Tomato yellow top virus: Its distribution, characteristics and transmission by the aphid Macrosiphum euphorbiae (Thom.)

Abstract

A study of the virus disease of tomato plants known as tomato yellow top is reported. The spread of the virus in eastern Australia from the Sydney metropolitan area in the period 1952–1960 is summarized and the current geographic distribution of the disease outlined. Symptoms of the disease on tomato plants, including the effect of plant vigour and age, are described. Symptoms on Physalis floridana are also described. Attempts to transmit the virus by mechanical means were unsuccessful, and no seed transmission was observed. The virus was transmitted by grafting and by the potato aphid, Macrosiphum euphorbiae, apterae of which appear to be the principal vector. Under experimental conditions the aphid required a minimum feeding period of 90 min to acquire the virus and 30 min to inoculate healthy seedlings. Optimal transmission of the virus was attained with an acquisition feed of 8 hr and an inoculation feed of 3 hr. Inoculated plants developed symptoms after 18–21 days. Infective aphids were able to cause transmission after moulting, and serially for 10 days without further feeding on infected plants. The virus was thus found to be of the "persistent" type. A weed, Solanum nigrum, is susceptible to tomato yellow top virus, and it is suggested that it is a source of infection for crops of tomatoes.