Rafael Perl-Treves
Plant–herbivore interactions are controlled by a variety of defense mechanisms in the plant and counter-adaptation mechanisms in the herbivore. The broad mite (BM), Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae), is an important pest of vegetables and flowers worldwide. It produces persistent physiological changes that result in organ deformation and growth inhibition. Female mites disperse by phoresy, mostly by whiteflies. We studied BM host–plant (host) selection and evaluated the effect of the jasmonic acid (JA)-dependent defense pathway on BM preference and performance. We compared the behavior of BMs on two Solanum lycopersicum L. isogenic lines, wild-type "Castlemart" (wt), which is resistant to BM, and defenseless-1 (def-1), a JA pathway mutant. Reduction in plant height and leaf number was measured as indicator of damage, and light microscopy was used to characterize tissue damage on both hosts. Upon BM feeding, infested def-1 plants exhibited severe symptoms, ablation of epidermis, enlargement and compaction of mesophyll cells, and polyphenolic compounds accumulated in the collapsed epidermis. Wild-type tomatoes were not affected, and smaller progeny developed on their leaves, compared to mutant leaves. In response to BM attack, the plants induced transcripts of the JA pathway. We performed choice experiments, where mites were allowed to choose between different hosts, and phoresis experiments, where detachment of phoretic BM females from whitefly vectors on different hosts was examined. In both experiments, BM discriminated between resistant wt tomato and susceptible def-1. In addition, phoretic mites preferred, in a dose-dependent manner, paper discs treated with def-1 eluate. Pre-treatment of mutant leaves with JA reduced mite disembarking on def-1 leaves and reduced the number of progeny. This study stressed the importance of the JA pathway and JA-induced volatile cues in BM host choice behavior, their fitness, and extent of damage to tomato plants.
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