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.
Egg masses ofMeloidogyne exiguafrom coffee plants are subjected to a range of microbial populations and these resident soil organisms in the egg masses may affect nematode communities. The incidence of fungi and bacteria inM. exiguaegg masses was investigated and the toxic effect of their volatile organic compounds (VOCs) was tested on second-stage juveniles (J2). Bacteria and fungi were isolated from egg masses on coffee root and identified to species. The nematicidal activity of VOCs from bacterial and fungal strains was tested againstM. exiguainin vitroexperiments. Several bacterial and fungal strains were found inM. exiguaegg masses and produced VOCs that were toxic toM. exiguaJ2. Bacterial strains induced more nematode mortality compared with fungal strains. The continued colonisation of fungi and bacteria inM. exiguaegg masses occurred during the year and their VOCs reduced the viable inocula ofM. exiguaand should be explored as biocontrol agents.
RESUMOA infectividade e a reprodução de Meloidogyne javanica e de Heterodera glycines, em cultivar suscetível e resistente de soja, diferiram, de acordo com a temperatura do solo. A 28 o C o número de massas de ovos, total de ovos, de fêmeas e a porcentagem de sucesso de parasitismo dos juvenis do segundo estádio (J2) em cada cultivar (suscetível e resistentes) de soja infestada com M. javanica foram, significativamente maiores, comparados com as demais temperaturas (32º C, 26º C, 24º C e 20º C). Entretanto, a soma de juvenis do terceiro e quarto estádios (J3 e J4) foi maior em todas as cultivares, quando a temperatura submetida às plantas inoculadas com M. javanica foi de 20º C comparada com as demais temperaturas. A capacidade reprodutiva da fêmea (ovos por fêmea) de M. javanica foi sempre maior na cultivar suscetível em cada temperatura testada, porém, significativamente maior na cultivar suscetível colocada a 32º C comparada com as demais temperaturas. Nas relações H. glycines e soja, as temperaturas testadas proporcionaram valores semelhantes para a população total (fêmeas e cistos) na cultivar resistente. Na cultivar suscetível, a temperatura de 28º C aumentou significativamente o número de fêmeas, total de fêmeas e cistos e a porcentagem de parasitismo de J2 de H. glycines, comparada com todas as demais temperaturas. Termos para indexação: Nematóides de galhas, parasistismo, Glycine max. ABSTRACTThe infectivity and reproduction of Meloidogyne javanica and Heterodera glycines in susceptible and resistant soybean cultivars differs according to soil temperatures. At 28 o C the egg-mass number, total eggs, and females, and percentage of parasitism success of second stage juveniles (J2) in each cultivar (susceptible and resistants) of infested soybean with M. javanica were significantly greater when compared to other temperatures (32º C, 26º C, 24º C and 20º C). However, the sum of third and fourth juvenile stages (J3 and J4) was greater in all cultivars when M. javanica inoculated plants were submitted to 20 o C. The female reproductive capacity (eggs per female) of M. javanica was always greater on susceptible cultivars in each tested temperature, but significantly greater in the susceptible cultivars submitted to 32 o C as compared to other temperatures. On the interaction between H. glycines and resistant soybean cultivars, the different temperatures resulted in similar values for the total population (females + cysts no.) on the resistant cultivars. On susceptible cultivars 28º C increased significantly the number of females, total females + cysts and the percentage of J2 parasitism of H. glycines as compared to all other temperatures.
Com vista ao estudo de atração e penetração de Meloidogyne javanica (Treub) Chitwood e Heterodera glycines (Ichinoe) em soja (Glycine max L.), desenvolveu-se uma técnica empregando-se segmento de raiz com 2cm de comprimento. Nos segmentos de raiz de soja infectados, observou-se que a penetração de juvenis de segundo estádio (J2) de M. javanica ocorre pela coifa seguida de migração entre os feixes vasculares do cilindro central. Juvenis de H. glycines penetraram, aproximadamente, 15mm da coifa. A região seccionada da raiz de soja atraiu três vezes mais J2 de M. javanica do que a região da coifa, mas esta não foi tão atrativa para J2 de H. glycines. A obstrução conjunta da coifa e do local seccionado reduziu (83%) a penetração de J2, tanto de M. javanica quanto de H. glycines. Quando apenas um desses locais foi obstruído, a outra extremidade livre compensou o processo atrativo. Portanto, as substâncias atrativas são liberadas por essas extremidades. A penetração de J2 de M. javanica foi maior no segmento de raiz quando comparada com a plântula intacta de soja. Entretanto, os J2 de H. glycines penetraram menos em segmentos de raiz e em plântulas sem folhas, quando comparados com plântulas intactas e com as seccionadas no colo. Portanto, na cultivar de soja "Embrapa 20", a atração e os locais de penetração de J2 de H. glycines e M. javanica são diferenciados. Esta técnica poderá ser útil nos estudos de atração e penetração de outros nematoides endoparasitas.
Pratylenchus brachyurus se destaca entre as espécies de fitonematoides que mais causam prejuízos na cultura da soja no Brasil. O trabalho teve como objetivo avaliar as interações de diferentes grupos químicos no tratamento de sementes para o controle de P.brachyurus. Os experimentos foram conduzidos em casa de vegetação sendo o delineamento inteiramente casualizado, composto por nove tratamentos e seis repetições, sendo Produto A = tiofanato metílico; Produto B = piraclostrobina; Produto C = fipronil; Produto formulado A+B+C = piraclostrobina + tiofanato metílico + fipronil e Padrão controle = abamectina. As interações químicas foram: Produto A+B = tiofanato metílico + piraclostrobina; Produto A+C = tiofanato metílico + fipronil; Produto B+C = piraclostrobina + fipronil. Tratamentos com sementes sem aplicação de produtos foram mantidos como controle. Todos os produtos combinados apresentaram efeito antagônico, porem o composto fipronil isolado ou combinado com o composto tiofanato metílico se destacou no controle de P. brachyurus.
Corynespora cassiicola which cause the target spot in soybeans can lead to significant reductions in grain yield. Chemical control mechanisms recommended for disease control was performed with low efficacy in the field due to loss of the pathogen sensitivity to fungicides. This study evaluated the effect of fungicides in inhibiting C. cassiicola using in vitro test. Four isolates from different regions of Rio Verde -GO were used. The experimental design was completely randomized with nine treatments and five doses (0.0, 0.1, 1.0, 10 and 100 mg). The fungicides, in the various concentrations, were added in PDA medium and poured into Petri dishes, 80 mm in diameter. Then 5 mm discs, containing fungy mycelia, were transferred to the center of the plate and incubated in growth chamber at 25°C with photoperiod of 12 h. The mycelial growth in colony diameter was measured every 24 h. The inhibition percentage of each fungicide on various isolates of fungi was determined, by observing area under the curve of mycelial progress (AUCMP) and by determining the mycelial growth speed rate (MGSR) was determined. All treatments showed a decrease in SRMG with increased applied dose, the fungicide fluazinam had the best performance, with 100% mycelial growth inhibition at all dose tested and in both areas in which the isolate was obtained. The choice of product and dose to be applied directly will be helpful in the chemical control programs ensuring higher yields at the end of the crop cycle.
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