Effect Of Two Viruses Infection On The Growth And Physiological And Biochemical Characteristics Of Pear Plants

Virus infection is common in commercially cultivated pear(Pyrus spp.)trees.Apple stem grooving virus(ASGV)and Apple stem pitting virus(ASPV)are two important viruses infecting pear trees and naturally dispersed by using virus-infected materials.Currently,the application of certified virus-free plants is considered to be the most effective way to control pear viral diseases worldwide.To understand the effect of virus infection on the growth,physiology and biochemistry,in this study,virus-free and virus-infected of in vitro and in vivo cultured pear plants were used as materials and their growth speed,root development,enzyme activity and phytohormone levels were comparatively investigated.Results are listed as follows:1.The plant height and proliferation amount of virus-infected and virus-free in vitro cultures of four pear cultivars,including Pyrus pyrifolia cv.Jinshui no.2,P.communis cv.Confenence,P.communis cv.Red Clapp Favonite,and P.sinkiangensis cv.Korla were comparatively measured in this study.Results showed that the co-infection of Apple stem grooving virus(ASGV)and Apple stem pitting virus(ASPV)significantly decreased the growth and proliferation of in vitro plants of Confenence,but the single infection of ASGV or ASPV had less effect for that of Jinshui no.2,Red Clapp Favonite and Korla.Meanwhile,the rooting ability of Jinshui no.2 and Confenence was tested.Strong inhibition of ASGV infection to root development was observed for in vitro plants of Jinshui no.2,but not for Confenence.2.The total chlorophyll content and the activities of three enzymes GS,SOD and POD in the above virus-free and virus-infected in vitro cultures of four cultivars were determined.Results showed that the chlorophyll content in virus-free cultures was higher than that in virus-infected cultures of corresponding cultivar.Moreover,the difference was significant in virus-free and virus-infected cultures of Jinshui no.2 and Confenence.The effect of viruses on the activities of GS,SOD and POD differed among different cultivars.The activities of GS,SOD and POD significantly increased in ASGV-infected Jinshui no.2 cultures.Whilst,only SOD activity was induced by ASGV in Red Clapp Favonite.The co-infection of ASGV and ASPV in Conference increased the activity of GS.However,ASPV infection did not affect the activities of the above three enzymes in Korla.3.The IAA,CTK and ABA titers in short tips,stem bases and rooting regions of virus-free and virus-infected cultures of Jinshui no.2 and Conference were examined using high performance liquid chromatography.The expression level of CTK was tested using qRT-PCR.Results showed that during root induction period,ASGV infection significantly increased CTKs/IAA ratio and decreased IAA/ABA ratio in the rooting region of in vitro plants of Jinshui no.2.Nevertheless,for in vitro plants of Confenence,these values were rarely influenced by ASGV and ASPV infection.The result indicated that the changes of CTKs/IAA and IAA/ABA ratios might be responsible for rooting inhibition of in vitro plants of Jinshui no.2.The result was in consistent with CKK levels in the corresponding cultures.These results indicated that ASGV infection significantly altered the levels of CTKs/IAA and IAA/ABA in the rooting region of Jinshui no.2 stems,which might be responsible for serious inhibition to root development.4.The growth,chlorophyll content and activities of three enzymes GS,SOD and POD in 1-3 year old virus-free and virus-infected plants of Hohsui,Confenence and Red Bastlett were comparatively analyzed.It was found that virus infections decreased plant height,stem diameter and the development of new branches,and the effect was more serious on Hohsui plants.However,chlorophyll content and activities of three enzymes GS,SOD and POD varied depending on pear cultivars,virus species and growth periods of plants,but not directly related to virus infections.