Hydrogel capsules as new approach for increasing drying survival of plant biostimulant gram-negative consortium.

Several plant growth-promoting bacteria (PGPB) are gram-negative, and their cell viability is affected during the bio-inoculant production. Hence, formulation-drying processes provide challenges that limit the adoption of these beneficial microorganisms in sustainable agricultural production. Among delivery system strategies for gram-negative PGPB, the encapsulating cells in biopolymeric materials are emerging as a promising alternative. This research aims to evaluate the effect of additives and crosslinking agents on the survival of the consortium of Herbaspirillum frisingense AP21, Azospirillum brasilense D7, and Rhizobium leguminosarum T88 in hydrogel capsules. Three crosslinkers and diverse potential drying protectors were tested. Calcium gluconate provides notable consortium survival advantages regarding colony-forming units (CFUs) (losses of up to 4 log CFU) compared to calcium lactate and calcium chloride (up to 6 log CFU). Additives such as skimmed milk, whey protein, and Gelita® EC improve the recovery of viable cells after the drying process, demonstrating an increase in cell survival of the three bacteria by up to 4 log CFU. The combination of these substances into a capsule prototype extends the storage stability of bacterial consortium up to 3 months at 18 ± 2 °C. This study expands the knowledge for formulating gram-negative PGPB consortium, regarding the crosslinker and drying protector relationship on encapsulation processes with drying survival and further storage stability performance. KEY POINTS: • Hydrogel immobilization formulation approach for PGPB consortium • Enhancing drying survival of gram-negative PGPB consortium • Increasing storage stability of PGPB consortium at 18 °C.

Phosphate-Solubilizing Bacteria with Low-Solubility Fertilizer Improve Soil P Availability and Yield of Kikuyu Grass.

Inoculation with phosphate-solubilizing bacteria (PSB) and the application of phosphorus (P) sources can improve soil P availability, enhancing the sustainability and efficiency of agricultural systems. The implementation of this technology in perennial grasses, such as Kikuyu grass, for cattle feed in soils with high P retention, such as Andisols, has been little explored. The objective of this study was to evaluate the productive response of Kikuyu grass and soil P dynamics to BSF inoculation with different P sources. The experiment was conducted on a Kikuyu pasture, which was evaluated for 18 months (September 2020 to March 2022). Three P fertilizers with different solubility levels were applied: diammonium phosphate (DAP) (high-solubility), rock phosphate (RP), and compost (OM) (low-solubility). Moreover, the inoculation of a PSB consortium (Azospirillum brasilense D7, Rhizobium leguminosarum T88 and Herbaspirillum sp. AP21) was tested. Inoculation with PSB and fertilization with rock phosphate (RP) increased soil labile P and acid phosphomonoesterase activity. Increased grass yield and quality were related with higher soil inorganic P (Pi) availability. This study validated, under field conditions, the benefits of PSB inoculation for soil P availability and Kikuyu grass productivity.

Does Organomineral Fertilizer Combined with Phosphate-Solubilizing Bacteria in Sugarcane Modulate Soil Microbial Community and Functions?

Soil bacterial and fungal communities are suitable soil ecosystem health indicators due to their sensitivity to management practices and their role in soil ecosystem processes. Here, information on composition and functions of bacterial and fungal communities were evaluated at two phenological stages of sugarcane (six and twelve months, equivalent to the most intensive vegetative stage and to final maturation, respectively) when organomineral fertilizer, combined with phosphate-solubilizing bacteria (PSB), was added into the soil. Organic compost enriched with apatite (C + A) or phosphorite (C + P) and compost without phosphate enrichment (C) were used in the presence or absence of PSB. In addition, we used a control fertilized with soluble triple superphosphate. The differences were more related to the sampling period than to the type of organomineral fertilizer, being observed higher available phosphorus at six months than at twelve months. Only in the C treatment we observed the presence of Bacillaceae and Planococcaceae, while Pseudomonadaceae were only prevalent in inoculated C + A. As for fungi, the genera Chaetomium and Achroiostachys were only present in inoculated C + P, while the genus Naganishia was most evident in inoculated C + A and in uninoculated C + P. Soliccocozyma represented 75% of the total fungal abundance in uninoculated C while in inoculated C, it represented 45%. The bacterial community was more related to the degradation of easily decomposable organic compounds, while the fungal community was more related to degradation of complex organic compounds. Although the microbial community showed a resilient trait, subtle changes were detected in microbial community composition and function, and this may be related to the increase in yield observed.

Potential of Herbaspirillum and Azospirillum Consortium to Promote Growth of Perennial Ryegrass under Water Deficit.

