Research On Distribution And Transmission Roots Of Apple Latent Virus In Apple Shoots In Vitro

At present, the apple cultivation area and total production of our country rank the top,but it is low per unit area yield and poor quality. Apple Virus disease is one of theimportant reasons for this phenomenon. Many researchers propose that virus-freecultivation could radically control apple virus diseases. Currently virus-free seedlings aremostly from the tissue culture materials in vitro saved after the detoxification treatments.But in the actual production we find the phenomenon that virus-free seedlings still have thepossibility of virus recrudescence after long-playing preservation and propagation, whichindeed bring hidden danger to the virus-free production in a certain extent. So, if we couldaccurately grasp the expression, distribution, transmission routes of apple latent virus invitro, it would be conducive to clear the appropriate storage condition, prevent thetransmission of viruses and advance the process of non-toxic cultivation conducively. TheFQ-PCR system and RT-PCR system were used to determine the distribution, content,spread of apple latent virus in apple plantlets. The main results were as follows:1. Research on the distribution and content change of ASGV and ACLSV in tissue cultureconditionsP22infected with both ASGV and ACLSV was used as the material and the FQ-PCRsystem was used to detect the expression of the two viruses in different plantlet positions,culture days and temperatures. The results were as follows:(1) In tissue culture conditions the virus relative content differed in different parts, theaccumulation rules were also varied with virus types. The ASGV relative content of the top1cm was the highest, the center1cm followed, the base1cm was the lowest, showed thatASGV was accumulated on the top and center of plantlets. The accumulation rule ACLSVwas on the base and center, the relative content from high to low expressed as the base>the center> the top.(2) Different culture temperatures also have an effect on the content of apple latentvirus in plantlets. The relative content of ASGV and ACLSV from high to low expressed as5℃＞25℃＞32/38℃＞35℃.2. Study on the effects of apple latent virus elimination by alternating heat therapy in vitroFour apple rootstocks and cultivars（Malus xiaojinensis., JAZZ, Malus robusta Rehd., Huahong）infected with ASGV, ACLSV and ASPV were used as materials.32/38℃alternating heat therapy was used to eliminate apple viruses. and the RT-PCR system wasused to detect and real-time track viruses in virus-free plantlets. The results were asfollows:Virus-free seedling by heat therapy still had the possibility of virus recrudescence.The detection sequence was that ASGV was detected firstly, ACLSV followed, ASPV wasthe latest. So it was necessary to detect, real-time track and update virus-free seedlingsregularly.3. Research on the transmission routes of ASGV and ACLSV in tissue culture conditionsIn order to determine the transmission routes and speed of ASGV and ACLSV, P22infected with ASGV and ACLSV and non-toxic plantlets were used as materials and fivekinds of spread ways were simulated artificially. The results were as follows:(1) In tissue culture conditions, the transmission routes of ASGV and ACLSV hadmicrografting, root touch, tools, culture medium and virus sap. In addition, thetransmission risk from high to low were the tendency: micrografting＞root touch＞tools＞culture medium＞virus sap.(2) In tissue culture conditions, whether apple viruses inoculated at the upper end orlower end of the plant ecology,on the fifth day, viruses could be detected near the virusinoculation part. On the tenth day, virus detection rate reached about90.00%. Thetransmission speed of viruses inoculated at lower end was faster than those at the upperend. Compared with ACLSV, ASGV spread faster and had the higher infection rate.