Herbicidal Effects and Cellular Targets of Aqueous Extracts from Young Eucalyptus globulus Labill. Leaves

Allelopathic effects of Eucalyptus extract and wood vinegar on germination and sprouting of rapeseed (Brassica rapa L.)

Eucalyptus plantations are usually characterized by low biodiversity due to allelopathy effects. Wood vinegar is considered a complex growth regulator that can promote plant growth at low concentrations. However, there is information scarcity about the co-application of eucalypt leaf water extract and wood vinegar on plants. This study aimed at clarifying whether wood vinegar can protect seed germination against suppression by eucalypt-induced allelopathy. We examined germination behavior and seedling elongation characteristics in rapeseed (Brassica rapa L.) treated with different solutions of wood vinegar and eucalypt leaf water extract. The results showed that eucalypt leaf water extracts, wood vinegar solutions, and their mixture allelopathically suppressed seed germination rate. After rapeseed sprouting, eucalypt leaf water extracts promoted root elongation, stem elongation, and fresh weight elongation. Malondialdehyde content was also lower under the influence of eucalypt leaf water extract. Mixture of high concentration of eucalypt leaf water extract and lower concentration of wood vinegar significantly promoted root elongation. Therefore, both eucalypt leaf water extract and wood vinegar are complex plant growth regulators, which can be used to inhibit or stimulate plants at different ontogenic stages. During the seed germination period, both eucalypt leaf extracts and wood vinegar could be used as weed inhibitors. Conversely, during the period of sprouting (seedling establishment), low concentrations of eucalypt leaf extracts and wood vinegar can promote growth.

Eucalyptus globulus Leaf Aqueous Extract Differentially Inhibits the Growth of Three Bacterial Tomato Pathogens

As available tools for crop disease management are scarce, new, effective, and eco-friendly solutions are needed. So, this study aimed at assessing the antibacterial activity of a dried leaf Eucalyptus globulus Labill. aqueous extract (DLE) against Pseudomonas syringae pv. tomato (Pst), Xanthomonas euvesicatoria (Xeu), and Clavibacter michiganensis michiganensis (Cmm). For this, the inhibitory activity of different concentrations of DLE (0, 15, 30, 45, 60, 75, 90, 105, 120, 135, and 250 g L^-1) was monitored against the type strains of Pst, Xeu, and Cmm through the obtention of their growth curves. After 48 h, results showed that the pathogen growth was strongly inhibited by DLE, with Xeu the most susceptible species (15 g L^-1 MIC and IC₅₀), followed by Pst (30 g L^-1 MIC and IC₅₀), and Cmm (45 and 35 g L^-1 MIC and IC₅₀, respectively). Additionally, using the resazurin assay, it was possible to verify that DLE considerably impaired cell viability by more than 86%, 85%, and 69% after Pst, Xeu, and Cmm were incubated with DLE concentrations equal to or higher than their MIC, respectively. However, only the treatment with DLE at 120 g L^-1 did not induce any hypersensitive response in all pathogens when treated bacterial suspensions were infiltrated onto tobacco leaves. Overall, DLE can represent a great strategy for the prophylactic treatment of tomato-associated bacterial diseases or reduce the application of environmentally toxic approaches.

Herbicide Use in the Era of Farm to Fork: Strengths, Weaknesses, and Future Implications

Climate change mitigation is a major concern of the European Union (EU). In 2019, the EU presented the European Green Deal (EGD), a new environmental strategy that aimed to neutralize climate change by 2050. Within its policy areas, the EGD included the Farm to Fork (F2F) Strategy that aims to reduce pesticide use by 50%, by 2030. This reduction was proposed due to the supposed negative effects of pesticides on the environment and its biota. Among the different pesticide groups (herbicides, fungicides, insecticides, etc.) though, herbicides are perhaps the hardest to reduce. This review aimed to shed light to any factors that might hinder the reduction of herbicide use; thus, the implementation of the Farm to Fork Strategy underlines some of its weaknesses and highlights key points of a viable herbicide reduction-related policy framework. The literature suggests that integrated weed management (IWM) consists perhaps the most suitable approach for the reduction of herbicides in the EU. Even though it is too soon to conclusively assess F2F, its success is not impossible.

