Aphid transmission of cauliflower-mosaic virus

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does not appear. First page follows. Summary ELEVEN SPECIES OF APHIDS that do not multiply on cauliflower plants in nature were demonstrated to be vectors of the cauliflower-mosaic virus, five of them being more efficient vectors than three aphid species that do breed on cauliflower. Of three aphid species that breed on cauliflower under natural conditions, the cabbage aphid, Brevicoryne brassicae (Linnaeus), was a more efficient vector of the virus (in single-insect tests) than the turnip or false cabbage aphid, Rhopalosiphum pseudobrassicae (Davis), and the green peach aphid, Myzus persicae (Sulzer). Natural infectivity of the cabbage aphid was demonstrated. None of twenty-one varieties of cauliflower experimentally infected with the virus by the cabbage and green peach aphids was resistant to the disease. Mechanical inoculation was more efficient than transmission by the cabbage, turnip, or green peach aphid. In tests with hourly transfers, most transmissions occurred within 2 hours after the aphids had fed on a mosaic-infected plant. Aphids acquired the virus in 15 to 25 minutes on a diseased plant (5 to 10 minutes actual feeding time) and transmitted it in feeding periods as short as 5 or 10 minutes. In tests with short feeding periods, most of the transmissions occurred during the first 10 minutes after transfer from the infected plant, but an occasional aphid transmitted the disease during the second or third 10-minute period. The cabbage and green peach aphids recovered the virus from inoculated cauliflower plants many days before the first symptom appeared. Mechanical inoculation of healthy cauliflower seedlings and annual stock plants with the centrifuged virus extract from crushed, infective cabbage aphids produced 18 per cent infection.