Mycoplasma Like Organisms or Pleuro Pneumonia Like Organisms (PPLO)

Abstract

Mycoplasma like Organisms is the smallest of microorganisms causing plant disease. Viruses are acutely small (they can be seen only with the aid of an electron microscope), being composed of nothing more than a protein shell consisting a small amount of genetic material. Plant viruses commonly survive year-round in perennial weeds and trees or insect vectors, and are transmitted to other plants via feeding activities of certain insects, usually aphids, through grafting and by mechanical means. Mycoplasma-like organisms (mycoplasmas, spiroplasmas and rickettsias) are usually considered to be somewhere between bacteria and viruses in size, shape and function. These organisms are the cause of 'yellows' type diseases and are transmitted to plants during leafhopper feeding. Mosaic is characterized by a light green to yellow leaf mottling, usually accompanied by abnormal leaf growth. Vein banding is marked as a light green to yellow band around the leaf veins which may become dark with time. Ring spot forms rings of light green to yellow alternating bands with the normal green of the leaf. Stunting usually accompanies with all of the previous symptoms. Some virus diseases do not show any visible symptoms other than a yield reduction. Many virus and mycoplasma diseases are transmitted from one plant to another by insects, some are transmitted by grafting and others are transmitted by mechanical means. These diseases are found to be difficult to control. Some are controlled by resistant varieties, by using of virus free seed or planting stock, eradicating the alternate host and by controlling the insects that transmit the diseases.