Dai Kusumoto

Monoterpene and sesquiterpene emissions from Sugi (Cryptomeria japonica) based on a branch enclosure measurements

Abstract Sugi ( Cryptomeria japonica ) is the dominant tree species in the forested area of Japan. The forested area is approximately 250 000 km 2 and covers almost 70% of total area of Japan. However, there is little information available on biogenic volatile organic compounds (BVOCs) emissions from Sugi trees. BVOCs are known to have an important role in atmospheric chemistry due to their high reactivity and aerosol formation potential. Emissions of monoterpenes and sesquiterpenes, which are groups of BVOCs, were measured from Sugi using a bag enclosure system over four seasons at the Tanashi Experimental Station, located in a suburban area of Tokyo, Japan. Six monoterpenes accounted for the major emissions, and total monoterpene emission ranged up to 0.4 µg g –1 (dw) h –1 . The emission rates of both β –farnesene; which is a sesquiterpene, and monoterpenes clearly showed temperature dependence. Only β –farnesene was detected in the sesquiterpene fraction and determined to have a larger emission rate compared to that of total monoterpenes. The coefficient β for total monoterpene and β –farnesene calculated by G93 algorithm were 0.10 and 0.22, respectively. However, β showed largely different values on August (monoterpenes) and April (β–farnesene). The emission rates of β – farnesene show almost the same values in measured individuals and ranged from the detection limit (approximately 0.1 ng g –1 (dw) h –1 ) to 1.5 µg g –1 (dw) h –1 . The basal emission factor of monoterpenes in summer and sesquiterpenes in spring were generally lower compared to other seasons. This study indicated that Sugi trees in suburban areas emit sesquiterpene at a higher rate than total monoterpenes.

Virulence of Raffaelea quercivora isolates inoculated into Quercus serrata logs and Q. crispula saplings

This study was conducted to compare the virulences of various isolates of Raffaelea quercivora—a fungus that causes Japanese oak wilt disease—towards Japanese oak trees. Five isolates were collected from a wide range of Japan and inoculated into Quercus serrata logs and Q. crispula saplings. The tangential length of the discolored sapwood in the Q. serrata logs differed significantly among the isolates. The trend in isolate virulence was similar for the Q. serrata logs and the Q. crispula saplings. This is the first report suggesting that there is variability in virulence among isolates of R. quercivora.

Determination and potential importance of diterpene (kaur-16-ene) emitted from dominant coniferous trees in Japan

Reactive volatile organic compounds (VOCs) are known to affect atmospheric chemistry. Biogenic VOCs (BVOCs) have a significant impact on regional air quality due to their large emission rates and high reactivities. Diterpenes (most particularly, kaur-16-ene) were detected in all of the 205 enclosure air samples collected over multiple seasons at two different sites from Cryptomeria japonica and Chamaecyparis obtusa trees, the dominant coniferous trees in Japan,. The emission rate of kaur-16-ene, was determined to be from 0.01 to 7.1 μg dwg(-1) h(-1) (average: 0.61 μg dwg(-1) h(-1)) employing branch enclosure measurements using adsorbent sampling followed by solid phase-liquid extraction techniques. The emission rate was comparable to that of monoterpenes, which is known major BVOC emissions, collected from the same branches. In addition, total emission of kaur-16-ene at 30°C was estimated to exceed that of total anthropogenic VOC emissions.

Comparison of histological responses and tissue damage expansion between resistant and susceptible Pinus thunbergii infected with pine wood nematode Bursaphelenchus xylophilus

Pine wilt disease caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, has been epidemic and has had disastrous impacts on pine forests and forest ecosystems in eastern Asia. Many pine species in this area are susceptible to this disease. Pinus thunbergii is particularly susceptible. In Japan, tree breeders have selected surviving trees from severely damaged forests as resistant candidates, and have finally established several resistant varieties of P. thunbergii. However, this breeding procedure requires much time and effort due to the lack of physiological and phenotypical information about resistance. To investigate the resistance mechanisms of selected P. thunbergii, we compared histochemical responses, tissue damage expansion, and PWN distribution in resistant and susceptible clones of P. thunbergii after PWN inoculation. The results suggested that the mechanisms of resistance are as follows: damage expansion in the cortex, cambium, and xylem axial resin canals are retarded in resistant trees soon after inoculation, probably due to the induction of wall protein-based defenses. Suppression of PWN reproduction was particularly caused by inhibition of damage expansion in the cambium. The slow expansion of damage in each tissue provides time for the host to complete the biosynthesis of lignin in the walls of cells that surround the damaged regions. This lignification of cell walls is assumed to effectively inhibit the migration and reproduction of the PWNs. The mechanism of initial damage retardation is presumed to be a key for resistance.

