It depends, generally, the real-time PCR can distinguish two-fold expression difference, see, Ben Bubner, et al. 2004. Two-fold differences are the detection limit for determining

transgene copy numbers in plants by real-time PCR. therefore, I think if there are at least two-fold difference between the RNAi and the Wild, Real-time PCR should be ok. Real-time principally is quantitative PCR, just follow a standard protocol

to Deyong Zhao ：thank you for your answer！But the RNAi effection offen more than Two-fold differences towards WT. Whether it over the limit?