Factors Affecting Synergistic CMV/LSV Co-infection on Nicotiana benthamiana and Lilium davidii Duch

Objective Factors affecting the synergism of co-infection of cucumber mosaic virus (CMV) and lily symptomless virus (LSV) on Lilium davidii Duch in comparison to Nicotiana benthamiana were studied.

Methods  CMV and LSV virions purified from diseased lily plants were used to infect N. benthamiana and L. davidii by the friction inoculation and DAS-ELISA methods. Same concentration, temperature, relative humidity, and sequence of CMV and LSV inoculations optimal for a synergistic effect on N. benthamiana were applied on L. davidii. Relative expressions of the two viral coat protein (CP) genes in the inoculated new leaves of the plants were determined with synergistic effect examined by RT-qPCR.

Results The optimum synergistic effect was observed by using 3.57% CMV and 12.50% LSV CMV ( 14.29 % ) and LSV ( 16.67 % ) to inoculate CMV 48 h prior to LSV at 25°C and 60% RH. Disease symptoms appeared sooner on the co-infected plants than those individually inoculated with CMV or LSV. The major symptoms included 重度花叶、失绿 (loss of green color?)、明脉 and curled leaves on top of the plants during the late growth period. The contents of CMV and LSV in the infected plants were 10.37 ng·mL^-1 and 3.66 ng·mL^-1, respectively, which were 1.45 and 1.11-folds those in the plants of single infection. The CMV content was significantly higher than LSV, as CMV being the passive synergistic virus, while LSV is the synergistic virus. After inoculating in lily scales and being cultured under the optimal conditions for 60 d, the relative expression detected by RT-qPCR on CMV-CP in the new leaves of L. davidii co-infected with the two viruses was significantly higher than those on LSV-CP or CMV-CP and LSV-CP in the leaves of lily plants infected by the two viruses individually. The co-infection synergisms on L. davidii and on N. benthamiana appeared to be identical.

Conclusion N. benthamiana and L. davidii inoculated with 3.57% CMV for 48 h followed by 12.50% LSV at 25°C and 60% RH were shown to have the same synergism. The contents of the two viruses were higher in co-infected plants than those in single inoculated counterparts, and the passive synergistic CMV significantly increased in concentration in comparison to the synergistic LSV.