Scanning electron microscopy detection of phytoplasmas and other phloem limiting pathogens associated with emerging diseases of plants

Scanning electron microscopy (SEM) was applied to detect the phytoplasmas and other phloem inhabiting pathogens associated with some emerging diseases of agricultural crops. The original technique of specimens’ preparation was used to observe the internal structure of phloem tissue. Phytoplasma cells ranging from 400 to 2000 nm were observed in phloem tissue of all analyzed samples of different crops and wild plants with strong foliar malformations and other diverse symptoms of yellow type diseases. Some asymptomatic samples had low concentration of phytoplasmas. In phloem tissue of some samples of Solanaceae (tomato and pepper) along with phytoplasmas groups of geminated particles characteristics of geminiviruses (Geminiviridae) were detected, as well as some rod shaped bacteria. In some samples from diseased citrus species (Rutaceae) phytoplasmas were observed together with large (up to 2500 nm) rickettsia-like bacteria, very similar to those reported for Candidatus liberibacter. A high content of organic and inorganic crystals and starch granules were noted in diseased plants, a phenomenon supposedly related with pathogenic pathway.