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91.
通过对建国以来我省天然林资源的消长变化状况和天然林资源现状的论述 ,分析了我省天然林资源下降的主要原因 ,提出保护和恢复天然林必须要建立强有力的管理机构 ,全面禁止采伐天然林 ,并依造科学技术 ,保护天然林及其生物多样性 相似文献
92.
93.
《Scandinavian Journal of Forest Research》2012,27(4):337-346
Abstract Stem bases of 210 Fraxinus excelsior trees of three different health categories were sampled by the means of an increment borer in declining ash stands in northern Lithuania. From this number, 15 sound-looking, 132 declining and 63 dead trees from three discrete plots yielded 352 isolates, representing 75 fungal species. In addition, mycelial fans and rhizomorphs typical of Armillaria spp. from 205 and 20 trees, respectively, were sampled and subjected to fungal isolations. Species richness was similar in trees from each health category, but community structures differed, indicating that species composition of wood-inhabiting fungi in stems changes along with the changes in tree health condition. Armillaria cepistipes was the most common species (86 isolates from 210 wood samples, or 41.0%), isolated more frequently and consistently than any other potential tree pathogen. It also showed abundant occurrence on a majority of trees in the form of mycelial fans and rhizomorphs, from which 64 and 14 isolates of the fungus were obtained, respectively. The population structure of A. cepistipes revealed the presence of 53–93 genets per hectare, some of which extended up to 30–55?m. 相似文献
94.
随着社会的进步和经济的发展,人们对切花的需求量越来越大,越来越受人们的重视。简单说明切花的分类和方法,主要介绍切花采后衰败的原因及保鲜措施,以达到提高切花品质,延长其插花寿命及观赏期的目的。 相似文献
95.
C. G. J. Belpaire G. Goemans C. Geeraerts P. Quataert K. Parmentier P. Hagel J. De Boer 《Ecology of Freshwater Fish》2009,18(2):197-214
Abstract – Since the 1980s, the European eel Anguilla anguilla stock is in steep decline. Lipid reserves are essential to cover energetic requirements for silver eel migration and reproduction. Two large and independent data sets from Belgium and The Netherlands show an average one-third decrease in fat contents of yellow eels over the past 15 years. Also Le Cren's relative condition factor decreased. On the basis of the somatic energy reserves, reproductive potential of eels from various latitudes over Europe was estimated, assuming fat levels in yellow eel are indicative of those in silver eels. Only large individuals, females as well as males, with high lipid content seem to be able to contribute to the spawning stock. The decrease in fat content in yellow eels may be a key element in the stock decline and raises serious concerns about the chances of the stock to recover. 相似文献
96.
KIMMINS J P 《中国林业科技(英文版)》2008,(1)
Site degradation and yield decline of forest have attracted increasing attention from forest managers and scientists. Studies conducted by researchers from a variety of disciplines and perspectives have led to a variety of competing hypotheses concerning the causes of the problem. In this paper we review evidence of such a yield decline and examine the problem and its possible way to identify the individual contributions of the many determinants of yield decline, and their interactions. 相似文献
97.
98.
Crop residue destruction strategies that enhance rather than inhibit reproduction of Monosporascus cannonballus 总被引:1,自引:0,他引:1
M. E. Stanghellini † M. M. Waugh K. C. Radewald D. H. Kim D. M. Ferrin T. Turini 《Plant pathology》2004,53(1):50-53
Destruction of infected crop residue is a management strategy commonly recommended for the control of many plant diseases. Based upon knowledge of the biology of the root-infecting fungus Monosporascus cannonballus , this strategy is a likely candidate for use in the management of vine decline of melons caused by this pathogen. Specifically, ascospores, the primary survival structure and inoculum for root infection, are produced on infected melon roots primarily after crop termination. Thus, destruction of infected roots prior to reproduction would be a very practical method of preventing inoculum build-up in soil. Results from this study demonstrated that two plant residue destruction methods commonly used by growers at crop termination [i.e. foliar application of a herbicide (glyphosate) and mechanical destruction of vines] significantly enhanced, relative to untreated controls, the rapidity and extent of pathogen reproduction on infected roots left in field after harvest. 相似文献
99.
Identification, occurrence and pathogenicity of Rhizopycnis vagum on muskmelon in Spain 总被引:1,自引:0,他引:1
J. Armengol † A. Vicent P. Martínez-Culebras B. D. Bruton J. García-Jiménez 《Plant pathology》2003,52(1):68-73
Rhizopycnis vagum is a recently described coelomycetous fungus that contributes to vine decline of muskmelons in Honduras, Guatemala, Texas and California. This fungus has been associated with roots of muskmelon plants affected by vine decline in most Spanish muskmelon production areas. Isolates were collected from 1996 to 2000 and identified from their cultural and morphological characteristics and by sequencing the ITS region of the ribosomal coding nuclear DNA (rDNA) and phylogenetic analysis. A few isolates from muskmelon with growth characteristics similar to R. vagum were identified as Phoma terrestris . Watermelon, Cucurbita hybrids used as rootstocks for watermelon production, Amaranthus sp. and grapevine were also hosts for R. vagum . Based on disease reaction in muskmelon roots, the pathogenicity of 10 isolates of R. vagum from different hosts and geographical origins was verified. The fungus caused root discoloration, corky lesions, and eventually the presence of pink coloration on the roots. Rhizopycnis vagum appears to be a minor pathogen that contributes to muskmelon vine decline complex in Spain through infection of roots. 相似文献
100.
The pathogenicity of five species of Phytophthora to English walnut was studied in a greenhouse experiment. Phytophthora cinnamomi was the most aggressive species, causing severe root rot and seedling mortality. The other species tested, P. cambivora , P. citricola , P. cactorum and P. cryptogea , did not induce visible crown symptoms on seedlings 2 months after inoculation. Some strains of P. cambivora and P. cactorum also caused taproot damage to seedlings. All except one of the tested isolates caused significant necrosis of fine roots and a significant reduction of root weight compared with noninoculated seedlings. Reduction of above-ground plant development was not statistically significant. While P. cinnamomi is well known as an aggressive primary pathogen of English walnut, the other species of Phytophthora may act as predisposing factors to walnut decline, affecting root system development and increasing host vulnerability to environmental stress. 相似文献