Meloidogyne javanica is one of the main nematodes that attack soybean crops and although genetic resistance is the ideal control measure, few cultivars are described as resistant among the innumerous cultivars recommended for the Central Region of Brazil. In this context, we aimed to evaluate the reaction of 29 soybean cultivars to M. javanica. Two experiments were conducted under greenhouse conditions in a completely randomized design with six replications. The plants were inoculated with a suspension of 2000 eggs and J2 of M. javanica and the evaluations occurred sixty days after the inoculation (DAI), determining the nematode population density and the reproduction factor. Based on the results from these two experiments we conducted another experiment selecting four soybean cultivars, one moderately resistant and three with an unknown behavior. These cultivars were inoculated with different concentrations of M. javanica inoculum. The experiment was conducted in a completely randomized design in a 4 x 4 factorial scheme with twelve replications. Evaluations were carried out at 10 DAI by observing the number of J2 and J3/ root system. At 45 DAI the nematode population density in the roots was evaluated. Of the soybean cultivars tested, none behaved as resistant. However, the cultivars UFU Carajás and BRSGO Paraíso presented less M. javanica development in the roots compared to the P98Y70 and NS 7478 and as the inoculum pressure was increased, the penetration and development of the nematode in the roots increased.Additional keywords: inoculum concentration; penetration; resistance; root-knot nematodes. ResumoMeloidogyne javanica é um dos principais nematoides que atacam a cultura da soja e, embora a resistência genética seja a medida de controle ideal, existem poucas cultivares descritas como resistentes dentre as inúme-ras cultivares recomendadas para a Região Central do Brasil. Neste contexto, objetivou-se avaliar a reação de 29 cultivares de soja ao nematoide M. javanica. Foram conduzidos dois experimentos em condições de casa de vegetação, instalados em delineamento inteiramente casualizado, com seis repetições. As plantas foram inoculadas com uma suspensão de 2.000 ovos e J2 de M. javanica, e as avaliações ocorreram sessenta dias após a inoculação (DAI), determinando-se a densidade populacional do nematoide e o fator de reprodução. A partir dos resultados destes experimentos, foram selecionadas quatro cultivares de soja, sendo uma moderadamente resistente e três com comportamento desconhecido, e foram inoculadas com diferentes concentrações de inó-culo de M. javanica. Este experimento foi conduzido em delineamento inteiramente casualizado, em esquema fatorial 4 x 4, com doze repetições. Avaliações foram realizadas aos 10 DAI, observando-se o número de J2 e J3/sistema radicular. Aos 45 DAI, avaliou-se a densidade populacional do nematoide nas raízes. Entre as cultivares de soja testadas, nenhuma se comportou como resistente. Porém as cultivares UFU Carajás e BRSGO Paraíso apresentaram menor desenvolv...

Conduziu-se experimento em casa de vegetação para avaliar a eficiência de duas técnicas de coloração de raízes de soja cultivar Emgopa 313, infectadas pelos três principais fitonematóides que afetam a cultura: Heterodera glycines, Meloidogyne incognita e Pratylenchus brachyurus. Foram realizadas três avaliações aos 10, 17 e 25 dias após o plantio da soja em solo naturalmente infestado, com os nematóides avaliados. A técnica empregando clareamento com NaOCl e fucsina ácida e a técnica que emprega lacto-glicerol e fucsina ácida foram eficientes na coloração dos nematóides, permitindo a sua visualização no interior do tecido radicular. Em função da duração do ciclo de vida do P. brachyurus não foi possível a visualização desses nematóides nos tecidos radiculares na primeira avaliação empregando a técnica do clareamento e coloração com fucsina ácida, e na segunda avaliação, em ambas as técnicas testadas. Para tecidos mais tenros a técnica que emprega o clareamento seria a mais indicada por facilitar a visualização dos nematóides, já que os tecidos sofrem certa descoloração, e por utilizar uma menor quantidade de corante, o que auxilia no processo de descoloração.

