Cultural factors influencing adventitious shoot and plantlet formation from slash pine cotyledons

Cultural factors affecting in vitro shoot and subsequent plantlet formation of slash pine (Pinus elliotti Engelm.) cotyledons were investigated. Basal media composition, N⁶-benzylaminopurine (BAP) concentration and exposure time significantly influenced bud induction in cotyledons cultured under a continuous photoperiod of 35–40 mol m^–2 s^–1 at 24 ± 1 °C. The largest number of adventitious shoots was obtained after 28 days exposure to 66 M BAP-supplemented modified Gresshoff and Doy 1 (GD1) medium. Relatively high frequencies of large shoots were obtained after a 14-day exposure to 22 M BAP-supplemented Brown and Lawrence (BL) or 66 M BAP-supplemented GD1. Adventitious shoots derived from 21- or 28-day exposures to BAP developed more slowly and were smaller in size than those derived from a 14-day exposure to the cytokinin. Shoot differentiation and subsequent growth were also influenced by basal media, media concentration, and presence of activated charcoal in the medium. The percentage of cotyledons forming shoots was highest on half-strength GD1 medium containing activated charcoal. Rooting was achieved in vitro under a continuous photoperiod of 60–70 mol M^–2 S^–1. Roots were formed when excised shoots were planted on GD 1/2 medium supplemented with 2.68 M 1^–1 a-napthaleneacetic acid (NAA) with or without BAP for 14 days. The proposed technique of slash pine propagation using cotyledon explants can produce up to 100 seedlings per embryo.     

Micropropagation of western hemlock (Tsuga heterophylla [Raf.] Sarg.) from embryonic explants

An in vitro propagation protocol is described for western hemlock, an important forestry species in Canada. For shoot bud induction, embryonic explants were placed initially on one-third strength Schenk and Hildebrandt medium containing 5 M N⁶-benzyladenine (BA) or 5 M BA in combination with either 5 M kinetin or 5 M 2-isopentenyl adenine for 14 days. The explants were transferred to basal medium without cytokinins for 3 weeks, and then to basal medium containing 0.05% activated charcoal. Elongating shoots were subcultured every 4 weeks on charcoal medium. Shoots, 10 mm in stem height, were rooted either in agar or sterilized peat/perlite (1:1). Up to 70% of the shoots formed roots when they were transferred to the latter, moistened with 1/2 strength Gresshoff and Doy medium containing 5 M -naphthaleneacetic acid. About 90% of the plantlets survived transfer to greenhouse conditions.     

Maximum effective lumen and pit pore sizes of the earlywood and the latewood of never dried loblolly pine sapwood

Summary Measurements of the air pressure required to initially displace a saturating liquid and allow a slow continuous stream of air bubbles to pass through wood cross sections of different thickness, together with the equilibrium surface tension of the saturating liquid, make it possible to calculate the maximum effective opening radii. Previous measurements were made for wood as a whole over complete annual rings. Measurements reported here were made separately for earlywood and latewood. Extrapolating plots of the maximum effective opening radius-cross section thickness, for thicknesses below the maximum fiber length, to zero thickness gave maximum lumen radii of 16 m for the earlywood and 10.3 m for the latewood. The values are only slightly greater than the calculated average values. Extrapolating the plots in the opposite direction to zero opening radius gave approximate maximum lumen or fiber lengths for the earlywood of 6 mm and for the latewood of 5 mm. The maximum effective opening radii for cross sections thicker than the maximum fiber length give maximum effective communicating pore radii. These values continue to decrease, with increasing thickness of the cross sections due to the decreasing probability of the largest openings falling in any one series path through the structures. The maximum effective pit pore radius for passage through fifty pits in series was 0.8 m for the earlywood and 0.28 m for the latewood.Paper No. 3787 of the Journal Series of North Carolina State University Agricultural Experiment Station, Releigh, N. C.     

