Transmission of GLV by vector aphids, by contact, through seeds, and translocation within the seedling bulbs were investigated. The winged aphids were trapped from the middle of April to the last decade of October by the yellow pans in rakkyo fields. Number of the trapped aphids rapidly increased at the beginning of May until the end of the month. It reached maximum in summer and gradually decreased in September. The predominant vector was Myzus persicae and the second species was Aphis

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... . GLV was transmitted by Myzus persicae at the rate of 10-20 % when it was acquired for 5-60 minutes on the diseased Allium fistulosum, A. wakegi, or A. chinense and then fed for 10-60 minutes on A. chinense. Neotoxoptera formosana also transmitted GLV from A. fistulosum or A. chinense to A. chinense at the rate of 10-30 %. Contact transmission of GLV from leaves of the infected rakkyo to healthy plants was never observed. Seed transmission of GLV in Vicia faba was not detected. GLV reinfected virus-freed rakkyo plants in the fields at 26.7 % in autumn of the same year and at 50.0 % in the next spring. However, the infection by aphids was fairly prevented by using the cheese cloth tunnel coverings. GLV was translocated at the rate of 20-69 % from the bulbs of newly infected rakkyos to the divided bulbs which produced infected divided bulbs without exception in the next generation. All the divided bulbs produced from naturally infected rakkyos were also infected with the virus. ELISA values for different parts of the infected bulbs showed that GLV was more concentration at inner part than outer scales and upper part than lower part in the bulbs. GLV was less concentrated in the bulbs of the newly infected plants than those of naturally infected plants, indicating that the concentration in the bulbs may affect the rate of transmission through division of the bulbs.