High Temperature Effect on PNRSV

A possible point of confusion among those that feel that PNRSV is not a "big deal" is that they do not realize that high temperatures also have a negative effect on the health of PNRSV. There is literature evidence that this is true even within the living plant.

      PNRSV infections in Peach have been reported to vary with the season (i.e. temperature). The following is the abstract of the published, refereed paper (please, keep in mind the reversal of our seasons with theirs). I have added bold print  to indicate important sections. Their results are consistent with the casual observations that many have made that, in many roses, the symptoms are observable in the spring but disappear in the summer.

Authors: Dal Zotto, A.; Nome, S. F.; Di Rienzo, J. A.; Docampo, D. M.
Author Address: Instituto de Fitopatologia y Fisiologia Vegetal INTA, 5009, Cordoba, Argentina.
Title: Fluctuations of Prunus necrotic ringspot virus (PNRSV) at various phenological stages in peach cultivars.
Published in: Plant Disease, volumn 83, pages 1055-1057, (1999).
Abstract: " Fluctuations in Prunus necrotic ringspot virus (PNRSV) concentration were researched in single plants of six peach (Prunus persicae) cultivars-Kurakata, Red Haven, Nectar Red, Start Delicious, Meadowlark, and Loadel-by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) of dormant buds (May, June), flowers (September), new sprouts (November), and mature leaves (January) (Southern Hemisphere). The optimum extract dilution (sample weight per buffer volume) to detect the virus was also quantified. The average absorbance patterns of the six cultivars show a steady increase in virus concentration, ranging from A405nm 0.61 in May to A405nm 0.86 in July for dormant buds, to A405nm 1.22 in September in flowers, to 1.53 in November in new sprouts, where the highest concentration was found.  Virus concentrations in mature leaves drop to values similar to those of noninfected plants in January (A405nm 0.12). The yearly average (six noninfected peach trees) ranged from A405nm 0.04 to A405nm 0.08. This drop coincides with an increase in summer temperature and attenuates foliation symptoms caused by PNRSV.
Analysis of dormants buds, flowers, or new sprouts with 5-cm-long leaves was reliable to differentiate infected from noninfected plants. Cluster analysis of absorbance profiles for single plants of cvs. Loadel and Meadowlark, however, showed a comparatively low profile, with a drop at flowering time (A405nm 0.20 in September) close to the average of healthy controls. The difference between infected and healthy plants did not become apparent in all cultivars from the analysis of plants at a given phenological stage, for example by the analysis of flower only, the material most preferred to diagnose the virus. Therefore, plants should be analyzed during flowering and sprouting or flowering and dormancy (dormant buds)."

END OF ABSTRACT

Contrary to early "thinking" plants do have immune systems, how much of this decrease is due only to the higher temperature and how much is due to the combination of the plant's natural defenses being able to overcome the temperature weakened virus, I do not have information about at this time.