Tissue culture micropropagation of Douglas-fir

A procedure was developed for plantlet production from embryos of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco]. The Medium for Conifer Morphogenesis, used at full strength, and supplemented with 10 M benzyladenine for 17 days produced an average of 6.8 shoots on more than 90% of the embryos. The percentage of shoot-forming embryos as well as the average number of shoots per embryo varied significantly among eight seedlots. For secondary multiplication, 89% of the adventitious shoots produced axillary buds on MCM with 5 M benzyladenine. However, 0.5 M BA was more suitable for the elongation of axillaries. Rooting ranged from 0–87% depending upon the treatment. The highest percentage was obtained with a 7-week incubation in peat:perlite containing 1/5-strength medium, 1% sucrose and 2.7 M naphthaleneacetic acid, followed by 5 weeks on peat:perlite with 1/5-strength major and minor salts, full iron and organics, 1% sucrose and 0.1% charcoal.     

Five heavy metals in propagules of ten mangrove species of China

Five heavy metals in the propagules of 10 mangrove species in China have been investigated. The results revealed that the levels of five heavy metals in most of the propagules were lower than the background levels of the soil. The levels of copper, manganese, zinc, cadmium, and lead in the propagules varied at about 2.1–7.8 g/g, 3.9–28.0 g/g, 5.7–60.0 g/g, 0.014–0.057 g/g, and 0.018–0.038 g/g, respectively. On average, the levels of five heavy metals were in the order Zn > Mn > Cu > Cd > Pb. The biological absorption coefficients were 0.02–1.30 for copper, manganese, zinc, and cadmium and about 0.0007–0.0020 for lead in propagules, showing the following order: Zn > Cd > Cu > Mn > Pb. The above results indicate that the five heavy metals have low accumulation in most of the propagules of 10 mangrove species and are at safe levels for the effective utilization of mangrove resources.     

Ultrastructure of pits inPinus banksiana lamb

Summary The cross-sectional view of pitting between various cell types inPinus banksiana Lamb. was studied at the ultrastructural level. Cell types inPinus banksiana include longitudinal tracheids, ray tracheids, ray parenchyma cells, buffer cells and epithelial cells. Two common characteristic features of bordered pit-pairs between longitudinal tracheids are an initial pit border and a thickened torus at the center of the pit membrane. The shape and size of the pit border and torus of bordered pit-pairs between two compression wood cells, and between the last-formed latewood longitudinal tracheid and first-formed earlywood longitudinal tracheid were different from those in the earlywood and latewood longitudinal tracheids. The pit border on the ray tracheid side varied in size and shape due to wall dentation. No initial pit border was found on the pit border of the ray tracheid side. The shape of bordered pit-pairs between two ray tracheids varied considerably due to irregularity of the dentate cell wall. The size of bordered pit-pairs in longitudinal tracheids was between 16 m to 20 m, which was twice the diameter of bordered pit-pairs in ray tracheids. Bordered pitpairs at the end wall of two ray tracheids appeared to be the smallest at 5 m, Pit aspiration occurred in the bordered pit-pairs with or without a torus. In the heartwood zone, some half-borders pit-pairs between tracheary and ray parenchyma cells showed an additional secondary wall on the ray parenchyma cell side. Plasmodesmata were found in the half-bordered pit-pairs as well in the simple pit-pairs. Blind pits were observed between a ray tracheid and a longitudinal tracheid. Bordered pit-pairs between two buffer cells were also observed. The possible functions of buffer cells were discussed.Use of transmission electron microscope provided by the Science Instrumentation Lab, Lakehead University and the technical assistance provided by Mr. A. MacKenzie, Director of Science Instrumentation Lab are gratefully appreciated     

Mangrove forest productivity and biomass accumulation in Hinchinbrook Channel,Australia

Data on stand structure and rates of photosynthesis were used to estimate net canopy carbon fixation and carbon accumulation as living biomass in mangrove forests in Hinchinbrook Channel, Australia. Total annual canopy net carbon fixation was estimated to be about 29tCha–1yr–1. This equates to about 204,000tCyr–1 for all mangrove forests in Hinchinbrook Channel. Of this, only about 12% was stored as living plant biomass. Although it is not yet possible to present a robust carbon balance for mangrove trees, the remainder is presumably lost through plant respiration, litter fall, root turnover and exudation of organic compounds from roots.     

