REVIEW OF STUDIES ON THE CADANG-CADANG DISEASE OF COCONUT

The cadang-cadang of coconut is a blight characterized by die-off of t rees until the patch is laid bare. The symptoms are as follows. Water- soaked spots are produced on leaflets, and the leaves become small as the disease grows severe; the crown of leaves is parted into two group s (a tuft of young leaves and a group of old, horizontal or drooping l eaves), and the stipules are profuse and persistent. On the trunk, the leafscars are far apart in the mild stage but very close together in the severe stage. The fruits are big and profuse in the mild stage; in the severe stage of the disease, the fruits are few, small, misshapen , and scarified. To explore the likelihood that the disease is pathoge nic, field surveys were undertaken designed to follow its spread. The researchers hypothesized that the disease originated in San Miguel Isl and, Tabaco, Albay, and fanned out to outlying areas including the pro vinces of Sorsogon, Camarines Sur, Camarines Norte, and Catanduanes. T his pattern of spread may be mooted. Complementarily, there were exten sive attempts to transmit the disease mechanically and biologically us ing insect vectors. The rare claims of having successfully transmitted the virus (gauged by the production of water-soaked spots on leaflets ) have not been verified. More recently, extensive studies were conduc ted to prove the viroid nature of the disease. The viroid (ccRNA) was characterized biochemically as regards reaction to solvents, behavior in electrophoretic separation, and size of molecule and its structure. On the other hand, the search for a soil constituent as causative fac tor of the disease became focused on the rare earth, especially lantha num. Given in low concentration, lanthanum was beneficial to short-liv ed plants or to young perennials; however, in the long run, perennials got killed late in life by dilute solution of lanthanum.