الفهرس 
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Abstract
Three different phytoplasma isolates (i.e. witches’ broom, phyllody and big bud) were isolated from naturally infected tomato plants collected from Giza, Ismailia, Bani-Sueif, Fayoum and Qena governorates in Egypt. The observed symptoms included big buds, swollen flower buds with green petals or phyllody, deformation and yellowing of leaves, purple-colored leaves; many infected plants gained a bushy appearance or witches’ broom and some tomato fruits of green polygonal shape with seeds atrophy. Different techniques for transmission of phytoplasma to healthy tomatoes and periwinkles were tested, including mechanical inoculation, wedge grafting, parasitic plant dodder (Cuscuta campestris), insects in the family Cicadellidae (leaf hopper, Empoasca decipiens) and in germinated seeds within the infected fruit, suggesting mechanical inoculation and seed-transmissible were not feasible while, the positive results were obtained by the other three techniques.
Phytoplasma was successfully detected using light microscope with the application of Dienes’ stain in sections of naturally infected plants in several locations of Egypt. Electron micrograph of the phloem tissues of inoculated tomato and periwinkle plants showed rounded or irregular bodies of diameter 200-600 nm.
Light and transmission electron microscopic examination of the effect of phytoplasma infection on anatomical and ultrastructural changes in tomato plants revealed deterioration effects on the stem, flower petiole or leaflets tissues and important histological variations included general disorganization and deformation of phloem tissues.
Phytoplasma-DNA was successfully extracted and identified by sensitive and specific nested-PCR using universal phytoplasma-specific primer pairs P1/P7 and R16F2n/R16R2, in all regions of the screened governorates except Giza, as well as interactions of phytoplasma with experimentally host plant. The DNA sequencing, phylogenetic analysis and the multiple alignments for the sequences of the Egyptian clones with each other and with the other sequences of phytoplasma strains on GenBank suggested that we may have three different phytoplasma isolates (witches’ broom, phyllody and big bud) infecting tomato plants in Egypt and listed under accession numbers KT225548, KT230865 and KT225545, respectively.
Three methods were done towards the production of phytoplasma-free tomato plantlets through tissue culture using antibiotic compound (tetracycline hydrochloride in three concentrations 25mgL-1, 50mgL-1 and 75mgL-1), irradiation by three doses (3, 5 and 10Gy) of gamma ray and natural compound (1ml of garlic juice). All treatments proven to be a very useful effect against phytoplasma, except concentration 25 mgL-1 of tetracycline hydrochloride substance. The findings of this study have proven treatment at lower dose of gamma rays (3 Gy) of efficient methods on growth promotion