An allele responsible for seedling death in Pinus radiata D!Don

When inbred, most outcrossing species show high mortality, manifested at several life stages. The occurrence of homozygotes for deleterious or lethal alleles is believed to be responsible. Here, we report the identification of an allele responsible for the death of selfed Pinus radiata D. Don seedlings in their first month after germination. Among 291 S-1 seedlings of plus-tree 850.55, 76 died within 1 month of emergence. Their death appears to be caused by a single recessive lethal allele, SDPr (seedling death in Pinus radiata). SDPr is located in a linkage group with 28 RAPD markers, the closest of which is ai05800a. Of the 76 seedlings that died, megagametophytes of 73 could be genotyped. Of these, 71 had the null (no band) allele of ai05800a: only two had the band allele. Of the 190 surviving S-1 diploids that were genotyped, only two individuals were homozygous for the null allele of ai05800a. By two different methods, the map distance between SDPr and ai05800a was estimated to be between 1.0 and 2.7 cM respectively. The frequency of band and null alleles in the combined population of dead and surviving seedlings and in un-sown seeds shows no evidence of selection at this locus prior to germination.