Effects Of Relative Humidity On The Vector Of Rose Rosette Disease, Phyllocoptes Fructiphilus (Eriophyidae), And Incidence Of Disease Symptoms

The eriophyid mite Phyllocoptes fructiphilus Keifer (Acari: Eriophyidae) transmits rose rosette virus to rose (Rosa spp.; Rosaceae) while feeding, which causes serious disease referred to as rose rosette disease. Although there is no cure once rose plants are infected with rose rosette virus, understanding the response of P. fructiphilus and rose rosette disease to abiotic factors such as relative humidity may help to develop management strategies for the disease. The major objective of the current study was to determine the effect of relative humidity on the abundance of P. fructiphilus, as well as the incidence and severity of rose rosette disease symptoms. An experiment was conducted in environmentally controlled chambers where potted pink double knock-out rose plants were maintained at 20, 60, and 95% relative humidity after introducing about 20 P. fructiphilus individuals by attaching a 7-cm-long, field-collected terminal to the branches of potted plants. The densities of P. fructiphilus were recorded at biweekly intervals for 12 wk. The proportion of terminals with rose rosette disease symptoms (disease incidence) and severity of rose rosette disease symptoms was assessed using the Horsfall-Barratt scale at biweekly intervals for 14 wk. The results show that the number of P. fructiphilus individuals was significantly greater under a moderate 60% relative humidity than under a high (95%) or low (20%) relative humidity (P < 0.05). However, the incidence and severity of rose rosette disease symptoms were significantly higher under 95% relative humidity relative humidity regimen than under 20% relative humidity regimen (P < 0.05). The implications of these results on the breeding program and management of P. fructiphilus and the incidence of rose rosette disease are discussed.