Plant growth-promoting bacteria (PGPB) can mitigate the effect of abiotic stresses on plant growth and development; however, the degree of plant response is host-specific. The present study aimed to assess the growth-promoting effect of Herbaspirillum (AP21, AP02), Azospirillum (D7), and Pseudomonas (N7) strains (single and co-inoculated) in perennial ryegrass plants subjected to drought. The plants were grown under controlled conditions and subjected to water deficit for 10 days. A significant increase of approximately 30% in dry biomass production was observed using three co-inoculation combinations (p < 0.01). Genomic analysis enabled the detection of representative genes associated with plant colonization and growth promotion. In vitro tests revealed that all the strains could produce indolic compounds and exopolysaccharides and suggested that they could promote plant growth via volatile organic compounds. Co-inoculations mostly decreased the in vitro-tested growth-promoting traits; however, the co-inoculation of Herbaspirillum sp. AP21 and Azospirillum brasilense D7 resulted in the highest indolic compound production (p < 0.05). Although the Azospirillum strain showed the highest potential in the in vitro and in silico tests, the plants responded better when PGPB were co-inoculated, demonstrating the importance of integrating in silico, in vitro, and in vivo assessment results when selecting PGPB to mitigate drought stress.

Dry-Caribbean Bacillus spp. Strains Ameliorate Drought Stress in Maize by a Strain-Specific Antioxidant Response Modulation.

Drought is a global problem for crop productivity. Therefore, the objective of this research was to evaluate five dry-Caribbean Bacillus spp. strains in drought stress amelioration in maize plants. Maize seeds were single-strain inoculated and sown in pots under greenhouse conditions. After 12 days, plants were subjected to 33 days of drought conditions, i.e., 30% of soil field capacity, and then collected to measure leaf and root dry biomass, plant height, antioxidant enzymes, proline accumulation, and P+, Ca2+, and K+ uptake. Results correlated drought stress amelioration with the inoculation of Bacillus spp. strains XT13, XT38 and XT110. Inoculated plants showed increases in dry biomass, plant height, and K+ and P+ uptake. The overall maize antioxidant response to bacterial inoculation under drought stress showed dependence on proline accumulation and decreases in ascorbate peroxidase and glutathione reductase activities. Moreover, results suggest that this stress amelioration is driven by a specific plant-strain correlation observed in antioxidant response changes in inoculated plants under stress. Also, there is a complex integration of several mechanisms, including plant growth-promotion traits and nutrient uptake. Hence, the use of dry-Caribbean plant growth-promoting Bacillus strains represents an important biotechnological approach to enhance crop productivity in arid and semi-arid environments.

Gluconacetobacter diazotrophicus Changes The Molecular Mechanisms of Root Development in Oryza sativa L. Growing Under Water Stress.

BACKGROUND: Inoculation with Gluconacetobacter diazotrophicus has shown to influence root development in red rice plants, and more recently, the induced systemic tolerance (IST) response to drought was also demonstrated. The goal of this study was to evaluate the inoculation effect of G. diazotrophicus strain Pal5 on the amelioration of drought stress and root development in red rice (Oryza sativa L.). METHODS: The experimental treatments consist of red rice plants inoculated with and without strain Pal5 in presence and absence of water restriction. Physiological, biochemical, and molecular analyses of plant roots were carried out, along with measurements of growth and biochemical components. RESULTS: The plants showed a positive response to the bacterial inoculation, with root growth promotion and induction of tolerance to drought. An increase in the root area and higher levels of osmoprotectant solutes were observed in roots. Bacterial inoculation increased the drought tolerance and positively regulated certain root development genes against the water deficit in plants. CONCLUSION: G. diazotrophicus Pal5 strain inoculation favored red rice plants by promoting various root growth and developmental mechanisms against drought stress, enabling root development and improving biochemical composition.

Soil mesofauna in consolidated land use systems: how management affects soil and litter invertebrates

Soil mesofauna consists of small invertebrates that live in the soil or litter and are sensitive to climatic conditions, management systems, plant cover and physical or chemical soil attributes. These organisms are active in the cycling of nutrients, since they fragment the organic matter hereby accelerating microbial decomposition. The aim of this study was to evaluate the invertebrate community in no-tillage, conventional tillage, minimum tillage and secondary forest in regeneration to determine the relationship of mesofauna to litter, soil attributes, management and seasonality. Therefore, ten soil samples in each system and eight litter samples in no-tillage and the forest were taken over four seasons. These samples remained in Berlese extractors for seven days for quantification and identification of mesofauna. For each fauna sample, soil samples were collected for chemical analysis. Next, diversity indices and richness were calculated and multivariate analyses were used to establish relationships between the mesofauna, soil attributes and management. In the soil, mites were more abundant in the agricultural systems than in the forest, but the springtails, sensitive to low moisture and high temperature, were more abundant in the forest. Diversity and richness were higher in soil from the forest than under other systems. In no-tillage, there was a lower density of soil mesofauna, however, under this system, many invertebrates live in litter, since litter is the main food resource for them. In forest litter, we found lower invertebrate density and higher diversity than in no-tillage. Carbon, basic cations, pH, Al and V% were the attributes that best explained fauna variability in the systems.

