Detection of quantitative trait loci for wood strength in Cryptomeria japonica

Cryptomeria japonica D. Don (sugi) is one of the most important forest tree species in Japan. The progeny of a cross between the cultivars Iwao-sugi and Boka-sugi were analyzed using RAPD markers, with the pseudo-test-cross strategy, to construct linkage maps of the parental cultivars. A total of 355 segregating loci were detected among 72 offspring: 200 and 155 markers being distributed in Iwao-sugi and Boka-sugi, respectively. In Iwao-sugi, 119 markers with confirmed map positions were assigned to 21 linkage groups covering 1756.4 cM. In Boka-sugi, 84 markers with confirmed map positions were assigned to 14 linkage groups covering 1111.9 cM. The framework map distance in Iwao-sugi and Boka-sugi provides about 62 and 40% coverage, respectively, of the total genome, estimated to be approximately 2800 cM in length. Using genetic linkage maps constructed in this study, 15 QTLs were detected that are associated with the modulus of elasticity (MOE), an important indicator of wood strength. The QTLs for MOE explained about 45% of its total phenotypic variance. Some QTLs associated with different phenotypic traits were located on the same linkage groups. Some of the QTLs for MOE measured by two different methods (the hanging method and the tapping method) were located independently on the different linkage groups.