Bacterial adaptation to rhizosphere soil is independent of the selective pressure exerted by the herbicide saflufenacil, through the modulation of catalase and glutathione S-transferase.

Herbicides cause oxidative stress in nontarget microorganisms, which may exhibit adaptive responses to substances they have not previously encountered. Nevertheless, it is unclear whether these characteristics occur in bacteria isolated from agricultural soil. Two possible adaptation strategies of Stenotrophomonas sp. CMA26 was evaluated in agricultural soil in Brazil, which is considered stressful due to the intense use of pesticides. The study focused on degradation and antioxidant enzymes in response to the herbicide Heat, which was absent at the isolation site. The results indicated that higher concentrations of herbicide led to more intense stress conditions during the initial periods of growth. This was evidenced by elevated levels of malondialdehyde and peroxide, as well as a significant reduction in growth. Our data show that herbicide degradation is a selection-dependent process, as none of the 35 isolates from the same environment in our collection were able to degrade the herbicide. The stress was controlled by changes in the enzymatic modulation of catalase activity in response to peroxide and glutathione S-transferase activity in response to malondialdehyde, especially at higher herbicide concentrations. This modulation pattern is related to the bacterial growth phases and herbicide concentration, with a specific recovery response observed during the mid phase for higher herbicide concentrations. The metabolic systems that contributed to tolerance did not depend on the specific prior selection of saflufenacil. Instead, they were related to general stress responses, regardless of the stress-generating substance. This system may have evolved in response to reactive oxygen species, regardless of the substance that caused oxidative stress, by modulating of the activities of various antioxidant enzymes. Bacterial communities possessing these plastic tolerance mechanisms can survive without necessarily degrading herbicides. However, their presence can lead to changes in biodiversity, compromise the functionality of agricultural soils, and contribute to environmental contamination through drift.

Selection of endophytic fungi from comfrey (Symphytum officinale L.) for in vitro biological control of the phytopathogen Sclerotinia sclerotiorum (Lib.)

Biological control consists of using one organism to attack another that may cause economic damage to crops. Integrated Pest Management (IPM) is a very common strategy. The white mold produced by Sclerotiniasclerotiorum (Lib.) causes considerable damage to bean crops. This fungus is a soil inhabitant, the symptoms of which are characterized by water-soaked lesions covered by a white cottony fungal growth on the soil surface and/or the host plant. Possible biological control agents taken from plants are being investigated as phytopathogen inhibitors. These are endophytic microorganisms that inhabit the intercellular spaces of vegetal tissues and are often responsible for antimicrobial production. The objective of the present study was to select endophytic fungi isolated from comfrey (Symphytumofficinale L.) leaves with in vitro antagonist potential against the phytopathogenic fungus S. sclerotiorum. Twelve isolates of endophytic fungi and a pathogenic strain of S. sclerotiorum were used in the challenge method. With the aid of this method, four endophytes with the best antagonistic activity against S. sclerotiorum were selected. Pathogen growth inhibition zones were considered indicative of antibiosis. The percentages of pathogenic mycelia growth were measured both with and without the antagonist, resulting in growth reductions of 46.7% to 50.0% for S. sclerotiorum. These analyses were performed by evaluating the endophytic/pathogenic mycelia growth in mm/day over an eight-day period of antagonistic tests.

O controle biológico consiste no uso de organismos que atacam outros que causam danos a culturas de plantas. Esta é uma estratégia muito utilizada no Controle Integrado de Pragas (CIP). O mofo branco, causado por Sclerotiniasclerotiorum (Lib.), causa danos em culturas de feijão. Este fungo é encontrado no solo e seus sintomas são caracterizados por lesões úmidas cobertas por micélios algodonosos, crescidos a partir do solo e/ou da planta hospedeira. Há relatos de pesquisas buscando agentes potenciais de controle biológico isolados de plantas para controlar fungos fitopatogênicos. Entre estes agentes encontram-se os microrganismos endofíticos, habitantes de espaços intercelulares de tecidos vegetais, muitas vezes responsáveis pela produção de substâncias antimicrobianas. Este trabalho teve por objetivo selecionar linhagens endofíticas isoladas de folhas de confrei (Symphytumofficinale L.), com potencial de antagonismo in vitro contra a linhagem fitopatogênica S. sclerotiorum. Doze linhagens de fungos endofíticos foram utilizadas na técnica de desafio em placa contra um isolado patogênico de S. sclerotiorum. Com o auxílio desta técnica, quatro linhagens com melhor atividade antagonística contra S. sclerotiorum foram selecionadas. Zonas de inibição no crescimento da linhagem patogênica foram consideradas como indicativo de antibiose. Foram efetuadas análises da porcentagem de elongação micelial com e sem antagonismo, mostrando resultados de 46,7% a 50,0% de redução no crescimento micelial do fitopatógeno. Estas análises consistiram de avaliações das medidas do crescimento em mm/dia das linhagens endofíticas/patogênica em testes de antagonismo.