Please particularly notice the section about temperature dependence. Pages 131-132.

"One trend that was noted throughout all project objectives is the tendency of RRV titer to go below detectable levels in the hot Texas summer months. This change is accompanied by little or no symptom expression and improvements in plant health. Upon further research, it is proposed that a “heat masking” phenomenon (Szittya, et al., 2003) is occurring in summer months (May-August). There are several instances of this effect occurring throughout the project. In field trials, when roses would be PCR tested in March, many times the plants would yield Ct values in the strong positive range for RRV. However, when tested in August or November, very few of the roses would yield a positive result. In the same set of experiments, light RRD symptoms would occur in cooler months (November-March), but would disappear when the temperature began to rise. In transmission experiments, the same effect was noticed, however it was more extreme due to much higher temperatures in greenhouses. The differences in RRV has also been noted in primer sets. I have observed that the RRV(db) primer set (Di Bello, et al., 2017) tends be more sensitive in samples taken in August-March, whereas the primer set RRV2 (Dobhal, et al., 2016) yields more sensitive results on samples in AprilSeptember. While heat masking refers to more external factors, it is also related to changes in RNA silencing (Chung, et al., 2016). In extreme heat, RNA silencing by plants tends to be more effective against viruses, reducing the number of viral particles in plants. RNA silencing is also what provides the heat masking effect as it can allow asymptomatic leaves to emerge at higher temperatures (Chung, et al., 2016). It is proposed that higher temperatures affect a possible suppressor of silencing that is produced by RRV, allowing 132 the host plant’s RNA silencing machinery to be more effective in reducing viral loads in plants. Heat related RNA silencing is also proposed to be part of why known susceptible cultivars of roses remain infected with RRV, yet asymptomatic, for more than 18 months."