Gas Exchange, Root Morphology and Nutrients in Maize Plants Inoculated with Azospirillum brasilense Cultivated Under Two Water Conditions

HIGHLIGHTS Azospirillum brasilense stimulates root growth in maize under water deficit. Maize inoculated with A. brasilense shows greater photosynthesis under drought conditions. Under water deficit, maize plants inoculated with A. brasilense showed greater water use efficiency (WUE).

Abstract The objective of this study was to evaluate the gas exchange, root morphology and nutrient concentration in maize plants inoculated with A. brasilense under two water conditions. The experiments were carried out in a greenhouse, one under irrigation and the other under water deficit. The treatments consisted of four A. brasilense inoculants (control (without inoculation), Az1 (CMS 7 + 26), Az2 (CMS 11 + 26) and Az3 (CMS 26 +42). At the V6 plant stage, water stress was imposed on maize plants for 15 days. The phytotechnical characteristics, gas exchange, root morphology, root dry matter and macronutrient analysis were evaluated after 15 days of water deficit imposition. The water deficit caused a reduction in the development of maize plants. The presence of A. brasilense Az1 under the same condition yielded higher photosynthesis, carboxylation efficiency, water use efficiency, and greater soil exploration with increased length, surface area and root volume of plants. Inoculation by A. brasilense increased root system volume by an average of 40 and 47% under irrigation and water deficit, respectively, when compared to non-inoculated plants. The inoculant Az1 attenuated the deleterious effects caused by drought and yielded the best growth of the root system, resulting in the tolerance of maize plants to water deficit.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P

Abstract Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P

Abstract Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Selection of efficient rhizobial symbionts for Cratylia argentea in the cerrado biome / Seleção de rizóbios eficientes na simbiose com Cratylia argentea no bioma cerrado

ABSTRACT: Cratylia argentea is a leguminous shrub native to the cerrado, which has great potential for forage production and recovery of degraded areas. This study aimed to isolate, characterize, and select efficient rhizobial strains in symbiosis with Cratylia argentea . Rhizobacteria were isolated from the nodules of 12-month-old plants and cultivated in pots containing cerrado soil. Twenty-five bacterial strains were obtained, which displayed extensive variability with respect to morphological and symbiotic characteristics. Cratylia argentea seeds were planted in pots containing 5kg of cerrado soil and maintained in the greenhouse. The treatments consisted of 25 rhizobial isolates, two controls (without nitrogen and without inoculation), with or without nitrogen fertilization (5mgN·plant-1·week-1), and four replications. Plants were cultivated for 150 days after planting seeds to evaluate nodule number, nodule dry weight, shoot and root dry weight, shoot and root N content, and relative and symbiotic efficiency. Thirteen isolates improved shoot dry weight (up to 65.8%) and shoot nitrogen concentration (up to 76%) compared with those of control treatments. Two isolates, 4 (CR42) and 22 (CR52), conferred higher symbiotic efficiency values of approximately 20%. Therefore, these two rhizobial isolates displayed the highest potential as beneficial inoculants to optimize the symbiotic efficiency for Cratylia and to increase the incorporation of nutrients and biomass into the productive system in the cerrado.

RESUMO: Cratylia argentea é uma leguminosa arbustiva nativa do cerrado, com alto potencial para produção de forragem e recuperação de áreas degradadas. Este trabalho teve como objetivo isolar, caracterizar e selecionar estirpes de rizóbios eficientes na simbiose com C. argentea . As bactérias foram isoladas de nódulos de plantas com 12 meses de idade, cultivadas em solo de cerrado, em vasos. Foram obtidas 25 estirpes, que apresentaram alta variabilidade em relação às características morfológicas e simbióticas. Sementes de C. argentea foram plantadas em potes contendo 5kg de solo de cerrado, e mantidos em casa de vegetação. Os tratamentos consistiram em 25 isolados, controle (sem N e sem inoculação) e adubação nitrogenada (5mgN·planta-1·semana-1), em quatro repetições. As plantas foram colhidas 150 dias após o plantio para avaliar o número e a massa seca de nódulos, a massa seca e concentração de nitrogênio da parte área e das raízes. Foram calculadas as eficiências relativas e simbióticas. Treze estirpes se destacaram quanto ao acúmulo de massa seca (até 65,8%) e acúmulo de nitrogênio (até 76%), da parte aérea, em relação ao tratamento controle. Dentre estas, as estirpes 4 e 22 apresentaram maiores eficiências simbióticas (em torno de 20%). Portanto, estas estirpes apresentaram potencial para formulação de inoculantes, visando otimizar o processo simbiótico rizóbio- Cratylia e a incorporação de biomassa e nutrientes em sistema produtivos no cerrado.

