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Abstract
Sweet potato is considered as one of the important food crop in the world. In Egypt it grown in only about 30,000 Fed. This area was distributed over 12 governorates and concentrated in Delta and north parts. Sweet potato crop is subjected to several viral infections causing considerable yield losses especially there is no enough attention to control viruses. The aim of this study is to focus on viral disease incidence in some production areas, isolate and identify the most important and prevalent virus(s) of sweet potato, and to study the effect of the virus on protein content of Ipomoea and some other Convolvulaceae plants.
To determine the disease incidence of viral infections, 17 fields represented the main sweet potato cultivars and hybrid grown in Egypt, were inspected during two grown seasons 2004/2006. External virus symptomatic plants were calculated and their percentage ranged from 1.80 to 34.50% of 19216 total observed samples. Inspections revealed that, cultivar Mabrouka was highly infected with viruses followed by cv. Abees and than by the hybrid Menofia 6/96. Incidences of infections were 22.18, 9.75 and 4.42% respectively in three different locations.
Detection of seven sweet potato viruses was carried out by ELISA. Symptomatic (179) and asymptomatic (77) plants, collected from three main productive governorates (Kalyoubia, Gharbia and Damietta) were tested. Positive reaction was observed in 70.3% and 14.2% respectively. However, 41 samples were obtained from Menofiea governorate and tested only for Sweet potato feathery mottle virus (SPFMV), which was available at that time. This virus was detected in 22.5% of the symptomatic plants and not detected in any asymptomatic plants regarding the highly occurrence of SPFMV in the tested samples so, the present study is concentrated on this virus.
Two isolates of SPFMV were biologically isolated from Kalyoubia (Ka) and Gharbia (Gh) governorates and kept on I.nil and I. setosa and confirmed by ELISA. The host range of these two isolates was found to be restricted to some hosts belonging to family Convolvulaceae. Convolvulase arvensis, Ipomoea batatas, Ipomoea nil, Ipomoea purpurea and Ipomoea setosa were showed different degrees of susceptibility to inoculation with the two isolates.
Several phosphate buffer solutions were used for mechanical inoculation of SPFMV. Buffer C (PBS + ascorbic acid + DECA) was found to be the most effective buffer in this respect. In general, SPFMV was not easily sap transmissible and the fore finger method of inoculation was more effective than slashing. However, it was not transmitted by injection.
Regarding insect transmission of SPFMV, Myzus persicae Sulz. was found to be more effective than Brevicoryne brassicae L. The virus was transmitted also by grafting, but did not transmit neither by dodder nor by seeds.
Immunosorbet electron microscopy revealed that SPFMV particles are a flexible rod about 830 nm in length and about 15 nm in width.
Reverse transcriptase- polymerase chain reaction (RT-PCR) showed products of 411 bp in agarose gel from plants infected with SPFMV, but not from healthy ones, as the expected size of the used primers (SPfMV1, SPFMV2).
Homologous to the deduced nucleic acids sequence of the region of RT-PCR of SPFMV .there was a highly homology at the primer region in different isolates of SPFMV, that means there was a conserved region with the primer sequence which has been used as detector for the presence or absence of the virus.
Qualitative protein content in infected plants with SPFMV showed that many bands were disappeared may be due to viral infection.