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.

The biochemical defense mechanisms of amphibians involve cutaneous secretions of bioactive molecules with antimicrobial activity. This study evaluated the in vitro activity of methanolic extracts from cutaneous secretions of two amphibian species of the Bufonidae family, Rhaebo guttatus and Rhinella marina, in the control of the phytopathogens Fusarium udum, Fusarium solani, Colletotrichum truncatum, Aspergillus flavus, Rhizoctonia solani, Macrophomina phaseolina, and Calonectria pseudometrosideri. The R. guttatus extract decreased the mycelial growth of F. udum, F. solani, A. flavus, and M. phaseolina at some tested concentrations. The R. marina extract decreased the mycelial growth of C. truncatum at the concentration of 0.5 mg mL-¹, and inhibited the mycelial growth of A. flavus at concentrations of 0.1 and 0.5 mg mL-¹, which was similar to the inhibition by the positive control. The R. marina extract also decreased the microsclerotia production by R. solani at concentrations of 0.2 and 0.3 mg mL-¹. In addition, the extracts inhibited conidial sporulation and germination at varying degrees. The inhibition of appressoria formation in C. truncatum by the R. guttatus and R. marina extracts was 85-99% and 63-100%, respectively. Our results demonstrated that treatment with extracts from R. guttatus and R. marina cutaneous secretions showed antifungal activity against the studied phytopathogens.

RESUMO:A intensificação tecnológica na agricultura moderna e o uso indiscriminado de fungicidas para o controle de doenças de plantas causam danos ao ambiente e favorecem o surgimento de raças de patógenos resistentes a produtos químicos. Nesse sentido, buscam-se métodos de controle alternativo que sejam eficientes no controle populacional de patógenos em plantas, menos agressivos ao meio ambiente e ao homem. A ativação dos mecanismos de defesa, como a produção de fitoalexinas, pode ser uma alternativa viável na indução de resistência e no controle de doenças em algumas plantas cultivadas. Assim, o presente trabalho objetivou verificar a capacidade de indução de fitoalexinas em cotilédones de soja e mesocótilos de sorgo oriundos de extratos brutos aquosos e tinturas de plantas de espécies florestais. As espécies florestais utilizadas foram Angelim (Hyemenolobium petraeum), Cambará (Qualea albiflora) e Eucalipto (Corymbia citriodora). Os resultados obtidos mostraram que os extratos brutos aquosos são eficientes na indução de fitoalexinas do tipo gliceolina em cotilédones de soja, sendo que a espécie responsável por maior acúmulo desse composto foi o eucalipto. Em mesocótilos de sorgo, os extratos brutos aquosos de Angelim e Cambará induziram o acúmulo das fitoalexinas deoxiantocianidinas em baixas concentrações (1 e 5%). As tinturas induziram a produção de fitoalexinas nas concentrações de 10 e 15% em cotilédones de soja e não apresentaram produção de fitoalexinas em mesocótilos de sorgo. PALAVRAS-CHAVE:Extrato bruto aquoso; Indução de resistência; Tinturas.