Study on the factors underlying the epidemic of Nicotiana benthamiana co-infected by alfalfa mosaic virus and white clover mosaic virus

The objective was to clarify the factors underlying the epidemic of Nicotiana benthamiana coinfected by alfalfa mosaic virus (AMV) and white clover mosaic virus (WCMV) under indoor conditions. In this experiment, phosphate buffer saline (PBS) inoculation was used as a control, and the effects of different concentrations of AMV and WCMV inoculated alone and in combination, temperature, and relative humidity on the incidence of infection in N. benthamiana and changes in the content of two viruses were studied. The results showed that the most suitable concentrations of AMV and WCMV for infection when inoculated alone were 20% (AMV ꞉ PBS = 1 ꞉ CMV ꞉ PBS = 1 ꞉ 1), respectively, while the most suitable concentrations of the two viruses when inoculated in combination were 75% and 25% (AMV ꞉ WCMV = 3 ꞉ 1), respectively. Thus, co-inoculation of the viruses at these concentrations represented the most suitable condition for the incidence of infection in N. benthamiana. Under AMV and WCMV compound inoculation, the most suitable temperature and relative humidity were 25 ℃ and 60% and the average disease index was 80.12. Compared with AMV and WCMV inoculation alone, the disease index increased by 22.36% and 45.28% and the virus content increased by 2.11 and 1.60 times when N. benthamiana was inoculated with both viruses, respectively. In conclusion, the incidence of N. benthamiana infection was the most serious when the temperature was 25 ℃, RH was 60%, and the compound inoculation concentrations of AMV and WCMV were 75% and 25%.