Research On The Elimination Of Latent Viruses In Pyrus Pyrifolia By Thermotherapy And Chemotherapy

Apple chlortotic leaf spot virus (ACLSV), apple stem grooving virus (ASGV) and apple stem pitting virus (ASPV) were the most popular viruses in pear plants. Previous surveys indicated that about 86.3% of pear trees in China were infected by these viruses(Wang et al, 1994). The most efficient measure for the controlling of these virus diseases is planting virus-free germplasm(Wang et al, 2002). In this study, thermotherapy, chemotherapy combined with merstem-tip culture were used for the virus elimination from in vitro Pyrus pyrifolia cv. "Fengshui" . Results were illustrated as following:1. The effect of three thermotherapy measures on the growth of in vitro Pyrus pyrifolia cv. "Fengshui" were compared. Results showed that treatment under 37℃ for 25 to 35 days could seriously inhibit the growth of theses plants, and resulted in the death of most treated plants and the reducing of proliferation rate and plant height. Treatment under 32/38℃ (8h/16h) gave a much lower death rate and the proliferation rate and height of treated plants did not show much difference from un-treated control plants. The effect of treatment under 34℃/42℃ was between these two treatments.2. Viruses of in-vitro plants regenerated from shoot tips of plant treated by thermotherapy were detected by PAS-ELISA and dot -blot hybridization. Results showed that three treatments under different temperatures had similar effect on titers of there viruses in regenerated plants, and the longer treatment period was, the lower the titers of viruses were. The efficiency of virus elimination was different for various treatments. Thermotherapy under 37℃ for 35 days combined shoot tip culture in a size 1mm could eliminate tested viruses. For treatment under 32/38℃, no virus-free plants were obtained. When the treatment temperature was raised to 34℃/42℃, all plants regenerated from shoot tip in a size 0.5mm of plants treated for 50 days were virus free. Results also showed that ACLSV could be more easily eliminated than ASPV and ASGV with a five-day shorten treatment period.3. Based on above results, three pear varieties were treated under 34℃/42℃ for virus elimination. Results showed that these varieties showed different sensitivities to such a high temperature. However, a 100% efficiency of virus elimination was achieved after a 50—60 day thermotherapy period combined shoot-tip culture in a size 0.5mm.4. Ribavirin was used for the virus elimination by adding it to MS medium at different amounts and for different culturing periods, and the growth characteristics and efficiency of virus elimination were evaluated. Plants grown in MS containing ribavirin...