الفهرس 
Literature reviewOnly 14 pages are availabe for public view
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Abstract
S. lycopersicum, is a major agricultural crop grown all over the world, with a global production of over 189 million tons in 2021. According to the Food and Agriculture Organization’s official website, Egypt ranks sixth in the world in tomato production, with over 6.2 million tons produced in 2021, after China, India, Turkey, the United States of America, and Italy. However, widespread persistent growth of tomatoes, it is vulnerable to a variety of pathogens such as bacteria, fungi, and viruses. Many viruses are spreading because of global agricultural trade.
TYLCD is one of the most damaging plant diseases, destroying tomato crops all over the world. It has spread to many countries around the world. TYLCV genus Begomovirus, family Geminiviridae is a global threat to agriculture. TYLCV originated in the Middle Eastern Mediterranean region, and since then has spread to many regions of the world. Geminiviruses, cause significant yield losses in tomato production around the world including Egypt. TYLCV is ranked third based on its scientific and economic importance of viruses that affect the production of tomatoes. It causes quantitative and qualitative yield losses frequently reached to 100% in some tomatoes yield.
The global spread of TYLCV in tomatoes is highly dependent on virus transmission in a persistent and circulative manner by its sole vector, the whitefly, Bemisia tabaci. The TYLCV genome is 2.7 kb of single-stranded circular DNA encodes six open reading frames (ORFs), organized bidirectionally into transcriptional units that are separated by an Intergenic Region (IR).
TYLCV symptoms include reduced leaf size, upward leaf curling, yellowing of young leaves, stunted growth, flower abortion, inward rolling of tomato leaf margins and interveinal yellowing of leaflets. TYLCV has a very diverse host range, and it has been detected in 49 species belonging to 16 families.
Early detection of TYLCV is critical for effective management due to its severity. Traditional TYLCV’s detection methods involve sample preparation to identify viral DNA or proteins. Serological techniques based on immunoblotting, conventional PCR, restriction fragment length polymorphisms, loop-mediated isothermal amplification, real-time PCR, and rolling circle amplification have all been developed and used to detect TYLCV-infected tomatoes. The nucleic acid-based PCR method is the most used for plant pathogen detection due to fast, and highly specific and sensitive.
However, disease management is complicated by the widespread nature and the diverse host range. Because ”prevention is better than cure” there are several approaches to control TYLCV have been developed based on conventional methods such as quarantine regulation and IPM and nonconventional ways such as molecular and biological approaches such as the application of physical barriers, chemical insecticides for limiting vector populations, several genetic engineering strategies have been investigated as gene editing and RNAi technology.
RNAi has recently proven a highly effective and powerful functional genomics tool for silencing gene expression in crop improvement. Even though RNAi stability in plants is critical, the RNAi-mediated gene suppression approach opens up new avenues in developing eco-friendly biotech approaches for crop improvement by knocking out specific genes for better stress tolerance and incorporating novel traits in various plant species.
RNAi mechanisms through a large dsRNA cleavage by a DCR ribonuclease into discrete 21:25 nt RNA fragments siRNA. the strands of the siRNA are separated to the guide strand, which is complementary to the target RNA and the anti-guide strand (helper strand), which is further degraded. The guide strand is then loaded onto an AGO ”slicer” protein, which forms the RISC complex, which anneals it to the target mRNA, forming a duplex with it; then the target RNA is cleaved by the RISC slicer activity.
In an attempt to find an alternative to combat TYLCV infection, an in-silico approach was employed to predicate the possible siRNA-generating sequences that could knock down TYLCV in infected plants.
We found that specific governorates in Egypt, such as Giza, El-Minia, Qalyubia, El-Beharia, and Ismailia, may be termed TYLCV settlers. TYLCV was detected by a rapid, reliable, and robust molecular detection and identification tool of TYLCV in tomato germplasm to guarantee the safe and sustainable production of tomato-free TYLCV with the newly designed primers that could be used to quickly screen the presence of the TYLC virus to amplify partial sequences 690 bp of TYLCV genome spanning the trans-activator protein (C2), replication enhancer protein (C3) genes, partial parts of replication (Rep) and coat protein (CP) genes from naturally infected tomato plants. The DNA sequence analyses of the current Egyptian isolate was annotated and deposited in the GenBank with an accession ID MZ546492 revealed high nucleotide sequence identities (98.99 %) to TYLCV isolates in the GenBank.
The host range of TYLCV included members within the families Cucurbitaceae, Chenopodiaceae, Cruciferae, Solanaceae, Lamiaceae, Compositae and Fabaceae. No symptoms were developed when tomato and other crops were inoculated mechanically. Whitefly carries TYLCV successfully transmit TYLCV some are susceptible to virus C. sativus, C. pepo, C. annum cv Chilli, D. stramonium and P. vulgaris, all developed TYLCV disease symptoms so they may serve as a natural reservoir for TYLCV. While Chenopodium amaranticlor, Solanum melongena, Vicia faba, Brassica oleracea var. capitate, M. sativa and L. sativa showed no symptoms and did not react systemically with TYLCV.
We designed RNAi construct targeting the TYLCV that may provide potential resistance for tomato plants against TYLCV infection and generated a list of possible oligonucleotides that could be synthesized in the laboratory and transformed to the plant prior to viral infection to stimulate the plant to resist. Whenever these plants are infected with TYLCV, they will be able to produce siRNAs that guide TYLCV RNA degradation, thereby alleviating and reducing its severity. These sequences were designed based on the thermodynamic stability of the produced siRNA. Nonetheless, the efficiency of these sequences requires in vivo evaluation.