Matéria seca e acúmulo de nutrientes em genótipos de milho contrastantes quanto a aquisição de fósforo / Dry matter and mineral nutrition in efficient corn genotypes in relation to phosphurus acquisition

Com o intuito de avaliar o efeito do estresse de P sobre atributos morfológicos do sistema radicular de genótipos de milho contrastantes quanto a eficiência na aquisição de fósforo, conduziu-se um experimento em casa-de-vegetação da Embrapa Milho e Sorgo, Sete Lagoas, MG, onde foram testados oito genótipos de milho, provenientes do programa de melhoramento da Empresa. O delineamento experimental utilizado foi o inteiramente casualizado, em esquema fatorial 8 x 2, com três repetições, correspondendo a oito genótipos (três linhagens: L1 = ineficiente, L2 e L3 = eficientes; e cinco híbridos: H1, H2 e H3 = eficientes, H4 e H5 = ineficientes) e dois níveis de P (baixo e alto). As plantas foram crescidas em solução nutritiva com duas concentrações de P equivalentes a 2,3 µM e 129 µM. A composição da solução nutritiva foi a seguinte, em mg L-1: N-NO3 152; N-NH4 18,2; Ca 141,1; K 90,1; Mg 20,8; S 18,8; Fe 4,3; Mn 0,5; B 0,27; Cu 0,04; Zn 0,15; Mo 0,08; Na 0,04 e HEDTA 20,06. Aos 18 dias do transplantio, verificou-se que, sob condições de estresse de P em solução nutritiva, os híbridos H5, H1 e H2 apresentaram os maiores valores de massa seca total e da parte aérea, em relação aos demais. De modo geral, tanto os híbridos como as linhagens, quando foram crescidos em solução com baixo nível de P, apresentaram maior relação raiz/parte aérea, do que os materiais que cresceram em solução com alto nível do nutriente. A concentração de N na parte aérea das plantas foi significativamente superior no tratamento com baixo nível de P na solução nutritiva. Os híbridos H1 e H2 e a linhagens L3 acumularam as maiores quantidades de P na parte aérea, independentemente do nível de P na solução. Esses resultados foram influenciados pelas maiores produções de produção de matéria seca apresentadas pelos referidos materiais. Independente do nível de P houve variação no conteúdo do nutriente na parte aérea dos híbridos, não sendo observado o mesmo comportamento para as linhagens.

With the objective of evaluating the effect of phosphorus stress on morphological attributes of the root system of corn genotypes contrasting in relation to phosphorus efficiency, an experiment was carried out in nutrient solution in greenhouse at Embrapa Milho e Sorgo, Sete Lagoas, MG, in the months of november and december of 2001. The experiment design was totally at random, in an 8 x 2 factorial scheme with three repetitions, corresponding to eight genotypes (three lineages: L1 = inefficient, L2 and L3 = efficient, and five hybrids: H1,H2 and H3 = efficient, H4 and H5 = inefficient) and two phosphorus levels (low = 2.3 mM and high = 129 mM). The seedlings were grown in nutrient solution with a following composition: in mg L-1: N-NO3 152; N-NH4 18,2; Ca 141,1; K 90,1; Mg 20,8; S 18,8; Fe 4,3; Mn 0,5; B 0,27; Cu 0,04; Zn 0,15; Mo 0,08; Na 0,04 e HEDTA 20,06. At 18 days after transplanting, the results showed that, under conditions of P stress in nutritive solution, the hybrids H5, H1 and H2 presented the largest values of total and shoot dry matter, in relation to the others. In general, the hybrids and inbred lines when were grown in solution with low level of P, they presented larger root-shoot relationship, than the materials grew in solution with high level of the nutrient. The concentration of N in the shoot of the plants was superior in the treatment with low level of P. The hybrids H1 and H2 and the inbred line L3 accumulated the largest amounts of P in the shoot, independently of the level of P in the solution. Independent of P level, there was variation in the nutrient content in the shoot of the hybrid, while in inbred lines were not observed the same behavior.