Identification of AFLP markers linked to a resistance gene against pine needle gall midge in Japanese black pine

Bulked segregant and AFLP analyses of two mapping populations (R17 x S6 and R17 x S1) were used to identify markers linked to Rpgm, the only known gene responsible for resistance to pine needle gall midge in Pinus thunbergii Parl. Rpgm was found to be bracketed by ACCC/CCTTT(190) on one side at a distance of 6.6 cM and ACGT/CCCGC(250) at 15.3 cM on the other side. The segregation of these markers was analyzed in two other families in order to determine their phase and transferability. One of the two additional resistant parents carried ACCC/CCTTT(190) in the homozygous state while the marker was in coupling (plus marker allele linked with an R allele) in a resistant parent, R17. The marker ACGT/CCCGC(250) was in a repulsion phase in R17 and was not detected in the other two resistant pine trees. Out of four AFLP markers identified, only ACGT/CCAAT(290) was transferable in all resistant trees tested, although its phase was opposite for different trees. These results indicate that in applying those markers to select resistant trees, the phase state of the markers in each resistant tree with respect to Rpgm needs to be considered.