RESUMO

The soybean green stem and foliar retention syndrome (GFSR) [1], caused by Aphelenchoides besseyi, is reported in Brazilian fields located at the States of Mato Grosso, Pará, Amapá, Tocantins, and Maranhão, which correspond to warm climates with well-defined rainfall patterns when the air humidity is high during several consecutive days. Studies showed that the infection of plants by A. besseyi occurs in regions with a high frequency of rains and under temperatures higher than 28 °C, when the nematode founds adequate conditions to migrate from soil to shoot parts of plants to initiate its parasitism [2]. One of the challenges was the difficulty in simulating the natural conditions for the disease development, which needs luminosity, high temperatures, and moisture. These conditions can be reproduced using modern growth chambers, but these equipment are onerous and scarce in most Brazilian research centers. So, for the studies with A. besseyi and different plant hosts, it is difficult to reproduce the environmental conditions similar to those found in the field where this nematode is reported, especially under the operational and economic points of view. Considering these environmental conditions and the necessity in conducting studies under controlled environments with this pathossystem aiming a detailed investigation about the symptoms and the nematode parasitism, but also to isolate the effects due to exclusively the nematode parasitism instead of other effects that occur under field conditions, especially in crops like soybean, common bean, and cotton [1], [2], [3], [4], the objective of this project was to develop a growth chamber for the cultivation of these plants under controlled environmental, simulating the necessary conditions for the GFSR development. For this, we used an environmental chamber [5] as the base to our project, where we could find the important aspects that need to be adjusted to suit our purpose.•We developed a plant growth chamber to be used under greenhouse conditions for the studies with Aphelenchoides besseyi and different host plants.•The soybean green stem and foliar retention syndrome (GFSR) needs specific environmental conditions of humidity and temperature for the development of the characteristic symptoms and for the nematode multiplication in the parasitized plants.•This method simulates adequately the environmental conditions found in the field, since the chamber is installed inside a greenhouse, assuring the reliable observation of the plant behavior in relation to the pathogen and allowing the conduction of experiments of this nature in regions different from those where the disease naturally occurs.

RESUMO

Several species of nematodes are known to cause losses to cowpea (Vigna unguiculata) throughout the world. In Brazil, Aphelenchoides besseyi was described as causing damage on soybean, cotton, and common bean, but no report was found about the parasitism of this nematode in cowpea. This study aimed to verify the host reaction of cowpea cultivars to A. besseyi. The experiment was conducted under greenhouse conditions, using two A. besseyi populations as inocula, obtained from symptomatic soybean and cotton plants collected in naturally infested fields. Cultivars Imponente, Aracê, Guariba, Tumucumaque, Nova Era, and Tracuateua were inoculated with 500 A. besseyi of each population, separately, into soil, and after 30 days from the inoculation nematodes were extracted from shoot systems. Both populations were able to parasitize all the cowpea cultivars. Independently of the cultivar, cowpea plants exhibited symptoms of leaf deformation similar to those described for soybean, cotton, and common bean and, in addition, severe brooming was observed, with the interior of the stems being porous and necrotic. To our knowledge, this is the first report of parasitism by A. besseyi of cowpea in Brazil, under greenhouse conditions, increasing the list of hosts of this nematode.

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The green stem Aphelenchoides besseyi and gall Meloidogyne incognita phytonematodes cause soybean yield losses. Thus, the objective of this study was to evaluate the effects of different populations of A. besseyi and M. incognita on soybeans. The experiment had 10 treatment groups [T1: control, T2: A. besseyi (500), T3: M. incognita (2,000), T4: A. besseyi (250) + M. incognita (2,000), T5: A. besseyi (500) + M. incognita (2,000), T6: A. besseyi (250) + M. incognita (4000), T7: A. besseyi (500) + M. incognita (4,000) individuals, T8: A. besseyi (250) + M. incognita (8,000), T9: A. besseyi (500) + M. incognita (5,000), and T10: A. besseyi (1,000) + M. incognita (8,000) individuals] with six replicates. Inoculations were done on day 10 after soybean germination, and evaluations were conducted after 60 d. Plant height, shoot fresh weight, root fresh weight, number of pods (NP), pod fresh weight, number of grains (NG), grain yield (GY), amount of A. besseyi in the shoot, and M. incognita in the roots were analyzed. The 500 A. besseyi + 8,000 M. incognita treatment reduced all variables and led to considerable damage to soybean development. In addition, GY, NG, and NP were reduced in the different nematode population density groups, influencing soybean agronomic characteristics.(AU)

