http://ir.lib.ruh.ac.lk/handle/iruor/7348 2026-05-12T14:28:04Z http://ir.lib.ruh.ac.lk/handle/iruor/15787 Trehalose Induces Antagonism towards Pythium debaryanum in Pseudomonas fluorescens ATCC 17400 Gaballa, A.; Abeysinghe, P.D.; Urich, G.; Matthijs, S.; De Greve, H.; Cornelis, P.; Koedam, N. Pseudomonas fluorescens ATCC 17400 shows in vitro activity against Pythium debaryanum under conditions of iron limitation. A lacZ reporter gene introduced by transposon mutagenesis into the P. fluorescens ATCC 17400 trehalase gene (treA) was induced by a factor released by the phytopathogen Pythium debaryanum. The induction of the lacZ gene was lost upon treatment of the Pythium supernatant with commercial trehalase. A trehalose concentration as low as 1 mM could induce the expression of treA. The mutation did not affect the wild-type potential for fungus antagonism but drastically decreased the osmotolerance of the mutant in liquid culture and suppressed the ability of P. fluorescens ATCC 17400 to utilize trehalose as a carbon source. A subsequent transposon insertion in treP, one of the trehalose phosphotransferase genes upstream of treA, silenced the lacZ gene. This double mutant restricted fungal growth only under conditions of high osmolarity, which probably results in internal trehalose accumulation. These data confirm the role of the disaccharide trehalose in osmotolerance, and they indicate its additional role as an initiator of or a signal for fungal antagonism. 1997-09-03T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/15786 Genetic differentiation between Bruguiera gymnorhizaand B. sexangula in Sri Lanka Abeysinghe, P.D.; Triest, L.; De Greef, B.; Koedam, N.; Hettiarachi, S. The identification of populations of Bruguiera sexangula, Bruguiera gymnorhiza and their putative hybrids in the field is difficult using only morphological and phenological characters. Using a PCR based technique, RAPD (Random Amplified Polymorphic DNA), the genetic variation of Bruguiera populations was studied from contrasting climatic and geographic regions along the southwest coastal region of Sri Lanka. Out of 45 primers screened, 20 primers allowed us to observe polymorphism, not only between species (interspecific) but also within the species (intraspecific). Analysis of RAPD data appears to be helpful in determining the genetic relationship among populations of B. gymnorhiza and B. sexangula. RAPD markers revealed that the two species are well separated without any hybrid position between the two taxa though they occur in mixed stands. Although sampling sizes of populations of this study were small, genetic variation among B. gymnorhiza and B. sexangula populations could be observed. For B. sexangula, it was possible to differentiate each of the three populations, even when using a small number of primers. 1999-01-01T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/15785 Genetic and geographic variation of the mangrove tree Bruguiera in Sri Lanka Abeysinghe, P.D.; Triest, L.; De Greef, B.; Koedam, N.; Hettiarachi, S. The variation in two Bruguiera species in populations from different climatic and macrogeographic regions along the western to southeastern coastal area in Sri Lanka was studied using RAPD (Random Amplified Polymorphic DNA). Intra- and interspecific variation was observed using 20 primers of the 45 primers screened. Some primers showed diagnostic banding patterns and allowed unambiguous differentiation between B. sexangula and B. gymnorhiza without any indication of hybrid individuals. RAPD markers were also used to produce a similarity matrix among individuals of a species. A higher degree of polymorphism was observed within populations of B. gymnorhiza in Rekawa, situated in the climatically intermediate (between the wet and dry) zone, than within populations from the wet zone (Galle and Negombo). RAPD data analysis did not reveal a clear relationship between genetic differences and macrogeographical variation along the western and southern coastal area in Sri Lanka, but indicated that a small population of B. sexangula was genetically different. A more pronounced genetic difference at the population level in B. sexangula than in B. gymnorhiza is suggested. ©2000 Elsevier Science B.V. All rights reserved. 2000-01-01T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/15784 Comparative study of the disjunct zonation pattern of the grey mangroove Avicennia marina(Forsk) vierh. In gazi bay (Kenya). Dahdouh-Guebas, F.; De Bondt, R.; Abeysinghe, P.D.; Kairo, J.G.; Cannicci, S.; Triest, L.; Koedam, N. The disjunct zonation pattern of Avicennia marina (Forsk.) Vierh., frequently observed along the Kenyan coast as a landward and a seaward zone, has been studied on a morphological level and complemented with preliminary genetic data. The objective was to describe the two zones in-depth in order to provide a background ecological setting that may be used in explanations on the emergence of such a bimodal zonation. The vegetation structure in the two zones is described by means of the Braun-Blanquet relevé and PCQ-methods, root- and leaf-morphological characteristics, and environmental variables to provide a background ecological setting. The two zones show considerable differences in physiognomy of A. marina trees, and indicate that the differences may constitute an environmental response. Results show that in the landward A. marina zone, tree heights, leaf sizes, density, and total length of pneumatophores tend to be smaller as compared to the same attributes of the trees in the seaward zone. Differences in leaf stomatal density and in above- and below-ground pneumatophore length, the latter closely related to the effect of inundation, were observed. This suggests a considerable adaptability and plasticity with respect to environmental conditions. The hypothesis for the genetic analysis was that mangrove fringes as close as 105 m from one another constitute a same genetic pool. Preliminary genetic analysis using 48 amplified DNA fragments (RAPD - Randomly Amplified Polymorphic DNA) from 37 landward and seaward trees revealed significantly different frequencies for four DNA fragments, indicating that there might be less contact and genetic interchange between the two zones than within each zone. Whether this phenomenon, coupled to the different environmental conditions, can lead to further divergence cannot be answered yet. 2004-01-01T00:00:00Z