Genetic mapping in (Populus tomentosa x Populus bolleana) and P. tomentosa Carr. using AFLP markers

The AFLP genetic linkage maps for two poplar cultivars were constructed with the pseudo-test-cross mapping strategy. The hybrids were derived from an interspecific backcross between the female hybrid clone "TB01" (Populus tomentosa x Populus bolleana) and the male clone "LM50" ( P. tomentosa). A total of 782 polymorphic fragments were obtained with a PCR-based strategy using 49 enzyme-nested ( EcoRI/ MseI) primer combinations. Six hundred and thirty two of these fragments segregated in a 1:1 ratio ( P<0.01), indicating that these DNA polymorphisms are heterozygous in one parent and null in the other. The linkage analysis was performed using Mapmaker version 3.0 with LOD 5.0 and a maximum recombination fraction (theta) of 0.3. Map distances were estimated using the Kosambi mapping function. In the framework map for "LM50" (P. tomentosa), 218 markers were aligned in 19 major linkage groups. The linked loci spanned approximately 2,683 cM of the poplar genome, with an average distance of 12.3 cM between adjacent markers. For "TB01" (P. tomentosa x P. bolleana), the analysis revealed 144 loci, which were mapped to 19 major linkage groups and covered about 1,956 cM, with an average distance of 13.6 cM between adjacent markers. These maps covered about 87% and 77% of the estimated genome size of parents "LM50" and "TB01", respectively. The maps developed in this study lay an important foundation for future genomics research in poplar, providing a means for localizing genes controlling economically important traits in P. tomentosa.