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Germination Patterns (germination + pattern)

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Life Sciences	100%

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]

Environmental signals for seed germination reflect habitat adaptations in four temperate Caryophyllaceae

FUNCTIONAL ECOLOGY, Issue 3 2008
F. Vandelook
Summary 1Requirements for dormancy break and seed germination are specific for all species and depend chiefly on phylogeny, geographical distribution, habitat preference and life cycle. Studying germination requirements of closely related species with a similar geographic distribution allows one to attribute variation in germination requirements to differences in habitat preference between the species. 2We investigated requirements for dormancy break and the effect of environmental signals on induction of germination in seeds of four closely related Caryophyllaceae species growing in a variety of habitats (Moehringia trinervia, Stellaria holostea, S. nemorum and S. graminea). The species studied depend on disturbances in the vegetation for seed germination and subsequent seedling establishment. 3Seedlings of all four species emerged both in summer and spring. Stellaria nemorum and M. trinervia, both growing in temperate forests, emerged mainly in summer under a closed forest canopy. Seeds of S. graminea, occurring in grasslands, did germinate in summer at an open site, but could not germinate under a closed forest canopy. Seedlings of S. holostea were observed in late summer when buried at an open site or in early spring when sown in a forest patch. 4Seeds of S. holostea and M. trinervia were completely dormant at dispersal in early summer, while germination was low in fresh seeds of S. graminea and S. nemorum. Dormancy was broken, to a certain extent, during all three after-ripening treatments applied (dry storage, cold and warm stratification). 5The effect of three gap-detection signals (light, fluctuating temperatures, nitrates) on germination of fresh and dry stored seeds was tested. Seeds of S. holostea only germinated in response to daily fluctuating temperatures. Although light was the most important signal affecting germination of S. graminea and M. trinervia, we also observed a positive effect of fluctuating temperatures and nitrates on germination. The effect of fluctuating temperatures on germination of S. nemorum was small in both light and dark incubated seeds. Seed germination in this species generally occurred in response to addition of light and nitrates. 6This study on dormancy breaking and germination requirements of the four species enabled us to expose, sometimes subtle, differences in germination requirements. These contrasting germination patterns were related to differences in the species' habitat preferences. [source]

Seed moisture content affects afterripening and smoke responsiveness in three sympatric Australian native species from fire-prone environments

AUSTRAL ECOLOGY, Issue 8 2009
SHANE R. TURNER
Abstract Germination of freshly collected seeds of three sympatric herbaceous species native to fire-prone environments in south-western Australia was significantly improved through the application of novel combinations of dry heat, gibberellic acid, smoke water and dry afterripening. For fresh seeds, combinations of dry heat, gibberellic acid and/or smoke water resulted in >80% germination in Austrostipa elegantissima (Poaceae) and Stylidium affine (Stylidaceae) seeds and >60% germination in Conostylis candicans (Haemodoraceae) seeds, compared with <10% germination of control seeds. For fresh seeds, two broad germination patterns were observed in response to smoke water: nil , low germination for both control and smoke water-treated seeds (A. elegantissima and S. affine); and a significant smoke response (35%) compared with control seeds (1%) (C. candicans). During afterripening, high germination for A. elegantissima seeds was achieved following 3 months storage of seeds at equilibrium relative humidities of 23,75%, but seeds stored at 5,13% equilibrium relative humidities took 6,36 months to achieve similar levels of germination. Germination of C. candicans seeds also increased after 3 months storage, to >60% at each equilibrium relative humidity and further increases over time were slight. For S. affine seeds >60% germination was achieved only after 36 months storage at 50% equilibrium relative humidity. Seeds from all three species were smoke-responsive at some point, but the interaction/effects of afterripening on the smoke response varied significantly between species. This study highlights an apparent effect of seed dormancy status on response to smoke and a surprisingly high level of ecological variation in pre-germination requirements (cues) for these co-occurring species that may relate to variation(s) in microsite selection forces operating on the soil seed bank of the different species. [source]

Seed ecology of a Mediterranean perennial herb with an exceptionally extended flowering and fruiting season

BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2003
F. XAVIER PICÓ
Lobularia maritima is a Mediterranean short-lived herb with a flowering and fruiting season that lasts for ten months. Previous studies have shown that recruitment in periods other than autumn of the flowering season has few demographic implications; that is contributes little to the population growth rate. Since environmental conditions in periods other than autumn would allow recruitment, we examined to what extent the seed ecology of L. maritima accounts for recruitment shortage for the greater part of the year. To this end, we studied the effects of selfing and outcrossing on seed production and germination, within- and between-year variation in seed mass and germination, seed characteristics in the soil seed bank throughout the year, and the effect of temperature as a factor controlling seed germination. Results indicate that selfing does not decrease recruitment, and thus the observed changes in visitation rate and pollinator composition throughout the year cannot account for differences in recruitment. Germinability decreases throughout the year, suggesting a possible cost in reproduction associated with extended flowering. L. maritima has a transient seed bank whose seeds also experience a decrease in their germination throughout the year. Finally, temperature affects seed germination patterns, indicating the existence of quiescence mechanisms that prevent germination in the months prior to the summer drought. Overall, the results obtained support and, at least partly, explain the recruitment patterns of L. maritima observed in the field. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142, 273,280. [source]