New Alder Disease in Spreewald Biosphere Reserve – Causes and Incidental Factorsofanepidemic
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Nachrichtenbl. Deut. Pflanzenschutzd., 58 (6), S. 141–147, 2006, ISSN 0027-7479. ©Eugen Ulmer KG, Stuttgart Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Pflanzenschutz im Forst1 ; Technische Universität Dresden, Institut für Forstbotanik und Forstzoologie2 New alder disease in Spreewald biosphere reserve – causes and incidental factorsofanepidemic Neuartiges ErlensterbenimBiosphärenreservat Spreewald –Ursachen und Begleitfaktoren einer Epidemie Jörg Schumacher1 ,Sindy Leonhard1 ,Britt Maria Grundmann2 ,Andreas Roloff2 Abstract Zusammenfassung Since the new Alder disease was established in the biosphere re- Seitdem im Jahre 1998 das neuartige ErlensterbenimBio- serve Spreewald in 1998, it has spread widely in this region. A sphärenreservat Spreewald erstmalig nachgewiesen wurde, hat research project was started in 2001 in order to develop measures die Krankheit bereits eine weite Verbreitung in der Region ge- that limit the further spread of the epidemic. funden. Im Rahmen eines Forschungsprojektes wird deshalb seit The average proportion of infected trees in the biosphere re- dem Jahr 2001 versucht, Maßnahmen zur Eingrenzung oder serve is 24 %in spring of 2004. Stand age and site caused a sig- Bekämpfung der Epidemie zu entwickeln. nificant variation in this proportion. Phytophthora alni appeared Erhebungen zufolge, beträgt der mittlere Anteil der infizierten to be the most frequent cause of the disease. On 20 %of the trees Bäume im Untersuchungsgebiet gegenwärtig 24 %, wobei al- infected by Phytophthora spp. additionally fruiting bodies of 10 ters- und gebietsbezogene Unterschiede bestehen. Als häufigster different white-rot fungi were found which accelerate the Verursacher der Erkrankung konnte Phytophthora alni nachge- progress of the disease or cause further damage to the trees. wiesen werden. Zusätzlich wurden an ca. 20 %der primär durch Due to continuous sampling statements about the seasonal ac- Phytophthora spp. erkrankten Bäume Pilzfruchtkörper von ins- tivity of P. alni can be derived. The development of the pathogens gesamt zehn verschiedenen Weißfäuleerregern festgestellt, die seems to come to ahalt during the winter months from Decem- zu einer Beschleunigung des Krankheitsprozesses beitragen oder ber to March. Therefore winter flooding does not lead to further nachhaltige Schäden bewirken. spread of the disease. In contrast high infection rates were found Aufgrund kontinuierlich erfolgter Probenahmen lassen sich in stands that were flooded during the growing season. Notable Aussagen über die jahreszeitliche Aktivität von P. alni ableiten. differences were also caused by stand establishment practises. Danach scheint die Entwicklung des Erregers während der frost- Alders planted on sufficiently high hills or banks were only reichen Monate Dezember bis März weitestgehend unterbunden rarely damaged. Afurther important factor is the frequency of zu sein. Winterliches Hochwasser führt deshalb nicht zu einem flooding. While single or episodic infections may be overcome Fortschreiten der Krankheit. Hohe Infektionsgrade ergeben sich by the tree, frequent or permanent contact with the infectious wa- insbesondere nach Überschwemmungen während der Vegeta- ter usually leads to an acute disease process and rapid dying of tionsperiodeinden Beständen und Uferabschnitten mit geringem the trees. Flurniveau. Die auf ausreichend hohen Rabatten oder Hügeln The high pH-values in the rivers of the forest provide gepflanzten Erlen weisen entweder keine oder nur vereinzelt favourable conditions for vegetative propagation and distribu- Schädigungen auf. Außerdem übt die Überflutungshäufigkeit ei- tion of the micro-organisms. Alaboratory experiment revealed nen hohen Einfluss auf die Pathogenese aus. Während einmalige that the sporangia are optimally produced within apH-range oder episodische Infektionen vom Wirt mitunter überwunden from 6 to 7. Beyond this, the formation of sporangia is particu- werden, führt periodischer oder permanenter Kontakt mit dem larly stimulated by the host-specific exudates of the fruits and the infektiösen Wasser meistens zu einem akuten Krankheitsverlauf bark, and to alesser extent by the fine roots. und zügigen Absterben der Bäume. Investigations into the susceptibility of the seeds to diseases Die hohen pH-Werte in den Fließgewässern des Spreewaldes have shown, that P. alni is able to infest germinal fruits at the sur- liefern günstige Voraussetzungen für die vegetative Fortpflan- face of the water.Hence, spreading of disease via the seeds is zung und Verbreitung von P. alni. Ein Laborversuch zeigte, dass possible in principle, survival of the pathogen outside the water die Sporangien in einem pH-Bereich