Reasearch On Virus Elimination From Pear By Two Chemical Reagents Combined With Thermotherapy And The Rooting And Transplanting Of In-vitro Pear Cultures

Pear trees are commonly infected by three viruses Apple chlorotic leaf spot virus, Apple stem grooving virus and Apple stem pitting virus. These viruses are naturally disseminated by infected propagating materials. Their insect vector is unknown. Therefore, the development of virus-free germplasm and cultivate virus-free plants is the most effective measure for the control of these viral diseases. In order to construct a effective virus elimination system suitable for different pear germplasms, in-vitro cultured pear plants infected with latent viruses were used as materials for the evaluation of the virus elimination efficiency of quercetin and ribavirin treatment combined with thermotherapy. Meanwhile, the media suitable for the rooting of in-vitro pear cultures and the transplanting of rooted pear plants. Results as follows:1. The in-vitro plants of Pyrus communis L. cv.’Starkrimson’ and ’Red Bastlett’ were used as materials. Those plants were pretreated by in quercetin solution, and then transplanted onto the MS media containing different quercetin at different concentrations, and cultured at room temperature,35℃and32/38℃, respectively. The results of virus detection by RT-PCR showed that quercetin alone or quercetin treatment combined with thermotherapy at relatively low temperature can not eliminate ASPV and ASGV.2. The in-vitro plants of Pyrus communis L. cv’Red Bastlett’were used as materials, transplanted onto MS media containing both quercetin and ribavirin at different concentrations, and cultured in a growth room or under themotherapy at35±0.5℃. Results showed that those treatments had no significant effects on in-vitro pear plants excerpt those combined with thermotherapy reducing the growth of some plants. Shoot tips about0.5mm long were cutted from those plants treated for different perids to regenerate new plants. These plants were subjected to virus detection by RT-PCR after two cycle culture. Results showed that the the MS medium containing both10μg/ml quercetin and20μg/ml ribavirin combined with thermotherapy could greatly improve the virus elimination efficiency. Plants regenerated from shoot tips treated under the conditions for40days were ASPV and ASGV free, and the virus elimination efficiency was100%. Futhermore, in-vitro plants of10cultivars were treated by the method. It was also found that the treatment have no effect on the growth of most cultivars excerpt that the height and proferlitaration were slightly reduced. Virus detection by RT-PCR showed that all regenerated plants were ASPV free. The ASGV elimination rate was87.5%for’Xuehua’and’Conference, and75%for ’Jinxiang’. The ASGV elimination rate for all other cultivars were100%.3. Two media:1/2MS+2.5mg/1IBA+1.5mg/1NAA and1/2MS+0.5mg/1IBA+2.0mg/LNAA were selected out for the rooting of in-vitro plants of Pyrus pyrifolia (Burm.f.) Nakai ’Jinshui2’ and Pyrus communis L.’Red Bastlett’, Respectively. Futhermore, a medium contain clay:vermiculite:nutrient soil:turf=1:1:1:1was selected for the transplantation of rooted in-vitro plants of’Jinshui2’, and the survival rate of those plants was about20%at20days post transplantation.4. The effects of virus infection on rooting of in-vitro pear plants were evaluated by using virus-infected and virus-free in-vitro cultures of’Jinshui2’,’Red Bastlett’,’Conference’as materials. Results showed that the effect entensity of virus infection on the rooting of was cultivar depended. The in-vitro plants of virus-infected’Jinshui2’’ failed to root. The virus-infection significantly reduced the rooting rate, the avarege root length and amout of roots of in-vitro culture’Red Bastlett’ plants. However, the rooting of’Conference’ in-vitro plants was less effected by the virus infection.