The adaptation of tomato mosaic virus to resistant tomato plants

Tomato mosaic virus derived from susceptible tomato plants (the standard virus) was cultured in resistant plants. Sap from non-inoculated leaves of resistant tomato plants infected with virus from the resistant host was more infective and contained more virus particles than leaf sap of resistant plants infected with the standard virus. Leaves of resistant tomatoes infected with virus from the resistant host also showed more obvious symptoms. Susceptible plants infected with virus from resistant plants not only showed fewer symptoms than when infected with standard virus, but samples were less infective and contained less virus up to 26 weeks, when values for infectivity were similar. This modification in activity was not reversible and was obtained with two lines of tomato having different types of resistance. Passage of virus from resistant plants through susceptible plants did not impair its ability to infect resistant plants.     

The epidemiology of tomato mosaic: Sources of TMV in commercial tomato crops under glass

Of the several possible sources of tomato mosaic virus, seeds and root debris in the soil are considered to be of greatest importance. A survey of 374,000 seedlings on ten commercial holdings found 0.05% of them infected, and although these were removed virus had been spread to other young plants which did not show infection when transplanted into the growing houses, seven of twenty-two of which contained a few infected plants when sampled shortly after planting. Virus overwintering on clothing, and debris on structures, are thought to be of minor importance, and smoking tobacco is seldom a source of infection for the tomato crop. A further survey of seventy-eight samples from tomato crops in Britain confirmed the 1960-61 survey: all were infected with tomato strains of TMV, none with tobacco strains, but one of the 187 infected seedlings referred to above was carrying a tobacco strain. Petunia was not as satisfactory as a special cultivar of White Burley tobacco for distinguishing between the tobacco and tomato TMV isolates. Observations and tests on a commercial holding showed that TMV was readily carried from plants in infected glasshouses into clean ones by workers, and once introduced, spread rapidly within the crop.     

Strain changes in populations of tobacco mosaic virus from tomato crops

The incidence of tobacco mosaic virus (TMV) Strain 1 in tomato crops of TMV-susceptible cultivars increased from 12% in 1971 to 64% in 1974. This change coincided with the introduction of cross protection to reduce the effects of tomato mosaic. Of the isolates collected from nurseries where the technique was used in 1974, 94% were of Strain 1 compared with 39 % from the other nurseries. No new strains were found and all the isolates were tomato forms of TMV.     

Detection of Tobacco mosaic virus and Tomato mosaic virus in pepper and tomato by multiplex RT-PCR

Aims: To develop a highly sensitive and rapid protocol for simultaneous detection and differentiation of Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV) in pepper and tomato. In this study, we use the multiplex PCR technique to detect dual infection of these two viruses. Methods and Results: A multiplex RT–PCR method consisting of one‐tube reaction with two primer pairs targeted to replicase genes was developed to simultaneously detect TMV and ToMV in seed samples of pepper and tomato. Specific primers were designed from conserved regions of each of the virus genomes, and their specificity was confirmed by sequencing PCR products. RT–PCR detected up to 10^?6 dilution of total RNA extracted from infected leaves. Multiplex RT–PCR revealed the presence of both TMV and ToMV in three of 18 seed samples of tomato and one of 18 seed samples of pepper. Conclusions: The multiplex PCR assay was a cost effective, quick diagnostic technique, which was helpful in differentiating TMV and ToMV accurately. Significance and Impact of the Study: The multiplex PCR assay described in this study is a valuable tool for plant pathology and basic research studies. This method may facilitate better recognition and distinction of TMV and ToMV in both pepper and tomato.     

Strain-genotype interaction of tobacco mosaic virus in tomato

The symptoms and virus content of isogenic tomato genotypes differing by three tobacco mosaic virus (TMV) resistance factors, Tm-I, Tm-2 and Tm-2², were studied in relation to various isolates of TMV and four strains were identified. The common strain induced no symptoms on plants with any of the factors for resistance, one strain caused symptoms on Tm-I plants, one on Tm-2 plants and one on both Tm-I and Tm-2 plants and also on Tm-I Tm-2 plants. No strain induced symptoms on Tm-2² plants. The gene, Tm-I, was found to be dominant or incompletely dominant for preventing symptom development but was recessive or intermediate for limiting virus multiplication of the common strain. Both Tm-2 and Tm-2² were dominant for a hypersensitive response to the common strain. Virus multiplication was temperature-dependent. The background or varietal genotype did not affect virus multiplication. A systemic necrosis of Tm-2² plants occurred only when heterozygous Tm-2² was not protected by other factors against specific strains of TMV. The complexity of the host genotype, pathogen genotype and environment interactions are outlined and the exploitation of the resistance factors in tomato breeding discussed.     

The movement of tobacco mosaic viruses and potato virus X through tomato plants

Tomato aucuba mosaic virus, tobacco mosaic virus and potato virus X took 3'5-4, 5 and 3 days respectively to move from inoculated tomato leaflets into the petioles and stems
On reaching the stem each virus usually first moved downward, but in some plants both upward and downward movement occurred simultaneously and in a few
upward movement occurred first.
All three viruses travelled through the stem at approximately the same rate. Each was capable of travelling more than 80 cm. during the first 12 hr. after entering the stem, giving a minimal average rate of about 8 cm. per hr.
Uninfected pieces of stem invariably occurred between infected pieces. Maximum lengths of stem through which virus particles had apparently passed without causing infection, were 44.5, 49 and 39 cm. for the three viruses.