Artenisa Cerqueira Rodrigues

Interrelationship of Bradyrhizobium sp. and plant growth-promoting bacteria in cowpea: Survival and symbiotic performance

The objective of this study was to evaluate the survival of cowpea during bacterial colonization and evaluate the interrelationship of the Bradyrhizobium sp. and plant growth-promoting bacteria (PGPB) as a potential method for optimizing symbiotic performance and cowpea development. Two experiments using the model legume cowpea cv. “IPA 206” were conducted. In the first experiment, cowpea seeds were disinfected, germinated and transferred to sterilized Gibson tubes containing a nitrogen-free nutritive solution. The experimental design was randomized blocks with 24 treatments [Bradyrhizobium sp. (BR 3267); 22 PGPB; absolute control (AC)] with three replicates. In the second experiment, seeds were disinfected, inoculated according to their specific treatment and grown in Leonard jars containing washed and autoclaved sand. The experimental design was randomized blocks with 24 treatments [BR 3267; 22 BR 3267 + PGPB; AC] with three replicates. Scanning electron microscopy demonstrated satisfactory colonization of the roots of inoculated plants. Additionally, synergism between BR 3267 and PGPB in cowpeas was observed, particularly in the BR 3267 + Paenibacillus graminis (MC 04.21) and BR 3267 + P. durus (C 04.50), which showed greater symbiotic performance and promotion of cowpea development.

Plant Growth-Promoting Rhizobacteria: Key Mechanisms of Action

Plant growth-promoting rhizobacteria (PGPR) have gained worldwide importance and acceptance for their agricultural benefits through the application of combinations of different mechanisms of action, which allows increases in crop yield. This is due to the emerging demand for reduced dependence on synthetic chemical products and to the growing necessity of sustainable agriculture within a holistic vision of development and environmental protection. The use of selected plant-beneficial rhizobacteria may represent an important biotechnological approach to alleviate the negative effects of stress and to optimize nutrient cycling in different crops. Recent progress in our understanding of their action mechanisms, diversity, colonization ability, formulation, and application should facilitate their development as reliable components in the management of sustainable agricultural systems. In addition, numerous studies indicate increased crop performance with the use of these microorganisms. In this chapter, an understanding of the direct and indirect mechanisms of action of PGPR and their various benefits to plants are summarized and discussed.

Changes induced by co-inoculation in nitrogen–carbon metabolism in cowpea under salinity stress

To mitigate the deleterious effects of abiotic stress, the use of plant growth-promoting bacteria along with diazotrophic bacteria has been increasing. The objectives of this study were to investigate the key enzymes related to nitrogen and carbon metabolism in the biological nitrogen fixation process and to elucidate the activities of these enzymes by the synergistic interaction between Bradyrhizobium and plant growth-promoting bacteria in the absence and presence of salt stress. Cowpea plants were cultivated under axenic conditions, inoculated with Bradyrhizobium and co-inoculated with Bradyrhizobium sp. and Actinomadura sp., Bradyrhizobium sp. and Bacillus sp., Bradyrhizobium sp. and Paenibacillus graminis, and Bradyrhizobium sp. and Streptomycessp.; the plants were also maintained in the absence (control) and presence of salt stress (50 mmolL−1 NaCl). Salinity reduced the amino acids, free ammonia, ureides, proteins and total nitrogen content in nodules and increased the levels of sucrose and soluble sugars. The co-inoculations responded differently to the activity of glutamine synthetase enzymes under salt stress, as well as glutamate synthase, glutamate dehydrogenase aminating, and acid invertase in the control and salt stress. Considering the development conditions of this experiment, co-inoculation with Bradyrhizobium sp. and Bacillus sp. in cowpea provided better symbiotic performance, mitigating the deleterious effects of salt stress.

Symbiotic performance, nitrogen flux and growth of lima bean ( Phaseolus lunatus L.) varieties inoculated with different indigenous strains of rhizobia

