Occurrence, Etiology and Molecular Characterization of Phytoplasma Diseases on Solanum lycopersicum Crop in Egypt
Occurrence, Etiology and Molecular Characterization of Phytoplasma Diseases on Solanum lycopersicum Crop in Egypt
Eman A. Ahmed1, Osama Y. Shalaby2, Emad F. Dwidar2, Samah A. Mokbel1, Ahmed K. El-Attar1
ABSTRACT
Surveys were carried over the course of the 2012 and 2013 in different areas of
tomato-growing fields in Egypt (Giza, Ismailia, Bani-Sweif, Fayoum and Qena) in order
to determine the occurrence and distribution of phytoplasma associated with diseased
tomato plants (Solanum lycopersycum L.), and to identify and classify the phytoplasma
involved. A detection of infected tomato plants, which showed symptoms of big bud,
witches'-broom and phyllody, in all regions of the screened governorates, reacted
positively when assayed by nested polymerase chain reactions (PCR) using universal
phytoplasma-specific primer pairs P1/P7 and R16F2n/R16R2. Similar assays were used
to detect phytoplasma interactions with experimentally host plant. Dienes’ stain was also
used for detection of natural infection of phytoplasma. The phloem of infected tissues
showed scattered area stained bright blue. Different techniques for transmission of
phytoplasma to healthy tomatoes and periwinkles in an insect-proof greenhouse were
tested, including mechanical inoculation, wedge grafting, parasitic plant dodder (Cuscuta
campestris), insects in the family Cicadellidae (leafhopper, Empoasca decipiens) and in
germinated seeds within the fruit, suggesting mechanical inoculation and seedtransmissible
were not feasible while the positive results were obtained by the other three
techniques for host plants with numerous symptoms obtained later. Transmission electron
microscopy (TEM) of experimentally inoculated samples, revealed phytoplasma in the
phloem of most of tested samples. Phytoplasma were observed as rounded bodies,
ranging in size from 200 to 600 nm. The molecular characterization was performed for
three different samples representing the different symptoms of phytoplasma through
cloning and direct sequencing. The DNA sequencing, phylogenetic analysis and the
multiple alignments for the sequences of the Egyptian clones with each other and with the
other sequences of phytoplasma strains on GenBank showed that we may have two
different phytoplasma isolates infecting tomato plants in Egypt.
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July 2014
Vol. 11, Iss. 2, Pages 1-310
