|Authors: ||S. Spiegel, R.R. Martin|
Determining the virological status of in vitro grown rosaceous plant material requires, in most cases, removing plantlets from test tubes and growing them out in a greenhouse to fully developed plants which are then indexed by grafting onto virus indicator plants.
Detection of strawberry mild yellow-edge disease (SMYE), among other virus diseases, in strawberry plantlets grown in vitro has followed this procedure.
This is a time-consuming process which causes delays in the release of plant material to breeders and/or growers.
Two approaches were made to detect virus directly in plantlets grown in vitro: a) Leaves were excised, under axenic conditions, from known infected plantlets and grafted onto greenhouse-grown Fragaria vesca indicators.
Following a protocol which resulted in high graft survival, indicators showed typical SMYE symptoms within 20–25 days. b) To detect the filamentous particles associated with SMYE in plantlets grown in vitro by immunosorbent electron microscopy.
Rod-shaped particles were trapped from homogenates of infected plantlets and not from healthy plants by the antiserum made against an expressed fusion protein.
This polypeptide consisted of the putative coat protein of the potexvirus associated with SMYE fused to glutathione transferase in the GEX-1 expression vector.
Blind tests performed with known-infected plantlets from five countries gave positive results consistently.
These results were later confirmed by grafting onto indicators.
It was also found that the concentration of particles in leaf homogenates was higher than in root homogenates.
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