Phytoplasma

Biology

Phytoplasma belongs wall-less bacterial group (Class Mollicutes). Previously know as mycoplasma like organisms (MLOs), phytoplasma are obligate, phloem-residing plant pathogens. Phytoplasmas were discovered by electron microscopy of ultra thin sections of infected plants by Japanese scientists Doi et al. (1967). These are ranging between 0.2 to 0.8 µm and are too small to be resolved by light microscope. Phytoplasmas are surrounded by tipple-layered plasma membrane and hence have a fluid shape, i.e., they are pleomorphic in nature and changes their shape. The membrane of phytoplasma consists of lipoprotein. Phytoplasmas are although wall-less, they closely related to the Gram-positive bacteria at the genetic level. Because of the lack of cell wall, they are resistant to the peptidoglycan-targeting antibiotics like, penicillin. Phytoplasmas are among smallest know cells and smallest genome of about 680-1600 kb. Their genome consists of both DNA as well as RNA. Little leaf, phyllody, witches' broom, big bud and flower virescence are symptoms of the diseases caused by phytoplasmas. Phytoplasmas parasitize following plants:

Sr.	Plant	Family	Disease
1.	Brinjal	Solanaceae	Little leaf of brinjal
2.	Sesamum	Pedaliaceae	Phyllody
3.	Sugarcane	Poaceae	Grassy shoot
4.	Peach	Rosaceae	Rosette
5.	Potato	Solanaceae	Stolbur of potato
6.	Tomato	Solanaceae	Big bud of tomato

Phytoplasmas are transmitted plant to plants through the insects (leaf hoppers), by seeds and other plant propagating materials and through the dodder.

References

• Doi, Y., Teranaka, M., Yora, K., and Asuyama, H. (1967). Mycoplasma or PLT grouplike microrganisms found in the phloem elements of plants infected with mulberry dwarf, potato witches’ broom, aster yellows or pawlownia witches’ broom. Ann. Phytopath. Soc. Japan. 33, 259–266. doi:10.3186/jjphytopath.33.259