High temperature inactivation of cucumber and alfalfa mosaic viruses in Nicotiana rustica cultures

Cucumber mosaic (CMV) and alfalfa mosaic (AlfMV) viruses could not be detected in Nicotiana rustica tissues cultured at 32 °C for 16–18 days or at 40 °C for 5 days, but infectivity remained high in comparable tissue cultured at 22 °C. Incubation of infected cultures at 28–30 °C resulted in an initial reduction followed by a partial recovery in the infectivity of both viruses. The infectivity of CMV in tissues grown between 12 and 32 °C was highest in cultures grown at 12 °C. Although CMV infectivity was not detected in cultures after 16–18 days at 32 °C, virus was eliminated only after a further 30 days at 32 °C. When cultures were transferred from 32 to 22 °C after shorter treatment periods, infectivity rapidly increased to levels higher than those of infected tissues grown continuously at 22 °C. At 40 °C, CMV was eliminated from infected tissues after 9 days and AlfMV after 7 days. Cultures grown continuously at 40 °C deteriorated rapidly but, when grown under diurnal alternating periods of 8 h at 40 °C and 16 h at 22 °C, they remained viable and CMV was also inactivated.