An epidemiological survey of Chrysanthemum chlorotic mottle viroid in Akita Prefecture as a model region in Japan

In epidemiological surveys on Chrysanthemum chlorotic mottle viroid (CChMVd) in various chrysanthemums cultivated in Akita Prefecture, Japan, in 2002–2005, approximately 20% of cultivars harbored CChMVd, including more symptomatic types than nonsymptomatic. Large-flowered cultivars were less frequently infected than small-flowered and spray types. The number of CChMVd-infected chrysanthemums is increasing, and the disease is found throughout major chrysanthemum-producing districts. Chrysanthemums infected only with CChMVd, in general, had no noticeable symptoms of disease. Most of those dually infected with known viruses and/or viroid also had no symptoms characteristic of chlorotic mottle disease. The lack of noticeable symptoms in major Japanese cultivars may have resulted in the unnoticed spread of the viroid.     

Effect of low temperature on breaking dormancy and flowering of Arisaema sikokianum (Araceae)

Arisaema sikokianum (Araceae) native to Japan is classified as a vulnerable species in the Red Data Book of Japan. Control of dormancy is essential for efficient corm production and forcing culture. Sprouting of both vegetative and reproductive corms was enhanced by exposure to low temperature. Vegetative corms exposed to low temperatures at 5 °C longer sprouted faster when grown at 20 °C. Effective temperatures for breaking dormancy was 5 °C. Reproductive corms treated at 5 °C longer showed shorter days to flower. Successful forcing culture was achieved; corms treated at 5 °C from November for 30 days flowered on 5th February.     

Ineffectiveness of pruning to control citrus huanglongbing caused by <Emphasis Type="Italic">Candidatus</Emphasis> Liberibacter americanus

The huanglongbing (HLB) disease of citrus trees, caused by Candidatus Liberibacter asiaticus and Ca. Liberibacter americanus, was first reported in Brazil in March, 2004. The presence of the disease has caused serious concerns among growers. Pruning experiments were conducted to determine if removal of symptomatic branches or the entire canopy (decapitation) would eliminate infected tissues and save HLB-affected trees. Pruning was done in five blocks on a total of 592 3- to 16 year-old ‘Valência’, ‘Hamlin’ or ‘Pêra’ sweet orange trees showing no symptoms or with two levels of symptom severity. Ten decapitated trees per block were caged and all trees were treated with insecticides to control the psyllid vector, Diaphorina citri. Mottled leaves reappeared on most symptomatic (69.2%) as well on some asymptomatic (7.6%) pruned trees, regardless of age, variety, and pruning procedure. Presence of the pathogen (Ca. Liberibacter americanus) in all symptomatic trees was confirmed by PCR. In general, the greater the symptom severity before pruning the lower the percentage of trees that remained asymptomatic after pruning.     

Mycoplasma iowae species-specific DNA probe

A Mycoplasma iowae (MI) species-specific DNA probe (designated pMI-2) of 6.0 kbp (kilobase pairs) was isolated from an MI strain I-695 genomic library prepared in plasmid pUC8 and Escherichia coli strain JM83. When labeled with [32]P by nick translation, the probe hybridized in dot blot assays with 6 reference strains and 8 field isolates of MI but not with 16 other known species of avian mycoplasmas. The pMI-2 probe detected a minimum of 1.5 ng of MI strain I-695 chromosomal DNA. Under identical conditions of hybridization, the probe did not hybridize with a high concentration (200 ng) of M. gallisepticum or M. synoviae chromosomal DNA.     

Chemical modification of wood by non-formaldehyde cross-linking reagents

Summary Using sulfur dioxide (SO₂) as catalyst, wood specimens were treated with nonformaldehyde cross-linking reagents such as glyoxal, glutaraldehyde and dimethylol dihydroxy ethyleneurea (DMDHEU). The results of dimensional stability, acoustic properties, and mechanical strength tests were compared with those obtained from formaldehyde treatment. With glyoxal and glutaraldehyde treatments, antiswelling efficiency (ASE) reached around 70%, which is comparable to the values attained by formaldehyde treatment, although the accompanying weight gain was much larger than for the latter, whereas DMDHEU did not give sufficiently high ASE. None of the treatments, significantly increased specific dynamic Young's modulus (E/) with the exception of the DMDHEU treatment, loss tangent (tan ) decreased substantially, about 50 and 60% in longitudinal and radial directions respectively, which were somewhat exceeding the formaldehyde treatment. The results suggested that the improvement of the dimensional stability and acoustic properties is partly attributed to the formation of cross-links.     

