STUDY OF THE MECHANISM OF RESISTANCE TO POTATO LEAFROLL VIRUS (PLRV) ACCUMULATION IN POTATO CLONE G8107(1)

Post-transcriptional gene silencing (PTGS) has been proposed as a natural mechanism by which plants recognize and degrade foreign nucleic acids, such as virus genomes. It was thought that such a mechanism might underlie the resistance of potato clone G8107(1) to PLRV accumulation. The idea was examined by graft transmission experiment in which, stem segments of potato clone G8107(1) as test plant and those of the cultivar Maris Piper (MP) (susceptible to PLRV) as control, were grafted on top of the stems of a PLRV-infected root sock plant of the cultivar MP. The virus-free scions of the cultivar MP (as receptors) were also grafted on top of both test and control grafts. The results indicated that the amounts of PLRV antigen in the receptor scions grafted on top of either test or control intermediate grafts were not substantially different, indicating that the presence of stem segments of the clone G8107(1) as intermediate graft has not affected the accumulation of PLRV in the receptor scions, grafted on top of them. Apparently, no silencing factor capable of degrading PLRV-RNA has been transmitted from clone G8107(1) to the cultivar MP. Therefore, the putative silencing factors are either not present in this clone or if there are, they are not transmitted. However, because it has been demonstrated that silencing is transmissible, it is less likely that the virus RNA degradation due to a gene silencing mechanism is involved in the resistance of this potato clone to PLRV. It seems more plausible that the inhibition of PLRV replication underlies the resistance rather than virus degradation.