of the same species would allow the comparison of the chromosomal localization of the markers (genomic sinteny). Confirmation of the reliability and usefulness of RAPDs in investigations on wild populations needs to be addressed for their proper utilization as conventional genetic markers. We report the results of the screening of 20 mapped RAPD loci over haploid megagametophytes from 48 individual trees of an Italian population of Norway spruce. Segregation analysis over the whole population confirmed previously reported evidence on the genetic origin of the RAPD marker bands in Picea abies (Bucci & Menozzi, 1993. Mol.Ecol.2:227-232). The good fit of the observed segregation ratios within families to the expected binomial distribution was consistent with a simple, dominant, Mendelian fashion of inheritance of RAPD markers. LOD scores for 190 pairs of loci were calculated over rashes of megagametophytes from 'informative' trees (double heterozygotes), and previously reported linkage relationships between pairs of linked markers were confirmed. Single-locus genotypes were inferred from haploid progeny-array data and were used to estimate linkage disequilibrium between loci. Significant deviations from equilibrium did not appear to be randomly distributed over loci. Most of the markers analyzed show an excess of heterozygotes and 5 out of 20 RAPD markers show significant deviations from Hardy-Weinberg equilibrium. A weak spatial structure was detected by spatial autocorrelation at the scale considered (O-180m), suggesting a lack of "family structure" due to isolation-by-distance. Non-random distribution of the genetic variability was limited to some lock. Di- and tri- locus spatial autocorrelation of loci showing linkage disequilibrium was also carried out.