DOWN-REGULATION OF GROUNDNUT ROSETTE VIRUS-REPLICATION BY A VARIANT SATELLITE RNA

Symptom production in groundnut plants infected with groundnut rosette Virus (GRV) depends on the presence of satellite RNA (sat-RNA) in the GRV culture, and sat-RNA Variants that induce only mild symptoms are known. One such variant drastically diminished the replication of GRV genomic RNA in infected Nicotiana benthamiana plants. This down-regula ting ability did not involve either of the two open reading frames in the sat-RNA but was controlled by a region near its 5' end, which is r equired for sat-RNA replication. When N. benthamiana plants were inocu lated with GRV and the mild satellite and challenged by inoculation wi th a GRV isolate (YB) containing a sat-RNA that induces yellow blotch symptoms, no symptoms appeared and little GRV genomic RNA or sat-RNA w as detected in the plants, provided the two inoculations were no more than 2 days apart A GRV isolate containing a sat-RNA that neither indu ces symptoms in N. benthamiana nor affects genomic RNA accumulation al so provided protection against yellow blotch symptom production if ino culated before or up to 2 days after isolate YB. However, in this case protection was incomplete and both GRV RNA and sat-RNA accumulated to normal levels. It is suggested that sequences from the mild sat-RNA m ay provide a novel source of resistance against rosette disease. (C) 1 997 Academic Press.