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Exotic Trees (exotic + tree)

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Life Sciences75%

Selected Abstracts

Mycosphaerella species associated with leaf disease of Eucalyptus globulus in Ethiopia

FOREST PATHOLOGY, Issue 4 2006
Alemu Gezahgne
Summary Eucalyptus spp. are among the most widely planted exotic trees in Ethiopia. Several damaging leaf pathogens are known from Eucalyptus spp. worldwide. Of these, Mycosphaerella spp. are among the most important, causing the disease known as Mycosphaerella leaf disease (MLD). Characteristic symptoms of MLD include leaf spot, premature defoliation, shoot and twig dieback. Recent disease surveys conducted in Ethiopian Eucalyptus plantations have revealed disease symptoms similar to those caused by Mycosphaerella spp. These symptoms were restricted to E. globulus trees growing in several localities in south, south western and western Ethiopia. The aim of this study was to identify the fungi associated with this disease. This was achieved by examining ascospore germination patterns, anamorph associations and sequence data from the Internal Transcribed Spacer (ITS) region of the rRNA operon, for representative isolates. Several different ascospore germination patterns were observed, suggesting that more than one species of Mycosphaerella is responsible for MLD on E. globulus in Ethiopia. Analysis of sequence data showed that three Mycosphaerella spp., M. marksii, M. nubilosa and M. parva were present. This is the first report of these three species from Ethiopia and represents a valuable basis on which to build further studies in the region. Résumé Les Eucalyptus comptent parmi les essences d'arbres exotiques les plus plantées en Ethiopie. Plusieurs pathogènes foliaires sont connus dans le monde pour occasionner des dégâts sur Eucalyptus. Parmi ceux-ci, les espèces de Mycosphaerella sont parmi les plus importantes, causant la maladie connue comme Maladie Foliaire àMycosphaerella (MFM, MLD en anglais). Les symptômes caractéristiques de la MFM comprennent des taches foliaires, une défoliation précoce et des dépérissements de pousses et de rameaux. Des campagnes de surveillance menées récemment dans les plantations éthiopiennes d'Eucalyptus ont révélé la présence de tels symptômes. Ces symptômes sont uniquement observés sur E. globulus dans plusieurs localités du sud, sud-ouest et ouest de l'Ethiopie. L'objectif de cette étude était d'identifier les champignons associés à cette maladie. Pour cela, des isolats représentatifs ont étéétudiés pour les modalités de germination des ascospores, les anamorphes associés ainsi que les données de séquence de la région ITS de l'opéron ADNr. Différentes modalités de germination des ascospores ont été observées, suggérant que plusieurs espèces de Mycosphaerella seraient associées à la MFM sur E. globulus en Ethiopie. L'analyse des données de séquence a montré la présence de 3 espèces : M. marksii, M. nubilosa et M. parva. Ceci constitue la première mention de ces 3 espèces en Ethiopie et une première étape pour envisager d'autres études dans cette région. Zusammenfassung Eucalyptus -Arten sind die am häufigsten angepflanzten exotischen Bäume in Äthiopien. An Eucalyptus kommen verschiedene Blattkrankheiten vor, wobei die Mycosphaerella -Arten als Verursacher der Mycosphaerella -Blattkrankheit (MLD) am bedeutendsten sind. Charakteristische Symtpome der MLD sind Blattnekrosen und vorzeitiger Blattfall sowie Trieb- und Zweigsterben. Bei der Inventur von Krankheiten in äthiopischen Eucalyptusplantagen wurden Symptome entdeckt, die denen von Mycosphaerella spp. ähnlich waren. Diese traten nur an E. globulus lokal in S-, SW- und W-Äthiopien auf. Ziel dieser Untersuchung war es, die damit assoziierten Pilze zu identifizieren. Hierzu wurde an repräsentativen Isolaten das Keimverhalten der Ascosporen, das Vorkommen von Anamorphen und die ITS-Sequenz des rRNA-Operons untersucht. Es wurden verschiedene Keimungstypen der Ascosporen beobachtet, was darauf schliessen liess, dass mehr als eine Mycosphaerella -Art für die Krankheit an E. globulus in Äthiopien verantwortlich ist. Anhand der Sequenzen wurden M. marksii, M. nubilosa und M. parva identifiziert. Dies ist der Erstnachweis für diese drei Arten in Äthiopien und eine Grundlage für weitere Studien. [source]

