Impact of Phytoplasma Infection on Phytohormone Levels, Vascular Tissue Morphology and Phloem Mass Flow in Napier Grass

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dc.contributor.authorOmenge, Keziah Moraa
dc.date.accessioned2019-10-29T09:20:33Z
dc.date.available2019-10-29T09:20:33Z
dc.date.issued2019-02
dc.descriptionA Thesis Submitted In Partial Fulfilment of the Requirements for the Award of the Degree of Master of Science (Biotechnology) in the School of Pure and Applied Sciences of Kenyatta University. February 2019en_US
dc.description.abstractThe Napier grass stunt (NGS) phytoplasma is a phloem limited bacterium that is transmitted by insect vector, Maiestas banda (Hemiptera: Cicadellidae). The phytoplasma causes NGS disease in Napier grass resulting into huge forage yield losses hence impacting negatively the economy of smallholder dairy farmers in East Africa. Phytoplasma infections causes massive changes in phloem physiology including the sieve elements which may lead to reduced rate of phloem mass flow that interfere with translocation of food in host plants. Hormonal imbalance also occurs in infected plants and is a defense mechanism used by the host plants to counteract the pathogen attack. Therefore, the structures of vascular tissues were examined using fluorescent microscopy and phytoplasmas were visualized by confocal microscopy using 4',6-diamidino-2- phenylindole (DAPI) dye while the rate of phloem mass flow determined using 5,6 carboxyfluorescein diacetate (CFDA) dye in healthy and phytoplasma infected Napier grass plants. The cells of phytoplasma were detected and quantified by real-time qPCR while the levels of phytohormones were investigated using liquid chromatography tandem-mass spectrometry (LC-MS/MS) method. The areas of all vascular tissues in phytoplasma-infected Napier grass leaves were significantly reduced as follows; vascular bundles (34.8 %), xylem vessels (42.6 %), phloem (27.2 %) and sieve elements (53.5 %). The individual and aggregates of phytoplasma cells were detected on the membranes of the sieve elements that demonstrated high yields aan average of 2.29×105 cells/μg of total DNA extracted in the plant leaves by qPCR results. The rates of phloem mass flow were significantly reduced by 40.7 % in the phytoplasma-infected plants. With the exception of SA and ABA, all measured phytohormones were affected by phytoplasma infection. The concentrations of cis-12-oxo-phytodienoic acid, jasmonic acid and jasmonic acid isoleucine were significantly reduced 3, 2 and 8 folds, respectively. This study sheds light on the significance and mechanisms of phytoplasma infectionen_US
dc.identifier.urihttp://ir-library.ku.ac.ke/handle/123456789/19961
dc.language.isoenen_US
dc.publisherKenyatta Universityen_US
dc.titleImpact of Phytoplasma Infection on Phytohormone Levels, Vascular Tissue Morphology and Phloem Mass Flow in Napier Grassen_US
dc.typeThesisen_US
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