I would like to study the interaction between cassava viruses and a sort of cassava genotypes. I would like to do this by measuring virus concentration. Is it right to call this virus titer/concentration? I am working with RNA viruses.
You can measure the titer in cell culture or in lab animals but the concentration of viral antigens by ELISA etc, concentration of the RNA by Real-Time PCR. It depends what you need for your research...
If you try to study the effect of virus in different hosts genotypes, real-time PCR is more indicated, because you can distinguish small differences in replication and quantify these. I guess, this is a central question in your work ..Good luck!
For doing the viral titre assay............ Plaque forming unit assay or Focus forming unit assay would be a good choice as it gives the count of live infecting particles rather than getting a count of nuclelc acid level from RT PCR which can be seen in non-infectious particles too.
To complete previous response you can also mesure the viral titer by TCID50 method (on vero cells for exemple) if you can detect a CPE with your virus.
The advantage of viral titer by PFU or TCID50 is to quantify replicative virus.