The effect of the gaseous state on bud induction and shoot multiplication in vitro in eastern white cedar

The effect of vessel type and the gaseous phase on the morphogenic response of Thuja occidentalis L. explants in vitro was studied. Explants were cultured in container types that varied in their degree of gas exchange. Traps for ethylene and CO₂ were employed. During shoot bud induction from embryonic explants, the number and elongation of shoot buds improved significantly when gastight, serum-capped flasks were used compared to the foam bung-capped flasks or the regularly used Petri dishes. Elimination of the two gases from the headspace of the flasks either singly or together reduced shoot bud induction and especially elongation of shoots. A similar response was seen during axillary bud development from cultured shoots. Ethylene and CO₂ accumulation promoted development and elongation of axillary shoots. An increase in the zeatin concentration in the medium produced a greater number of axillary shoots and higher levels of ethylene in the culture vessels. Removal of CO₂ caused gradual death of the shoots, while removal of ethylene alone reduced axillary shoot lengths significantly. Inclusion of aminoethoxyvinylglycine in the medium combined with ethylene traps produced an effect similar to the use of ethylene traps alone.     

Changes in the forest floor of Canadian southern boreal forest after disturbance

Abstract. The concentrations and contents of organic matter and nutrients in organic deposits on the forest floor were estimated along a 231-yr chronosequence following fire at the southern limit of the boreal forest in eastern Canada. The sampling design was stratified to take into account the variability related to the presence of the principal tree species as well as to the presence of large gaps created by a recent spruce budworm (Choristoneura fumiferana) outbreak. The forest floor showed a steady accumulation of organic matter and total nutrients with time-since-fire and a 50 % decrease in the concentrations of available P and K, but not N (as determined by aerobic incubation). The increase in forest-floor weight was accompanied by an increased storage of available N, Ca and Mg. The availability of N and Ca was more strongly affected by tree species and gaps than by time-since-fire. A high N-availability was observed under Betula papyrifera and in gaps, while high a Ca-availability was found near Populus tremuloides and Thuja occidentalis. In old sites, the forest floor of gaps, created by a recent spruce budworm outbreak, had a necromass similar to that of a young forest, but the low concentrations of available P and K of an old forest.     

Limitation of transpiration by hydraulic conductance and xylem cavitation in Betula occidentalis

The extent to which stomatal conductance (g_s) was capable of responding to reduced hydraulic conductance (k)and preventing cavitation-inducing xylem pressures was evaluated in the small riparian tree, Betula occidentalis Hook. We decreased k by inducing xylem cavitation in shoots using an air-injection technique. From 1 to 18 d after shoot injection we measured midday transpiration rate (E), g_s, and xylem pressure (Ψ_p-xylem) on individual leaves of the crown. We then harvested the shoot and made direct measurements of k from the trunk (2–3 cm diameter) to the distal tip of the petioles of the same leaves measured for E and g_s. The k measurement was expressed per unit leaf area (k_l, leaf-specific conductance). Leaves measured within 2 d of shoot injection showed reduced g_s and E relative to non-injected controls, and both parameters were strongly correlated with k_l At this time, there was no difference in leaf Ψ_p-xylem between injected shoots and controls, and leaf Ψ_p-xylem was not significantly different from the highest cavitation-inducing pressure (Ψ_p-cav) in the branch xylem (-1.43 ± 0.029 MPa, n=8). Leaves measured 7–18 d after shoots were injected exhibited a partial return of g_s and E values to the control range. This was associated with a decrease in leaf Ψ_p-xylem below Ψ_p-cav and loss of foliage. The results suggest the stomata were incapable of long-term regulation of E below control values and that reversion to higher E caused dieback via cavitation.     

The effects of triflumuron against the western flower thrips (Frankliniella occidentalis (Pergande)) on pepper: an evaluation based on the analysis of population dynamics

Abstract:  The population response of western flower thrips, Frankliniella occidentalis (Pergande) to triflumuron, growth regulator of the benzoyl-phenyl-urea group which performs a chitin-inhibiting action, was the subject of an experimental field test. The characteristics of the active ingredient (knock-down effect, temporal persistence and overall effect of the substance) were assessed in comparison with the responses of two synthetic insecticides (methiocarb, chlorpyrifos-methyl) and in relation to the different treatment strategies (number and dates of treatments). The results of the experimental tests were analysed using a specially developed innovative method, which allows to evaluate precisely and in quantitative terms the response of the system (modification in the population dynamics of thrips) to the treatment carried out. The observations performed highlight that, at the considered doses, triflumuron is characterized by a weak knock-down effect but by good temporal persistence which makes it a product endowed with a distinct larvicidal activity. Furthermore, its action is better overall than that of chlorpyrifos-methyl and is comparable with that of methiocarb.     

Mycorrhiza-like interaction by Morchella with species of the Pinaceae in pure culture synthesis

 Isolates from two species of Morchella were tested for ability to form mycorrhizae in pure culture synthesis with Arbutus menziesii, Larix occidentalis, Pinus contorta, Pinus ponderosa, andPseudotsuga menziesii. Ectomycorrhizal structures (mantle and Hartig net) formed with the four species of the Pinaceae but not with A. menziesii. Results are compared to previous studies on morel mycorrhizae and discussed in an ecological context. Accepted: 23 October 1999     

Elevated CO2-mediated plant VOCs change aggravates invasive thrips occurrence by altering their host-selection behaviour

