Abstract
Climate change will bring more drought periods that will have an impact on the irrigation practices of some crops like tomato, from standard water regime to deficit irrigation. This will promote changes in plant metabolism and alter their interactions with biotic stressors. We have tested if mild or moderate drought-stressed tomato plants (simulating deficit irrigation) have an effect on the biological traits of the invasive tomato red spider mite, Tetranychus evansi. Our data reveal that T evansi caused more leaf damage to drought-stressed tomato plants (≥1.5 fold for both drought scenarios). Mite performance was also enhanced, as revealed by significant increases of eggs laid (≥2 fold) at 4 days post infestation (dpi), and of mobile forms (≥2 fold and 1.5 fold for moderate and mild drought, respectively) at 10 dpi. The levels of several essential amino acids (histidine, isoleucine, leucine, tyrosine, valine) and free sugars in tomato leaves were significantly induced by drought in combination with mites. The non-essential amino acid proline was also strongly induced, stimulating mite feeding and egg laying when added to tomato leaf disks at levels equivalent to that estimated on drought-infested tomato plants at 10 dpi. Tomato plant defense proteins were also affected by drought and/or mite infestation, but T. evansi was capable of circumventing their potential adverse effects. Altogether, our data indicate that significant increases of available free sugars and essential amino acids, jointly with their phagostimulant effect, created a favorable environment for a better T. evansi performance on drought-stressed tomato leaves. Thus, drought-stressed tomato plants, even at mild levels, may be more prone to T evansi outbreaks in a climate change scenario, which might negatively affect tomato production on area-wide scales.
Highlights
Agricultural production faces the challenge to produce more food while constrained by a number of biotic and abiotic factors
We have shown that the inhibitory activity against serine proteases was not significantly induced in leaves attacked by T. evansi, when compared to non-infested tomato plants
We have found that the specific activities of both Polyphenol oxidase (PPO) and POD were significantly increased in response to T. evansi infestation
Summary
Agricultural production faces the challenge to produce more food while constrained by a number of biotic and abiotic factors. Drought is by far the leading environmental stress in agriculture that limits the global productivity of major crops by directly reducing plant potential yield [2], and by indirectly influencing their interactions with biotic factors, as a consequence, playing a critical role on the worlds food security. Drought induces metabolic changes in the plant, such as increased levels of free sugars and free essential amino acids, which according to the “Plant stress hypothesis” causes the plant to have a higher nutritional value for herbivores [6, 10, 11], and can play an important role in herbivore outbreaks [12, 13]. The resulting performance of phytophagous arthropods on drought-stressed plants will depends on the access they have to an optimal balance of nutrients in the plant according to their feeding habit [5], and their adaptation to plant defense compounds according to their grade of specialization [14]
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