Legumes, such as lima bean, can form symbiotic relationships with rhizobia and can therefore grow in nitrogen-poor soils. Lima bean varieties in symbiosis with indigenous rhizobia were evaluated for their symbiotic performance over three harvest periods. Four indigenous rhizobial strains (ISOL-16, ISOL-18, ISOL-19 or ISOL-35) were isolated from soil samples in lima bean fields and used separately to inoculate two lima bean varieties (‘boca de moça’ and ‘branca’). Uninoculated, unfertilized plants were used as controls, and uninoculated, nitrogen-supplied plants were used as the nitrogen control. All inoculated plants and the uninoculated control were cultivated using nitrogen-free nutrient solutions in the greenhouse. As expected, the uninoculated plants did not develop nodules on their root systems and were inferior in all evaluated parameters. The lima bean nodulated by Bradyrhizobium exhibited growth variables, nodules parameters, and nitrogen flux values superior to those of plants inoculated with Rhizobium. The highest total chlorophyll values were recorded in lima bean inoculated with Bradyrhizobium, confirming that these plants had the greenest leaves and likely have superior photosynthetic efficiency – a hypothesis supported by the greater growth exhibited by these plants. Nitrogen fixation efficiency was superior in lima bean nodulated by Bradyrhizobium, indicating that this microbe possesses a greater ability to fix nitrogen and provide it continuously to the host plant. The symbiosis between lima bean and Bradyrhizobium sp. ISOL-18 displayed the best values with respect to carbon and nitrogen flow. We conclude that Bradyrhizobium is the most effective at establishing an efficient and successful symbiotic relationship with lima bean and emphasize the potential value of Bradyrhizobium strains as inoculants in lima bean cultivation.

Severidade de antracnose em folhas de sorgo submetido a doses crescentes de silício

A antracnose foliar e causada pelo fungo Colletotrichum sublineolum Hann. Kabat et Bub. (sin. C. graminicola (Ces.) G.W. Wils.) em plantas de sorgo podendo reduzir a produtividade de graos e forragem, e o manejo adequado da nutricao mineral desta planta pode se apresentar como um mecanismo de controle sobre a antracnose. Dentre os minerais utilizados para o manejo de doencas, o silicio destaca-se por reduzir a severidade das doencas em varias culturas. Diante do exposto, este trabalho teve por objetivo avaliar a severidade da antracnose em diferentes genotipos de sorgo suplementados com doses crescentes de silicio. Para tal, realizaram-se experimentos em condicoes de casa de vegetacao e de campo onde os genotipos de sorgo DOW 1F305 e A9735R foram suplementados com doses crescentes de silicio (0; 500; 1.000; 1.500; 2.000; e 4.000 kg ha-1) e avaliados quanto a severidade da antracnose. Avaliou-se a severidade da doenca por meio de uma escala de notas e, em seguida, amostras foram coletadas para determinacao da concentracao de silicio nas folhas. Apos a analise dos resultados, concluiu-se que houve reducao na severidade da antracnose em resposta a adubacao com silicio para ambos os genotipos avaliados. Apesar do genotipo de sorgo DOW 1F305 acumular menores teores de silicio em suas folhas, este genotipo foi mais resistente ao ataque da antracnose foliar.

Antioxidant response of cowpea co-inoculated with plant growth-promoting bacteria under salt stress

Soil salinity is an important abiotic stress worldwide, and salt-induced oxidative stress can have detrimental effects on the biological nitrogen fixation. We hypothesized that co-inoculation of cowpea plants with Bradyrhizobium and plant growth-promoting bacteria would minimize the deleterious effects of salt stress via the induction of enzymatic and non-enzymatic antioxidative protection. To test our hypothesis, cowpea seeds were inoculated with Bradyrhizobium or co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and then submitted to salt stress. Afterward, the cowpea nodules were collected, and the levels of hydrogen peroxide; lipid peroxidation; total, reduced and oxidized forms of ascorbate and glutathione; and superoxide dismutase, catalase and phenol peroxidase activities were evaluated. The sodium and potassium ion concentrations were measured in shoot samples. Cowpea plants did not present significant differences in sodium and potassium levels when grown under non-saline conditions, but sodium content was strongly increased under salt stress conditions. Under non-saline and salt stress conditions, plants co-inoculated with Bradyrhizobium and Actinomadura or co-inoculated with Bradyrhizobium and Paenibacillus graminis showed lower hydrogen peroxide content in their nodules, whereas lipid peroxidation was increased by 31% in plants that were subjected to salt stress. Furthermore, cowpea nodules co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and exposed to salt stress displayed significant alterations in the total, reduced and oxidized forms of ascorbate and glutathione. Inoculation with Bradyrhizobium and plant growth-promoting bacteria induced increased superoxide dismutase, catalase and phenol peroxidase activities in the nodules of cowpea plants exposed to salt stress. The catalase activity in plants co-inoculated with Bradyrhizobium and Streptomyces was 55% greater than in plants inoculated with Bradyrhizobium alone, and this value was remarkably greater than that in the other treatments. These results reinforce the beneficial effects of plant growth-promoting bacteria on the antioxidant system that detoxifies reactive oxygen species. We concluded that the combination of Bradyrhizobium and plant growth-promoting bacteria induces positive responses for coping with salt-induced oxidative stress in cowpea nodules, mainly in plants co-inoculated with Bradyrhizobium and P. graminis or co-inoculated with Bradyrhizobium and Bacillus.