In order to provide basic information on genetic improvement potential in Cryptomeria japonica (sugi), we estimated genetic parameters, direct and indirect genetic gains and optimum selection ages for growth traits based on the data obtained from 429 progeny test sites located throughout Japan. Medians of narrow-sense heritabilites for height and diameter at breast height (DBH) were ranged in 0.289–0.445 and 0.235–0.276, respectively. The heritability of height significantly increased after the age of 15 years. On the other hand, there were no significant differences among ages in the heritability of DBH. Medians of the age-age genetic correlations were similar when the age differences of the pairs were the same, and tended to decrease as the age differences became larger for both height and DBH. The maximum efficiencies for gain per year when the target age is assumed to be 30 years were obtained at an age of 5 years in height and of 10 years in DBH, respectively. As the values at an age of 5 years in height varied greatly depending on test site, there would likely be selection errors. Thus, the early selection at 1/3 the target age is efficient in sugi.

Preventive plantation of resistant Pinus thunbergii seedlings is anticipated in non-epidemic areas of pine wilt disease (PWD) in Japan. The scions of resistant clones, which are required to establish a seed orchard for the production of resistant seedlings, might harbor Bursaphelenchus xylophilus (a pathogen of PWD), as they are grown in epidemic areas and artificially inoculated with B. xylophilus to verify their resistance. In this study, we analyzed within-tree distribution of B. xylophilus in inoculated grafts of a resistant P. thunbergii clone, Yuza-155, at two different times, 7 and 19 months after inoculation. Experimental evidence using both direct extraction of nematodes and a DNA-based detection technique demonstrated that the migration and propagation of inoculated nematodes were restricted mostly within the scion stems and rootstocks. In branch samples, nematodes were detected less frequently by the DNA-based method and no live nematodes were extracted at 7 months after inoculation, whereas at 19 months after inoculation, neither of the methods detected any nematodes. Thus, the probability that the current-year shoots of this resistant clone, Yuza-155, which initiated plant growth in the season following inoculation, are infected with B. xylophilus is quite low. Therefore, they may serve as pathogen-free scions for propagation of ramets of resistant P. thunbergii clones and construction of seed orchards in PWD non-epidemic locations.

Background and Objectives: To determine whether the progeny of pinewood nematode-resistant Pinus thunbergii Parl. clones selected in the southwestern region of Japan could be successful in reforestation in the northern region, we investigated the magnitude of the genotype–environment interaction effect on the resistance against Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle in P. thunbergii. Materials and Methods: We inoculated P. thunbergii seedlings of six full-sib families, with various resistance levels, with B. xylophilus in nurseries at three experimental sites in the northern and southern regions of Japan. All parental clones of the tested families originated from southwestern Japan, and selection of parental clones for resistance was performed in the same region. Sound rates after nematode inoculation were calculated, and survival analysis, correlation analysis and variance component analysis were performed. Results and Conclusions: Families with high sound rate in the southern region also showed a high sound rate in the northern region. In almost all cases, Spearman’s correlation coefficients for sound rates were more than 0.698 among sites. The variance component of the interaction between site and family was small compared to that of site and family separately. Thus, we conclude that the resistant clones selected in the southern region would retain their genetic resistance in the northern regions.

Pine wilt disease (PWD) caused by the pinewood nematode (PWN) (Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle) is a worldwide issue. Infection is considered to be promoted mainly by the increased air temperature, but it is important to investigate whether the effect of high temperature similarly influences the different ranks of resistant clone. In the present study, we conducted PWN inoculation tests using six common open-pollinated families of resistant Pinus thunbergii Parl. The tests were conducted at nurseries of five test sites across Japanese archipelago between 2015 and 2017. Our analysis focused specifically on temperature. Firstly, we examined the effects of test sites, inoculation year, and their interaction on unaffected seedling rate and found that the unaffected seedling rate of all tested pine families decreased as the cumulative temperature increased. We found that the unaffected seedling rate decreased as the cumulative temperature increased for all tested pine families. In general, higher cumulative temperatures were required for having an effect on the unaffected seedling rates of higher PWN-resistant families. Typically, early cumulative temperatures, i.e., 19 days after inoculation, had the greatest effect on the unaffected seedling rates of PWN-resistant pines. However, the relationship between cumulative temperature and predicted unaffected seedling rate follow similar rate for all families. Thus, the order of resistance level is maintained in terms of the cumulative temperature required for having an effect.

Ethanol immersion, forced air and seed coat colour sorting were tested for their ability to separate empty from full seeds in the seedlots of Pinus densiflora and Pinus thunbergii. The ethanol immersion technique removed 100% of the empty seeds, whereas forced air and seed coat colour sorting left some empty seeds. Ethanol immersion for less than five minutes did not inhibit seed germination. These results confirmed the usefulness of ethanol immersion for sorting empty seeds from full seeds in two Japanese species of Pinus.