Molecular Characterization of Cucumber Mosaic Virus and Structural Changes of Infected Sugar beet Plants
Molecular Characterization of Cucumber Mosaic Virus and Structural Changes of Infected Sugar beet Plants
Samah A. Mokbel, Eman A. Ahmed, Hanan F. El-Kammar, Ahmed A. Kheder
ABSTRACT
Background: Cucumber mosaic virus (CMV) is known to occur in sugar beet plants in Egypt and may
produce severe damage to infected plants. However, studies on the effect of the CMV on the cellular
and internal structures of sugar beet leaves were rare.
Methods: The CMV was isolated from sugar beet samples collected during November 2018 from the
Fayoum governorate, exhibited symptoms of mosaic and leaf malformation. Detection was performed
depending on the presence of specific antibodies against CMV, and isolation from local lesions on
Chenopodium amaranticolor as a local lesion host. Eleven plant species belonging to four families
were used to confirm the presence of CMV in the inoculum. Detection of the coat protein gene of
CMV in infected leaves has been done by reverse transcriptase-polymerase chain reaction (RT-PCR),
and the appearance of 678 bp bands confirmed the expected size of such gene. Light and transmission
electron microscopy were used to study the cytological and histological changes that occurred in the
leaves of the sugar beet plant by the pathogen, as well as, to determine some morphometric parameters
such as upper and lower epidermis thickness, midrib thickness, blade thickness, palisade tissue
thickness, spongy tissue thickness, height and width of the vascular bundle.
Results: Phylogenetic analysis results indicated that SEA-CMV-isolate under study (acc. no.
MT491996) closely related (99.9%) to Beet-EG-CMV-isolate (JX826591), isolated from sugar beet
plants from Kafr El-Sheikh governorate, Egypt during 2012. Results of sequence analysis confirmed
the classification of isolate SEA as a member of group IA. Infection of sugar beet leaves with CMV
resulted in the formation of amorphous inclusion bodies in the cytoplasm. Semi thin-sections of the
diseased sugar beet leaf blade showed changes in cellular organization and vascular bundles that reflect
the progression of the external symptoms. Electron micrograph showed isometric spherical virus
particles, measuring approximately 28 nm in diameter. Ultrathin sections showed chloroplast
malformations. The malformation appeared as a chloroplast broken envelope with the presence of
numerous long starch globules. Ultrathin sections revealed the virus-like particles filled the nucleus
while those in chloroplast formed a distinctive crystalline shape. The shape of the cell walls and the
structures of mitochondria changed under the effect of CMV in most cells.
Conclusion: The results demonstrate that the virus possesses dangerous effects that reduce the
functions of the chloroplasts in sugar beet plants that may perturb the photosynthesis in chloroplasts
and the synthesis of ATP in mitochondria. The results also show that the virus exerted influence on all
investigated parameters. The present study provides useful information for the cytological effects and
structural changes in sugar beet cells resulting from CMV infection.
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July 2020
Vol. 8, Pages 1-27
