甜瓜蔓枯病菌子实体法分离及A型菌株产孢条件研究

为解决甜瓜蔓枯病菌(Didymellabryoniae)组织分离法中枯萎病菌污染和单孢分离法操作复杂的问题,采用挑取单个子实体分离纯化获得甜瓜蔓枯病菌A型菌株。该菌株在12h荧光/12h黑暗的常规光照条件下,不能形成分生孢子器,但经过一定时间的暗处理和间歇紫外灯(12h紫外灯/12h黑暗)照射后则能够产生大量分生孢子。研究了光照、温度、pH值、培养基、碳源、氮源对产孢量的影响。综合各种因素,A型菌株产生分生孢子的最佳条件为:7d暗培养和4d间歇紫外灯处理的光照条件下,只含有磷酸二氢氨的马铃薯平板培养基,25℃时产生的分生孢子量最多。     

Genetic analysis of an attenuated <Emphasis Type="Italic">Papaya ringspot virus</Emphasis> strain applied for cross-protection

Papaya ringspot virus (PRSV) HA 5-1, a nitrous acid-induced mild mutant of severe strain HA, widely applied for control of PRSV by cross-protection, was used to study the genetic basis of attenuation. Using infectious clones, a series of recombinants was generated between HA 5-1 and HA and their infectivity was analyzed on the systemic host papaya and the local lesion host Chenopodium quinoa. The recombinants that contained mutations in P1 and HC-Pro genes caused attenuated infection on papaya without conspicuous symptoms, similar to HA 5-1. The recombination and sequence analyses strongly implicated two amino acid changes in the C-terminal region of P1 and two in HC-Pro of HA 5-1 involved in the attenuated infection on papaya. The recombinants that infected C. quinoa plants without local lesions contained the same mutations in the C-terminal region of HC-Pro for attenuated infection on papaya. We conclude that both P1 and HC-Pro bear important pathogenicity determinants for the infection on the systemic host papaya and that the mutations in HC-Pro affecting pathogenicity on papaya are also responsible for the inability to induce hypersensitive reaction on C. quinoa.     

Effect of cultural practices on the development of arabica coffee berry disease,caused by <Emphasis Type="Italic">Colletotrichum kahawae</Emphasis>

In the high altitude regions of Africa, coffee berry disease (CBD), caused by Colletotrichum kahawae, is the main constraint for arabica coffee (Coffea arabica) production. However, certain agricultural practices can reduce losses caused by the disease and thereby promote optimum production. On small family farms in Cameroon, mixed cropping with fruit trees, intercropping with food crops and maintenance pruning of coffee trees are very widespread agricultural practices that can affect CBD epidemics. Consequently, an epidemiological study was conducted to assess how cultural practices affected the disease in an arabica coffee smallholding in Cameroon. The disease was monitored on a weekly basis over four successive years (2002–2005) on coffee trees in diverse cultural situations. Cultural practices likely to reduce losses due to CBD were identified. The infection rate was significantly lower on coffee trees grown intensively than on coffee trees grown in the traditional manner. Coffee trees located under the shade of fruit trees were significantly less attacked than those located in full sunlight. In addition, berries on the leafless parts of branches, near the main trunk of the coffee tree, were less infected than those on leafy sections. These results show that maintenance pruning, removal of mummified berries, and mixed cropping with shade plants are cultural practices which create environmental conditions that limit CBD development.     

Hydraulic conductivity in roots of ponderosa pine infected with black-stain (Leptographium wageneri) or annosus (Heterobasidion annosum) root disease

Roots from healthy and diseased mature ponderosa pine, Pinus ponderosa Laws., trees were excavated from a site near Burns, Oregon. The diseased trees were infected with black-stain root disease, Leptographium wageneri Kendrick, or annosus root disease, Heterobasidion annosum (Fr.) Bref., or both. Axial hydraulic conductivity of the roots was measured under a positive head pressure of 5 kPa, and the conducting area was stained with safranin dye to determine specific conductivity (k(s)). In diseased roots, only 8-12% of the cross-sectional xylem area conducted water. Resin-soaked xylem completely restricted water transport and accounted for 13-16% of the loss in conducting area. In roots with black-stain root disease, 17% of the loss in conducting area was associated with unstained xylem, possibly resulting from occlusions or embolisms. Based on the entire cross-sectional area of infected roots, the k(s) of roots infected with black-stain root disease was 4.6% of that for healthy roots, whereas the k(s) of roots infected with annosus root disease was 2.6% of that for healthy roots. Although these low values were partly the result of the presence of a large number of diseased roots (72%) with no conducting xylem, the k(s) of functional xylem of diseased roots was only 33% of that for healthy roots. The low k(s) values of functional xylem in diseased roots may be caused by fungus induced occlusions preceding cavitation and embolism of tracheids. The k(s) of disease-free roots from diseased trees was only 70% of that for healthy roots from healthy trees. The disease-free roots had the same mean tracheid diameter and tissue density as the healthy roots, suggesting that the lower k(s) in disease-free roots of diseased trees may also have been caused by partial xylary occlusions.     