zwischen 6 und 7optimal being restricted however. produziert wurden. Darüber hinaus wird die Sporangienbildung Asurvey regarding the distribution of P. alni was also con- insbesondere durch wirtsspezifische Exsudate der Früchte, ducted in alder nurseries. In 2003 five of the ten nurseries inves- Rinde und Feinwurzeln stimuliert. tigated were infested by different subspecies of the pathogen. As Untersuchungen zur Krankheitsempfänglichkeit des Saatgutes aconsequence special management strategies were introduced in ergaben, dass P. alni in der Lage ist, keimfähige Früchte an der Brandenburg. Wasseroberfläche zu infizieren. Eine Ausbreitung der Krankheit durch das Saatgut ist daher prinzipiell möglich, eine Überdaue- Key words: New alder disease, Phytophthora alni, Alnus gluti- rung des Erregers in den Früchten außerhalb des Wassers jedoch nosa, secondary white-rot fungi, infection dynamics, seed sus- eingeschränkt. Eine im Jahr 2003 durchgeführte Untersuchung in ceptibility, vector function, nursery investigation zehn Baumschulen zeigte, dass fünf dieser Betriebe mit unter- Nachrichtenbl. Deut. Pflanzenschutzd. 58. 2006 142 J ÖRG S CHUMACHER et al., New alder disease in Spreewald biosphere reserve –causes and incidental factors of an epidemic schiedlichen Subspezies des Erregers verseucht waren. In Bran- 120 years in age were selected and 900 m² plots marked in these. denburg wurden daraufhin spezielle Vorbeugungs- und Bekämp- In these plots the percentage of diseased trees, extend of symp- fungsmaßnahmen eingeführt. toms, vigour,predisposition and secondary factors were recorded in spring (March/April) and in autumn (October/November). Stichwörter: Neuartiges Erlensterben, Phytophthora alni, Al- The spectrum of pathogens and their annual and environmen- nus glutinosa, sekundäre Weißfäulepilze, Infektionsdynamik, tal dynamics, respectively, were investigated by continuously Saatgutempfänglichkeit, Vektorfunktion, Baumschuluntersu- recording the rate of isolation of pathogens, pH of the water and chung the water level of the waterways. Pathogens in infected tissues (cambium, bark parenchyma) were isolated as described by S TREITO et al. (2002 b) and J UNG et al.(2004). In the rhizosphere 1Introduction of infected trees soil samples were taken and apple baits In 1993 anew Phytophthora diseaseofalder was discovered („Granny Smith“) placed for 8days. These were later analysed along riverbanks and in some young forest plantations in South- in the laboratory (cf. J UNG,1998; S CHUMACHER,2002). Juvenile ern Britain (GIBBS,1995; G IBBS et al., 1999). Since then it has leaves of oak (JUNG ,1998; J UNG et al., 2000 b) andalder beendetected in many other European countries (MATHIEU, seedlings were used as baits in soil. As amodification to this 1996; C ECH,1997; S CHMIDT et al.,1998and 1999; W ERRES, method freshly cut bark was used as well. The bark was cut from 1998; J UNG et al., 2000 a; S TREITO and G IBBS,2000; S ZABÓ et al., cleaned 2- to 3-year-old alder shoots in thin strips (c. 1–2 cm × 2000; S ANTINI et al., 2001; G IBBS et al., 2003).InGermany the 0,5 cm) using a scalpel. The bark baits were carefully placed onto disease was first diagnosed in 1994 (HARTMANN ,1995). The the surface of the water of flooded soil samples. Infected brown- cause is ahybrid Phytophthora, initially known as “the alder Phy- ish leaflets and bark pieces were plated onto selective PARPN- tophthora“, although sometimes also other Phytophthora spp. agar (V8-agar amended with 10 µg mL–1 pimaricin, 200 µg mL–1 have been isolated (BRASIER et al., 1995; W ERRES,1998; J UNG et ampicilin, 10 µg mL–1 rifampicin, 25 µg mL–1 pentachlorni- al., 2000 a; S CHUMACHER,2003 and J UNG andBLASCHKE,2004). trobenzene and 50 µg mL–1 nystatin) and incubated at 20 °C in Recently the pathogen was named Phytophthora alni with three the dark. After 24–48 h, hyphae were transferred onto V8-agar different subspecies (BRASIER et al., 2004). The typical symp- for identification. toms of the disease are bark necroses in the lower stem, increas- Since the alder Phytophthora does not form chlamydospores ing yellowing, crown transparency and small leaves as well as of- and the vigour of oospores is limited (DELCAN and B RASIER, ten an intensification of inflorescence and fructification (cf. 2001; J UNG andBLASCHKE,2003), it is likely that these micro-or- G IBBS,1995; H ARTMANN 1995; W ERRES,1998; J UNG et al., 2000 ganisms have alow potential to survive the winter in continental a; S CHUMACHER,2002). Europe. The sensitivity to low temperatures was tested with three Most records concern the species A. glutinosa,although A. in- isolates over a range of temperatures (0 to –15 °C) and frost du- cana (L.) M OENCH, A. viridis (CHAIX)DC ., and A. cordata D ESF. rations (3 and 30 d). may also be affected by alder Phytophthora.The new alder dis- In