Field measurements of gas exchange in Avicennia marina and Bruguiera gymnorrhiza

Diurnal gas exchange characteristics were measured simultaneously in two mangrove species, Avicennia marina and Bruguiera gymnorrhiza, over 7 d in summer (February–March), to compare their productivity. The study was undertaken in the Beachwood Mangroves Nature Reserve, Durban, South Africa, using fully expanded leaves of young and mature trees at the top of the canopy. Gas exchange was strongly influenced by photosynthetic photon flux density (PPFD), leaf temperature and the accompanying leaf to air vapour pressure deficit ( w). Carbon dioxide exchange was saturated at a PPFD of about 600 mol m^-2s^-1 in B. gymnorrhiza compared to 800 mol m^-2s^-1 in A. marina. Maximal CO₂ exchange occurred between 12h00 and 14h00 and was consistently greater in A. marina (8.8 mol m^-2s^-1) than in B. gymnorrhiza (5.3 mu;mol m^-2s^-1). Mean internal CO₂ concentrations ( c_i) were 260 l l^-1 in A. marina and 252 l l^-1 in B. gymnorrhiza. Photorespiratory activity was 32% in A. marina and 30% in B. gymnorrhiza. Mean water use efficiency (WUE) was 8.0 mol mmol^-1 in A. marina and 10.6 mol mmol^-1 in B. gymnorrhiza. Diurnal leaf water potentials ranged from –0.8 to –3.5 MPa and were generally lower in A. marina.     

In vitro and ex vitro rooting of micropropagated shoots using three green ash (Fraxinus pennsylvanica) clones

Shoot multiplication using seedling materials was achieved by subculture on Murashige and Skoog salts with Gamborg's B5 vitamins (MSB5) medium containing a combination of 5 M 6-benzyladenine (BA), 5 M thidiazuron (TDZ), and 1 M indole-3-butyric acid (IBA) with three green ash (Fraxinus pennsylvanica) clones, SD1009 (South Dakota origin), SD2002 (South Dakota origin), and KA2018 (Kansas origin). Shoots were rooted using in vitro and ex vitro methods. For in vitro rooting studies, elongated shoots were transferred to rooting plugs supplied with liquid MSB5 medium containing a 3×3 factorial arrangement of two different auxins, -naphthaleneacetic acid (NAA) and IBA, at three concentrations (0, 5, and 10 M). The most effective treatment for in vitro root number, root length, and shoot height was 5 M IBA. The three clones also were tested for ex vitro rooting using a quick dip in 1 mM NAA, 1 mM IBA, or control (no auxin). The maximal ex vitro rooting response occurred when shoot explants of the three clones were dipped in 1 mM IBA. Significant clonal differences were noted in response to in vitro and ex vitro rooting treatments. Rooted plantlets were acclimated to the greenhouse.     

A study on some anatomical parameters of the piercing-sucking process in leaves and branches of<Emphasis Type="Italic"> Pittosporum tobira</Emphasis> L. (Pittosporaceae) infested by the cottony cushion scale,<Emphasis Type="Italic"> Icerya purchasi</Emphasis> Maskell (Homoptera: Coccina,Margarodidae)