Effects of climate on the growth of exotic and indigenous trees in central Zambia

JOURNAL OF BIOGEOGRAPHY, Issue 1 2005
E. N. Chidumayo
Abstract Aim, Climate change has far-reaching effects on species and ecosystems. The aims of this study were to determine how climate factors affect the growth pattern of indigenous and exotic trees in Zambia and to predict tree growth responses to a warmer climate with the use of mathematical models. Location, Two savanna sites in central Zambia. Methods, Diameter at breast height (1.3 m above ground, d.b.h.) of 91 permanently marked trees belonging to three indigenous and four exotic species was measured fortnightly for periods of 1,2 years from 1998 to 2003. Correlation and regression analysis was used to determine the effect of climate factors (minimum, maximum and average temperature and rainfall) on monthly daily d.b.h. increment of each species. Regression models were used to predict the growth behaviour of trees under a 0.5 °C warmer climate. Results, Interactions between temperature and rainfall explained 60,98% of the variation in d.b.h. increment in all the tree species, except the exotic Eucalyptus grandis. For deciduous species, stem expansion was delayed by 2,12 weeks following leaf-flush and d.b.h. increment peaked during the rainy season. Evergreen and deciduous species could not be separated on the basis of annual d.b.h. increment because the higher growth rates of deciduous species compensated for the shorter growing period. Mathematical models predicted slight changes in d.b.h. growth pattern under a 0.5 °C warmer climate in five of the seven species. Significant changes in d.b.h. growth patterns were predicted in the indigenous Bridelia micrantha and exotic Gmelina arborea under a warmer climate. However, models failed to adequately represent potential soil water stress that might result from changes in tree growth patterns and a warmer climate. Main conclusions, Climate factors explained a large proportion of the variation in diameter growth of both indigenous and exotic trees, rendering it possible to model tree growth patterns from climate data. Tree growth models suggest that a rise in temperature of 0.5 °C is unlikely to induce significant changes in the growth behaviour of the majority of the studied species. However, because the growth behaviour of some species may be substantially affected by climate change, it is recommended that strategies for the future production of such climate-sensitive trees should incorporate aspects of climate change. [source]

Leaf litter breakdown in Patagonian streams: native versus exotic trees and the effect of invertebrate size

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2002
R. J. Albariño
Abstract 1.Nothofagus native forest in the Southern Andes is being progressively substituted by forestation with rapid growth of the exotic trees, mainly species of Pinaceae. The effect on stream processing dynamics is explored through in situ experiments. 2.The effects of leaf litter quality and macroinvertebrate size on in situ litter breakdown were analysed. Experiments were run in litter bags which allowed access of macroinvertebrate fauna in streams running through a dense forest of the deciduous Nothofagus pumilio. 3.In Experiment 1, the decay rates of N. pumilio leaves and Pinus ponderosa needles were measured during an autumn-winter period. N. pumilio decayed twice as fast as P. ponderosa (P<0.01). Shredders fed only on N. pumilio leaves. The total abundance of macroinvertebrates colonizing both treatments was similar; however, the biomass was higher in the N. pumilio treatment. Large shredders were only found colonizing N. pumilio leaves. Since no decay due to shredders was observed in P. ponderosa, the presence of macroinvertebrates in these litter bags was related to refuge and feeding on FPOM-biofilm resources. 4.In Experiment 2, N. pumilio leaf litter was exposed in order to allow (open bags) or restrict (closed bags) access of invertebrates. The invertebrate assemblage in open bags showed the similar pattern observed for N. pumilio in the first experiment. Gathering-collectors were generally smaller and dominant in number while shredder biomass was higher in open bags as a result of high individual biomass. N. pumilio decayed faster when the whole size spectrum of macroinvertebrates colonized the bags (P<0.01). However, feeding signs of small shredders were observed in closed bags, therefore their role on leaf litter breakdown in Andean streams should not be neglected. 5.The combined results of both experiments lead to the conclusion that the whole litter processing mechanism would be affected as a consequence of the substitution of native forest by exotic pine forestation. Copyright © 2002 John Wiley & Sons, Ltd. [source]