Definition

Phytoplasmas are pleomorphic, prokaryotic cells (they lack an organized and bounded nucleus) microorganisms that lack a cell wall. Mycoplasmas have the following additional characteristics: they have a triple-layer cell membrane, they contain DNA + RNA in the same cell, they contain ribosomes, they reproduce by binary fission.

Etymology ("phyto"). comb. form meaning "plant," from Gk. phyton "plant," lit. "that which has grown," from phyein "to grow".

Etymology ("plasma"). 1712, "form, shape" (earlier plasm, 1620), from L.L. plasma, from Gk. plasma "something molded or created," from plassein "to mold," originally "to spread thin," from PIE *plath-yein, from base *pele- "flat, to spread" (cf. L. planus "flat, level, even, plain, clear," Celtic *lanon "plain," O.E., O.H.G. feld, M.Du. veld "field," Rus. polyi "open," Slavic polje "flat land, field"). Sense of "liquid part of blood" is from 1845; that of "ionized gas" is 1928.

Discussion

There several forms of phtyoplasmas: spheroidal to ovoid, spiral, cylindrical and filamentous.Plant phytoplasmas can not be cultured on artificial media.They are resistant to most antibiotics, but are susceptible to tetracycline.Phytoplasmas are usually phloem-restricted (present in sap). They reproduce by budding or binary fission.They do not produce spores.Most phytoplasmas are transmitted from plant to plant by leafhoppers, but some are transmitted by psyllids or planthoppers.They can reproduce and grow within the bodies of their insect vectors.

Some of the most important diseases caused by phytoplasmas are: aster yellows, apple proliferation, coconut lethal yellowing, elm phloem necrosis, papaya bunchy top, peach X-disease, peach yellows, corn stunt, Dodonea yellows, watercress yellows.

Some symptoms include: vein-clearing, phloem necrosis, bushy tops, distortion, yellowing, stunting.