Pittosporum tobira L. (Family Pittosporaceae) is an important plant species grown in parks and gardens in Turkey. The cottony cushion scale, Icerya purchasi Maskell (Homoptera: Coccina, Margarodidae), is an important pest of P. tobira, and causes damage mainly to the leaves, branches and stems of the host plant. In spite of the great economic importance of I. purchasi to its host plant P. tobira, information has been limited on some basic anatomical parameters of the nature of the damage to leaves and branches. The present study was, therefore, initiated to investigate the insertion and penetration of stylets into the leaves and branches of P. tobira, the length of stylets and depth of penetration in both of these tissues, and penetration of stylets into the cortex, xylem and phloem tissues and into the secretory and non-secretory canals of the leaves and branches. The results showed great variations between the leaves and branches in all the criteria observed in I. purchasi infesting P. tobira. The study found 20 whole and 23 broken mouthparts in the leaves as compared to 3 whole mouthparts and 1 broken in the branches. Length of the stylets inserted into the leaves ranged from 33.83 m to 540.93 m and into the branches from 202.85 m to 340.8 m. The stylets reached greater depths in the leaves, at 540.93 m, as compared to 498.67 m in the branches. The stylets in the leaves were associated with 12 secretory canals, but with none in the branches. It was found that three stylets reached xylem in the leaves as compared to one in the branches. Similarly, 17 stylets in the leaves reached to the phloem, but only 2 in the branches. No stylets were found in the cortex of the leaves, but one was found in the branches. In the leaves, 11 stylets reached and remained in the non-secretory canals, but none in the case of the branches.     

Lateral fluxes of organic carbon in a mangrove forest partly contaminated with sewage wastes

Lateral fluxes of macrodetritus, particulate matter and dissolved organic carbon were determined. Samples were collected monthly at the mangrove forest–inshore water boundary and within the forest. Floating macrodetritus (mainly mangrove leaves) was collected by a net (2mm mesh size). Dissolved and particulate matter were separated by filtration (0.45m filter) and centrifugation. Dissolved and particulate carbon were determined by a total organic carbon analyser (SHIMADZU model TOC5000). There was a significant export of mangrove litter to the adjacent marine environment during spring tides. Rates of import and export of particulate matter in the forest were not statistically different. Translocation of material within the forest was clearly demonstrated. A relatively high export of macrodetritus was recorded at the marine fringe (mainly colonised by Sonneratia alba). There was low export of litter in the terrestrial fringe zone, a monospecific stand occupied by Avicennia marina (Forsk) Vierh. Net organic carbon export from the entire forest was 79×10⁶g C y^–1, dissolved organic carbon accounted for about 78% of the total export.     

Agrobacterium-mediated transformation of cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) somatic embryos

A simple method is presented for the unreported genetic transformation of cork oak (Quercus suber L.). Pro-embryo masses (PEMs) were induced on immature zygotic embryos applied to medium supplemented with 2.3 M 2,4-dichlorophenoxyacetic acid. The established PEMs were inoculated with Agrobacterium tumefaciens LBA4404/p35S GUS INT/pCAMBIA 1301 strain. Transformants were selected on hygromycin (HYG) 94 M-supplemented medium. Viable embryos constituted 13% of those selected on HYG during 4 months. Expression of -glucuronidase at 4 months following co-cultivation confirmed transformation in 5.8% embryos selected on HYG. This method forms a basis for genetic transformation of cork oak somatic embryos.     

Dimensional instability of cement bonded particleboard: Modelling CBPB as a composite of two materials

