Investigations on pathogenicity, invasion biology and population dynamics of the Pine Wood Nematode Bursaphelenchus xylophilus (Steiner und Buhrer 1934) Nickle 1970 in European conifers
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DissertationDate of Exam
25.04.2008Date of Publication
2008Advisor
Sikora, Richard A.Co-Referee
Goldbach, Heiner E.Metadata
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Abstract
Inoculation experiments with a life stage mixture of 2400 to 4000 B. xylophilus per sapling were conducted with three to four year old saplings in greenhouse and climate chambers adjusted at 25 C. To evaluate the development of Pine Wilt Disease (PWD), symptoms were assessed in six wilt classes and water content of wood and needles were recorded. Nematodes were extracted from shoots and roots using a modified Baermann funnel technique.
To determine the effect of B. xylophilus on mortality of P. sylvestris, nematodes were inoculated in 140 saplings with seven densities: 100, 300, 800, 2400, 4000, 6000, 10000. Nematodes were extracted four and twelve weeks after inoculation or at plant death if that occurred before end of experiment. Inoculum densities had no influence on mortality rate which was in general high (70-90 %). Higher population densities in saplings after four weeks were related to higher inoculum densities.
After screening 13 conifer species, P. sylvestris, P. cembra, P. nigra, P. strobus, P. pinaster, P. radiata, P. mugo and L. decidua could be identified as potential sensitive and susceptible hosts for B. xylophilus isolates from Portugal, China and North America. L. kaempferii was moderately susceptible and P. pinea was only susceptible against the isolate from Portugal. A. alba, P. abies and P. halepensis were no hosts for B. xylophilus.
Migration and population dynamics of PWN was studied on P. sylvestris saplings. Plants were divided into 17 segments and nematodes were extracted from each segment at nine sampling dates within a 27 day period after inoculation. The nematode population density per sapling reached three population peaks, 12, 19 and 27 days after inoculation. PWN could be isolated from all 17 segments six days after inoculation. Results indicate that B. xylophilus first migrate rapidly throughout the host before building up a high population level. Nematodes were found to develop several overlapping populations in time depending on the area of the sapling. Four consecutive stages of nematode invasion were observed: (1) Early migration, (2) Distribution and colonisation of all plant parts, (3) Population build up and (4) Retreat into the root-system.
The effect of temperature on population dynamics of PWN and pathogenicity towards P. sylvestris, L. decidua and P. abies was studied by inoculation of sapling with 4800 nematodes. Experiments were carried out in climate chambers at 15°C, 20°C and 25°C. Nematodes were extracted from shoots and roots at seven sampling dates during a 61 day period. Temperature had a major effect on the population dynamics of B. xylophilus in both susceptible conifer species. Temperature had no influence on the pathogenicity of PWN, as maximum mortality in P. sylvestris and L. decidua was reached when temperature exceeded 20°C. However no wilt symptoms were detected at 15°C in any conifer species. The population in P. sylvestris increased to approximately 4000 nematodes per gram dry matter in shoots at 25°C. At 20°C the maximum population density in shoots was approximately 2500 nematodes per gram dry matter. A threshold population density of B. xylophilus must be reached for induction of irreversible wilt in P. sylvestris.
Untersuchungen zur Pathogenität, Invasionsbiologie und Populationsdynamik des Kiefernholznematoden Bursaphelenchus xylophilus (Steiner und Buhrer 1934) Nickle 1970 in Europäischen Koniferen
Ziel der Arbeit war es, den Wirtspflanzenstatus Europäischer Koniferen gegenüber B. xylophilus zu klären und die Wechselbeziehung zwischen Nematoden, Wirtsbäumen und Temperatur zu untersuchen. Inokulationsversuche wurden mir einer Population von 2400 bis 4000 Nematoden pro Pflanze an drei bis vier Jahre alten Schösslingen im Gewächshaus und in Klimakammern durchgeführt. Die Versuche erfolgten bei einer Temperatur von 25°C, sofern nicht verschiedene Temperatureinflüsse untersucht wurden. Um die Entwicklung der Kiefernwelke zu bestimmen, wurde die Welke in sechs Klassen bonitiert und zusätzlich die Wassergehalte von Spross und Nadeln gemessen.
Um den Einfluss von B. xylophilus auf die Mortalität von P. sylvestris zu untersuchen, wurden insgesamt 140 Schösslinge mit sieben unterschiedlichen Populationsdichten inokuliert: 100, 300, 800, 2400, 4000, 6000, 10000. Die Inokulumdichte hatte keinen Einfluss auf die Mortalitätsrate. Sie war mit 70 % bis 90 % generell hoch. Vier Wochen nach Inokulation konnte ein Zusammenhang zwischen hoher Inokulationsdichte und hoher Populationsdichte in Schösslingen festgestellt werden.
Im Wirtspflanzen-Screening von 13 Koniferenarten konnten die Arten P. sylvestris, P. cembra, P. nigra, P. strobus, P. pinaster, P. radiata, P. mugo and Larix decidua als Wirte für die B. xylophilus-Isolate aus Portugal, China und Nord Amerika bestätigt werden. L. kaempferi war moderat anfällig gegen B. xylophilus. P. pinea wies eine moderate Anfälligkeit für das Portugiesische B. xylophilus-Isolat auf. A. alba, P. abies und P. halepensis waren keine Wirte für den Kiefernholznematoden.
