Print PagePathogen infection has divergent effects on plant responses to subsequent herbivory. For instance, viral infection may elicit host plant defenses and induce resistance to herbivory at one point while may inhibit plant defense and provide benefit for its vector at another. The variation in responses may also depend on the manipulation initiated by the vector, virus, or both. Here, we studied plant response to viral infection without the presence of the vector. We used tomato plants (Solanum lycopersicum cv. Ace) and two strains of Potato virus Y (PVYNO, PVYNTN) to (1) examine the effects of infection on plant resistance to the caterpillar, Trichoplusia ni, after three different infection periods, and (2) determine whether the virus influences the production of plant defensive enzymes (peroxidase and polyphenol oxidase), and phytohormones. We randomly assigned plants into two treatments (uninfected or infected) within three infection intervals (24 hours, 5 days, or 10 days). After each infection interval, plants were either used for chemical analysis or bioassays. For chemical analysis, excised leaflets from the third leaf were collected. For the bioassay, seven newly hatched T. ni larvae were released on each bagged plant and weight gain was measured to assay plant resistance.
Results/Conclusions
Our results showed that both strains of PVYNO and PVYNTN induced plant resistance against T. ni after 24 hours. Herbivore relative growth rate was 50% lower on virus infected plants compared to uninfected plants. This effect attenuated after 5 days, and the T. ni relative growth rate was not different between virus-infected and uninfected plants after 10 days. Both PVYNO and PVYNTN induced a similar resistance response to the plant. Similar results were found for leaf consumption; herbivores fed on infected plants ate less leaf tissue than their counterparts fed on uninfected tissue. Plant growth was not affected by the infection. Furthermore, PYV infection did not influence peroxidase and polyphenol oxidase activities or salicylic acid levels. Our data shows that the plants immediate response to virus infection has strong effects on herbivore performance but this effect ceased over time. This transient induced resistance may be an important component of the plant’s defense system or it may reflect manipulation by the virus. Further studies are needed to determine the compounds and enzymes that mediate plant responses to PVY infection.
