PATTERNS OF LINKAGE DISEQUILIBRIUM IN Pinus radiata

¹ Forest Research, Private Bag 3020, Rotorua, New Zealand

² Present Address: USDA Forest Service, Southern Institute of Forest Genetics, Saucier, MS 39574, USA

Linkage disequilibrium (LD) in Pinus radiata is of interest for a variety of reasons, ranging from the prospect of selection among unrelated genotypes based on DNA sequence information, to the assignment of function to genes of interest. Obtaining fundamental information on the patterns of disequilibria, at various levels of genome resolution, is therefore of key importance. We have begun to examine such patterns within specific genes expressed during xylogenesis; among both loosely and tightly linked (expressed and non-expressed) sequences on the same linkage group; and across the entire genome. Results to date indicate intragenic disequilibrium frequently exists over short stretches of DNA, but patterns can sometimes be quite complicated. Furthermore, we have found evidence for LD between linked markers, despite considerable expected physical distances between assayed polymorphisms. However, we have found no evidence for substantive chromosome or genome-wide disequilibria. We have also begun to examine the relationship between specific polymorphisms in genes that are differentially expressed during xylogenesis, with a model trait, juvenile wood density (JWD). Using a population of 1950 putatively unrelated trees from multiple sources in replicated trials, we found none of the polymorphisms in four genes were associated with JWD. However, we did find evidence for a relationship between JWD and a SSR marker that maps to a region with QTL for the same trait in two independent pedigrees. Latest results and conclusions will be presented.