Phytoplasma

Detailed description about phytoplasma and their general characters and examples has been mentioned

1. P hytoplasma N.H. SHANKAR REDDY 2 nd Ph.D. Plant Pathology Annamalai University

2. Phytoplasma are prokaryotic unicellular, gram + ve , pleomorphic and non motile They lack cell wall but bounded by a membrane & have cytoplasm, ribosomes and strands of nuclear materials. Phytoplasmas are mollicutes comes under the division Tenericutes of kingdom Protista.

3. Discovered by Doi et al. (1967) in the phloem of mulberry plants and named as MLO (mycoplasma like organism), later name changed to Phytoplasma in 10 th international congress of mycoplasmology .

4. Properties They belonging to the order Acholeplasmatales , and genus Phytoplasma , is at Candidatus stage. Contains both DNA, RNA along with ribosomes as genetic material, size ranges from 0.17 – 0.25µm Genome size ranges from 530–1350 kb, with low G+C content of DNA (23–29.5 %). Generally, present in sap of phloem sieve tubes. It cannot be cultured on nutrient agar medium, that why it referred called as ‘ Candidatus Phytoplasma’ ( candidatus means cannot be cultured ), but phytoplasma can grow in alimentary canal, haemolymph, salivary glands and different body parts of their insect vectors.

5. Phytoplasma have no flagella, and produce no spores. Cells can be differentiated through bacteriological filter and Koch postulated have not been proved. Two common symptoms of phytoplasma infection are Phyllody (floral parts are converted into leaf like structure), yellowing of leaves (colour of leaves due to disrupt of transport of carbohydrates) Phytoplasma is mainly transmitted by leafhopper (family - Cicadellidae ), but plant hoppers (family - Fulgoridae ) and psyllids are also been reported as vectors. Detected by using PCR (based on 16sr DNA) and fluorescent staining with either the DNA -specific stain 4,6-diamidino-2-phenylindole ( DAPI ) or the callose specific stain aniline blue or Dienes’ stain .

6. Eg – Little leaf of brinjal ( Leaf hopper - Hishimonus phycitis , Amrasca biguttula ) Sesame phyllody (Leaf hopper - Orosius albicinctus ) Grassy shoot of sugarcane ( Leaf hoppers - Saccharosydne saccharivora ) Coconut lethal yellowing (Plant hopper - Myndus crudus / Haplaxius crudus )

7. List of phytoplasma diseases Rice yellow dwarf Rice orange leaf Rice stripe Grassy stunt of Rice Giallume yellows of Rice Potato witches broom Potato phyllody Purple top roll of potato Marginal Flavescence of potato Purple top wilt of Potato Potato Stolbur Sesamum phyllody Little leaf of Brinjal Grassy shoot of Sugarcane Sandal spike Peach X disease Peach yellows Lethal yellowing of coconut Root wilt of coconut Apple Rubbery wood 21. Aster yellows 22. Mulberry dwarf 23. Witches broom of neem 24. Paulownia witches broom 25. Little of eucalyptus 26. Phyllody of marigold 27. Phyllody of Phlox 28. Yellows of Catharanthus roseus 29. Bushy stunt of Grewia asiatica 30. Jujube witches broom . 31. Grapevine yellows 32. Safflower phyllody 33. Rosette of Pegion pea 34. Little leaf of bottle brush 35. Clover dwarf 36. Onion yellow dwarf 37. Sweet potato witches broom 38. Plantago witches broom 39. Bush clover witches broom 40. Sumach witches broom 41. White leaf disease of sugarcane 42. Alfa alfa witches broom 43. Beet yellow wilt 44. Celery yellows 45.Citrus vein – phloem degeneration 46. Cotton virescence 47. Cotton small leaf 48. Groundnuts witches broom 49. Legume little leaf 50. Oat sterile dwarf 51. Pear decline