Guilherme Lafourcade Asmus

Ocorrência de Pratylenchus brachyurus e Meloidogyne incognita na cultura do algodoeiro no Estado do Mato Grosso

In a survey carried out in the state of Mato Grosso, Brazil, the lesion nematode, Pratylenchus brachyurus, and the root-knot nematode, Meloidogyne incognita, were found, respectively, in 94% and 3.7% of a total of 623 root and soil samples representing 21,793 ha. No visible aboveground symptoms in cotton (Gossypium hirsutum) plants infected by P. brachyurus were observed, except for typical root lesions. In contrast, plants with M. incognita usually exhibited pronounced symptoms of damage. The high frequency (94%) of P. brachyurus was unexpected and is of concern considering the fact that soybean (Glycine max) and corn (Zea mays), are both susceptible to this nematode and are used in crop rotation programs.

Cover crops for reniform nematode suppression in cotton: greenhouse and field evaluations

Foram realizados dois experimentos em casa de vegetacao e um experimento em campo, com o objetivo de avaliar a reacao de culturas de cobertura ao nematoide reniforme, Rotylenchulus reniformis, e seu efeito sobre a populacao do nematoide em uma area naturalmente infestada (2.359 nematoides/200cm3) e sobre a producao de algodao. As culturas de nabo forrageiro (Raphanus sativus), capim-mulato (Brachiaria ruziziensis x B. brizantha), sorgo forrageiro (Sorghum bicolor), tef (Eragrostis tef), capim-moa (Setaria italica), aveias amarela (Avena byzantina) e preta (A. strigosa), milheto (Pennisetum glaucum) e capim-pe-de-galinha (Eleusine coracana) comportaram-se como maus hospedeiros de R. reniformis nos experimentos em casa de vegetacao. Amaranto (Amaranthus cruentus) e quinoa (Chenopodium quinoa) foram bons hospedeiros de R. reniformis. No campo, as menores densidades dos nematoides foram observadas nas parcelas onde foram cultivados capim-mulato, nabo forrageiro e sorgo forrageiro. As maiores produtividades de fibra de algodao foram obtidas nas parcelas cultivadas durante o outono e inverno com capim-mulato ou sorgo forrageiro, quando comparadas com aquelas que permaneceram em alqueive. A produtividade de algodao correlacionou-se negativamente com o fator de reproducao do nematoide nas culturas de cobertura (P < 0,05) e com a populacao de R. reniformis no plantio de algodao (P < 0,01).

Effect of population densities of Heterodera glycines race 3 on leaf area, photosynthesis and yield of soybean

The effect of Heterodera glycines on photosynthesis, leaf area and yield of soybean (Glycine max) was studied in two experiments carried out under greenhouse condition. Soybean seeds were sown in 1.5 l (Experiment 1) or 5.0 l (Experiment 2) clay pots filled with a mixture of field soil + sand (1:1) sterilized with methyl bromide. Eight days after sowing, seedlings were thinned to one per pot, and one day later inoculated with 0; 1.200; 3.600; 10.800; 32.400 or 97.200 J2 juveniles of H. glycines. Experiment 1 was carried out during the first 45 days of the inoculation while Experiment 2 was conducted during the whole cycle of the crop. Measurements of photosynthetic rate, stomatic conductance, chlorophyll fluorescence, leaf color, leaf area, and chlorophyll leaf content were taken at ten-day intervals throughout the experiments. Data on fresh root weight, top dry weight, grain yield, number of eggs/gram of roots, and nematode reproduction factor were obtained at the end of the trials. Each treatment was replicated ten times. There was a marked reduction in both photosynthetic rate and chlorophyll content, as well as an evident yellowing of the leaves of the infected plants. Even at the lowest Pi, the effects of H. glycines on the top dry weight or grain yield were quite severe. Despite the parasitism, soybean yield was highly correlated with the integrated leaf area and, accordingly, the use of this parameter was suggested for the design of potential damage prediction models that include physiological aspects of nematode-diseased plants.

Inheritance of soybean resistance to Rotylenchulus reniformis

Genetic inheritance of soybean resistance to Rotylenchulus reniformis was studied by evaluating the phenotypic reaction of soybean plants to the nematode. The resistant (Forrest and Custer) and susceptible (BR96-25619) soybean cultivars used as parents as well as the F1, F2 and F2:3 derived from their crosses were infested individually with 1,000 eggs and vermiform R. reniformis. About 70 days after the infestation, the nematodes were extracted from the roots and the reproduction factors and the numbers of nematodes per gram of roots were estimated, and data were adjusted for genetic models. Results suggested a predominance of additive genetic effects controlling the nematode resistance reaction. Based on mean and variance genetic models, further genetic gains are expected in the crossing Custer x BR96-25619. The effect of genetic dominance is towards susceptibility. The presence of significant epistasis indicates the existence of at least two genes controlling resistance and that they are interacting. The normal continuous distribution of frequencies of the number of individuals in different classes of resistance indicates that the resistance to the reniform nematode is inherited quantitatively.

Resistance of soybean genotypes to the reniform nematode in a controlled environment

The aim of this study was to characterize the resistance to the reniform nematode of soybean genotypes derived from crosses with at least one parent resistant to Rotylenchulus reniformis or Heterodera glicynes, or to both. Two experiments in a greenhouse of Embrapa Western Region Agriculture, arranged in a completely randomized design, evaluated 199 genotypes with five replications. Sixty days after artificial inoculation (1000 eggs and larval forms), the nematodes were extracted from the roots and the genotypes evaluated for the number of eggs and larval forms per gram of root (NGR) and for the reproduction factor (RF). Sixty-five genotypes were resistant (RF <1.0), with mean RF significantly equal to M-SOY 8001. The highest number of lines resistant to reniform nematodes, in the different study combinations of crosses, were derived from the genotypes Custer, PI 437654, Fayette, BRSGO Ipameri, BRSMT Pintado, and BRS 262.

Raças de Heterodera glycines na região Nordeste de Mato Grosso do Sul

O nematoide de cisto da soja, Heterodera glycines, constitui-se em um dos principais entraves a producao de soja na regiao Nordeste de Mato Grosso do Sul. Apos um periodo de uso do manejo recomendado para as areas infestadas, observou-se a ressurgencia de altas densidades populacionais associada a severos danos a cultura, mesmo com a utilizacao de cultivares resistentes, fato que conduziu a hipotese da ocorrencia de mudanca nas racas do nematoide. Assim, nas safras de 2006/2007 e 2007/2008, foram amostradas lavouras de 22 propriedades nos municipios de Agua Clara, Chapadao do Sul e Costa Rica, com presenca confirmada de altas populacoes de H. glycines. Apos serem multiplicadas em soja cv. BRS 133 por ate tres geracoes, as populacoes oriundas de cada amostra foram submetidas ao teste padrao para a determinacao de racas, com a inclusao da variedade diferenciadora Hartwig, visando detectar eventual presenca das racas 4+ ou 14+. Detectou-se a presenca de quatro racas, com predominância da raca 4 (72,73% das amostras), seguida das racas 14, 5 e 6 (18,19%, 4,54% e 4,54% das amostras, respectivamente). Conclui-se que nao houve significativa alteracao nas racas de H. glycines que ocorrem na regiao Nordeste de Mato Grosso do Sul.