DETECTION OF POTATO-VIRUS-A, POTATO-VIRUS-M, POTATO-VIRUS-S, POTATO-VIRUS-X, POTATO-VIRUS-Y AND LEAFROLL AND POTATO SPINDLE TUBER VIROID FROM TISSUE-CULTURE PLANTLETS USING SINGLE LEAF DISCS

Using enzyme-linked immunosorbent assay (ELISA) and dot-immunobinding assay (DIBA) for potato viruses A (PVA), M (PVM), S (PVS), X (PVX), Y- N (PVYO), Y-O (PVYO) and leafroll (PLRV) and nucleic acid spot hybridi zation (NASH) for potato spindle tuber viroid (PSTVd), virus and viroi d were detected reliably from single leaf discs (6 mm) of tissue-cultu re plantlets. Leaf discs taken from leaf positions (1 to 8) (bottom to top) can be used for detection of all viruses except PLRV where the l ower leaves had higher concentrations of virus than the leaves from th e upper part of the plantlet. Virus cultures were maintained for 1 to 4 years in several potato cultivars. The levels of virus remained repr oducible except for PVM concentration, which was found to be very low in cv. Green Mountain. Using densitometry software, the DIBA spots wer e quantified and results were comparable to A(405) values obtained by ELISA. PSTVd concentration as measured by densitometry from spots of N ASH indicated no loss of viroid over 1-4 years in tissue culture in tw o potato cultivars.