Pulse water stress plays a dynamic role in plant responses to the herbivory by Bactericera cockerelli

Background/Question/Methods

The ability of plants to resist insect herbivory and pathogen infection depends on environmental factors that affect plant susceptibility. Water stress resulting from the scarcity of water can elicit plant susceptibility to insects and pathogens by changing plant physiological responses. Insects may prefer plants experiencing scarcity of water to exploit plant limited ability to mount defenses against herbivory. Thus, studying plant susceptibility to insects transmitting pathogens is crucial to enhance the understanding of pest outbreaks in the context of the world’s global climate changes. This study was conducted to evaluate the susceptibility of Solanum lycopersicum to the infestation of Bactericera cockerelli (psyllid) under water stress conditions. Four-week-old tomato plants were randomly assigned to one of the weekly water regimes (50 ml or 200 ml) for two weeks. Plants were tested for plant water pressure and relative water content to verify for pulse water stress. Treated plants of similar size and physical appearance were caged individually with 10 adult psyllids for no-choice infestation assay or caged in pair with 10 adult psyllids for choice infestation assay. The number of psyllids colonized the plants was measured weekly and was used to evaluate plant susceptibility. 

Results/Conclusions

Plants treated with 50 ml of weekly water regime had significantly higher chamber pressure (X²(1, N = 45)= 29.41, p < 0.0001) and had significantly lower relative water content (X²(1, N = 45)= 12.12, p < 0.0005) than plants treated with 200 ml of weekly water regime. Thus, 50 ml and 200 ml plants were used as water-stressed and control plants, respectively. In the no-choice study, we found that water-stressed plants were significantly more susceptible to adult psyllid infestation during one week (F (1, 16) = 5.16, p = 0.0373) and two weeks infestation (F (1, 16) = 16.07, p = 0.0010). Furthermore, the mean number of total offspring was significantly higher on water-stressed plants than on control plants after one week (F (1, 16) = 4.37, p = 0.0264) and two weeks F (1, 16) = 3.63, p = 0.0374). In the choice study, we also found significantly higher adult in water-stressed plants than the control plants (F (1, 62) = 5.44, p = 0.023). Water-stressed plants may have more amino acid and less defensive compounds than the control plants, which may explain why there were more psyllids on water-stressed plants.