الفهرس 
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Abstract
ENGLISH SUMMARY : 1. Isolation and identification of PVY Diagnosis of potato plants naturally infected with viral diseases was achieved and plants which exhibited symptoms like viral symptoms were collected. Many symptoms related to PVY infection such as mosaic, yellowing between veins, mottling, stunting, chlorosis and necrosis were observed. In the present study, identification of PVY was done through virus symptomatology, host range, stability, mode of transmission, particle morphology, DAS-ELISA and RT-PCR assays. Thirteen plant species/cultivars (S. tuberosum cv. Spounta, S. tuberosum cv. Cara, D. metel, D. stramonium, N. tabacum cv. White burley, C. amaranticolor, S. lycopersicum, S. melongena, C. annuum, P. vulgaris, V. faba, B. oleracea and L. sativa) belong to five botanical families were tested to determine the response as hosts to infection with PVY. Nine of tested plants species/cultivars (S. tuberosum cv. Spounta, S. tuberosum cv. Cara, D. metel, N. tabacum cv. White burley, C. amaranticolor, S. lycopersicum, S. melongena, C. annuum, P. vulgaris) reacted to PVY isolate in different symptoms, but four of plant species (D. stramonium, V. faba, B. oleracea and L. sativa) did not react against PVY isolate. Transmission of PVY was done by mechanical inoculation from infected potato to healthy plants of D. metel and vice versa with 100% success. However, it was transmitted from infected potato plants to healthy ones by M. persicae with 80% success. The thermal inactivation point (TIP) of PVY was between 55-60°C; dilution end point (DEP) was 10-4 and longevity in vitro was between 2 and 3 days. The size of PVY was approximately 11×700 nm with rod flexible shape as revealed by TEM study. DAS-ELISA method was used and confirmed the presence of PVY in tested plants using polyclonal antibodies specific to PVY. In addition, PVY was identified by RT-PCR through isolation of total RNA from leaves of PVYN-infected potato cv. Spounta plants and healthy ones. 2. Ultrastructure of cytopathological responses to PVY-necrotic strain. Ultrastructural responses of plant cell organelles in leaf tissues of potato cv. Spounta towards PVY (PVY-necrotic and ordinary strains) infection, was investigated using an electron microscope. Numerous cytopathological alterations in cell wall, middle lamella, nucleus, chloroplast, mitochondria, endoplasmic reticulum and peroxisomes have been observed compared to healthy tissues. Splitting, destroying, joining to neighbor protoplasts and necrosis in cell wall were observed. Cell nucleus was changed to lobe-like shape, damage in envelope, enlargement of pore complexes. Mitochondria were increased in number, elongated and destroyed. Many changes in chloroplasts such as deformation, reducing size and number, damage of envelope and grana thylakoids, were observed. Virus particles and cytoplasmic inclusions were observed in ultra-thin sections. To our knowledge, obtained results showed that, only peroxisomes could be responsible organelles for induction of necrotic symptoms, because they were increased in number and frequently existed only in plant cells infected with PVY-necrotic strain. 3. Control of Potato virus Y using antiviral chemical compounds. The present study aimed to investigate three antiviral compounds at different concentrations as follows: ribavirin (100, 200 and 400 mg/l), acyclovir (200, 400 and 800 mg/l) and oseltamivir (37.5, 75 and 150 mg/l). All treatments reduced the virus concentration in the preventive and curative applications compared to the PVY-infected control treatment. Oseltamivir and ribavirin were the most effective compounds in reducing virus concentration (0.442 and 0.447, respectively) followed by acyclovir (0.493) compared to the PVY-infected control treatment (0.744) when virus was measured two weeks after inoculation. All applied compounds did not affect the chlorophyll content, leaf number/plant and plant height, when compared to PVY-infected control treatment after 40 and 80 days from planting. Interestingly, only the leaf area was affected with no significant differences between preventive and curative applications. Fresh and dry weight of potato plants estimated after 95 days from planting were also affected by all compounds. The highest fresh weight per plant was obtained by ribavirin (19.72 g) followed by acyclovir (19.50 g) and oseltamivir (17.55 g) compared to the PVY-infected control treatment (12 g) and the healthy, untreated control (24.66 g) with significant differences between preventive and curative applications. All three compounds treatments significantly increased the dry weight in the same order with no significant differences between preventive and curative applications, in case of tuber weight.