The title of this thesis is: "GRAPEVINE FANLEAF VIRUS: BIOLOGY, BIOTECHNOLOGY AND RESISTANCE"

H.Kuska comment: In discussing PNRSV spread or lack of spread in roses, I recommend that the spread studies be done in cool climates as plants have an immune system that operates well at high temperatures but is not as effective at low temperatures. See:
http://home.roadrunner.com/~kuska/high_temperature_effect_on_pnrsv.htm

This thesis has some experimental data that support this temperature dependent immune system model:

"Multiple experiments that iteratively tested individual variables showed that systemic GFLV infection was correlated with lower ambient greenhouse temperatures,....."

"Higher cooling degree days (hotter temperatures) had negative effects on the frequency of agroinfection (Table 4-3). This corresponded to observations that systemic infection was difficult to achieve in the low frame greenhouse in summer when temperatures regularly approached daytime highs of 32�C. In contrast, when temperatures remained close to the set 22�C constantly,
systemic infection frequencies were improved."

http://ecommons.library.cornell.edu/handle/1813/37170