ROLE OF CYTOKININS IN THE ACQUIRED RESISTANCE TOWARDS AN INFECTION OF A TNV ISOLATED FROM STRAWBERRY

When plants of Chenopodium amaranticolor were inoculated with a TNV strain isolated from Strawberry (Faccioli 1969, 1974) which caused local necrosis, inhibition of virus biosynthesis was experienced (Faccioli and Rubies-Antonell, 1976), and systemic acquired resistance, towards a TNV challenge inoculation, found (Faccioli 1979). In both inoculated and upper uninoculated resistant leaves an antiviral factor (AVF) was isolated (Faccioli and Capponi, 1980). Sistemic resistance was also acquired by plants which were sprayed in the lower leaves with a 0.01% HgCl₂ solution, also causing necrosis, although in such plants AVF was not detected.

Determination of cytokinin activity by the soybean callus bioassay of Miller (1963) modified by Krasnuk (1971) and the radish cotiledon bioassay of Letham (1971), showed, in both locally infected and HgCl₂-rubbed leaves, a higher cytokinin activity, 3 to 4 days after inoculation (appearance of local lesions).

In particular Letham’s bioassay, which was the most sensitive and less time-consuming test, showed that TNV-inoculated leaves had a cytokinin activity, expressed in mole equivalents of kinetin and zeatin, respectively 7 and 16 times higher than that of buffer-rubbed leaves (control). HgCl₂ treated leaves, with many more local lesions, had an even higher cytokinin activity: 88 and 260 times approximately that of the relative control.

In upper uninoculated or non treated leaves of plants either TNV-inoculated or HgCl₂ treated in the lower leaves, a higher cytokinin activity was also found.

In the former ones such activity was 39 and 56 times higher, and in thelatter about 4 and 5 times higher than upper leaves of buffer-rubbed plants.

TNV challenge inoculation of upper leaves resulted in a 25 to 30% reduction of lesion number when lower leaves of the plants were TNV inoculated 3 to 4 days earlier, or HgCl₂ sprayed 1 ½–2 days earlier.
Virus content of such upper leaves was 26 to 28% less than that of leaves belonging to plants buffer rubbed on the lower ones.

To establish whether or not cytokinin increase was in

III International Symposium on Small Fruit Virus Diseases

G. Faccioli, C. Rubies-Autonell, R. Albertini

https://doi.org/10.17660/ActaHortic.1982.129.5