QTL Mapping of Pine Wood Nematode (PWN) Resistance in Pinus thunbergii

Pine wilt disease (PWD) is caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, and is a chronic problem to pine forests (Pinus thunbergii and Pinus densiflora) in Japan. We selected two mapping populations of resistance (S₁ of PWN resistance cultivar ‘Namikata 73’ and F₁ of ‘Tanabe 54’בTosashimizu 64’) and infected them with PWN. Phenotypic trait was evaluated with levels of disease symptom (5 levels) every week until 10 week after PWN infection. In the S₁ population, one PWN resistance QTL was mapped with 56 molecular markers on linkage group 8. In the F₁ population, two resistance QTLs were mapped with 131 molecular markers on linkage groups 8 and 12. A major resistance QTL named PWNRLG8 (LOD score 4.71-6.45) with a large phenotypic effect (10.9-20.2 %) was mapped in both populations to chromosome 8. Another resistance QTL was mapped on linkage group 12 (Tanabe 54×Tosashimizu 64). These data provided first evidence for common resistance mechanisms against PWN. QTLs identified in this study would be useful for marker-assisted selection in PWN resistant breeding programs in Pinus thunbergii because resistance tests are time consuming and laborious.