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Title: Characterization of begomoviruses infecting Lycopersicon esculentum L. and metabolite profiling of resistant & susceptible cultivars
Authors: Siddique, Riffat
Keywords: Biological & Medical Sciences
Issue Date: 2017
Publisher: Lahore College for Women University, Lahore.
Abstract: Tomato, an economically important crop is heavily affected by Tomato Leaf Curl Disease (ToLCD) and Tomato Yellow Leaf Curl Disease (ToYLCD), caused by whitefly transmitting geminiviruses (family Geminiviridae; genus Begomovirus). Begomoviruses containing single stranded DNA are bipartite with two genomic segments (DNA-A and DNA-B), mostly found in both areas of biospheres i.e. the New World (NW) and Old World (OW), but thought to be originated from OW viruses. Monopartite viruses (having a single genomic component equivalent to the DNA-A of bipartite begomoviruses) are mostly restricted to the OW, usually associated with alphasatellite or betasatellite. Betasatellites are dependent on DNA-A for encapsidation, replication and are vital for infectivity of several host plants as well as encode for a pathogenicity determinant the βC1 protein. Alphasatellites are selfreplicating and their function in begomoviruses infections is unclear. Begomoviruses among geminiviruses cause great economic losses by infecting various plants. Cultivated Tomato is considered the most appropriate host for the evolution and emergence of monopartite and bipartite begomoviruses as it is widespread and infected by highest number of begomoviruses than any other species. Diversity of begomoviruses associated with recent disease severity of Tomato in various regions of the Pakistan was evaluated during this study. Recent incidences and severity of ToLCD was exploited by collected infected plant samples from major Tomato cultivation areas of Punjab (Lahore and Faisalabad) and Khyber Pakhtunkhawa (KP; Swat, Dir and Malakand) during year 2013-2015. Full length 40 DNA-A, 41 DNA-B components, 19 betasatellites and 05 alphasatellites were cloned, sequenced and submitted into the International DNA databases. Phylogenetic analysis, based on complete nucleotide sequences, identified the presence of 05 begomoviruses, 02 betasatellite and 02 alphasatellite species. The identified begomoviruses species were Tomato leaf curl Kerala virus (ToLCKeV), Tomato leaf curl virus (ToLCV), Papaya leaf curl virus (PaLCuV) Tomato leaf curl New Delhi virus (ToLCNDV) and Tomato leaf curl Palampur virus (ToLCPalV). Isolated betasatellites were Papaya Leaf Curl Betasatellite (PaLCuB) and Cotton Leaf Curl Multan Betasatellite (CLCuMuB). Whereas alphasatellites identified were Tomato Leaf Curl Pakistan Alphasatellite (ToLCPKA) and Okra Leaf Curl Alphasatellite (OLCuA). We humbly claim to identify three begomoviruses (ToLCKeV, ToLCV and PaLCuV) of tomato plant for xiii the first time in Pakistan. Among different strategies being followed to control begomoviruses infection, natural resistance produced by Tomato yellow (Ty) genes has been proved useful. However, single Ty gene containing cultivars did not show broad spectrum resistance, in contrast to two or many Ty genes containing pyramided cultivars which were considered more promising under high disease pressure and were evaluated against Tomato leaf curl New Delhi virus (ToLCNDV). Thirteen Ty resistant cultivars developed by pyramiding Ty-1/Ty-3, Ty-2, Ty-3 and Ty-5 resistance genes in various combinations were analyzed. Ty cultivars and the susceptible native Nagina variety were evaluated for resistance by agro inoculation of bipartite ToLCNDV which is prevalent in Pakistan and is infecting many economically important crops. Results from this study showed that R5, R6, R10, R11 & R13 cultivars showed complete, R2, R3 & R9 moderate, R12 mild, R7 & R8 very less while R14, R15 and Nagina cultivars showed no resistance against ToLCNDV. ToLCNDV DNA-A and DNA-B titer in systemic leaves was determined by Southern hybridization which exhibited comparable virus titer to symptoms severity observed in each cultivar. These resistant and susceptible cultivars were further exploited for metabolites identification by GCMS technique. This analysis led to the identification of various compounds, mainly aliphatic hydrocarbons, diterpenes, triterpenes, phenol, alcohols, esters, fatty acids, aldehydes and ketones etc. The illustrated research was conducted for the better understanding of diversity of begomoviruses and associated satellites, resistance evaluation of Ty cultivars followed by their GCMC analysis. A more detailed understanding of begomoviruses disease complex may allow development of better control methods in future.
Gov't Doc #: 21087
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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