Response of gas exchange rates in <Emphasis Type="Italic">Abies firma</Emphasis> seedlings to various additional stresses under chronic acid fog stress

In order to clarify the chronic influence of acid fog on the gas exchange rates of momi fir (Abies firma Sieb. et Zucc.) trees, we exposed them to simulated acid fog (pH 3) for 3 years. The composition of the acid fog was similar to that observed in a region where momi fir trees have been declining, and it contained organic acids. We then treated the firs with various additional stresses, such as drought, low temperature, fine root cutting, ozone exposure, soil acidification, nitrogen load, and rhizosphere aluminum stress. Under chronic exposure to acid fog, the momi fir seedlings exhibited a pattern of stomatal behavior whereby they excessively opened in summer and closed in winter. Furthermore, the stomata of these seedlings tended to open during drought stress, and their needles were visibly injured after ozone exposure. The net photosynthesis rates of the seedlings exposed to acid fog were regulated by their stomatal aperture, rather than directly by acid fog. These results suggest that acid fog exposure disturbs the control of stomatal function in the momi fir seedlings. In addition, we found that chronic acid fog exposure suppressed the decrease in net photosynthesis rate, due to its nitrogen load.     

Stand structure and the regeneration ofChamaecyparis pisifera (Sieb. et Zucc.) Endl. on sites with different soil development in an old-growth coniferous forest, central Japan

Stand structure and the regeneration ofChamaecyparis pisifera on sites with and without well-developed soil in an old-growth coniferous forest, Akasawa Forest Reserve, central Japan, were investigated, along with their relationships to other important coniferous species. Of stems ofC. pisifera≥5 cm diameter at breast height, stems with intermediate size were absent in stands on the developed-soil site, while those with smaller size increased in stands on the undeveloped-soil site, which supported a higher density ofC. pisifera. In the stands without recent tree-fall of canopy stems on the developed-soil site, canopy stems ofC. pisifera were distributed uniformly and the understory stems, patchily. On the other hand, both canopy and understory stems ofC. pisifera in stands on the undeveloped-soil site were distributed patchily. In the understory,C. pisifera occurred as clonal patches formed by vegetative reproduction on various types of microsites including bare rocks. However, the clonal patches did not occur in a stand on the developed-soil site with dense saplings of an evergreen conifer,Thujopsis dolabrata, which can expand vegetatively with a well developed soil layer. Gap formation may induceC. pisifera to develop tree-form stems from shrubby clonal patches. On developed-soil sites,C. pisifera stands that survive a long disturbance-free period on this site need catastrophic disturbance for their regeneration, which will eliminateT. dolabrata in the understory and create bare soil for colonization ofC. pisifera from seeds. On undeveloped-soil sites,C. pisifera replaces itself continuously by effective vegetative reproduction. Ground instability and the wet condition of this site may promote the replacement.     

Initial shapes of stress-strain curve of wood specimen subjected to repeated combined compression and vibration stresses and the piezoelectric behavior

This study investigated the relationship between the initial shape of the stress (σ)-strain (ε) curve of a Chamaecyparis obtusa wood specimen subjected to repeated combined compression and vibration stresses at various angles between the fiber direction and load direction and the piezoelectric behavior. The main findings of the study are: (1) the σ-ε curve became convex initially, and then the stress was proportional to the strain. The σ-ε curve had almost the same shape during both loading and unloading. (2) The σ-piezoelectric voltage (P) curve was nonlinear, with a maximal point or cusp on the curve, which had almost the same shape during both loading and unloading, as was also observed for the σ-ε curve. (3) The plot of the first derivative of the stress [dσ/dε (= σ′)] against ε was nonlinear. The σ′-ε and P-ε curves at various angles were fairly similar. (4) The stress at the maximal point (or cusp) of the σ-P curve decreased with an increase in the angle between the fiber direction and load direction. The tendency of the stresses was very similar to that of Young’s modulus and compression strength calculated from Hook’s law and Hankinson’s law, respectively.