One of the most notorious pathogens affecting tobacco production is tobacco bacterial wilt (TBW), caused by Ralstonia solanacearum. Controlling TBW is a global issue, and developing more resistant cultivars is one of the solutions. Therefore, this study investigated the effectiveness of recurrent selection (RS) as a breeding strategy to enhance resistance to R. solanacearum in tobacco. We also aimed to identify the appropriate progeny type for RS. The trials were carried out in an area where the pathogen is known to occur, with seedlings inoculated with R. solanacearum to assure the presence of the pathogen. The incidence of the pathogen was evaluated over two seasons. In the first year, we utilized 100 S-1:2 progeny from the original population (cycle 0) and 108 half-sib progeny of cycle I. In the subsequent year, we evaluated 196 S0:1 progeny of CI and 176 half-sib progeny of cycle II. Additionally, to ensure the presence of the pathogen, we inoculated R. solanacearum 40-45 days after transplanting the seedlings. The incidence of the pathogen was assessed based on the number of plants showing symptoms (%). Although the difference between cycle 0 and cycle II was relatively small, the results suggest that recurrent selection was successful in accumulatingresistance alleles, as reflected in the positive association between disease resistance and agronomic traits.
Soybean monoculture (Glycine max) and second-crop corn succession in the Cerrado reduce soil quality and compromise long-term productivity. Adopting conservation practices such as crop rotation, cover crops, and multifunctional rhizobacteria is essential for sustainable soybean cultivation in the region. This study aimed to determine the effect of mixes of cover crops grown in the second crop in rotation with upland rice and co-inoculation of soybeans with multifunctional rhizobacteria on the physical, chemical, and biological quality of the soil and the nutrient accumulation, biomass production, production components, and yield of the soybean crop. The experiment was conducted in a randomized block design, arranged in a 7x2 factorial scheme, with 14 treatments and four replications. Treatments included five cover crop mixes and two fallows (rice/fallow/soybean and soybean/fallow/soybean), with or without co-inoculation of seeds with Bacillus sp. (BRM 63573) and Serratia marcensces (BRM 32114). Rotation with upland rice and cover crop mixes provided higher P and Zn content in the soil, higher activity of the β-Glycosidase enzyme, lower density, better total porosity, lower incidence of phytopathogenic fungi Fusarium solani and Rhizoctonia solani and greater biomass production, greater macro and micronutrient content in the aerial part, greater number of pods per plant and grain yield of the soybean crop concerning the areas that remained fallow. Fallow 2 (soybean/fallow/soybean) provided the worst results for most of the analyzed variables. Co-inoculation provided higher soil microporosity, lower density of the phytopathogenic fungus (Fusarium oxysporum) in the soil, and greater biomass production and nutrient accumulation in the shoot of soybean plants compared to treatment without co-inoculation.
The use of cover crops during the winter period is the foundation of the no-till system and provides physical, chemical, and biological benefits to the soil. A high biomass input from cover crops and benefits related to nutrient cycling also enhance the presence of beneficial soil microorganisms. Thus, this study aimed to evaluate dry matter phytomass production, the soil coverage curve with cover crops, and the decomposition curve of dry matter phytomass in monoculture and cover crop mixtures in a subtropical environment. The following cover crop treatments were evaluated during the winters of 2022 and 2023 using a randomized block experimental design: black oat, rye, common vetch, forage radish, black oat + common vetch, black oat + forage radish, black oat + common vetch + forage radish, rye + common vetch, rye + forage radish, and rye + common vetch + forage radish. Dry matter phytomass production, soil coverage, and dry matter phytomass decomposition were measured using the litter bag method. Black oat and forage radish in monoculture stood out for their dry matter phytomass production, and forage radish excelled in mixed treatments, presenting values exceeding 50% of the composition in all cases. Soil coverage was adequate for black oat, rye, common vetch, and forage radish in monoculture and their intercropping systems. After 150 days of decomposition, black oat and rye exhibited the lowest decomposition rates, and the cover crop mixtures showed intermediate decomposition rates, confirming their suitability as autumn/winter cover crops in subtropical environments.
The use of nitrogen fertilizers in maize crops must be reduced, and a potential alternative is the use of diazotrophic bacteria of the genus Azospirillum. This research aims to characterize the efficiency of the association with Azospirillum brasilense (Az) among maize genotypes on grain yield. Forty-eight experimental single-cross maize hybrids obtained from the cross in a partial diallel scheme between eight and six inbred lines were used. The maize hybrids were evaluated in seven environments, considering the grain yield (GY) without nitrogen (N) topdressing and without Az inoculation, GY with N topdressing and without Az inoculation, GY without N topdressing but with Az inoculation, and the efficiency to Az. The hybrids’ GY varied in the presence of Az, indicating a differential response to the bacteria and confirming that this association enables the selection of more efficient genotypes since some hybrids maintained similar yield levels when N topdressing was replaced by Az inoculation. Low or medium correlation estimates were obtained among the considered traits, indicating a low correspondence between yields under the different conditions and between yields and the efficiency of the association with Az, suggesting that indirect selection for these traits is not efficient. These results indicate that it is possible to select the most efficient maize genotypes.
Cadmium (Cd) and lead (Pb) contamination in agricultural and urban soils poses significant environmental and human health risks, especially in areas impacted by metallurgical waste. In this study, the efficacy of four biochars produced from rice straw (RSB), sugarcane bagasse (SBB), sewage sludge (SSB), and filter cake (FCB), in immobilizing Cd and Pb and improving soil chemical properties, was assessed. An incubation experiment was conducted using contaminated soil from Santo Amaro, Brazil, a site historically affected by lead smelting. Biochars were applied at 10% (w/w), and their effects on soil pH, nutrient availability, organic matter (SOM), and metal fractionation were evaluated. Compared with the control treatment, the SBB and FCB treatments significantly reduced the availability of Cd (~30%) and Pb (~20%). These biochars also increased phosphorus (P) availability and increased the SOM content. Sequential extraction indicated a shift of Cd and Pb from labile to more stable forms, particularly the reducible and residual fractions, suggesting improved long-term immobilization. The superior performance of SBB and FCB was attributed to their higher SOM and P contents, as well as functional groups that promote metal complexation. Overall, the findings demonstrate the potential of nutrient-rich, waste-derived biochars as a sustainable and cost-effective solution for the remediation of heavy metal-contaminated soils. The results highlight the importance of selecting biochars based on feedstock characteristics and underscore the need for field-based studies to evaluate their long-term stability and the effects on metal uptake by plants.
