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W minionych 2 latach z siewek kasztanowca z objawami brunatnienia wierzchołków korzeni i ich pękania oraz z porażonej podstawy pędów irgi wyizolowano Phytophthom cambivora. Gatunek ten wykryto również w podłożach spod zamierającej irgi i cyprysików Lawsona. Izolaty tego czynnika chorobotwórczego kolonizowały tkanki korzeni, części pędów oraz blaszki liściowe 3 gatunków roślin. Stwierdzono zróżnicowaną reakcję badanych gatunków roślin na P. cambivora, jak również różnice w szybkości zasiedlania tkanek przez testowane izolaty, w tym zwłaszcza na cyprysiku.
During the last 3 years new Phytophthora species were detected on diseased Chamaecyparis spp., Thuja spp., Microbiota decussata, Picea and Pinus species and cultivars. On Chamaecyparis, beside P. cinnamomi known in Poland since 1993, P. cambivora, P. citricola and P. cryptogea were isolated from diseased roots and stem base. On Thuja spp., beside P. citricola. P. cinnamomi and P. cryptogea were isolated mainly from diseased shoots. On M. decussata, P. citricola is the next important agent causing shoot rot. On Picea and Pinus spp. P. cactorum, P. citricola and P. citrophthora were isolated from diseased stem bases and roots. All Phytophthora species, used for inoculation of coniferous shoot parts caused necroses. On the top part of Chamaecyparis spp., Juniperus stricta and J. virginiana ring spot disease incited by Pestalotiopsis sp. was observed during the last 2 years.
Phytophthoracambivora was isolatedfrom the bark lesions of two 10- and 15-year-old of analysed alder trees. Additionally, Botrytis cinerea, 3 Fusarium species, Mucor spp., P. alni and Trichoderma spp. were recoveredfrom diseasedtissues. Isolates of P. cambivora from six plant species, used for inoculation of alder seedlings andplant parts, causedthe development of necrosis. Isolate from Chamaecyparis lawsoniana was the weakest pathogen whereas those from Abies alba, Acer pennsylvanicum and Alnus glutinosa were the strongest
Pathogenic oomycetes represented mainly by the species of Phytophthora genus are among the most dangerous plant pathogens. They pose a serious threat for agricultural as well as wild plants, and are involved in forest decline worldwide. Over 140 pathogenic Phytophthora species have been identified so far. The common infection symptoms include rotting of below− and aboveground parts of plants, causing weakness and slow decline of infected trees. The economic losses caused by certain Phytophthora species may rich even 100%. Globalization and border opening have facilitated the transport of plant material between countries and continents, thus increased the risk of transfer of various Phytophthora genus representatives to new geographical locations. Global warming (e.g. mild winters) have facilitated the expansion of species from southern to northern Europe. Among Polish Phytophthora isolates are species that have previously been known only in nurseries (e.g. P. cactorum), but nowadays they are also isolated from forests (e.g. oak stand in the Krotoszyn Plateau). It suggests the pathway from nurseries to stands with plant for plantings and attached soil. There are also new species, that have not been isolated so far in the world (P. polonica) or found far away from Poland (P. fragaliaefolia in Japan on strawberry). The possible natural pathways are birds and water courses. In Mazowsze and Wielkopolska regions (C and W Poland) the polyphagous P. cinnamomi was found on pedunculate oaks (Quercus robur). This species causes significant damage to red oak forest in France, but also threats Jarrah forests in the Australian ecosystem (it attacks ca. 1000 species of plants). Fortunately, in addition to time consuming and laborious classic methods of Phytophthora identification, based on morphology and physiological properties, molecular methods that are based on immunological tests and chromosomal or mitochondrial DNA markers identification have come into common use. Despite morphological similarity to true fungi, oomycetes are more closely related to diatoms and brown algae, and have several structural features that differentiate them from fungi, including the cell wall composed of cellulose instead of chitin. That is one of the reasons that fungicides have a limited use in the fight with Phytophthora infections. Additionally, type of ecological niches that are settled by pathogenic oomycetes (root remnants in soil, watercourses) hinders the chemical combating. Biocontrol, i.e. the use of interspecies interactions between microorganisms (bacteria, fungi) to limit the growth and development of pathogens, seems to be a reasonable alternative.
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