Previous papers have quantitatively indicated that the total movement of cement bonded particleboard (CBPB) is equal to the sum of the movement of its components. This paper examined the efficacy of the law of mixtures when applied to the movement of a wood-cement composite under internal swelling or shrinkage stresses. Abundant data generated in companion papers were first manipulated to develop the universal formulae for predicting the movement of components. In conjunction with previous numerical results from image analysis of the structure of CBPB, and the orientated elasticity and stress algorithms, the models for theoretically predicting mass and dimensional changes of CBPB were derived. Validation studies were conducted and these demonstrated an excellent agreement of the theoretical predictions with experimental data for both mass and dimensional changes of CBPB due to internal swelling or shrinkage stresses during adsorption and desorption. The success also implied that CBPB can be treated as a composite and its properties can be well derived by the law of mixtures even though CBPB is an unusual type of composite having a very high volume fraction of wood chips, but a very high mass fraction of cement paste.Notation E_RT Mean transverse modulus of elasticity of wood - E_L Longitudinal modulus of elasticity of wood - E_p Modulus of elasticity of cement paste - E_wa Modulus of elasticity of embedded wood chips at angle - E Modulus of elasticity of wood chips at direction - E Modulus of elasticity of wood chips at direction - G_LRT Mean transverse shear modulus of wood - L(T)_cp Length/width (thickness) change of CBPB at angle - L(T)_p Length (thickness) change of cement paste - m_pf Mass fraction of cement paste in unit mass of CBPB - m_wf Mass fraction of wood chips in unit mass of CBPB - M_cpj Mass change of CBPB at the various conditions tested - M_pj Mass change of cement paste at corresponding conditions - M_wj Mass change of wood chips at corresponding conditions - M(L; T)_w/P Mass, length or thickness changes of wood chips or cement paste at various conditions - t Duration of exposure - _LRT Mean transverse Poissons ratio of wood - V_pf Volume fraction of cement paste in unit mass of CBPB - V_wf Volume fraction of wood chip in unit mass of CBPB - _cp Density of CBPB - _k Density of wood chip or cement paste - _cp Overall stresses of CBPB at angle - _L Stress in the longitudinal direction of wood - _RT Mean stress in the transverse direction of wood - _p Stress of cement paste - _w Stress of the wood chips at angle - Stress of the wood chips at direction - Stress of the chip at direction - _cp Strain in CBPB - _p Strain of cement paste - _WL Strain in the length of wood chips - _WT Strain in the thickness of wood chips - _w Strain in wood chips - Angle between the longitudinal direction of wood chips and surfaces or edges of CBPB - Angle between wood chips and edges (length direction) of CBPB - Angle between wood chip and vertical coordinate - A, B, C Coefficients related to the feature of materials and exposure conditions The senior author wishes to thank Professor W.B. Banks of University of Wales, Bangor for his constructive discussions and assistance and the British Council for partly financial support.     

Nitrogen use by <Emphasis Type="Italic">Pinus densiflora</Emphasis> trees growing on a Mt. Fuji lava flow

To quantify the nitrogen (N) use by Pinus densiflora trees growing on an infertile lava surface, N pools, N requirement and N uptake through fine roots and N deposition from the atmosphere were estimated. The N requirement and the N uptake of fine roots were 55.5kgNha^–1year^–1 and 39.7kgNha^–1, respectively. Thus, the ratio of N uptake to N requirement of the fine roots was 71.5%. Including fine-root contribution, the total N requirement of the P. densiflora trees was 98.6kgNha^–1year^–1, and the total N uptake was 64.2kgNha^–1year^–1. Thus, the N uptake of the P. densiflora trees was 64.1% of the N requirement, indicating that P. densiflora trees growing on an infertile lava surface obtain some of their N from below-ground organic material layers every year and the contribution of N storage in trees for their growth is not any higher than indicated in previous reports that excluded fine-roots contribution. The wet N deposition of our research forest was only 5.8% of the N requirement of the P. densiflora trees and only 8.9% of the N uptake. Movement of the below-ground organic material layer N concentrations in the F- and L-layers coincides with needle development and fine-root growth, suggesting the possibility that P. densiflora trees extract N from the organic N of those layers for growth.     

