Abstract:
Sesame (Sesamum indicum L.), family Pedaliaceae is one of the most ancient cultivated oilseed crops among the edible annual
group in Egypt and all over the world. Phytoplasmas are pathogens of many plant species throughout the world including sesame
causing a large variety of symptoms ranged from mild yellowing to death of infected plants. Symptomatic samples including
green leaf-like floral organs, virescence, phyllody and proliferation were collected from infected sesame field in Giza
Governorate. This research was undertaken to develop a diagnostic tool to identify phytoplasmas recently discovered infecting
sesame in Egypt, and to classify them according to their phylogenetic group. Direct and nested PCR primers of 16S-23SrRNA
gene, paired with phytoplasma universal primer followed by strain-specific PCR primers were used in this study. Spacer Region
(SR) primers were employed for identification of Phytoplasma group associated with sesame symptoms. Results showed the
presences of mixed infections of phytoplasma in the tested sesame samples which collected from the field with different type of
Phytoplasma like symptoms. Results also indicated that polymerase chain reaction with primers from sequencing of 16S-32S
rRNA and from SR opened new paths for research on phytoplasma identification and classification. Nested PCR has been applied
to overcome problems related to sensitivity of phytoplasma detection, although this approach is more time consuming and subject
to template. Unfortunately, nested-PCR also meets some difficulties: unspecific bands, false positives or negatives caused by
DNA and contamination of single or nested PCR. Therefore, confirmation of PCR results by using different primer pair
combinations (generic and group-specific) seems to be the way for correct phytoplasma identification in the examined sesame
