Background The bacterial-spot disease caused by different Xanthomonas species is one of the major tomato diseases that reduce crop production and quality. Pesticides indiscriminate usage has resulted in an increase in resistant bacterial strains as well as contamination of farmers, consumers and the environment. Plant growth-promoting bacteria and humic acids can act as elicitors of plant defence mechanism causing extensive transcriptional and metabolic reprogramming which, in turn, produce a range of plant chemical defences. The purpose of this study was to study how humic acids and plant growth-promoting bacteria, when applied to the substrate, affected the severity of bacterial spot symptoms in tomato leaves. Materials and methods One-month-old Micro-Tom tomato (Solanum lycopersicum L.) were transferred to 3 L pots filled with a sterile mixture of sand and vermiculite (2:1, v:v) and treated or not (control) with 250 mL of 4.5 mmol C. L−1 of humic acids, Herbaspirillum seropedicae (108 CFU. mL−1) and the combination of humic acids plus H. seropedicae. One day after substrate treatment, the leaves were inoculated (or not) with X. euvesicatoria (Xe). The area below the disease progression curve based on severity scores and the number of symptomatic leaflets was used to assess phytopathogen virulence. The concentration of oxalic, citric and succinic acids in leaf extracts were determined using HPLC analysis. Results Sole or combined H. seropedicae (BAC) and humic acids (HA) application promoted shoot and root growth related to control when plants were challenged with Xe pathogen. For plants inoculated with Xe, more significant plant-growth promotion results were obtained for HA + BAC treatment. The first visible symptoms were observed 16 days after inoculation with 2 × 104 CFU. g−1 of Xe cells in leaves of control plants. HA and BAC applied alone or combined reduced disease severity. Only plants treated with HA were able to reduce disease incidence (number of the leaflets with symptoms). Organic acids, such as oxalic, citric and succinic acids, rose in Xe-inoculated leaves. The reduced amount of organic acids in diseased leaves treated with HA + BAC may be linked to a decrease in disease progression. Conclusion Humic acids and H. seropedicae increased growth by modulating the content of organic acids in leaf tissue, attenuating the symptoms of the bacterial spot disease. Graphic abstract
The objective of this study was to evaluate soil macrofauna as a bioindicator of soil quality in successional agroforestry systems and secondary forests. The study was conducted in the southern lower region of Bahia in Brazil, in two areas: a successional agroforestry system (AFS18) and native forest (NF). AFS18 consists of two species: mahogany (Khaya ivorensis and Khaya grandifoliola), açaí (Euterpe oleracea), cacao (Theobroma cacau) and banana (Musa spp.). Sampling was carried out in the dry (June) and rainy (October) seasons of 2019, and eight soil monoliths were collected in both areas. A total of 889 individuals from the soil macrofauna were sampled. The highest frequency (RF) of taxons occurred in NF in the rainy season, and the groups that stood out were: Oligochaeta with 42% FR in ASF18, Formicide with 33.9% in NF and Isoptera with 58% in AFS18. The macrofauna structure of the soil varied according to the time of collection. The density of macrofauna individuals differed between areas only in the dry season. The highest number of ind.m² was observed in the area NF (378) when compared to ASF18 (196). TOC, Mg2+, Al3+ and CTC were related to AF on both occasions of collection and AFS18 in the rainy season, K+, P and pH were associated with AFS18 in the dry season. The diversity, equitability and richness of the soil macrofauna was greater in AF area. HFA18 in the rainy season was similar to NF, favoring colonization of the area by soil macrofauna organisms.
The use of humic substances in agriculture as a biostimulant emerged as one of the promising methods to promote sustainable production. Different molecular, biochemical, and physiological processes are triggered, resulting in nutrient efficiency use and protection against abiotic stress. Understanding plant changes promoted by humic substances is essential for innovative and tailored biostimulation technologies. Cell metabolites are the final target of the response chain, and the metabolomic approach can be helpful in unveiling pathways related to plant response. This study aimed to evaluate a global metabolic alteration of rice leaves induced by humic acids (HA) applied in a hydroponics system. Using 1H NMR and GC-TOF/MS analysis, we observed a significant decrease in all main metabolites classes in leaves treated with HA, including lipids, organic acids, amino acids, and carbohydrates. Metabolites in higher concentrations in HA-treated plants are candidates as markers of HA bioactivity, including amino acids, intermediates of tricarboxylic acid cycle, and lipids, and aromatic compounds related to plant-stress response.
No sistema de colheita mecanizada da cana-de-açúcar, uma quantidade considerável de resíduos vegetais, denominados de palha ou palhada (folhas secas, bainhas, ponteiros e pedaços de colmo), é acumulada no solo. O acúmulo dessa palhada causa no solo alterações de ordem física e biológica, melhorando a fertilidade do solo sob essas condições. O manejo inadequado dos agroecossistemas conduz à degradação do ambiente edáfico e, por conseguinte, ao detrimento de sua funcionalidade dentro dos sistemas biológicos. Os impactos que ocorrem no solo devido às mudanças de manejo devem ser avaliados, para tal, a fauna edáfica torna-se um excelente bioindicador, devido a sua estreita relação com os processos que advêm do compartimento serapilheira-solo e sua peculiar suscetibilidade à interferência no ambiente, à composição da comunidade da fauna edáfica reflete a funcionalidade do ecossistema e, unido à densidade, pode explanar as alterações decorrentes das interferências antrópicas na cobertura vegetal. As coberturas vegetais e os diferentes sistemas de cultivo, agem diretamente sobre a comunidade da fauna edáfica, reduzindo a densidade e a diversidade das comunidades em relação à um ecossistema natural. Por meio do estudo da fauna edáfica pode-se além de avaliar a qualidade do solo, ter uma maior compreensão do sistema de produção que este solo comporta, visto que a mesma está intimamente relacionada aos processos de ciclagem de nutrientes e decomposição da matéria orgânica na interface solo-planta.
The objective of this work was to test and evaluate different configurations of artificial neural networks (ANNs) for modeling tree stem taper in Eucalyptus spp. in strands in the microregion of Pirapora, Minas Gerais. The data used came from 8,410 Eucalyptus spp. at different speeds. The quantitative variables measured were: age, total height, diameter at the height of 1.30 m (dbh), diameter and height in different positions on the stem. The only qualitative variable measured was the clone. Four scenarios were evaluated: scenario 1 with Ht, dbh, hi, A and Clone inputs; scenario 2 with Ht, dbh, hi and Clone; scenario 3 with Ht, dbh, hi and A; and scenario 4 with Ht, dbh and hi. We tested different ANNs topologies of the Multilayer Perceptron type. The ANNs 102 (neurons in the hidden layer = 18; function = Exponential; algorithm = Rprop), 91 (neurons in the hidden layer = 19; function = Exponential; algorithm = Rprop), 13 (neurons in the hidden layer = 7; Function = Exponential; Algorithm = SCG) and 27 (neurons in the hidden layer = 6; function = Exponential; algorithm = Rprop) presented the best measures of statistical accuracy in training to predict the bottleneck in scenarios 1, 2, 3 and 4, respectively. The ANN 103 (neurons in the hidden layer = 19; function = Exponential; algorithm = Rprop) from scenario 1 presented good statistical results in the validation. Thus, the ANNs were efficient in predicting the diameter along the Eucalyptus spp stem.
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