Characterization of the Different Electrophoretic Forms of the Cadang-Cadang Viroid

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Abstract
The relationship between symptom development and changes in the fast and slow electrophoretic forms of the 2 cadang-cadang disease-associated RNA (ccRNA-1 and ccRNA-2) has been examined. The fast form of each is present in trees for up to 2 yr before the appearance of symptoms, indicating an incubation period of .apprx. 2 yr. Trees showing the first symptoms (on the nuts) contain only the fast form of the ccRNA; the development of leaf symptoms coincides with the first detection of the slow form. After this time, both slow and fast forms are found in the newly developing fronds for the next 9-12 mo. but then, as symptoms develop, new fronds contain only the slow form. Thus, at later stages of disease, only the slow form can be detected in all fronds. The fast form of ccRNA-1 and/or ccRNA-2 thus appears to be the infectious form in nature. The number of nucleotides in the 4 ccRNA as determined by polyacrylamide gel electrophoresis under denaturing conditions are ccRNA-1 fast, 250; ccRNA-1 slow, 300; ccRNA-2 fast, 500; ccRNA-2 slow, 600. On the basis of 2-dimensional fingerprints of RNase A and T1 digests of the 4 ccRNA, it was concluded that the ccRNA are composed of repeated sequences of ccRNA-1 fast, and each of the ccRNA-2 forms is a dimer of the respective ccRNA-1 form.