2018 ASHS Annual Conference

Producing virus free plants from infected plants is difficult using standard heat treatment/apical meristem excision procedures for virus elimination due to challenging technical aspects of the procedures and less than optimal growth conditions for plant cells. In this study, the use of the antiviral agent ribavirin (RIB) to produce strawberry mild yellow edge virus (SMYEV) free strawberry plants (Fragaria x ananassa Duch.) from infected in vitro cultures was examined. Well developed in vitro strawberry crowns infected with SMYEV grown on modified Murashige and Skoog medium were used for each treatment. For the first treatment, 0.5 µM thidiazuron (TDZ) was added to the medium for 26 days, followed by 26 days with 200 µM RIB but without TDZ. These were then transferred to hormone and RIB free media for plantlet development. For the second treatment, the plantlets were cultured with RIB for 26 days without the TDZ pretreatment, and for the third treatment plantlets were multiplied with TDZ without RIB. After the treatments, plantlets were transplanted to the greenhouse over the next 3 month period of the experiment as they became large enough. A total of 34, 87 and 50 plants from each respective treatment (TDZ then RIB; RIB no TDZ; TDZ no RIB) were grown to maturity during the experiment in preparation for SMYEV testing by ELISA. Initial tests showed 2 (5.9%), 8 (9.2%) and 0 plants negative for SMYEV, respectively. Repeat testing of the putatively virus negative plants reduced the number to 1 (2.9%) and 6 (6.9%) virus negative plants. One plant, #76TDZ, was chosen as an explant donor to initiate new in vitro cultures because it produced numerous runners in the greenhouse suitable for culture initiation. After successful initiation and culture multiplication, five plants from the new culture were established in soilless media in the greenhouse for maturation. These plants subsequently tested negative for SMYEV. The combination of TDZ for rapid in vitro multiplication followed by ribavirin proved to be 2.3 times more effective at producing SMYEV virus free strawberry plants compared to culture without TDZ, and no virus negative plants were developed in the absence of ribavirin. The procedure is less technically demanding than heat treatment/apical meristem culture procedures for virus elimination and may be less likely to produce soma-clonal variants commonly produced from apical meristem culture. It may also be a viable procedure for elimination of additional viruses in strawberry besides SMYEV.