Entre as espécies de fitonematoides que provocam perdas de produção à cultura da soja estão os nematoides da haste verde (Aphelenchoides besseyi) e o das galhas (Meloidogyne incognita). Diante disso, o objetivo deste trabalho foi estudar os efeitos de diferentes níveis populacionais de A. besseyi e M. incognita na soja. O experimento foi realizado com nove combinações de diferentes níveis populacionais dos nematoides (T1 ­ Controle não inoculado, T2 - A. besseyi 500 indivíduos, T3 - M. incognita 2000 indivíduos, T4 - A. besseyi + M. incognita 250 + 2000 indivíduos, T5 - A. besseyi + M. incognita 500 + 2000 indivíduos, T6 - A. besseyi + M. incognita 250 + 4000 indivíduos, T7 - A. besseyi + M. incognita 500 + 4000 indivíduos, T8 - A. besseyi + M. incognita 250 + 8000 indivíduos, T9 - A. besseyi + M. incognita 500 + 8000 indivíduos e T10 - A. besseyi + M. incognita 1000 + 8000 indivíduos) e seis repetições. As variáveis analisadas foram: altura de planta, massa fresca da parte aérea (MPA), massa fresca de raízes (MR), número de vagens (V), massa fresca de vagens (MV), número de grãos (G), massa fresca de grãos (MG), quantidade de A. besseyi na parte aérea e de M. incognita nas raízes. O mapa de calor indicou que populações iniciais inoculadas de 500 A. besseyi + 8000 M. incognita apresentou maiores danos ao desenvolvimento da soja, reduzindo todas as variáveis analisadas. As variáveis MG, G e V reduziram na presença de diferentes densidades populacionais das espécies de fitonematoides nematoides, influenciando negativamente o desenvolvimento da soja.(AU)

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PREMISE: Photosynthetic stems represent a source of extra carbon in plants from hot and dry environments, but little is known about how leaves and photosynthetic stems differ in terms of photosynthetic capacity, trait coordination, and responses to seasonal drought in subtropical systems. METHODS: We studied photosynthetic, hydraulic, morphometric (specific leaf area [SLA], wood density [WD]), and biochemical (C and N isotopes) traits in leaves and photosynthetic stems of 12 plant species from a sarcocaulescent scrub in the southern Baja California Peninsula, Mexico, in wet and dry seasons. RESULTS: Leaves and stems had similar mean photosynthetic capacity, as evaluated by chlorophyll fluorescence traits, indicating similar investment in leaf and stem photosynthesis. We did not find a relationship between stem hydraulic conductivity and leaf or stem photosynthetic traits. However, we found resource allocation trade-offs, between WD and both stem hydraulic conductivity and SLA. Leaf and stem photosynthetic traits did not change with season, but specific stem area was one of the few traits that changed the most between seasons-it increased during the dry season by as much as 154% indicating substantial water storage. CONCLUSIONS: Our results indicate the same proportional investment in photosynthetic capacity and dry matter in both leaves and photosynthetic stems across all 12 species. We identified multiple strategies at this seasonal site, with species ranging from high WD, low SLA, low hydraulic conductivity, and high specific bark area on one end of the spectrum and opposite traits on the other end.

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RESUMO

From February to November 2003, the mass and morphological composition offorage from Brachiaria decumbens cv. Basilisk pastures under four different doses of nitrogen (75,150, 225 and 300 kg/ha/year) were evaluated. The pastures were managed under continuousstocking with growing cattle. The data were grouped within three periods: February to April,May to August and September to November. Randomized block design with subdivided plots and two repetitions was used. The plots correspond to the nitrogen (N) doses, while the subplotsto the time of the evaluation. In the period from May to August, the forage mass in the B.decumbens pasture increased linearly related to the N dose. The percentage of green leaf blade(GLB) was lower in the May/August period if compared to the other periods. The highest percentagevalues for green stem (GS) ocorred February/April. The relation between LFV masses and CVwere influenced by the period of evaluation, reaching higher values in September/November.When 75 kg ha-1 of N was applied, the senescent tissue (ST) participation in the pasture did notvary throughout the months of the year. However, when whith doses of 150 kg ha-1 of N wereapplied, the percentage of ST was lower for February/April in comparison to the other periods.The percentages of GFB and GS increased linearly and positively as the N doses increased in theFebruary/April. The structure of the B. decumbens pasture under continuous stocking is influencedinteractively by the nitrogen doses and time of the year. Nitrogen fertilization improves thestructure of the B. decumbens pasture under continuous stocking managed with the same meanheight.

