الفهرس 
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Abstract
The objectives of this study are 1) isolate and identify PSTVd based on biological, chemical and molecular properties and nucleotide sequence, 2) genetic variability of some potato genotypes to PSTVd by biochemical and molecular markers, 3) elimination of PSTVd through Meristem-tip culture, thermotherapy, chemotherapy, electrotherapy treatments. As well as, production of PSTVd- free microtubers and conservation of PSTVd in vitro by calli cultures.
Number 93 tuber samples of naturally infected potato plants cv. Diamond were collected from EL-Menoufia and Behera governorates during autumn season. These samples were tested against PSTVd by NASH. PSTVd was isolated biologically on H. muticus L and Cy. tetragonolaba L and was propagated on tomato cv.Super Marmande. TIP of PSTVd isolate was 85- 90ºC, DEP was 10-9 to 10-10 and LIV was 4 days. PSTVd isolate was mechanically transmitted by infectious sap and with low proportion by aphid (Myzus persicae). It was found that PSTVd was transmitted via persistant manner when encapsidated with PLRV. Also, it was transmitted 100% by potato tubers and 96.66 % by tomato seeds. Selection of nine- isolates from PSTVd gave different symptoms on potato tubers, tomato and an identical relative mobility on S-PAGE but differed in the intensity of band. The PSTVd–isolate No.9 gave the highest conc. and it was detected by R- PAGE and RT- PCR assay using a specific primer for CCR. A major c-DNA product was approximately 359 bp. Southern- and dot- blot hybridization were used to confirm the authenticity of the PCR- product. The 359 bp amplified c-DNA was hybridized with DIG- labeled PSTVd cDNA. The partial nucleotide sequence of PSTVd-EG isolate was compared with five geographical distinct PSTVd– isolates available from GenBank revealed high sequence identity (89-84 %). On the other hand, secondary structure minimum free energy for PSTVd was -116.51 kcol /mol. Eight potato local cultivars and seven wild species were varied in response to PSTVd-infection and determination of genetic variability of some potato genotypes resistant, tolerant, hypersensitive and immune under PSTVd infection by biochemical markers using SDS- PAGE and molecular markers using RAPD and ISSR.
The PSTVd-isolate was eliminated from infected potato plants by meristem-tip culture, chemotherapy using (ASA, 2-TU and Virazole), thermotherapy (21, 3-4, 5, 8 and 21 ºC /3 mon.) and electrotherapy. In addition to, production of microtubers in vitro using growth substances (Coumarin, Virazole and 5-Benzyl amino purine and Jasmonic acid), thus Coumarin gave the highest number, weight and size of microtubers. PSTVd-isolate was conserved in vitro through calli cultures.
Key words: Potato, PSTVd, R- PAGE, RT-PCR, Southern-blot, Dot-blot hybridization, Nucleotide Sequencing, Secondary structure, Molecular markers, Elimination.