Construction of genetic linkage map and identification of a novel major locus for resistance to pine wood nematode in Japanese black pine (Pinus thunbergii)

Abstract

AbstractBackgroundPine wilt disease (PWD), which is caused by the pine wood nematode (PWN)Bursaphelenchus xylophilus, is currently the greatest threat to pine forests in Europe and East Asian countries including Japan. Constructing a detailed linkage map of DNA markers and identifying PWD resistance genes/loci lead to improved resistance inPinus thunbergii, as well as otherPinusspecies that are also susceptible to PWD.ResultsA total F1mapping population of 188 individuals derived from a cross between the PWD-resistantP. thunbergiivarieties ‘Tanabe 54’ (resistant rank 2 to PWD) and ‘Tosashimizu 63’ (resistant rank 4 to PWD) was inoculated with PWN, and was evaluated for disease symptoms. To perform linkage analysis for PWN resistance, a set of three maps was constructed; two parental maps generated using the integrated two-way pseudo-testcross method, and a consensus map with population-type cross-pollination. The linkage map of ‘Tanabe 54’ consisted of 167 loci, and covered 14 linkage groups (LGs), with a total genetic distance of 1214.6 cM. The linkage map of ‘Tosashimizu 63’ consisted of 252 loci, and covered 14 LGs, with a total genetic distance of 1422.1 cM. The integrated consensus map comprised 12 LGs with the basic chromosome number ofP. thunbergii, and a total genetic distance of 1403.6 cM. Results from quantitative trait loci (QTL) analysis using phenotype data and linkage maps indicated that PWN resistance is controlled by a single dominant allele, which was derived from the ‘Tanabe 54’ female parent. This major QTL was located on linkage group 3 and was designatedPWD1forPINE WILT DISEASE 1.ConclusionsThePWD1locus is a major resistance QTL located on thePinusconsensus LG03 that acts in a dominant manner to confer pine wood nematode resistance. Information from the present study will be useful forP. thunbergiibreeding programs to improve resistance to PWD, and also to help identify susceptibility genes inPinusspecies.