No período de fevereiro a novembro de 2003 foram avaliadas a massa e a composiçãomorfológica da forragem em pastos de Brachiaria decumbens cv. Basilisk sob quatro doses denitrogênio (75, 150, 225 e 300 kg/ha/ano). Os pastos foram manejados sob lotação contínua combovinos em recria. Os dados foram agrupados em três períodos: fevereiro a abril, maio a agostoe setembro a novembro. Foi adotado o esquema de parcelas subdivididas e o delineamento emblocos casualizados, com duas repetições. As parcelas corresponderam às doses de nitrogênio (N),enquanto que as subparcelas foram as épocas de avaliação. No período de maio a agosto, a massade forragem no pasto de B. decumbens aumentou linearmente em função da dose de N. A percen-tagem de lâmina foliar verde (LFV) foi inferior no período de maio/agosto em relação aos demaisperíodos. Os maiores valores de percentagem de colmo verde (CV) ocorreram em fevereiro/abril. A relação entre as massas de LFV e CV foi influenciada somente pelo período de avaliação,com maiores valores em setembro/novembro. Quando aplicaram-se 75 kg ha-1 de N, a participa-ção de tecido senescente (TS) no pasto não variou significativamente entre os meses do ano.Contudo, quando foram aplicadas doses acima de 150 kg ha-1 de N, o percentual de TS foi inferiorno período de fevereiro/abril em comparação aos demais períodos. As percentagens de LFV e deCV aumentaram linear e positivamente com a dose de N no período de fevereiro/abril. A estru-tura do pasto de B. decumbens sob lotação contínua é influenciada de forma interativa pelas dosesde nitrogênio e épocas do ano. A adubação nitrogenada melhora a estrutura do pasto de B.decumbens sob lotação contínua e manejada com mesma altura média.

Assuntos

RESUMO

From February to November 2003, the mass and morphological composition of forage from Brachiaria decumbens cv. Basilisk pastures under four different doses of nitrogen (75, 150, 225 and 300 kg/ha/year) were evaluated. The pastures were managed under continuous stocking with growing cattle. The data were grouped within three periods: February to April, May to August and September to November. Randomized block design with subdivided plots and two repetitions was used. The plots correspond to the nitrogen (N) doses, while the subplots to the time of the evaluation. In the period from May to August, the forage mass in the B. decumbens pasture increased linearly related to the N dose. The percentage of green leaf blade (GLB) was lower in the May/August period if compared to the other periods. The highest percentage values for green stem (GS) ocorred February/April. The relation between LFV masses and CV were influenced by the period of evaluation, reaching higher values in September/November. When 75 kg ha-1 of N was applied, the senescent tissue (ST) participation in the pasture did not vary throughout the months of the year. However, when whith doses of 150 kg ha-1 of N were applied, the percentage of ST was lower for February/April in comparison to the other periods. The percentages of GFB and GS increased linearly and positively as the N doses increased in the February/April. Th

No período de fevereiro a novembro de 2003 foram avaliadas a massa e a composição morfológica da forragem em pastos de Brachiaria decumbens cv. Basilisk sob quatro doses de nitrogênio (75, 150, 225 e 300 kg/ha/ano). Os pastos foram manejados sob lotação contínua com bovinos em recria. Os dados foram agrupados em três períodos: fevereiro a abril, maio a agosto e setembro a novembro. Foi adotado o esquema de parcelas subdivididas e o delineamento em blocos casualizados, com duas repetições. As parcelas corresponderam às doses de nitrogênio (N), enquanto que as subparcelas foram as épocas de avaliação. No período de maio a agosto, a massa de forragem no pasto de B. decumbens aumentou linearmente em função da dose de N. A percentagem de lâmina foliar verde (LFV) foi inferior no período de maio/agosto em relação aos demais períodos. Os maiores valores de percentagem de colmo verde (CV) ocorreram em fevereiro/ abril. A relação entre as massas de LFV e CV foi influenciada somente pelo período de avaliação, com maiores valores em setembro/novembro. Quando aplicaram-se 75 kg ha-1 de N, a participação de tecido senescente (TS) no pasto não variou significativamente entre os meses do ano. Contudo, quando foram aplicadas doses acima de 150 kg ha-1 de N, o percentual de TS foi inferior no período de fevereiro/abril em comparação aos demais períodos. As percentagens de LFV e de CV aumentaram