Some effects of temperature and of virus inhibitors on infection of french-bean leaves by red clover mottle virus

Keeping French-bean plants before inoculation at 36, 32 or 28 degrees C. for 1-2 days increased their susceptibility to infection with red clover mottle virus, but longer exposures to 36 and 32 degrees C. decreased susceptibility. Susceptibility increased most rapidly at 36 degrees C. The number of infections was unaffected by changes in post-inoculation temperatures between 12 and 24 degrees C., but decreased above 24 degrees C. The rate virus multiplied increased with increase of temperature up to 28 degrees C., but the maximum virus concentrations reached at 18, 24 and 28 degrees C. were very similar and above the maximum reached at 30 degrees C. Thiouracil inhibited infection slightly but neither it nor azaguanine affected the multiplication of red clover mottle virus in French bean. Trichothecin inhibited infection and interfered with virus accumulation. Inhibition of infection was associated with macroscopic injury to the leaves, and washing leaves up to 1 hr. after inoculation prevented both inhibition and leaf damage. Virus multiplication was not resumed when leaves were transferred from trichothecin solutions to water.