An “electronic nose” as a potential device for fire detection of forest product fire loads in enclosures

Abstract

Saving lives and properties are of primary importance in fire disasters. Unfortunately, current fire detectors are not fast enough to allow the detection of many fires, especially, at the smouldering stages. Some preliminary studies on laevoglucosan (LG), as an important product from cellulose degradation, have shown interesting properties and could be detected by devices classified as “electronic noses” (e-noses). In the present work, the mechanisms of pyrolysis of some ligno-cellulosic materials were investigated using thermo-gravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy and by a tube furnace with a view to determining the major degradation products from wood, white paper and cardboard samples. Additionally, an odour sensor, made of tin oxide semiconductor thin film, was employed to evaluate its sensitivity in detecting LG. It was found that LG can be readily found among the thermal degradation products of cellulosic materials in question, and that the metal oxide sensor employed was sufficiently sensitive in detecting its presence. Therefore, the work opens up the potential of using such a sensor as an “e-nose” for the early detection of fires stemming from forest product fire loads in storage places and in other enclosures.     

Comparing genetic diversity in agroforestry systems with natural forest: a case study of the important timber tree Vitex fischeri in central Kenya

It is possible that current tree domestication practices undertaken by farmers reduce the genetic base of tree resources on farms, raising concerns regarding the productivity, sustainability and conservation value of agroforestry ecosystems. Here, we assessed possible changes in genetic variation during domestication in the important and heavily utilised timber species, Vitex fischeri Gürke (syn. Vitex keniensis), by comparing geographically proximate forest and farm material in central Kenya. Employing RAPD analysis, a total of 104 polymorphic markers revealed by five arbitrary primers were scored in a total of 65 individuals, 32 from forest and 33 from farmland. Despite concerns of possible genetic erosion, forest and farm stands did not differ significantly in levels of genetic variation, with H values of 0.278 and 0.269, respectively. However, Mantel tests did reveal greater geographically related associative genetic structure among individuals in farm rather than forest material, with r _M values of 0.217 and 0.114, respectively. A more detailed analysis of structure suggested this could be due to local variation in origin of some on-farm trees. Implications of data for the genetic management of V. fischeri stands during farmer-led tree domestication activities are discussed. At present, there appears little reason to reject on-farm V. fischeri as a source of germplasm for future on-farm planting or for conservation purposes, although this situation may change and will require monitoring.     

Technical change in forest sector models: the global forest products model approach

Technical change is developing rapidly in some parts of the forest sector, especially in the pulp and paper industry where wood fiber is being substituted by waste paper. In forest sector models, the processing of wood and other input into products is frequently represented by activity analysis (input–output). In this context, technical change translates in changes over time of the input–output (I–O) coefficients and of the manufacturing cost (labor, capital, and materials, excluding wood and fiber). In the case of the global forest products model, the I–O coefficients and the manufacturing costs are determined empirically from historical data, while correcting for possible reporting errors. The method consists of goal programming. The objective function is the sum of the weighted absolute value of the deviations from estimated and observed production in each country of interest. The constraints express the relationship between the multiple output (sawnwood, panels, pulp, paper) and input (wood, waste paper, other fiber) and prior knowledge on the limits of the I–O coefficients. The paper presents observed technical changes from 1993 to 2010 and projections to 2030 with their consequences for the global forest sector in terms of prices, production and consumption, value added, and carbon sequestration in forest biomass.     

Transverse shrinkage in G-fibers as a function of cell wall layering and growth strain

Transverse drying shrinkage was measured at microscopic and mesoscopic levels in poplar wood characterised by an increasing growth strain (GS), from normal to tension wood. Results show that: (a) the drying shrinkage, measured as a relative thickness decrease, was significantly higher for G-layer (GL) than for the other layers (OL), GL shrinkage was not significantly correlated with GS, and OL shrinkage was negatively correlated with GS. (b) In gelatinous fibre (G-fibre), lumen size increased during drying and this increase was positively related with GS, but in normal wood fibre, lumen size decreased during drying. These findings suggest that GL shrank outwards (i.e., its internal perimeter increases), so that its shrinkage weakly affected the total cell shrinkage and the mesoscopic shrinkage was controlled by the OL shrinkage which shrank inwards (i.e., its external perimeter decreases). (c) Measurements done on 7 × 7 mm2 thin sections evidenced a negative correlation between transverse shrinkage and GS, significant in T direction but weak in R direction. These observations at both levels allow to discuss the contribution of GL to the mesoscopic shrinkage of tension wood.