Identification of QTL for Pine Wood Nematode Resistance in Japanese Black Pine (Pinus thunbergii)

Pine wilt disease (PWD) is caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, and is a very serious problem in pine forests (Pinus thunbergii and Pinus densiflora) in Japan. A breeding project to develop pine varieties resistant to pine wilt disease was started in 1978 in western Japan, and related projects are promoting throughout Japan. In this study, we attempted to identify a novel genetic locus for PWN resistance from an F₁ population by the QTL analysis with the genetic linkage map. We constructed genetic linkage maps of the resistance cultivers ‘Tanabe 54’ and ‘Tosashimizu 64’ using F₁ seedlings derived from a cross between these cultivars. The ‘Tanabe 54’ map consisted of 162 loci covering 14 linkage groups, and the ‘Tosashimizu 64’ map consisted of 243 loci covering 13 linkage groups. Phenotypic segregations indicated that the PWN resistance in the population was possibly controlled by one or two dominant genes. As the result of QTL analysis, the major resistance QTL was located on linkage group 10, which suggested that allele harbored by ‘Tanabe 54’. A major QTL 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.