Plants, get ready, the eating insects are coming! prime defense of Phaseolus vulgaris on plant resistance and tolerance mechanisms

In the last decade, attention has been drawn to a defense priming mechanism between plants of the same species through volatile organic compounds so that neighboring plants can prepare for the potential arrival of herbivorous insects. The induction of plant response priming by Tetranychus urticae Koch (Tetranychidae) in Phaseolus vulgaris (Fabaceae) seedlings was evaluated through different communication pathways, focusing on resistance mechanisms (physical and chemical defenses: thickness, hardness, and foliar phenols) and plant tolerance (stem length, diameter, leaf area, and number of leaves). Five treatments were established: (1) Emitting seedling (with T. urticae ); (2) direct communication (sender and recipient seedlings separated at 40 cm with free transfer of mites); (3) aerial communication (sender and recipient seedlings communicated aerially at 40 cm, but physically excluded from T. urticae ); (4) positive control (seedling isolated but with T. urticae ); and (5) negative control (seedling isolated and without T. urticae ). Plant defense priming responses were recorded, interestingly, by different means of communication: aerial for tolerance and direct for resistance. When responses were induced by air rather than directly, trade-offs between plant resistance versus tolerance to herbivory were found. Notably, the principal component analysis showed a clear grouping of the variables of tolerance toward air communication and resistance toward direct communication. This strongly suggests the existence of different activation pathways for plant communication depending on tolerance and resistance mechanisms, a potential result of energy production costs.