Globally rising atmosphere CO₂ has been predicted to affect the emission of plant volatile organic compounds (VOCs) and the interaction with insect herbivores. CO₂-mediated plant VOCs change might contribute to develop effective management strategies for insect pests by using VOCs related biological control methods. In this study, we analysed the effect of elevated CO₂ on the host-selection behaviour of western flower thrips (Frankliniella occidentalis) and studied how they were affected by the release of VOCs from kidney bean plants (Phaseolus vulgaris). A four-chamber olfactometer was used to quantify the host-selection of F. occidentalis for P. vulgaris. Elevated CO₂ increased F. occidentalis' selection for P. vulgaris wounded by mechanical damage (MD) and thrips infestation (TI) that might via regulating the gene expression of CSP1, CSP1-q, OBP1 and OBP1-q in F. occidentalis. Besides, we cultivated kidney beans at ambient CO₂ (400 ppm) and elevated CO₂ (800 ppm), and quantified the emission of plant VOCs by using GC-MS. Thirty VOCs belonging to ten chemical groups were identified from P. vulgaris, including aromatic hydrocarbons, ethers, alkanes, cycloalkanes, alcohols, alkenes, aromatic derivatives, phenols, ketones and esters. Furthermore, six VOCs from P. vulgaris were significantly affected by CO₂ level, wounding way and the interaction between them, including ethyl benzene, 1,3-dimethyl benzene, 1,3-dimethyl-4-ethyl benzene, (E,E,E,E)-squalene, 2,6-ditert-butyl-4-methyl phenol and dioctyl phthalate. Our study indicates that elevated CO₂ might increase the host-selection of F. occidentalis for wounded P. vulgaris due to the changed plant VOCs.     

Production of microsclerotia of the fungal entomopathogen Lecanicillium lecanii (Hypocreales: Cordycipitaceae) as a biological control agent against soil-dwelling stages of Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract

Microsclerotia (MS) production by two isolates of Lecanicillium lecanii on various culture media is described, and the efficacy of MS against western flower thrips is evaluated. High concentrations of MS (2.9–3.1×10⁵·mL^?1) were produced in media with C:N ratios of 7.4:1 and 10.3:1 by isolate SN21. Bioassays using soil-incorporated MS resulted in significant infection and mortality of thrips.     

三种抗生素对西花蓟马存活率及肠道可培养细菌的影响

为阐明抗生素对西花蓟马的作用,选用氨苄青霉素(AMP)、氯霉素(CAP)和硫酸链霉素(SM)等3种抗生素分别采用薄膜饲喂法和叶片浸渍法处理西花蓟马,研究3种抗生素对西花蓟马死亡率及对肠道可培养细菌的影响。结果表明抗生素对西花蓟马的死亡率有明显的影响,随着浓度的增加和处理时间的延长死亡率升高,在薄膜饲喂法和叶片浸渍法处理下,西花蓟马均是在3种抗生素浓度为50.00 mg/mL处理72 h时死亡率最大,薄膜饲喂法对西花蓟马死亡率的影响高于叶片浸渍法。在2种饲喂方式下,25.00 mg/mL氨苄青霉素和50.00 mg/mL硫酸链霉素处理72 h后对西花蓟马肠道内可培养细菌的去除效果最好;浓度为50.00 mg/mL氯霉素在薄膜饲喂法中处理24 h后对西花蓟马肠道细菌去除效果最好,但叶片浸渍法没有明显的作用。结果说明,西花蓟马死亡率及肠道细菌的去除效果与抗生素种类、浓度和处理时间相关,也与处理方法有关。     

球孢白僵菌对黄瓜代谢产物及西花蓟马取食行为的影响

球孢白僵菌Beauveria bassiana灌根处理黄瓜后,发现西花蓟马Frankliniella occidentalis对叶片危害面积显著低于对照组;为探究产生这一现象的原因,测定黄瓜叶片中防御酶系和次生代谢产物等含量变化,采用直流刺吸电位仪(direct current electrical penetration graph,DC-EPG)分析西花蓟马成虫取食黄瓜叶片的行为.球孢白僵菌对黄瓜灌根后叶片中过氧化氢酶(CAT)、过氧化物酶(POD)和超氧化物歧化酶(SOD)含量均呈上升趋势,其中CAT活性增加最高,增加率为37.26％;丙二醛MDA的含量呈下降趋势;可溶性蛋白、类黄酮的含量增加.DC-EPG显示西花蓟马在经球孢白僵菌处理的黄瓜上,取食时间和次数均低于对照组.结果表明,黄瓜植株经球孢白僵菌处理后防御酶物质增加,进而导致西花蓟马对叶片危害下降,利于对西花蓟马的防治.     

Empirical support for a despotic distribution in a California spotted owl population

Territorial species, such as the spotted owl (Strix occidentalis),are predicted to follow an ideal despotic distribution. However,debate exists on whether wild populations actually meet theassumptions of an ideal distribution, such as perfect perceptualabilities (i.e., the ability to recognize high- and low-qualitysites without error). Because this hypothesis has importantlife history ramifications for spotted owls, we investigatedwhether occupancy rates of California spotted owl (S. o. occidentalis)territories in the San Bernardino Mountains of southern Californiapositively correlated with a qualitative "potential fitness"(denoted by _pf) estimated from survival and reproduction ofterritorial owls. Spotted owls in our study tended to occupyterritories with the highest _pf, supporting the assumption ofideal perceptual abilities within this population. However,this relationship was noisy, and we suggest that some individualsdo not assess site quality accurately because of perceptuallimitations, prey dynamics, and large territory sizes. Furthermore,dispersal processes, high survival rates, and long life spansof spotted owls may be other key factors preventing some individualsfrom selecting sites of the highest quality and, consequently,our ability to precisely estimate _pf.