Solomon, J.J.2014-07-172014-07-172007-02In : XXI National conference of the Electron Microscope Society of India, RRL, Thiruvananthapuram (17th to 19th December) 1997http://hdl.handle.net/123456789/4220Root (wilt) disease, a non-lethal but debilitating malady of coconut reported over a century ago, now occurs throughout 0.41 million ha in Kerala, South India. It causes annual losses of about 968 million nuts; palms of all age groups are affected. Investigations on the etiology of the disease have failed to produce evidence for the involvement of fungi, bacteria, nematodes, viruses, viroids, protozoa, or nutritional and physiological factors. Ultrastructural studies of juvenile tissues of diseased palms revealed phytoplasmas (mycoplasma-like organisms, MLOs) in phloem sieve tubes. Constant association of phytoplasmas with the disease has been established. Dienes1 and fluorescent staining schedules to detect phytoplasmas were standardized. A sero-diagnostic and a physiological test have been developed for early detection of the disease. Surveys of putative insect vectors on coconut identified a leafhopper, Sophonia greeni, a planthopper, Proutista moesta, and a lace-bug, Stephanitis typica Tingidae, as putative vectors. Phytoplasmas have been detected in the salivary glands of the lace-bug and planthopper following acquisition feeding and incubation on diseased palms. The vector role of the lace-bug has been established; transmission of the disease by the planthopper is under experimentation. Experimental transmission of the disease from coconut to periwinkle, Catharanthus roseus, was achieved through dodder laurel, Cassytha filiformis. Vascular sap collected from healthy and diseased palms was analysed to synthesize a medium for culturing the organism but the phytoplasmas failed to grow in various cell-free media and in chick embryos. However, the organisms could be maintained in tissues of diseased palms micropropagated in vitro in plant tissue culture media. Remission of symptoms observed in significantly higher numbers of tetracydine-treated palms further confirmed the mycoplasmal etiology of the disease.enArticle