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Tomato Yellow Top Virus: Host Range, Symptomatology, Transmission, and Variability. Sher Hassan, Graduate student, Department of Plant Pathology, Washington State University, Pullman 99164; P. E. Thomas(2), and G. I. Mink(3). (2)(3)Research plant pathologist, USDA, ARS, and plant pathologist, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser 99350. Phytopathology 75:287-291. Accepted for publication 12 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-287.

Tomato yellow top (TYT) is a destructive disease of tomato caused by tomato yellow top virus (TYTV). Terminal growth of field-infected plants is characteristically bright yellow, often with a purplish cast on lower leaf surfaces. Leaflets are ovate, cupped upward with constricted margins, and reduced in size. Blossoms often die and abscise and fruits are frequently asymmetrical. The causal virus was not transmitted mechanically or through seed but was readily transmitted by the green peach aphid (Myzus persicae) in a circulative manner. Symptoms produced by 66 TYTV isolates varied but all produced TYT symptoms on tomato plants, no symptoms or mild potato leafroll (PLR) symptoms on potato, and typical of PLR symptoms on Physalis floridana and Datura tatula. Potato leafroll virus (PLRV) isolates from Washington produced very mild symptoms on tomato, distinct from those of TYTV. Green peach aphid acquired TYTV in a minimum acquisition period of 2.5 hr and transmitted in a minimum access period of 2 hr after a minimum latent period of 20- 24 hr. Aphids retained infectivity for life and the virus was not transmitted transovarialy to offspring. A single aphid routinely transmitted the virus to susceptible hosts and no difference in severity occurred when 5, 10, or 15 aphids were used per inoculation. Based on host range, symptomatology, and transmission characteristics, TYTV appears to be related to, but distinct from, PLRV and beet western yellows virus (BWYV).