Comparison of Sapwood Discoloration in Fagaceae Trees After Inoculation with Isolates of Raffaelea quercivora, Cause of Mass Mortality of Japanese Oak Trees

The mass mortality of oak trees has been prevalent in Japan since the late 1980s. The fungus Raffaelea quercivora is transmitted by an ambrosia beetle, Platypus quercivorus, which causes mortality. The beetle is able to bore galleries into the sapwood of most Fagaceae trees in Japan; however, the level of mortality caused by R. quercivora and P. quercivorus differs greatly among tree species. Previous studies by our research group have demonstrated that the virulence of R. quercivora differs among isolates when inoculated into Quercus serrata logs. However, interactions between the virulence of R. quercivora isolates and the susceptibility of other fagaceous species have yet to be elucidated. In this study, we inoculated the fresh logs of 11 fagaceous species with isolates of low and high virulence, and measured the tangential widths of discolored sapwoods 3 weeks after inoculation. Although the discoloration widths of Q. crispula sapwood were similar among all isolates, those of Q. serrata and Q. acutissima tended to increase with the more virulent isolates. Sapwood discoloration in Q. glauca, Q. acuta, Q. salicina, Lethocarpus edulis, and Castanopsis sieboldii was greatly increased by highly virulent isolates. Discoloration in Fagus japonica was not influenced by any of the isolates. The logs of Q. crispula and Q. serrata but not Q. glauca were significantly more discolored by a low-virulence isolate compared with standing trees. The various virulent isolates induced unique sapwood discoloration characteristics in each species, which may explain species-specific differences in mortality rates.

Commensal relation between Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) and Monochamus alternatus (Coleoptera: Cerambycidae) within pine trees

Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle causes pine wilt disease and is transmitted by Monochamus alternatus Hope adults in Japan. To determine the effects of the beetle larvae on the nematode population and the effects of the nematode population on beetle larval growth, we inoculated fresh pine bolts with various combinations of B. xylophilus, M. alternatus, and the blue-stain fungus Ophiostoma minus (Hedgc.) Syd. & P. Syd., the food of the nematodes. We also compared the content of ergosterol among the phloem, xylem, and larval frass. The nematode density was 22 or 25 times higher in frass than in phloem and the lowest in xylem, indicating positive effects of beetle larvae on the nematode population growth. Frass had twice higher ergosterol content than the phloem, indicating the fungal mycelial content was greatest in the frass. The difference in the content of fungal mycelia could explain in part the difference in B. xylophilus density between the frass and phloem. By contrast, B. xylophilus did not affect the growth and developmental rate of M. alternatus. This study showed that the relation between the beetle and nematode populations changes from mutualism to commensalism corresponding to the dispersal to reproduction stages of the nematode population.

Discoloration induced by Raffaelea quercivora isolates in Quercus serrata logs and its relation to phylogeny: a comparison among isolates with and without the Japanese oak wilt incidence including outside of Japan

Japanese oak wilt (JOW) has been prevalent in Japan since the late 1980s. Infections of the fungus, Raffaelea quercivora Kubono et Shin. Ito, which is transmitted by an ambrosia beetle [Platypus quercivorus (Murayama)], can cause JOW. Although R. quercivora, P. quercivorus, and oak trees are distributed in other Asia–Pacific countries, the incidence of JOW has not been reported outside Japan. In this study, we collected R. quercivora isolates from 5 Asian countries, including Japan, and compared their ability to induce sapwood discoloration by inoculating Q. serrata logs. The tangential widths of the discoloration in sapwoods inoculated with non-Japanese isolates were equivalent to or greater than those of the 2 Japanese isolates. This indicates that a lack of JOW incidence outside Japan is not because of the lowered ability of R. quercivora to spread discoloration compared with the Japanese isolates. Statistical analyses of the relationship between discoloration and phylogeny based on DNA sequences of actin and chitin synthase showed that the discoloration width was independent of phylogenetic relatedness among the isolates. To discuss why the occurrence of JOW has not been reported outside Japan, further studies (e.g., on host susceptibility and P. quercivorus aggression) throughout Asia are needed.