Im Wirtspflanzen-Screening von 13 Koniferenarten konnten die Arten P. sylvestris, P. cembra, P. nigra, P. strobus, P. pinaster, P. radiata, P. mugo and Larix decidua als Wirte für die B. xylophilus-Isolate aus Portugal, China und Nord Amerika bestätigt werden. L. kaempferi war moderat anfällig gegen B. xylophilus. P. pinea wies eine moderate Anfälligkeit für das Portugiesische B. xylophilus-Isolat auf. A. alba, P. abies und P. halepensis waren keine Wirte für den Kiefernholznematoden.
Für Untersuchungen zum Einfluss der Temperatur auf die Populationsdynamik von B. xylophilus und auf die Pathogenität gegenüber P. sylvestris, L. decidua and P. abies wurden Schösslinge mit Nematoden inokuliert. An sieben Probenterminen wurden Nematoden innerhalb eines Zeitraumes von 61 Tagen aus Spross- und Wurzelteilen extrahiert. Die Versuche wurden in Klimakammern bei Temperaturen von 15°C, 20°C und 25°C durchgeführt. Die Temperatur hatte einen Einfluss auf die Populationsdynamik von B. xylophilus in beiden anfälligen Wirtsarten. Nematoden entwickelten sich nicht in P. abies. Temperatur hatte keinen Effekt auf die Pathogenität des Nematoden. Die maximale Mortalität wurde bei Überschreiten von 20°C in P. sylvestris und L. decidua festgestellt. Keine der Koniferenarten zeigte Welkesymptome bei 15°C. Die Population in P. sylvestris erreichte mit 4000 Nematoden pro Gramm Trockenmasse höhere Dichten bei 25°C als bei 20°C. Daraus kann abgeleitet werden, dass die irreversible Welke in P. sylvestris durch eine Schwellenpopulation von B. xylophilus induziert wird.
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Classification (DDC)
570 Biowissenschaften, Biologie 580 Pflanzen (Botanik)Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5N-14685
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5N-14685,
author = {{Matthias Daub}},
title = {Investigations on pathogenicity, invasion biology and population dynamics of the Pine Wood Nematode Bursaphelenchus xylophilus (Steiner und Buhrer 1934) Nickle 1970 in European conifers},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2008,
note = {The objectives of the present study were to identify potential European host trees for the Pine Wood Nematode (PWN) and to investigate the interrelationship between PWN, host trees and temperature.
Inoculation experiments with a life stage mixture of 2400 to 4000 B. xylophilus per sapling were conducted with three to four year old saplings in greenhouse and climate chambers adjusted at 25 C. To evaluate the development of Pine Wilt Disease (PWD), symptoms were assessed in six wilt classes and water content of wood and needles were recorded. Nematodes were extracted from shoots and roots using a modified Baermann funnel technique.
To determine the effect of B. xylophilus on mortality of P. sylvestris, nematodes were inoculated in 140 saplings with seven densities: 100, 300, 800, 2400, 4000, 6000, 10000. Nematodes were extracted four and twelve weeks after inoculation or at plant death if that occurred before end of experiment. Inoculum densities had no influence on mortality rate which was in general high (70-90 %). Higher population densities in saplings after four weeks were related to higher inoculum densities.
After screening 13 conifer species, P. sylvestris, P. cembra, P. nigra, P. strobus, P. pinaster, P. radiata, P. mugo and L. decidua could be identified as potential sensitive and susceptible hosts for B. xylophilus isolates from Portugal, China and North America. L. kaempferii was moderately susceptible and P. pinea was only susceptible against the isolate from Portugal. A. alba, P. abies and P. halepensis were no hosts for B. xylophilus.
Migration and population dynamics of PWN was studied on P. sylvestris saplings. Plants were divided into 17 segments and nematodes were extracted from each segment at nine sampling dates within a 27 day period after inoculation. The nematode population density per sapling reached three population peaks, 12, 19 and 27 days after inoculation. PWN could be isolated from all 17 segments six days after inoculation. Results indicate that B. xylophilus first migrate rapidly throughout the host before building up a high population level. Nematodes were found to develop several overlapping populations in time depending on the area of the sapling. Four consecutive stages of nematode invasion were observed: (1) Early migration, (2) Distribution and colonisation of all plant parts, (3) Population build up and (4) Retreat into the root-system.
The effect of temperature on population dynamics of PWN and pathogenicity towards P. sylvestris, L. decidua and P. abies was studied by inoculation of sapling with 4800 nematodes. Experiments were carried out in climate chambers at 15°C, 20°C and 25°C. Nematodes were extracted from shoots and roots at seven sampling dates during a 61 day period. Temperature had a major effect on the population dynamics of B. xylophilus in both susceptible conifer species. Temperature had no influence on the pathogenicity of PWN, as maximum mortality in P. sylvestris and L. decidua was reached when temperature exceeded 20°C. However no wilt symptoms were detected at 15°C in any conifer species. The population in P. sylvestris increased to approximately 4000 nematodes per gram dry matter in shoots at 25°C. At 20°C the maximum population density in shoots was approximately 2500 nematodes per gram dry matter. A threshold population density of B. xylophilus must be reached for induction of irreversible wilt in P. sylvestris.},
url = {https://hdl.handle.net/20.500.11811/3263}
}
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