Pine wood nematode-resistance ranking of resistant Japanese black and red pine clones in seed orchards of Kagawa prefecture based on 21 years of seedling nematode-inoculation test data

Abstract

To consider effective diffusion of pine wood nematode-resistant seedlings, the ranking of nematode-resistance levels for resistant pine clones formerly developed in southwestern Japan (in the 1980s) has been evaluated in Kyushu ("Kyushu resistance ranking"), but information regarding the ranking's applicability knowledge in other locations is insufficient. In the present study, we analyzed 21 years of nematode-inoculation test data for 14 Pinus thunbergii and 56 Pinus densiflora-resistant clones collected from resistance seed orchards in Kagawa prefecture, Kansai breeding region. Then, we determined the ranking of clones' resistance in Kagawa ("Kagawa resistance ranking") based on the least-square mean values and examined the relationship between the two rankings. The survival tree rate of progenies significantly varied between clones of both species, as well as between test years, indicating the influence of year-to-year variation in testing environments. Nevertheless, there were significantly positive correlation coefficients between the rankings of Kyushu and Kagawa for both species, indicating clones with commonly high survival rates in both locations. These results showed that resistance ranking in a particular location is almost applicable in the other locations within a breeding and distribution region, and contributes to the earlier seed orchard improvement in each region with the check of location-dependent resistance fluctuation.