Abstract
Two isolates of Cucumber mosaic virus (CMV), CMV-wild tobacco (from Alexandria governorate) and CMV-cucumber (from Kafr El-Sheikh governorate) were investigated in this study. Cytological studies on epidermal strips of Nicotiana glutinosa leaves separately infected with each isolate revealed the presence of viral crystalline inclusion bodies within the infected cells. Electron microscopy of ultrathin sections of CMV infected N. glutinosa leaves showed significant alterations in the shape and internal structure of chloroplasts. The cell wall had serrated edges in infected cells but was more severe in cells infected with CMV-wild tobacco isolate compared to those infected with CMV-cucumber isolate. CMV-cucumber isolate was partially purified from systemically infected leaves of N. glutinosa. The ratio A260/ 280 was 1.0 and the concentration of the virus in the preparation was estimated using an extinction coefficient of E260nm0.1%, 1cm = 5. Yield of purified virus was about 2.8 mg/100 g fresh weight of infected N. glutinosa leaves. Electron microscopy of the purified preparation of CMV showed the presence of numerous spherical particles with a mean particle diameter of 28 nm. Amplified real-time reverse transcription-polymerase chain reaction (qRT-PCR) product of coat protein gene of each isolate was purified and sequenced. Sequences of both isolates had been submitted to GenBank Database and ware assigned accession number (LT669766) for CMV-cucumber isolate and (LT706517) for CMV-wild tobacco isolate. The sequences were edited using Chromas Pro. Version 1.34 software and compared with previously subgrouping of 27 isolates of the virus retrieved from the GenBank database. Both CMV-wild tobacco and CMV-cucumber isolates were closely related to the isolate with the accession number AJ585086 with a similarity of 97.07% and 98.54%, respectively, suggesting that the two isolates belong to subgroup II. According to the available literature, this is the first report in Egypt where CMV isolates belonging to subgroup II have been obtained
Highlights
Cucumber mosaic virus (CMV) is a member of the family: Bromoviridae and genus: Cucumovirus (Sastry et al, 2019)
Histological and cytological changes induced by CMV Examination of inclusion bodies by light microscopy Crystalline inclusion bodies (CIB) were observed in the epidermal strips from the lower surface of N. glutinosa leaves infected with each CMV isolates (12 days post inoculation DPI) by following standard method (El-Baz, 2004; Megahed, 2008; Taha, 2010)
Histological and cytological changes induced by CMV Careful examination of epidermal strips and ultrathin sections of N. glutinosa leaf tissues separately infected with either CMV-cucumber isolate, or CMV-wild tobacco isolate and phosphate buffer mock-inoculated healthy leaves, by both light microscopy and transmission electron microscopy, revealed the occurrence of a number of cytological and histopathological changes as described hereunder
Summary
Cucumber mosaic virus (CMV) is a member of the family: Bromoviridae and genus: Cucumovirus (Sastry et al, 2019). Numerous strains of CMV have been reported from all over the world classified into two major subgroups, I and II, based on serology and nucleotide sequence homology (Owen et al, 1990; Hull, 2002; Sulistyowati et al, 2004), host reaction (Daniels, 1992), and restriction fragment length polymorphism (RFLP) (Sialer et al, 1999). These two subgroups, I and II, generally show about 75% sequence similarity, whereas strains in the same subgroup show 90 - 99% sequence identity (Takeshita et al, 2004). Attempts were made to reveal the likely presence of CMV isolates belonging to subgroup II among those subjected to this study
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