A Proximal Sensor-Based Approach for Clean, Fast, and Accurate Assessment of the Eucalyptus spp. Nutritional Status and Differentiation of Clones

Several materials have been characterized using proximal sensors, but still incipient efforts have been driven to plant tissues. Eucalyptus spp. cultivation in Brazil covers approximately 7.47 million hectares, requiring faster methods to assess plant nutritional status. This study applies portable X-ray fluorescence (pXRF) spectrometry to (i) distinguish Eucalyptus clones using pre-processed pXRF data; and (ii) predict the contents of eleven nutrients in the leaves of Eucalyptus (B, Ca, Cu, Fe, K, Mg, Mn, N, P, S, and Zn) aiming to accelerate the diagnosis of nutrient deficiency. Nine hundred and twenty samples of Eucalyptus leaves were collected, oven-dried, ground, and analyzed using acid-digestion (conventional method) and using pXRF. Six machine learning algorithms were trained with 70% of pXRF data to model conventional results and the remaining 30% were used to validate the models using root mean square error (RMSE) and coefficient of determination (R²). The principal component analysis clearly distinguished developmental stages based on pXRF data. Nine nutrients were accurately predicted, including N (not detected using pXRF spectrometry). Results for B and Mg were less satisfactory. This method can substantially accelerate decision-making and reduce costs for Eucalyptus foliar analysis, constituting an ecofriendly approach which should be tested for other crops.

Biocontrol Potential of Essential Oils in Organic Horticulture Systems: From Farm to Fork

In recent decades, increasing attention has been paid to food safety and organic horticulture. Thus, people are looking for natural products to manage plant diseases, pests, and weeds. Essential oils (EOs) or EO-based products are potentially promising candidates for biocontrol agents due to their safe, bioactive, biodegradable, ecologically, and economically viable properties. Born of necessity or commercial interest to satisfy market demand for natural products, this emerging technology is highly anticipated, but its application has been limited without the benefit of a thorough analysis of the scientific evidence on efficacy, scope, and mechanism of action. This review covers the uses of EOs as broad-spectrum biocontrol agents in both preharvest and postharvest systems. The known functions of EOs in suppressing fungi, bacteria, viruses, pests, and weeds are briefly summarized. Related results and possible modes of action from recent research are listed. The weaknesses of applying EOs are also discussed, such as high volatility and low stability, low water solubility, strong influence on organoleptic properties, and phytotoxic effects. Therefore, EO formulations and methods of incorporation to enhance the strengths and compensate for the shortages are outlined. This review also concludes with research directions needed to better understand and fully evaluate EOs and provides an outlook on the prospects for future applications of EOs in organic horticulture production.

Untargeted metabolomic profiling of fresh and dried leaf extracts of young and mature Eucalyptus globulus trees indicates differences in the presence of specialized metabolites

Aqueous extracts from Eucalyptus globulus leaves contain a wide variety of specialized metabolites, mainly polyphenols and appreciable amounts of volatile compounds, which are responsible for their diverse biological activities, such as antioxidant, antimicrobial, and allelopathic features. For this reason, several studies have been conducted to explore the composition of E. globulus leaf extracts for multiple therapeutic and commercial applications. However, so far, the available bibliographic reports only refer to the chemical composition of extracts prepared with leaves from mature trees, leaving much to clarify about the composition of juvenile eucalyptus leaf extracts. Furthermore, there is no consensus regarding the type of leaves, fresh or dried ones, to be used in the extraction procedure, considering the highest recovery of biologically active compounds. In this sense, this study aimed to characterize the chemical composition of aqueous extracts prepared with fresh and dried leaves from young and mature E. globulus trees. For this, leaf biomass from young and mature E. globulus trees was collected in three distinct places from a forest area, and after oven-drying a portion of the leaves, an extraction in hot water was carried out, followed by GC-MS and HPLC-MS/MS analyses. The results revealed that the maturity of eucalyptus trees and biomass drying significantly influenced the volatile and non-volatile composition of the aqueous extracts. Accordingly, while fresh leaf extracts of young trees had great levels of hydrolysable tannins, extracts prepared with fresh leaves from mature trees presented a wide range of terpenes. When dried leaf material was used, extracts had notorious contents of amino acids derivatives, C₁₃ norisoprenoids, fatty and other organic acids. Overall, this study showed, for the first time, that plant maturity (young vs mature) and pre-processing (fresh vs dried) of foliar biomass of E. globulus trees need to be considered in the preparation of leaf aqueous extracts depending on the desired purposes, since major changes in what regards biologically active compounds were found.