Recombination rate differences for pollen parents and seed parents in Pinus pinaster

Significantly less recombination was observed for the female gametes than for the male gametes in one individual of maritime pine (Pinus pinaster Ait.). Two segregating mapping samples of the same hybrid tree were used for genomic mapping. One sample consisted of diploid tissues from 192 F-2 seedlings. The other sample consisted of megagametophytes (haploid maternally derived nutritive tissue) extracted from 156 germinated F-2 seedlings. A total of 94 RAPD markers covering 65 per cent of the genome was used for constructing the maps with both samples. Comparison for the total length of the two maps shows that meiotic tic recombination differs between the haploid and the diploid mapping samples. Map distances in the diploid mapping sample were on average 14 per cent larger than in the megagametophyte sample, corresponding to a 28 per cent greater rate of recombination in the pollen parent. Departure from homogeneity of recombination rate was also tested by marker interval using a likelihood-based method. Inference for greater meiotic recombination during male gametogenesis was verified analytically. A genome-wide reduction in the female gamete's recombination rate in gymnosperms presents interesting evolutionary implications, as this is exactly the opposite trend to that in the angiosperms studied so far. Direct consequences for pine tree breeding are also discussed.