| Tobacco is an important economic crop in China.Virus diseases and aphids are important pests of tobacco,and Myzus persicae is efficient vector of potato virus Y(PVY).These pests seriously affect tobacco yield and quality.The number of tobacco germplasms preserved in China is more than 5000,but the resistance of most tobacco germplasms to aphids remains unknown.There is no systematic data on tobacco resistance to aphid in China.The effect of virus-infected tobacco on vector aphid and the mechanism of tobacco resistance to aphid are not clear.In order to clarify the interaction between tobacco-mediated aphids and aphid-borne virus diseases,and to explore whether tobacco resistance was affected by virus infection and the physiological mechanism of tobacco resistance,we used tobacco,M.persicae,PVY,and the newly identified Tobacco yellow virus(TYV)as the research systems.We studied the transmission mode and damage of TYV,the effects of two virus diseases on M.persicae behavior,ecological fitness,and the activation of tobacco defense system caused by M.persicae and virus diseases.Through the study,the resistance level of some tobacco varieties was identified,and the effects of two viruses on host selection behavior,growth,development and reproduction of M.persicae were clarified,and the early signal events in tobacco defense response induced by M.persicae were detected.These results could provide a scientific basis for tobacco resistance breeding and control of aphid-borne virus diseases.The main results are as follows.1.Identification of tobacco variety resistance to aphidTobacco resistance to aphids was identified by the aphid index method through a field experiment.The results indicated that different tobacco varieties showed significant differences in the resistance to M.persicae according to the quantity of aphid population in the field.Among the 69 tested materials,27 highly susceptible varieties were identified.accounting for 39.13%of all tested materials,and 14 highly resistant varieties were identified,accounting for 20.29%of all tested materials.Among the tested materials,there were 6 resistant varieties,7 moderately resistant varieties and 15 susceptible varieties.2.The transmission mode and damage of TYVThe transmission mode of the newly identified TYV and its effect on tobacco growth were determined.TYV could be transmitted by M.persicae.Tobacco plants infected by TYV showed symptoms such as leaf yellowing,leaves becoming smaller,and plant dwarfing.The number of TYV virions varied significantly with infection time,and virion replication reached its peak at 11～3 6 days after infection,then descend.3.Effect of TYV-infected tobacco on Myzus persicaeTobacco infected with TYV had significant effects on the reproductive characteristics and host selection behavior of M.persicae,and the effects at different infection stages also varied.The developmental duration of M.persicae fed on tobacco infected with TYV for 2 weeks was significantly shortened,the fecundity was significantly enhanced,and the reproductive period was significantly prolonged.Tobacco infected with TYV for 4 weeks had no significant effect on the developmental and reproductive periods of M.persicae,but the fecundity of the aphids was significantly reduced.After 2-3 weeks of TYV infection,the population quantity of apterous and alate aphids was significantly higher on TYV-infected plants than on healthy tobacco.Aphids preferentially selected tobacco plants infected with TYV for 2 and 4 weeks instead of healthy tobacco plants,but alate aphids that chose plants infected with TYV for 4 weeks migrated to healthy tobacco plants after 24 h.4.Effect of PVY-infected tobacco on Myzus persicaeTobacco infected with PVY had significant effects on body size,reproductive characteristics.Five morphological indexes—body length,body width,head width,cornicle length,and distance between the cornicles—of M.persicae fed on PVY-infected tobacco decreased significantly in comparison with M.persicae fed on healthy tobacco.There was no difference of the number,length,and width of the embryos,compound eyes spacing of the embryos of M.persicae between PVY-infected and healthy tobacco.There was no difference of the net reproductive rate(R0),mean generation time(T),intrinsic rate of natural increase(rm),and finite rate of increase(λ)of M.persicae between PVY-infected and healthy tobacco.EPG recordings showed that the time spent on the plant before the first probe,the duration of the first probe,and number of probes during the first hour increased significantly when M.persicae were fed on PVY-infected plants rather than non-infected plants.This finding indicated that the frequency of transient intracellular penetration of aphids in PVY-infected tobacco increased significantly over a short period.PVY-infected tobacco did not affect the feeding of M.persicae in the phloem.The leaf disc test showed that in a 5 h experiment,when presented simultaneously with PVY-infected and healthy tobacco leaves.M.persicae preferred to feed on the PVY-infected leaves.With increasing experiment time,aphids that colonized the PVY-infected leaves gradually relocated to the healthy leaves.The results showed that M.persicae preferred PVY-infected tobacco,and PVY-infected tobacco was beneficial to the host selection of M.persicae,and the increase in stylet penetration behavior of M.persicae may contribute to the acquisition and transmission of PVY.5.Emergence of Aphidius gifuensis promoted the PVY transmission by Myzus persicaeThe leaf disc test showed that the emergence of A.gifuensis enhanced the activity of M.persicae and significantly promoted the dispersal of M.persicae from PVY-infected leaves to healthy leaves.The cage test showed that A.gifuensis could significantly improve the transmission efficiency of PVY.On the 14th day after aphid inoculation,the incidence of PVY in tobacco treated with and without A.gifuensis was 79.17%and 50.00%,respectively.The above results proved that A.gifuensis could promote the transmission of PVY.6.Changes of calcium,hydrogen peroxide and antioxidant enzymes in tobacco induced by aphid feedingMyzus persicae feeding can induce defense responses in tobacco.We measured the transmembrane ion(Ca2+)and hydrogen peroxide(H2O2)fluxes by non-invasive micro-test technique(NMT),and also measured the activity of peroxidase(POD)and catalase(CAT)in susceptible and resistant tobacco varieties(G140 and Shai92414,respectively)fed upon by M.persicae.The results showed that M.persicae could induce changes in the flux velocity and direction of Ca2+ and H2O2 in healthy tobacco during a specific period after aphid feeding.After 2 h of aphid infestation,the Ca2+of G140 showed influx,while that of Shai92414 showed efflux,and H2O2 of G140 showed efflux,while Shai92414 showed influx.Ca2+ showed influx and H2O2 showed efflux 15 h after aphid infestation.Aphid feeding could still induce Ca2+ influx in PVY-infected tobacco,and there were differences among different varieties.Influx velocity of G140 Ca2+ was higher than that of Shai92414.There were some differences in enzyme activity among different aphid-resistant varieties.The POD activity of Shai92414 was higher than that of G140 when tobacco was not infested by aphids,and the CAT activities of the two varieties were similar.The CAT enzyme activity of G140 was higher than that of Shai92414 when tobacco was infested by aphids,but there was no significant difference in POD enzyme activity between the two varieties.In summary,there are differences in the tobacco resistance level to aphids among tobacco varieties.TYV can be transmitted by M.persicae.Tobacco infected with TYV or PVY has significant effects on growth and development,reproductive characteristics,and host selection behavior of M.persicae,and these effects contribute to the spread of the virus.PVY or TYV-infected plants attract M.persicae and promotes the transmission of the two viruses.Aphidius gifuensis enhances the dispersal behavior of M.persicae and has a potential effect on the spread of PVY.After aphid feeding and virus infection of tobacco plants with different aphid resistance levels,there are significant differences in Ca2+and H2O2 fluxes and antioxidant enzyme activities related to defense response in tobacco plants,which may be the reasons for the difference in aphid resistance of tobacco varieties. |
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