Intensive agriculture requires large inputs of chemicals to avoid losses caused by pathogen infections. Exploring the rhizosphere of plants, which is an area with enormous abundance and diversity of microorganisms, represents a promising strategy to protect plants from pathogens in a sustainable way. Recent studies revealed the importance of soil microbiome in the process of natural plant defense and how current management practices can interfere in the dynamics of these microbial communities shaping a protective microbiome. This review emphasizes the main findings related to changes in rhizosphere microbiome composition and functions during plant infection by soilborne pathogens. Understanding plant-microbiome interactions in the rhizosphere is key to develop microbiome-based strategies for assembling beneficial protective resident microbial communities in production systems.
RESUMO O tratamento de sementes com microrganismos visando promoção de crescimento e controle de Fusarium verticillioides é uma tecnologia que poderá ser utilizada para ampliar a sustentabilidade da cultura do milho. Para tanto, estudos com a utilização de microrganismos para tratamento de sementes visando ao controle de F. verticillioides e promoção de crescimento vegetal em milho são necessários para o desenvolvimento de bioprodutos. Onze isolados de Bacillus spp. foram testados quanto às características bioquímicas relacionadas com promoção de crescimento (produção de ácido cianídrico, ácido indolacético, sideroforos e catalase; solubilização de fosfato e assimilação de nitrogênio). Ainda in vitro foi avaliada a habilidade dos isolados de Bacillus em inibir o crescimento micelial e a germinação de conídios de F. verticillioides. Em casa de vegetação foi avaliado o efeito dos isolados de Bacillus spp. na promoção de crescimento e no controle de F. verticillioides em duas variedades de milho. Bacillus velezensis AP-03 e Bacillus sp. AP-210, não somente inibiram o crescimento micelial e a germinação de esporos, mas também promoveram o crescimento das plantas e controlaram F. verticillioides em sementes de milho em condições de casa de vegetação.
Objetivando avaliar o efeito de doses de fósforo e idades de corte na morfologia e valor nutritivo de folhas de B. brizantha Stapf cv. Marandu e correlacionar características anatômicas com o valor nutritivo, foi conduzido um experimento inteiramente casualizado com 4 repetições, em esquema fatorial 3 x 5, sendo 3 idades de corte (28, 56 e 84 dias) e 5 doses de P (20, 200, 400, 600 e 800 mg.dm-3). O capim-marandu foi cultivado em vasos de 4 dm3. Foram medidas as características morfológicas. E confeccionadas lâminas das folhas e as secções fotomicrografadas foram as áreas do esclerênquima (ESC), da bainha parenquimática dos feixes (BPF), do metaxilema (MET), do floema, das células buliformes, espessura do mesofilo (MES), das epidermes e a distância entre feixes. Determinou-se a produção de MS, e os teores de proteína bruta (PB), fibra em detergente neutro (FDN), fibra em detergente ácido (FDA), lignina, a digestibilidade in vitro da matéria seca (DIVMS). O aumento nas doses de P e idades de corte proporcionou aumento na MS e redução na DIVMS e PB. Houve correlações positivas entre o MET e FDA; mesofilo, células buliformes e BPF com a DIVMS e PB; e foram negativas entre floema, MET e ESC e PB.
Stenocarpella spp. causes stalk and ear rot in maize and overwinters in stubble during the off-season. Understanding the factors that guide saprophytic colonization is a crucial strategy for management. In this study, we analyzed the abiotic factors and crop management practices in relation to the inoculum of Stenocarpella spp. in stubble by qPCR. Soil samples were used for suppressiveness tests against Fusarium verticillioides, Fusarium graminearum, and Stenocarpella maydis. In the 29 fields, different levels of Stenocarpella spp. were detected. Only three fields were considered suppressive for the three pathogens. Heat maps showed that soil suppressiveness was inversely related to the pathogen concentration, and the suppressiveness of one pathogen was correlated with the suppressiveness of other pathogens. Under no-tillage systems in which rotation with soybeans was adopted, Stenocarpella spp. were detected at lower concentrations than in areas that adopted no-tillage systems with maize monocultures. While in tillage systems, the maize–maize monocropping increases the inoculum level of Stenocarpella spp. Crop rotation is a factor related to the observed reduction in the pathogen concentration and increases in the broad-spectrum antagonistic microbial communities. These communities guide the suppressiveness of soil-borne diseases in maize fields cultivated under tropical conditions.
The incorporation of organic matter to the soil not only improves nutrient content, but also reduces the survival of Stenocarpella, the causal agent of stalk rot, Diplodia ear rot, and grey leaf spot, in maize stubble. We evaluated the effect of organic waste incorporation on Stenocarpella survival in maize stalks, the activity of suppressiveness-related enzymes, and nutrient contents. We conducted the assays in the municipalities of Lavras and Sete Lagoas, Minas Gerais State, Brazil. Maize stalks infested with Stenocarpella were kept in field conditions for three months after poultry litter, swine manure, fish hydrolysate, compost sewage sludge, and urea application. Infested stalks, without residue amendment, were kept on surface or incorporated into the soil, representing negative and positive controls. Stenocarpella concentration in stalks was assessed using qPCR expressed as cycle threshold number. Sewage sludge, buried stalks, and stalks retained on the surface showed reduction of pathogen inoculum. Swine manure and urea did not reduce the quantity of DNA. In the experiment conducted in Lavras, poultry litter stimulated β-glucosidase, urease and hydrolysis of fluorescein diacetate activities when compared to the negative control. Sewage sludge, poultry litter, and swine manure increased Ca in the soil by 44 %, 38 % and 36 %, respectively, in the experiment conducted in Lavras. Poultry litter increased N total three months after application. The results indicate that organic wastes are promising in improving nutrient content, activity of hydrolysis-related enzymes, but Stenocarpella inoculum dynamics should be taken into consideration when deciding on the specific organic amendment.
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