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Heat Therapy and Stolon Apex Culture to Eliminate Mild Yellow-edge Virus from Hood Strawberry. R. H. Converse, United States Department of Agriculture, Agricultural Research Service, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331 U.S.A.; E. Tanne, The Volcani Center, Israel Ministry of Agriculture, Bet Dagan 50-250, Israel. Phytopathology 74:1315-1316. Accepted for publication 6 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-1315.

Strawberry mild yellow-edge virus (SMYEV) was eliminated from 4-mm-long stolon apex explants of Hood strawberry plants held at a constant 38 C in a growth chamber. Virus detection in each regenerated plant was by means of leaf graft analysis to a maximum of three indicator plants of Fragaria vesca. The percentage of virus elimination from these explants was directly related to the length of time that they had grown at 38 C. Equation I, which describes this linear relationship (Y = 70.35 - 1.69 X in which Y = arcsin of the square root of the fraction of plants infected with SMYEV and X = number of days at 38 C), predicts elimination of SMYEV from 50% of regenerated, 4-mm-long stolon apices excised from source plants after 15 days at 38 C and 100% after 42 days. SMYEV was also eliminated from regenerated stolon apices 0.25- 4 mm in length from infected Hood plants grown at greenhouse temperatures of 20- 25 C. Equation II, which describes this linear relationship (Y = 4.90 + 17.96 Z in which Y = arcsin of the square root of the fraction of plants infected with SMYEV and Z = explant length in millimeters) predicts elimination of SMYEV from 50% of explanted shoot apices that were 2.25 mm in length and 98.6% that were 100 μm in length. According to this equation, elimination of SMYEV does not occur from all explants from plants grown at ambient temperature regardless of their size. Heat therapy and stolon apex culture contribute independently to freeing explants of SMYEV and therefore can be combined to obtain increased reliability in developing strawberry clones free of SMYEV.