Soil mesofauna in consolidated land use systems: how management affects soil and litter invertebrates

Soil mesofauna consists of small invertebrates that live in the soil or litter and are sensitive to climatic conditions, management systems, plant cover and physical or chemical soil attributes. These organisms are active in the cycling of nutrients, since they fragment the organic matter hereby accelerating microbial decomposition. The aim of this study was to evaluate the invertebrate community in no-tillage, conventional tillage, minimum tillage and secondary forest in regeneration to determine the relationship of mesofauna to litter, soil attributes, management and seasonality. Therefore, ten soil samples in each system and eight litter samples in no-tillage and the forest were taken over four seasons. These samples remained in Berlese extractors for seven days for quantification and identification of mesofauna. For each fauna sample, soil samples were collected for chemical analysis. Next, diversity indices and richness were calculated and multivariate analyses were used to establish relationships between the mesofauna, soil attributes and management. In the soil, mites were more abundant in the agricultural systems than in the forest, but the springtails, sensitive to low moisture and high temperature, were more abundant in the forest. Diversity and richness were higher in soil from the forest than under other systems. In no-tillage, there was a lower density of soil mesofauna, however, under this system, many invertebrates live in litter, since litter is the main food resource for them. In forest litter, we found lower invertebrate density and higher diversity than in no-tillage. Carbon, basic cations, pH, Al and V% were the attributes that best explained fauna variability in the systems.(AU)

Characterization of diazotrophic phosphate solubilizing bacteria as growth promoters of maize plants / Caracterización de bacterias diazotróficas solublizadoras de fosfato como promotoras de crecimiento en plantas de maíz

Phosphorus is limiting for growth of maize plants, and because of that use of fertilizers like rock phosphate has been proposed. However, direct use of rock phosphate is not recommended because of its low availability, so it is necessary to improve it. In this study, a group of diazotrophic bacteria were evaluated as phosphate-solubilizing bacteria, for their production of indolic compounds and for their effects on growth of maize plants. Strains of the genera Azosporillum, Azotobacter, Rhizobium and Klebsiella, were quantitatively evaluated for solubilization of Ca3(PO4)2 and Rock Phosphate as a single source of phosphorous in SRS culture media. Additionally, the phosphatase enzyme activity was quantified at pH 5.0, 7.0 and 8.0 using p-nitrophenyl phosphate, and production of indolic compounds was determined by colorimetric quantification. The effect of inoculation of bacteria on maize was determined in a completely randomized greenhouse experiment where root and shoot dry weights and phosphorus content were assessed. Results showed that strain C50 produced 107.2 mg.L-1 of available-P after 12 days of fermentation, and AC10 strain had the highest phosphatase activity at pH 8 with 12.7 mg of p-nitrophenol mL.h-1. All strains synthetized indolic compounds, and strain AV5 strain produced the most at 63.03 µg.mL-1. These diazotrophic bacteria increased plant biomass up to 39 % and accumulation of phosphorus by 10%. Hence, use of diazotrophic phosphate-solubilizing bacteria may represent an alternative technology for fertilization systems in maize plants.

El fósforo es limitante para el crecimiento de plantas de maíz y debido a eso se ha propuesto el uso de fertilizantes como la roca fosfórica. Sin embargo, el uso directo de roca fosfórica no es recomendado por su baja solubilidad, por lo que es necesario mejorarlo. En este estudio, un grupo de bacterias diazotróficas fueron evaluadas como bacterias solubilizadoras de fosfato, productoras de compuestos indólicos y sus efectos sobre el crecimiento de plantas de maíz. Cepas de los géneros Azospirillum, Azotobacter, Rhizobium y Klebsiella fueron evaluadas cuantitativamente en la solubilización de Ca3(PO4)2 y roca fosfórica como única fuente de fósforo en medio de cultivo SRS. Adicionalmente, la actividad de la enzima fosfatasa fue cuantificada a pH 5.0, 7.0 y 8.0 usando p-nitrofenil fosfato y, la producción de compuestos indólicos fue determinada por cuantificación colorimétrica. El efecto de la inoculación de las bacterias sobre plantas de maíz fue determinado en un experimento en invernadero con un diseño completamente al azar donde los pesos secos de raíz y hojas y el contenido de fósforo fueron evaluados. Los resultados mostraron que la cepa C50 produjo 107.2 mg.L-1 de fósforo disponible después de 12 días de fermentación y que la cepa AC10 tuvo la más alta actividad fosfatasa a pH 8 con 12.7 mg de p-nitrofenol mL.h-1. Todas las cepas sintetizaron compuestos indólicos y la cepa AV5 produjo la más alta cantidad con 63.03 µg.mL-1. Estas bacterias diazotróficas incrementaron la biomasa de las plantas por encima del 39 % y de la acumulación de fósforo por el 10 %. Aquí, el uso de bacterias diazotróficas solubilizadoras de fosfato puede representar una alternativa tecnológica para los sistemas de fertilización en plantas de maíz.