Water circulation, groundwater outflow and nutrient dynamics in Mida creek, Kenya

The relationship between physical hydrodynamic processes and nutrients dynamics was investigated in Mida creek, a groundwater influenced mangrovefringed creek in Kenya between March 1996 and May 1997. The research involved spot and timeseries measurement of nitrate–nitrite, ammonia, silicates, phosphates, salinity, temperature, sealevel as well as tidal currents at seven stations located in the front, middle and backwater zones of the creek. Groundwater level as well as total dissolved solids' concentration, salinity, temperature and nutrients' concentration were also measured once every month in shallow wells (watertable<5m) located in the upper region of the creek. Results of the study show that nutrient concentrations vary with the tide and that, though there is no river drainage, they are of the same magnitude as in mangrove creeks with substantial river runoff. The peak concentrations of NH ₄ ⁺ –N (5.45M), NO ₂ –NO ₃ (5.63M), PO ₄ ^3– –P (0.58M) and SiO ₃ ^2– –Si (81.36M) in the creek occurred during flood tide, 2–3h before high waters. The (NO ₂ ^– + NO ₃ ^– )–N concentrations declined rapidly during ebb tide, reaching the minimum levels during low water. Contribution of groundwater seepage to the net nutrients flux (particularly on nitrite–nitrates) is largest in dry seasons. The study shows that groundwater outflow sustains the mangroves during periods of severe salinity stress and nutrients deficiency in dry seasons. This is essentially by limiting salinity increase and by boosting nutrient supply in dry seasons.     

The distribution of lignin in sprucewood as determined by ultraviolet microscopy

The distribution of lignin in black spruce has been determined quantitatively by the study of 0.5 m transverse sections in a UV microscope. The average lignin concentration in the compound middle lamella was about twice that in the secondary wall. The lignin concentration of the middle lamella at the cell corners of adjacent tracheids was nearly four times that in the secondary wall but the volume of the secondary wall was much greater than the volume of the middle lamella. Thus, for earlywood, 72% of the total lignin was in the secondary wall leaving only 28% in the compound middle lamella and cell corner middle lamella regions. The corresponding values for latewood were 82% and 18% respectively. Use of oblique longitudinal sections of 0.1 m thick permitted the resolution of the compound middle lamella. The lignin concentration in the true middle lamella was found to be equal to that in the cell corner middle lamella and the primary wall lignin content to be about twice that in the secondary wall.

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Zusammenfassung Die Verteilung des Lignins in Fichtenholz wurde quantitativ durch Untersuchung von 0,5 m dicken Querschnitten unter dem UV-Mikroskop bestimmt. Die mittlere Ligninkonzentration war in der Mittelschicht etwa doppelt so hoch wie in der Sekundärwand. Die Ligninkonzentration der Mittelschicht war in den an die Tracheiden anstoßenden Zellecken annähernd viermal höher als in der Sekundärwand, wogegen das Volumen der Sekundärwand wesentlich größer war als das der Mittelschicht. Dagegen befand sich beim Frühholz 72% des gesamten Lignins in der Sekundärwand und nur 28% fanden sich in der Mittelschicht selbst und in ihren Zelleckbereichen. Die entsprechenden Werte für Spätholz betragen 82% bzw. 18%. Die Anwendung von schrägen Längsschnitten von 0,1 m Dicke erlaubte die Auflösung der Mittelschicht. Die Ligninkonzentration in der Mittllamelle war gleich groß wie in der in den Zellzwickeln befindlichen Mittellamelle und der Ligningehalt der Primärwand war etwa doppelt so groß wie derjenige in der Sekundärwand.

     

Longitudinal shrinkage of wood — Part I: Longitudinal shrinkage of thin sections

Summary The possibility of using microtomed longitudinal sections of wood for the study of longitudinal shrinkage has been investigated using hoop pine (Araucaria cunninghamii Ait.). Cutting of the sections was shown to distort them and to affect their subsequent shrinkage. However, by increasing the inclination angle of the microtome knife, sections could be cut without change in longitudinal dimensions. The longitudinal shrinkage behaviour of such sections more than 80 m thick was little different from that of thicker sawn specimens.Measurements of longitudinal shrinkage using this technique showed that very thin sections (40 m) had greater longitudinal shrinkage than sawn wood. Partial delignification with sodium chlorite also increased longitudinal shrinkage. The longitudinal shrinkage was reproducible over successive cycles of moisture content change but not reversible, the length of a specimen at a given moisture content being less during desorption than at the same moisture content during adsorption. It is considered likely that the longitudinal shrinkage of wood is markedly affected by stresses which develop within the cell wall as the wood dries.

