Compostos secundários presentes em plantas medicinais podem desempenhar funções importantes em interações planta-patógeno, através de ação antimicrobiana direta ou ativando mecanismos de defesa de outras plantas que venham a ser tratadas com esses compostos. Com o objetivo de verificar o potencial de eucalipto (Eucalyptus citriodora) no controle alternativo de antracnose em pepino (Cucumus sativus), extrato aquoso (EA) desta essência florestal, autoclavado ou não autoclavado, nas concentrações de 0,1, 1, 5, 10, 15, 20 e 25% foi utilizado nos seguintes ensaios: indução de fitoalexinas em mesocótilos estiolados de sorgo (Sorghum bicolor) e em cotilédones de soja (Glycine max); fungitoxicidade in vitro sobre conídios de Colletotricum lagenarium; indução de resistência local ou sistêmica em plantas de pepino. Água e Bion foram utilizados como tratamentos controle. Os resultados indicaram que os EAs autoclavados e não autoclavados induziram a síntese de fitoalexinas em sorgo a partir da concentração de 1%. Em soja ocorreu síntese de gliceolina a partir de 10% e 15% dos EAs autoclavados e não autoclavados, respectivamente. Houve inibição total na germinação de esporos e formação de apressórios de C. lagenarium em concentrações de 20% e 1% do EA autoclavado, respectivamente. Para o extrato não autoclavado houve 75% de inibição da germinação de esporos em 25% do EA e inibição total da formação de apressórios em 15% do EA. Baseado no parâmetro tamanho de lesão, o extrato aquoso de E. citriodora, não autoclavado, apresenta potencial para induzir resistência local em pepino contra C. lagenarium.

Advances in nanotechnology, combined with the use of natural products, represent a promissing research field. Brazil is a country of a rich biodiversity, especially in the Amazon forest. Fruits commonly used by local communities, such as bacaba (Oenocarpus bacaba), are potentially important for prospection of industrial applications of natural products. In nanotechnology, microemulsions stand out for providing a modified release to conveyed substances. This work aimed to develop microemulsionated formulations of bacaba oil, characterize them and evaluate their stability. We determined the HLB (hydrophile-lipophilic balance) of bacaba oil for formulation development. Six formulations were selected from pseudoternary diagrams, which indicated the proportions of surfactants, aqueous phase and bacaba oil. The viability of these formulations was evaluated through stability tests. We provided the rheological characterization of the formulations, evaluated their potential antioxidant activity through the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method, and determined the hydrodynamic diameter of the droplets. The microemulsions were stable throughout the test period. Droplet diameter was below 200 nm, and the microemulsions were characterized as newtonian fluids, presenting an increase in antioxidant activity when compared with the diluted oil. Our results confirm the potential of bacaba oil in microemulsionated formulation as a suitable carrier for active compounds.

Cutaneous secretions produced by amphibians of the family Bufonidae are rich sources of bioactive compounds that can be useful as new chemical templates for agrochemicals. In crop protection, the use of elicitors to induce responses offers the prospect of durable, broad-spectrum disease control using the plant’s own resistance. Therefore, we evaluated the potential of methanolic extracts of cutaneous secretions of two species of amphibians of the family Bufonidae found in the Amazon biome—Rhaebo guttatus (species 1) and Rhinella marina (species 2)—in the synthesis of phytoalexins in soybean cotyledons, bean hypocotyls, and sorghum mesocotyls. Additionally, changes in the enzyme activity of β-1,3-glucanase, peroxidase (POX), and polyphenol oxidase (PPO) and in the total protein content of soybean cotyledons were determined. In the soybean cultivar ‘TMG 132 RR’, our results indicated that the methanolic extract of R. guttatus cutaneous secretions suppressed glyceollin synthesis and β-1,3-glucanase activity and increased POX and PPO activities at higher concentrations and total protein content at a concentration of 0.2 mg/mL. On the other hand, the methanolic extract of R. marina cutaneous secretions induced glyceollin synthesis in the soybean cultivars ‘TMG 132 RR’ and ‘Monsoy 8372 IPRO’ at 0.1–0.2 mg/mL and 0.2 mg/mL, respectively. The methanolic extract of R. marina cutaneous secretions also increased the specific activity of POX and PPO in ‘Monsoy 8372 IPRO’ and ‘TMG 132 RR’, respectively, and decreased the activity of β-1,3-glucanases in ‘Monsoy 8372 IPRO’. At 0.3 mg/mL, it stimulated phaseolin synthesis. The extracts did not express bioactivity in the synthesis of deoxyanthocyanidins in sorghum mesocotyls. The study in soybean suggests that the bioactivity in defense responses is influenced by cultivar genotypes. Therefore, these results provide evidence that extracts of cutaneous secretions of these amphibians species may contribute to the bioactivity of defense metabolites in plants.

