No abstract

Modern agricultural policies across the globe are committed to a significant reduction in chemical pesticide dependency; however, pest management strategies are still based on the use of synthetic pesticides. There is an urgent need to find new, sustainable and biorational tools for pest management programs. Plants communicate with each other and activate defense mechanisms against pests using Herbivore-Induced Plant Volatiles (HIPVs). The use of such HIPVs could be an ecologically sustainable alternative. However, as of now, there has been no comprehensive studies on HIPVs, from selection to practical use in industry production. Here, we describe the first case of an HIPV successfully implemented for pest control under commercial greenhouse conditions. In this research, tomato plants induced with (Z)-3-hexenyl propanoate [(Z)-3-HP] were less susceptible to the attack of economically important tomato pests. We designed and calibrated polymeric dispensers for the constant release of (Z)-3-HP. These dispensers maintained commercial tomato plant defenses activated for more than two months reducing herbivore pest damage without reducing plant productivity. Transcriptomic and metabolomic analyses of plants induced with (Z)-3-HP confirmed that genes involved in specialized anti-herbivore defense were upregulated, resulting in an increased production of fatty acid-derived compounds, activation of the lipoxygenase pathway and accumulation of specific defense compounds. Our work demonstrates under commercial greenhouse conditions how the release of HIPVs as elicitors of plant defenses via designed polymeric dispensers can be successfully integrated as a new biorational and sustainable tool for pest control.

When zoophytophagous mirids (Hemiptera: Miridae) feed on tomato plants they activate both direct and indirect defense mechanisms, which include the release of herbivore induced plant volatiles (HIPVs). HIPVs are capable of activating defense mechanisms in healthy neighboring plants. In this work, we investigated which of these mirid-induced HIPVs are responsible for inducing plant defenses. Healthy tomato plants were individually exposed to eight HIPVs [1-hexanol, (Z)-3-hexenol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, hexyl butanoate, methyl jasmonate and methyl salicylate] for 24 hours.Then, the expression level of defensive genes was quantified. All HIPVs led to increased expression of defensive genes by the plant when compared to unexposed tomato plants. In a further step, (Z)-3-hexenyl propanoate and methyl salicylate were selected to study the response of four tomato key pests and one natural enemy to tomato plants previously exposed to both HIPVs relative to unexposed control plants. Plants previously exposed to both HIPVs were repellent to Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) and Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), attractive to the parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae) and indifferent to Tetranychus urticae Koch (Acari: Tetranychidae). The volatiles emitted by plants previously exposed to both selected volatiles were also determined. Increased levels of C5 and C6 fatty acid-derived volatile compounds and β-ionone were detected, confirming that both HIPVs significantly activated the lipoxygenase pathway. These results are the starting point to advance the use of volatile compounds as defense elicitors in tomato crops.

Insect herbivory activates plant defense mechanisms and releases a blend of herbivore-induced plant volatiles (HIPVs). These volatile compounds may be involved in plant-plant communication and induce defense response in undamaged plants. In this work, we investigated whether the exposure of sweet pepper plants to HIPVs [(Z)-3-hexenol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, hexyl butanoate, methyl salicylate and methyl jasmonate] activates the sweet pepper immune defense system. For this, healthy sweet pepper plants were individually exposed to the each of the above mentioned HIPVs over 48 h. The expression of jasmonic acid and salicylic acid related genes was quantified. Here, we show that all the tested volatiles induced plant defenses by upregulating the jasmonic acid and salicylic acid signaling pathway. Additionally, the response of Frankliniella occidentalis, a key sweet pepper pest, and Orius laevigatus, the main natural enemy of F. occidentalis, to HIPV-exposed sweet pepper plants were studied in a Y-tube olfactometer. Only plants exposed to (Z)-3-hexenyl propanoate and methyl salicylate repelled F. occidentalis whereas O. laevigatus showed a strong preference to plants exposed to (Z)-3-hexenol, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, methyl salicylate and methyl jasmonate. Our results show that HIPVs act as elicitors to sweet pepper plant defenses by enhancing defensive signaling pathways. We anticipate our results to be a starting point for integrating HIPVs-based approaches in sweet pepper pest management systems which may provide a sustainable strategy to manage insect pests in horticultural plants.

The zoophytophagous mirid Pilophorus clavatus has been recently identified inhabiting citrus orchards in the Mediterranean region, where it feeds on several important citrus pests. In this work, we investigated whether the plant feeding by P. clavatus could induce defensive responses in citrus plants.Here, we show for the first time that the P. clavatus herbivory triggers the accumulation of the stressrelated hormones salicylic acid (SA) and jasmonic acid (JA) in citrus plants. Moreover, the SA and JA pathways enhanced plant defence mechanisms as the expression of genes encoding enzymes from both biosynthetic and responsive pathways were upregulated in P. clavatus punctured plants. We also investigated whether the induced defences could affect the plant host selection of Tetranychus urticae and the predatory mites Phytoseilus persimilis and Neouseiulus californicus. Neither T. urticae nor N. californicus preferred the odour source emitted by intact or P. clavatus-punctured plants in a Y-tube olfactometer assay. However, P. persimilis were significantly attracted to P. clavatus-induced plants.The performance of T. urticae was also compared when mites were released on control or previously P. clavatus-induced plants. Compared to the control, the infestation of T. urticae was significantly reduced up to 70% on those citrus plants previously activated by P. clavatus. Our results show for the first time that feeding of P. clavatus on citrus plants can have a dual beneficial effect due to its known predatory action and, at the same time, by inducing the plant's immune system.