Theses & Dissertations
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Item PATHOGENICITY OF HETERODERA SACCHARI (LUC AND MERNY) AND ITS INTERACTION WITH BOTRYODIPLODIA THEOBROMAE (PAT) ON SOME NERICA RICE CULTIVARS(2013) AKPHEOKHAI, L. I.The Cyst Nematode (CN), Heterodera sacchari, is an important pest that causes yield losses of upland rice. NERICA Rice (NR) is a widely-grown upland rice cultivar. Botryodiplodia theobromae (a rot fungus) exists in many agricultural lands and causes yield losses on crops. However, information on the pathogenicity and damage by CN on NR cultivars in Nigeria is scanty. Therefore, pathogenicity of CN on NR cultivars and its interaction with Botryodiplodia theobromae were investigated. Twenty-four upland cultivars were screened for resistance to H. sacchari by inoculating three-week old seedlings with zero and 5000 eggs of H. sacchari. Cyst rating following standard procedure was used to determine resistance/susceptibility. Pathogenicity of H. sacchari was conducted to determine nematode damage on NR1, NR2, NR3, NR8 and NR14 cultivars in pot and field experiments in two cropping seasons. Three-week old seedlings of each cultivar were inoculated in pot experiment at zero, 5000 and 10000 eggs of H. sacchari per pot in four replicates in a 5X3 factorial using Randomized Complete Block Design (RCBD). The field trial was a split-plot experimental design with nematode-treatment as main plot and the five NERICA rice cultivars as sub-plots. Interaction between H. sacchari and B. theobromae on NR was investigated in pot and microplot experiments using standard procedures. Three-week old seedlings of NR1 were inoculated at zero or 5000 eggs of H. sacchari alone, 5x105 spores ml-1 of B. theobromae alone and simultaneous inoculation of H. sacchari + B. theobromae per pot in four replicates in a RCBD. The same treatments were carried out for the seedlings in the microplots (50x50x75) cm. Plants were assessed for growth, yield and nematode-fungal damage. Root sections (14?m) of NR from the interaction experiment were prepared for histopathology studies using standard procedures. Photomicrographs of cell structural integrity and damage were taken. Data were analyzed using descriptive statistics and ANOVA at p=0.05. Twenty-one rice cultivars (seven improved Oryza sativa and 14 NR cultivars were rated susceptible), NR6 and NR8 were rated moderately resistant and CG14 was most resistant. Heterodera sacchari significantly reduced NR growth by 41.8%, root weight by 55.4% and yield by 67.7%. Interaction between H. sacchari and B. theobromae significantly reduced NR growth by 58.8% - 67.3%, root weight by 63.4% - 70.4% and yield by 62.2% - 75.4%, compared to single inoculation with H. sacchari or B. theobromae. Heterodera sacchari infection caused cellular disorganization, compression and disintegration. Syncytia with seven nuclei, were formed close to nematode head seven days after inoculation (DAI). Both CN and B. theobromae developed and reproduced when present on same root tissue. Fruiting bodies of B. theobromae enlarged and ruptured cortical cells and epidermal layer of root during ascospore discharge 7 DAI. Infection of both pathogens revealed dark necrotic regions, cellular compression, disorganization and disintegration. Syncytium was established by the nematode in presence of the fungus 9 DAI. Heterodera sacchari caused significant damage and yield reduction on NERICA Rice cultivars and its interaction with Botryodiplodia theobromae, synergistically reduced growth and yield of rice. However, CG14 was most resistant.Item ULTRASTRUCTURE OF GASTROINTESTINAL HELMINTHS AND THEIR HISTOPATHOLOGY IN COMMON FISHES OF LEKKI LAGOON LAGOS NIGERIA(2012) AKINSANYA, B.Parasitic infections of fish constitute one of the problems in aquaculture. The pathological conditions resulting from such infections cause significant mortalities among infected fish hosts. There is limited information on fish helminth parasites� ultrastructure that could provide guidelines for the identification and confirmation of parasite species that have been associated with economic losses in fishes. Thus, this study was undertaken to describe the fine surface morphology of helminth parasites and pathological conditions associated with helminthes infections. A total of 3040 randomly selected fishes belonging to eight families (Clariidae, Channidae, Mochokidae, Polypteridae, Bagridae, Malapteruridae, Cichlidae and Gobiidae) were procured from landing centres of fishermen from Lekki lagoon between November 2008 and November 2010. Fish samples were dissected and their gastrointestinal parts were examined for parasites and histopathology in physiological saline by microscopy. The parasites recovered were fixed in 70% alcohol and 2.5% glutaldehyde and examined for ultrastructural morphological details with scanning electron microscope. The infected gastrointestinal parts removed were fixed in Bouin�s fluid and processed using standard histological procedures and examined. Differences in parasite prevalence in relation to host sex were analysed using Chi-square. The parasite species observed were Electrotaenia malopteruri (Proteocephalidae); Indocucullanus genderi and Cucullanus longicollis (Cucullanidae); Procamallanus longus and Spirocamallanus spiralis (Camallanidae); Wenyonia spp. and Caryophyllaeus syrdarjensis (Caryophyllaeidae). Previously unreported ultrastructural features of some helminth parasites observed included wider disc-shaped rostellum-like organ, bean shaped unilocular suckers and lack of median line in between the unilocular suckers in E. malopteruri; lateral extension of cuticle and tail not curved in Procamallanus longus. Other previously unreported ultrastructural features included the presence of papillae at the caudal region, lack of distinct cephalic region and posterior end not bluntly pointed in Wenyonia spp.; single amphid and two submedian cephalic papillae in Cucullanus longicollis and spines on the curved tail in Indocucullanus genderi. Two additional lateral papillae and two small lips were observed in the mouth of Caryophyllaeus sp. The highest mean intensity of infection (7.8?19.5) was recorded for S. clarias with presence of necrotic debris within the gut lumen. Malapterurus electricus with a mean intensity of infection of (0.71?3.39) had necrosis of intestinal surface epithelium. Parachanna obscura with a mean intensity of (0.33?1.01) had hyperplasia of intestinal villi. The lowest mean intensity of infections (0.04?0.19) was recorded in Calamoichthys calabaricus with diffuse necrosis of the intestinal mucosa. Only E. malopteruri was found in M. electricus. In Tilapia zillii, Indocucullanus sp (35.7%) and Cucullanus sp (64.3%) were found while Procamallanus sp (59.4%) and Spirocamallanus sp. (40.6%) were found in P. obscura. In Synodontis clarias, Wenyonia spp (96.5%) and Caryophyllaeus sp. (3.5%) were found. Significant difference in the prevalence of infection between male and female fish host was observed in Synodontis filamentosus (p<0.01). Ultrastructural variations indicated increased precision in identification and confirmation of the parasites in the examined fish hosts. The different pathological lesions could have negatively affected these fishes and this could threaten the abundance and diversity of resident fish species in Lekki lagoon.