Water deficit, a common constraint in forestry, is the main cause of plant stress during plantation. The survival and growth of seedlings is also compromised by herbivory during establishment. The potential of nursery preconditioning to enhance survival chances of future trees by reducing palatability or attracting beneficial insects as a result of changes in chemical defences may be an answer to overcome this situation. Changes in essential oil production and composition were evaluated by GC and GC-MS in Eucalytus camaldulensis seedlings submitted to drought during four weeks at the last stage of nursery period (20 weeks). Significant changes in essential oil relative composition were found. Seedlings (young leaves) submitted to drought developed a terpenoid blend, which has been previously associated to mature leaves and related to their higher resistance towards herbivory. Total amount of non-oxygenated terpenes decreased by 44%, whereas some oxygenated sesquiterpenes (globulol, epiglobulol and ledol) were doubled, and 1,8-cineole content was enhanced by 28.3%.

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1. Plant genotype influences plant-herbivore interactions by affecting insect attraction, acceptance and development. Here we linked oviposition behaviour of the specialist willow sawfly Nematus oligospilus Förster (Hymenoptera: Tenthredinidae) with leaf traits on different Salix L. (Salicaceae) genotypes. This was done as a first step to find oviposition cues that guide females to their host plants.2. By means of choice and no-choice bioassays we analysed host selection according to willow genotype and leaf surface. We also studied larval performance, adult fecundity and effect of experience on host selection. Nematus oligospilus prefers to oviposit on S. nigra. The least preferred genotype, S. viminalis, showed better larval performance and highest adult fecundity. Host preference was not modified by larval feeding experience.3. By means of light and scanning electron microscopy we described ovipositor and leaf micromorphology. The egg is laid inside the epidermis or between the epidermis and adjacent chlorenchyma, showing a tight association with the leaf. Leaf toughness was lowest for S. nigra and higher for S. viminalis and S. babylonica. Total nitrogen and protein content were higher on S. viminalis and S. babylonica. Total phenolics and phenolic glycosides were the highest and more diverse on S. nigra. Salicin content levels correlate with oviposition preference, suggesting the role of salicylates as oviposition stimulants.4. Results suggest that oviposition preference on S. nigra may be related to lower leaf toughness and ease of injection of female saw-like ovipositor, and motivated by the presence of phenolic glycosides. Nitrogen levels may explain better larval performance and adult fecundity in S. viminalis. Thus, a balance among the different leaf traits determines the outcomes observed in this study.

Antioxidant capacity, total phenolic content and flavonoid glycosides profile were compared in C.album samples grown in intensively cultivated (IC) and nondisturbed (ND) soils to evaluate differences in their nutraceutical potential. Petroleum ether, methanol, and aqueous extracts were sequentially obtained from C. album dried samples. Methanol crude extract exhibited the highest antioxidant potential and phenolic content, which were significantly enhanced by soil deterioration. This feature was enhanced in its ethyl acetate/n-buthanol subextract that also yielded higher amounts of the fraction containing flavonoid glycosides in samples grown in IC soils. Compounds were isolated by activity guided fractionation, and chemical structure-antioxidant activity relationships were established. Chemical structures were elucidated by chemical and spectroscopic methods. Six known flavonoid glycosides were isolated, and their antioxidant activity was determined by DPPH assay. 1, quercetin-3-O-(2",6"-di-O-R-L-rhamnopyranosyl)-beta-D-glucopyranoside; 2, kaempferol-3-O-(2",6"-di-O-R-L-rhamnopyranosyl)-beta-D-glucopyranoside; 3, quercetin-3-O-beta-D-glucopyranosyl-(1'''-->6")-beta-D-glucopyranoside; 4, rutin; 5, quercetin-3-O-beta-D-glucopyranoside; and 6, kaempferol-3-O-beta-D-glucopyranoside. Triosides 1 and 2 were identified for the first time in C. album. Our results suggest that this edible weed, ubiquitously present in cultivated fields, should be considered as a nutraceutical food and an alternative source for nutrients and free radical scavenging compounds, particularly when collected from cultivated fields that seem to increase some of its advantages.

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