الفهرس 
The genus colletotrichumOnly 14 pages are availabe for public view
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Abstract
Colletotrichum is a large and diverse genus and one of the most important genera of plant pathogenic fungi, attacking a wide range of plants causing leaf spot, anthracnose and post-harvest diseases. The present study aimed to investigate the role of saponin degrading enzymes in the pathogenicity of Colletotrichum and host range with contrasting infection strategies. The first part of this study aimed to study morphological characterization of ten Colletotrichum species. The ten species were C. acutatum 507, C. capsici 141, C. destructivum .202, C. destructivum 709, C. gloeosporioidee 910, C. lindemuthianum 136, C. malvarum 717, C. orbiculare 941, C. sublineolum 895 and C. truncatum. This part included conidial morphology, conidial germination and appressorium formation. -Conidia are produced in acervuli. All isolates produce hyaline, unicellular, smooth-walled conidia, some produce ovoid, falcate or cylindrical conidia. In general, conidial length is considerably more variable than width. A septum is formed upon germination of the conidia, this is associated with the formation of a germ-tube. -Appresoria are formed at the end of a germ tube. All isolates in this study produce single cell melanized appressoria. Appressoria are ovoid, globose and subglobose or irregular in shape. -Setae are found to be present in all isolates. Setae are formed in acervuli. Setae are thick walled, melanized. Variations occur in their size and number of septation. In some isolates setae are abundant, in others they are few or sparse. -Variation in the growth rate of the same species occurred on the. different media. Potato dextrose agar medium (PDA) was the best for growth but Colletotrichum medium (CM) was the best for sporulation The second part aimed at screening the production of saponins degrading enzymes (P-glucosidases) by the ten Colletotrichm species. from this screening, programme two species were selected, C. destrmctivum LARS 709 and C. capsici LARS 14 1. C. desfructivum 709 is a biotrophic species isolated from alfalfa and C. capsici 141 is a necrotrophic species, which grows intramurally and isolated from cowpea. Therefore these isolates were selected for comparison, in addition to three mutants obtained fi-om the wild types (C. destructivum 709-4, C. destructivum 709-12 and C. capsici 141-17) by insertional mutagensis. Pglucosidases of these isolates were analyzed biochemically using isoelectric focusing and ion exchange chromatography. -Preliminary screening for the assay of the activity of saponin degrading enzymes (P- glucosidase, EC 3.2.1.21) of the 10 isolates showed that C. destructivum 709 and C. capsici 141 produced high enzyme activity than the other isolates. -C. destructivum 709 wild type produced j3-glucosidase and tomatinase activity more than C. capsici 141 wild type and the higher enzyme activity was recorded after 10 days for both. -C. ’ca~sici 141. wild type produced 8-glucosidase enzyme activity more than C. capsici 141-17 mutant. -C. destructiwm 709 wild type produced P- glucosidase enzyme activity more than C. destructivum 709-4 and 709-12 mutants. -Biochemical analysis of P-glucosidase enzyme activity by isoelectric focusing illustrated that j3-glucosidase activity assayed by 0-nitrophenyl P-D glucopyrenoside (ONPG), methylumbilleferyl P-D glucopyrenoside (MUG) and tomatine for C. desfructiwm 709 wild type had two peaks for all the three substrates at pH 3.9and pH 6.8. -Analysis of P-glucosidase of C. destructivum 709-4 mutant by isoelectric focusing showed that C. destructivum has only one peak for 0-nitrophenyl P-D glucopyrenoside (ONPG) and methylumbilleferyl P-D glucopyrenoside (MUG) at pI 3.5 The third part was designed for the study of pathogenicity, host range and infection processes of C. destructivum LARS 709 and C. capsici LARS 141 wild types and the mutants. The hosts were cv.blackeye and cv.IT82-E60 (@a unguiculata), lentil (Lens culinaris) and alfalfa (Medicago sativa). -All the test hosts were resistant to C. capsici 141-17 mutant, while they were all susceptible to C. destructiwirn 709 wild type. For the other isolates the response of the two cultivars of cowpea ( cvs. Blackeye and IT82-E60) was similar for each fbngal isolate. They were both susceptible to C. capsici 141 wild type, while they were resistant to each of C. destructivum 709-4 and 709-12 mutants. On the contrary, alfalfa and lentil were both resistant to C. capsici 141 wild type and susceptible to each of C. destructivum 709-4 and 709-12 mutants. -Both cowpea cultivars were found to be similar in the pathogenicity, so cowpea cv. blackeye, alfalfa and lentil were used in infection processes using C. destructivum 709 wild type and 709-4 mutant. -Infection process in cowpea with C. destmctim 709 wild type ended at 168 h with the production of acervuli with single setae. -Both C. destructivum 709 wild type and C. destructivum 709-4 mutant were pathogenic on alfalfa and lentil but in cowpea the mutant gave superficial flecking. Pathogen behaviour on the host surface and the initial penetration processes were studied by scanning electron microscopy (SEW. . -Cellulose acetate membrane was used to investigate the detached appressoria developed on the leaf surface using Cryo- SEM.. The result illustrated that penetration pores were present on the surface of appressoria after 30 and 48h. and even after 4 days fiom inoculation. -To detect any structural defense of the host plant against completing the infection by the mutant compared by the wild type, aniline blue fluorescence test was used to stain calloses, and fluorescence microscopy showed very small papillae (wall appositions) under the appressorium at the 4 th day after inoculation by C. destmctivum 709-4 mutant. These might have prevented fkrther fkngal development. Another reason for stopping penetration, could be a chemical defense of the host, which might be developed using the natural product (saponin) by the plant. -On the other hand, in the plant infected by C. destructivurn 709 wild type incased mycelium was observed inside the infected cell, which means that papillae were not enough to prevent penetration and the hyphae managed to advance through cells despite the barrier, where as these papillae stopped penetration in mutant.