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Zusammenfassung Die Möglichkeit, Mikrotom-Längsschnitte zur Prüfung der Längsschwindung zu verwenden, wurde an Hoop Pine (Araucaria cunninghamii Ait.) geprüft. Dabei zeigte sich, daß die Längsschnitte beim Schneiden verschoben werden, was die nachfolgende Schwindung beeinflußt. Nachdem der Schnittwinkel des Mikrotommessers vergrößert worden war, konnten die Schnitte ohne Veränderung der Längsabmessungen abgetrennt werden. Das Längsschwindungs-Verhalten solcher Schnitte von über 80 m Dicke unterschied sich nur wenig von demjenigen dickerer, gesägter Proben.Messungen der Längsschwindung mit Hilfe des beschriebenen Verfahrens zeigten, daß sehr dünne Schnitte (40 m) eine größere Längsschwindung aufweisen als gesägte Schnitte. Die teilweise Delignifizierung mit Natrium Chlorit erhöhte ebenfalls die Längsschwindung. Die Längsschwindung blieb während aufeinanderfolgender zyklischer Feuchtigkeitsänderungen reproduzierbar, war aber nicht umkehrbar. Die Länge einer Probe war, bei gleichem Feuchtigkeitsgehalt während der Desorption geringer als während der Adsorption. Es darf als wahrscheinlich angesehen werden, daß die Längsschwindung des Holzes deutlich durch Spannungen beeinflußt wird, die sich beim Trocknen des Holzes innerhalb der Zellwand entwickeln.

     

The measurement of tensile creep in thin wood strips

Summary Tensile creep of 100 m thick wood strips cut parallel to the grain was measured using a high resolution high accuracy creep apparatus. Rigorous attempts were made in both design and use of the apparatus to reduce errors to a minimum: the standard deviation of the random errors about a smoothed curve was assessed as 0.34 m. By comparing elongation of strips under load with control strips at zero load viscous and visco-elastic elongation may be accurately measured.     

Interactions between the striped stem borer <Emphasis Type="Italic">Chilo suppressalis</Emphasis> (Walk.) (Lep., Pyralidae) larvae and rice plants in response to nitrogen fertilization

A screenhouse experiment was conducted to examine the damage and compensation in rice plants when injured by the striped stem borer, Chilo suppressalis (Walker), larvae at tillering stage, as well as larval survival and development of the insect at different nitrogen (N) fertilization levels. Potted plants were fertilized at late seedling stage at the rates 0, 200, 400, 600 and 800mgN/pot, respectively. More deadheads were caused as fertilization increased. Plants compensated well for injury at the fertilization concentrations of 200 and 400mgN/pot by producing new tillers, but such compensation did not take place at 600 and 800mgN/pot. Two weeks after infestation, the highest number of remaining healthy tillers was found in plants fertilized at 400mgN/pot. Larval survival varied little among the treatments 200 to 800mgN/pot. Larval weight attainment and/or developmental rate increased with increasing fertilization level from 200 to 600mgN/pot, but both declined rapidly as fertilization reached 800mgN/pot, indicating the great dependence of plant suitability on N fertilization levels. Conclusively, both the compensation response of rice plants and their suitability for C. suppressalis larvae could be significantly affected by N fertilization levels.     

Eine neue Virose beim Schwammspinner,Lymantria dispar L. (Lep., Lymantriidae)

A new virosis in caterpillars of Lymantria dispar L. (Lep., Lymantriidae) Caterpillars ofL. dispar found in the Apennin-mountains near Genua, Italy, showed a new virosis in a low percentage. The pathogen is characterized by the enormous dimensions (max. 20 ) and the cubic form of the polyhedra. It causes a nuclear hypertrophie particularly within the haemocytes,