RAPD Genome maps of Douglas-fir

Abstract

We present linkage maps and estimate genome length for two hybrid individuals of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], a coniferous tree species of wide distribution in the western United States. The hybrids were produced by crosses between the coastal (var. menziesi~) and interior (var. glauca) varieties. Haploid megagametophytes from 80 seeds of each individual were analyzed using 81 10-by random amplified polymorphic DNA (RAPD) primers selected for polymorphism, fragment strength, and repeatability in preliminary segregation analysis. Most (82-90%) of the segregating fragments followed the expected 1:1 Mendelian segregation; however, 10-18% showed significant segregation distortion (P < .05) among megagametophytes of the two trees. In one tree, 201 of 221 segregating loci analyzed were combined into 16 major linkage groups of 4 or more loci (plus 1 group of 3 loci, 3 groups with pairs of loci, and 11 unlinked loci); in the other, 238 of 250 segregating loci were combined into 18 major groups (plus 2 groups of 3 loci each and 6 unlinked loci). Analyses of the distribution of markers indicated highly significant clustering in both trees (P < .001). Including flanking regions and unlinked loci, both trees had linkage maps of similar length, 2600 cM and 3000 cM; expected total map size ranged from 2800 to 3500 cM based on method-of-moments estimation. When a common RAPD protocol was used, more than one-third of the RAPD markers segregated in both hybrids. These maps of Douglas-fir are among the largest reported for conifers, a possible consequence of its 13 haploid chromosomes.