Contrasting effects of resistant and susceptible tomato plants on tomato mosaic virus multiplication

Abstract

SUMMARYMultiplication of tomato mosaic virus (strain of tobacco mosaic virus) in susceptible and in resistant tomato plants was studied by assaying the infectivity and virus content of sap from non‐inoculated leaves on infected plants. In susceptible plants, infectivity and virus particle number increased rapidly to a maximum at about 14 days after inoculation; leaves produced subsequently contained less virus. In resistant plants, no virus was detected in non‐inoculated leaves until 5 weeks after inoculation. Infectivity then gradually increased at a somewhat higher rate than did numbers of virus particles. The concentration of virus in resistant plants remained lower than in susceptible ones. At first the ratio of infectivity to particle number was larger for samples from the susceptible than the resistant line, but the ratio from the resistant line increased slowly until it eventually equalled that from the susceptible one.Virus cultured in either of two lines of tomato with different types of resistance invaded healthy plants of either line more readily than virus cultured in the susceptible variety. Resistant lines seem to select self‐invasive new forms of tomato mosaic virus.