INVESTIGATION OF CHRYSANTHEMUM VIRUSES 1. ASPERMY FLOWER DISTORTION

Tomato aspermy virus alone distorted some chrysanthemum flowers, and aggravated symptoms produced by other chrysanthemum viruses. First-season infection affected only a proportion of the blooms; in subsequent seasons nearly all flowers showed symptoms with increased severity. TAV had a wide host range, and was transmitted by five species of aphid infesting chrysanthemums. Infectivity was non-persistent in aphids. Negligible spread of TAV occurred by propagation methods, and the virus was not transmitted through seeds or soil. The physical properties were similar to other non-persistent mosaic-type viruses. No protection was found in tests with three strains of cucumber mosaic virus, or with five other viruses. Comparison of TAV with four strains of CMV showed that TAV differed more from the CMV strains than the latter did among themselves. Suggested control measures include thorough rogueing of chrysanthemum stocks at flowering time, care in selecting new 'sports', and control of aphids, especially early in the season.