RAPD Genome maps of Douglas-fir

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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. menziesii) and interior (var. glauca) varieties. Haploid megagametophytes from 80 seeds of each individual were analyzed using 81 10-bp 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 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.

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