RESISTANCE OF TOMATO INFECTED WITH CUCUMBER MOSAIC-VIRUS SATELLITE RNA TO POTATO SPINDLE TUBER VIROID

Tomato (Lycopersicon esculentum cvs Rutgers and Lichun) plants were fi rstly pre-inoculated either with a cucumber mosaic virus (CMV) isolate containing satellite RNA (CMV-S52) or with a CMV isolate without sate llite RNA, and then challenged 14 days later with a severe strain of p otato spindle tuber viroid (PSTVd). Also, tomato plants transformed wi th CMV satellite cDNA and non-transgenic control plants were directly inoculated with PSTVd. Protection effects were assessed by the observa tion of symptoms and by assay of PSTVd accumulation in tomato plants u sing return polyacrylamide gel electrophoresis and silver staining. Th e results indicated that the satellite-transgenic plants and plants pr e-inoculated with CMV-S52 showed much milder symptoms of PSTVd infecti on than the respective control plants. The concentration of PSTVd RNA in the satellite-transgenic plants and CMV-S52 pre-inoculated plants w as reduced to about 0.02-0.03 of the controls. PSTVd infection did not increase the amount of satellite ds-RNA in plants. It is concluded th at the plant resistance to PSTVd is induced by the presence of satelli te RNA rather than the CMV infection. It is suggested that as there is considerable sequence similarity between satellite RNA and PSTVd, bas e pairings may be a cause of reduction of both symptoms and the accumu lation of PSTVd.