Crotalaria breviflora (Fabaceae) is used as green manure crop because of its nitrogen fixation and nematode control (Nascimento et al. 2020). In April 2018, leaf wilting, flower rot, and stem necrosis symptoms were observed on C. breviflora with 100% incidence, in Sorriso (12° 33′ 31″ S, 55º 42′ 51″ W), Santa Carmem (11° 55′ 52″ S, 55º 16′ 47″ W), and Sapezal (12º 59′ 22″ S, 58º 45′ 52″ W) counties in the state of Mato Grosso, Brazil. Three monosporic isolates were isolated from symptomatic leaves, cultivated in potato dextrose agar (PDA) medium, and deposited at the Cultures Collection of the University of Brasilia (codes CCUB 1293, CCUB 1667, CCUB 1668). Colonies on PDA were white and cottony with presence of hyaline and coenocytic hyphae. The mycelia later became pale yellow with abundant reproductive structures. Sporangiophores were hyaline, aseptate, unbranched, and apically dilated to form a clavate vesicle, which produced secondary vesicles bearing sporangiola. Secondary vesicles were clavate, light brown, and 37 to 51 µm in diameter. Sporangia were brown to dark brown, globular to ellipsoid, 115 to 140 µm long, and 96 to 122 µm wide. Sporangiospores (n=30) were brown to reddish-brown, ellipsoid to ovoid, with longitudinal striae, 14 to 19 µm long, and 8 to 12 µm wide. Some with hyaline appendages at both ends. Their morphological characteristics were consistent with the descriptions of Choanephora cucurbitarum (Kirk 1984). To confirm the identity, the DNA of the three isolates was extracted and the sequences of Small Subunit (SSU), Large Subunit (LSU), and complete Internal Transcribed Spacer (ITS) of rDNA were amplified using V9G, ITS3, and LR5 primers (GenBank acc. no: MN897836, MN897837 and MN897838). The sequences were aligned with the MAFFT software. The alignment matrix was subjected to Maximum Likelihood (ML) analysis using RAxML v. 8 and Bayesian Inference performed in MrBayes v.3.1.2. The tree was edited in the FigTree software. The sequences showed 100% identity with the sequences from C. cucurbitarum found on the GenBank. To confirm pathogenicity, a suspension at 5.4 ×10⁶ spores/ml was prepared from a 15-day-old culture grown at 25°C and sprayed on asymptomatic plants of C. breviflora. Sterilized water was sprayed as the control. Plants were kept in a humid chamber at 20°C for 48 h. Initial symptoms were visualized 16 days after inoculation. Complete necrosis of leaves and stems with spore mass on infected tissue was observed 19 days after inoculation. To satisfy the Koch’s postulates, the fungus was successfully reisolated from the infected tissues. No symptoms were observed on the control plants. In Brazil, this pathogen has been reported on Brassica oleracea var. capitata, Capsicum annuum, Crotalaria spectabilis, Cucurbita sp., and Vigna unguiculata (Alfenas et al. 2018; Mendes and Urben, 2019). C. cucurbitarum has been reported to have a wide range of hosts (Farr and Rossman, 2020). It can infect the crops grown in rotation or in succession, including common bean, corn, cotton, quinoa, soybean, and sunflower. Therefore, this pathogen is of epidemiological importance and poses a threat to the croplands where environmental conditions are conducive to the disease to develop and spread. To our knowledge, this is the first report of C. cucurbitarum causing leaf and flower wilt, and stem rot on C. breviflora in the world. Acknowledgment We thank the Environmental Sciences Graduate Program, Federal University of Mato Grosso, University of Brasilia, PROPeq/PROPG-UFMT, EMBRAPA, CODEX/UFMT, Institute of Agricultural and Environmental Sciences (ICAA)/UFMT and CAPES for providing the Master's scholarship. References Alfenas, R. F., et al. 2018. Plant Dis.102:1456. https://doi.org/10.1094/PDIS-10-17-1610-PDN, Google Scholar. Farr, D. F., and Rossman, A. Y. 2020. Fungal Databases, Syst. Mycol. Microbiol. Lab., ARS, USDA. Retrieved May 26, 2020 from https://nt.ars-grin.gov/fungaldatabases/, Google Scholar. Kirk, P. M. 1984. Mycol Paper. 152:1. Google Scholar. Mendes, M. A. S., and Urben, A. F. 2020. Fungos relatados em plantas no Brasil, Retrived May 26, 2020 from http://pragawall.cenargen.embrapa.br/aiqweb/michtml/fgbanco01.asp, Google Scholar. Nascimento, D. D. et al. 2020. Bioscience Journal. 36:713. https://doi.org/10.14393/BJ-v36n3a2020-42248, Google Scholar.

Plantas medicinais apresentam potencial para o controle de fitopatógenos devido ao efeito direto sobre o agente patogênico ou indireto pela ativação de mecanismos de defesa como as fitoalexinas. Assim, o presente trabalho teve por objetivo verificar o efeito antifúngico e elicitor de frações obtidas da citronela (Cymbopogon nardus), a partir dos extratos brutos metanólico (EME) e etanólico (EET) dessa planta. Os extratos EME e EET foram fracionados em cromatógrafo de coluna de filtração em gel (CFG) obtendo-se três frações a partir do extrato metanólico (FMI, FMII e FMIII) e duas frações para o extrato etanólico (FEI e FEII). Os pesos moleculares para as frações FMI, FMII, FMIII, FEI e FEII foram 69,29; 40,51; 18,72; 65,89 e 24,11 kDa, respectivamente. As frações obtidas nas CFG foram utilizadas em bioensaios de germinação de esporos e formação de apressórios por Colletotrichum lagenarium e, de indução de fitoalexinas em mesocótilos de sorgo e cotilédones de soja. Observou-se que não houve efeito significativo das frações de EME e EET analisadas sobre a germinação e formação de apressórios pelo patógeno. Quanto ao acúmulo de fitoalexinas em cotilédones de soja, não houve efeito significativo das frações FMI, FMII, FMIII, FEI e FEII. Entretanto, observou-se efeito significativo das frações obtidas na CFG, sobre a produção de fitoalexinas em mesocótilos de sorgo, onde os maiores acúmulos destas fitoalexinas foram promovidas pelas frações FMI e FMIII, diferindo significativamente do tratamento controle. Com base nos resultados obtidos, é possível concluir que frações parcialmente purificadas obtidas de EME de C. nardus apresentam potencial para induzir o acúmulo de fitoalexinas em mesocótilos de sorgo.