Soybean crops are attacked by several pathogens. Among these, there are nematodes of the Meloidogyne genus, which are responsible for yield reduction. Among several control methods against these pathogens, one consists of using resistant cultivars. The objective of this study was to evaluate the reaction of 27 soybean cultivars to the nematode Meloidogyne incognita race 3. Two experiments were conducted under greenhouse conditions, in a completely randomized design, with 27 treatments and six replications. Plants were kept in plastic cups with capacity for 400 mL of sterilized substrate (soil + sand) and were artificially inoculated with a suspension of 2000 eggs and J2 of M. incognita race 3/plant. Evaluations were performed sixty days after inoculation (DAI), in order to determine nematode population density in the roots and reproduction factor (RF). Through experiment results, four soybean cultivars were selected, of which three were resistant (BRSGO Paraíso, NA 7255 RR and NS 7490 RR) and one was susceptible (BRSGO Santa Cruz). The cultivars aforementioned were inoculated with four different M. incognita Race 3 inoculum concentrations. Thus, an experiment was conducted in a completely randomized design, in a 4 x 4 factorial, with 12 replications. Evaluations were performed at 10 DAI, when the number of J2 and J3/root system was observed. At 45 DAI, nematode population density in the roots was evaluated. NS 7476, NS 7490 RR, NA 8015 RR, NA 7620 RR, BRSGO Graciosa, P98Y70, CD 237 RR, P98Y51 and UFU Milionária cultivars showed resistant behavior, as they were similar to the resistance standards used. NA 7255 RR and NS7490 RR cultivars behaved as M. incognita race 3-resistant with the use of the inoculum concentration of 4000 eggs/plant, which seems to be the ideal concentration to evaluate the reaction of cultivars to this nematode. Evaluations of M. incognita race 3 penetration in the roots were not a good parameter to evaluate cultivar behavior. Additional keywords: genetic resistance; inoculum concentration; root-knot nematode; root penetration. ResumoA cultura da soja é atacada por vários patógenos e entre esses estão os nematoides do gênero Meloidogyne, responsáveis pela redução de produtividade. Entre os vários métodos de controle desses patógenos, tem-se o uso de cultivares resistentes. O objetivo deste estudo foi avaliar a reação de 27 cultivares de soja ao nematoide Meloidogyne incognita raça 3. Dois experimentos foram conduzidos em condições de casa de vegetação, em delineamento inteiramente casualizado, com 27 tratamentos e seis repetições. As plantas foram mantidas em copos plásticos com capacidade para 400 mL de substrato (solo + areia) esterilizados e foram inoculadas artificialmente com uma suspensão de 2000 ovos e J2 de M. incognita raça 3/planta. As avaliações foram realizadas sessenta dias após a inoculação (DAI), determinando-se a densidade populacional do nematoide nas raízes e o fator de reprodução (FR). A partir dos resultados destes experimentos foram selecionadas quatro cultivare...

A series of factors can affect populations of H. glycines and even its life cycle, including inoculum density and genetic resistance of soybean cultivars. This study evaluated whether resistance reaction to H. glycines is effective in reducing nematode development under high inoculum concentration, as well as if such resistance reaction and inoculum density affect juvenil penetration and survival rate of H. glycines. Two trials were done using three soybean cultivars: one susceptible (BRS Valiosa RR) and two resistant (BRSGO Chapadões and BRSGO 8860RR) to H. glycines. The cultivars were subjected to four inoculum density (1,000, 2,500, 5,000 and 10,000 eggs and J2 per pot). The experimental design was completely randomized, in a 3 × 4 factorial scheme, with twelve replications. Two evaluations were done at 10 and 30 days after inoculation (DAI). Juvenile penetration in the roots was evaluated at 10 DAI and the number of females in the roots was estimated at 30 DAI. The survival rate was determined using both evaluations. Increasing initial density of H. glycines inoculum resulted in the increase of nematode final population in the susceptible cultivar, and the resistance reaction of soybean cultivars was not affected by the inoculum concentration. Penetration of J2 in the roots increased as inoculum density increased regardless of cultivar resistance or susceptibility. Nematode survival rate was greater in the susceptible cultivar.