Studies On Biological Basic Of The Interactions Between Green Rice Leafhopper,Rice Dwarf Virus And Their Host Rice Plants

Rice dwarf virus(RDV),a phytoreovirus in the family Reoviridae,is mainly transmitted by green rice leafhopper(GRLH),Nephotettix cincticeps(Uhler)(Hemiptera:Cicadellidae),in a persistent-propagative manner and is transovarially transmitted to offspring.It infects rice plants,causing considerable damage including stunted growth,white chlorotic specks on leaves,delayed and incomplete panicle exsertion.It has caused great decreases to rice yields in China,Japan,Korea,Philippines,and Nepal.In this paper,RDV and GRLH were used as the main objects to study the effects of RDV-infected rice plants on GRLH growth and development,population,feeding and reproduction behavior,we expect to explore the "double"damage mechanism by RDV and vector GRLH.And we determined the difference of volatiles,amino acids and defense-related genes between healthy and RDV-infected rice plants,trying to reveal the mechanism within the tritrophic relationship.Here,we report on the outcomes of experiments as follows:1 Influence of RDV-infected rice plants on GRLHs biological parameters and population growthCompared with healthy rice plants,nymphal duration and male adult longevity were significantly shorter on RDV-infected TN1 rice plants;male adult longevity and fecundity were significantly longer/higher,female nymphal duration was significantly shorter on RDV-infected Xiushuill rice plants.For the factor of RDV status on two variety,the GRLH biological parameters of female adult longevity and fecundity were significantly longer/higher,nymphal duration were significantly shorter by RDV-infection status.Among the five life table parameters,only net reproductive rates(R0)was significantly affected,but other four life table parameters,intrinsic rate of increase(rm),finite rate of increase(?),mean generation time(T)and population double time(DT)were not largely affected.The GRLH population was growing faster on RDV-infected rice plants and the total number of adults was significantly higher than healthy rice plants at the 4th,5th and 6th month after inoculation,but did not reach the statistically different level at the 7th month.2 Influence of RDV on GRLHs host plant selection preference and oviposition preferenceThe host plant selection preference of non-viruliferous or viruliferous(carrying RDV)GRLHs between RDV-free and RDV-infected plants were tested and they performed different feeding taxis to the rice plants.More non-viruliferous GRLHs were attracted to RDV-infected rice plants,and more viruliferous GRLHs preferred RDV-free rice plants.The results of oviposition preference showed that no significant difference between RDV-free and RDV-infected plants,indicated that RDV posed a negligible risk to GRLH oviposition preference.3 Influence of RDV on GRLHs odor selection preferenceWe used the four-field olfactometer to determine the odor selection preference of GRLHs.RDV-free insects preferred the odor of healthy or infected plants to air and they preferred the odor of RDV-infected rice plants to healthy plants.RDV-infected insects preferred the odor of healthy or infected plants to air and they preferred the odor of healthy plants to infected ones.We considered that plant viruses modify their hosts in this way that enhances their spread and transmission.4 Influence of RDV on GRLHs feeding behaviorUsing an electrical penetration graph(EPG),we determined that infection withRDV in the vector and in rice both altered the vector s feeding behavior.During the 6 h recording period,non-viruliferous GRLHs spent shorter times in non-penetration,much longer time in xylem feeding when fed on RDV-infected rice plants compared with RDV-free rice plants.Viruliferous GRLHs exhibited more salivation and stylet movement on RDV-free rice plants than RDV-infected.These behavior alterations in the vector may have adaptive advantages for RDV transmission,because more viruliferous vectors preferred RDV-free plants and greater salivation and stylet movement by viruliferous vectors on RDV-free hosts will promote virus inoculation,whereas more non-viruliferous vectors preferred RDV-infected plants and more sap ingestion by non-viruliferous vectors on RDV-infected hosts will promote virus acquisition.Our findings have implications for disease and vector management.5 Influence of RDV on the volatile organic compounds,amino acid compounds and the expression level of defense-related genesVolatile organic compounds in headspace of healthy and RDV-infected rice plants were collected and 24 organic compounds were identified by GC-MS.Compared with non-infected rice plants,content of 2-Heptanone,2-Heptanol and ?-Cedrene were largely higher in RDV-infected TN1 rice plants,content of Linalool was largely higher in RDV-infected Xiushui 11 rice plants.Amino acid compounds were also determined between non-infected and RDV-infected rice plants,there were 18 compounds were identified.Compared with non-infected rice plants,content of Ala and Met were largely increased in RDV-infected TN1 rice plants,content of Asp and Met were largely increased,content of g-ABA was largely decreased in RDV-infected Xiushui11 rice plants.We analyzed the virus titer and the expression level of defense-related genes(OsAOSI,OsICS,OsACS2)of RDV-infected rice plants with qRT-PCR at 15 d,30 d,45 d,60 d after inoculation.During the course of 15-45 d,the virus titer was gradually increased,reached its peak at 45 d,and then decreased at 60 d.Influence of RDV on the expression level of defense-related genes indicated that expression of OsICS was up-regulated,while expression of Os AOS1 and OsACS2 were down-regulated.Correlation analysis showed that there were no significant correlation between the expression level of defense-related genes and the virus titer.