RANDOM AMPLIFIED POLYMORPHIC DNA MARKERS TIGHTLY LINKED TO A GENE FORRESISTANCE TO WHITE-PINE BLISTER RUST IN SUGAR PINE

We have genetically mapped a gene for resistance to white pine blister rust (Cronartium ribicola Fisch.) in sugar pine (Pinus lambertiana Do ugl.) by using an approach which relies on three factors: (i) the abil ity to assay for genetic markers in the haploid stage of the host's li fe cycle, using megagametophyte seed tissue; (ii) a simple and clearly defined pathosystem; and (iii) the use Of random amplified polymorphi c DNA (RAPD) markers that can be quickly and efficiently evaluated, Re sistance to white pine blister rust in sugar pine is known to be contr olled by a single dominant gene (R), Maternal segregation of R and dom inant RAPD markers were scored simultaneously following collection Of megagametophytes for DNA assays and seedling inoculation with C. ribic ola. Bulked samples of haploid megagametophyte DNA from resistant and susceptible offspring of segregating full-sib and half-sib families we re used to evaluate 800 random decanucleotide primers. Ten loci linked with the gene for resistance to white pine blister rust were identifi ed and segregation data were obtained from five families. Six of the l inked markers were within 5 centimorgans of the gene, and one marker w as 0.9 centimorgan from R, These and other markers derived by this app roach may provide starting points for map-based cloning of this import ant gene.