Tetranychus ludeni (Acari: Tetranychidae) infestation triggers a spatiotemporal redox response dependent on soybean genotypes.

MAIN CONCLUSION: The redox homeostasis and photosynthetic pigments changes vary with Tetranychus ludeni infestation, with longer-cycle genotypes showing greater tolerance and efficiency in antioxidant defense. Infestations of Tetranychus ludeni Zacher (Tetranychidae) have been frequently observed in soybean plants. In this context, understanding the oscillation of redox homeostasis is crucial for detecting and assessing the stress levels caused in the plants by these organisms. The impacts of these infestations on redox metabolism and photosynthetic pigments are currently unknown. Therefore, we examined the hypothesis that T. ludeni infestations in soybean plants can influence redox homeostasis and photosynthetic pigments in a spatiotemporal manner, varying between different infestation times, modules and genotypes. For this purpose, soybean plants of the genotypes Monsoy, maturity group 5.7, and Brasmax, maturity group 6.3, grown in a controlled environment, were exposed to infestation and evaluated at two periods: 14 and 24 days. A variation in the distribution of T. ludeni within the infested plants over time increased the activity of ascorbate peroxidase and catalase, especially in Monsoy, reducing the content of hydrogen peroxide and superoxide, which prevented lipid peroxidation in the apical region in both genotypes. In the basal region, low chlorophyll indices corroborated by the yellow coloration of trifoliate leaves, high levels of membrane stability loss, and accumulation of hydrogen peroxide and superoxide characterized senescent trifoliate leaves in Brasmax, 24 days post infestation. Thus, the infestation of T. ludeni has a complex and significant impact on the redox metabolism of soybean plants, especially in shorter-cycle genotypes such as Brasmax. Furthermore, the oscillation of homeostasis can be considered as a good biochemical marker for selecting more suitable genotypes that are less sensitive and prone to infestations.

Impacts of cultivar and management practices on the diversity and population dynamics of mites in soybean crops.

The objective of this study was to evaluate the diversity and population dynamics of mites in soybean crops with different cultivars and management practices. The study was conducted in two soybean production fields in the municipalities of Mato Queimado (L1) and Três de Maio (L2), Rio Grande do Sul state, Brazil. Two transgenic cultivars were used, and insecticide applications varied among treatments. Sampling began at the V2 stage, with 60 leaves/area/collection that were sorted, mites were collected and identified using dichotomous keys. A total of 18,100 mites belonging to 12 species were found. Among the species, Tetranychus urticae Koch, Mononychellus planki (McGregor), and Tetranychus ludeni Zacher (Tetranychidae) were the most abundant, whereas the most abundant predatory mites were the phytoseiids Neoseiulus californicus McGregor and Neoseiulus idaeus Denmark and Muma, with N. idaeus being more abundant and present in all areas. The acarofauna was influenced by environmental conditions and management practices. Neoseiulus idaeus was commonly associated with populations of M. planki, T. ludeni, and T. urticae. Neoseiulus californicus tolerated pesticide use but was affected by severe water stress, whereas N. idaeus tolerated periods of low relative humidity and high temperatures.

Soybean Root Growth in Response to Chemical, Physical, and Biological Soil Variations.

Environmental conditions affect crop yield, and water deficit has been highlighted by the negative impact on soybean grain production. Radicial growth in greater volume and depth can be an alternative to minimize losses caused by a lack of water. Therefore, knowledge of how soybean roots behave before the chemical, physical, and biological attributes of the soil can help establish managements that benefit in-depth root growth. The objective was to evaluate the growth of soybean roots in response to chemical, physical, and biological variations in the soil, in different soil locations and depths. Six experiments were conducted in different locations. Soil samples were collected every 5 cm of soil up to 60 cm of soil depth for chemical, physical, and biological analysis. The roots were collected every 5 cm deep up to 45 cm deep from the ground. The six sites presented unsatisfactory values of pH and organic matter, and presented phosphorus, potassium, and calcium at high concentrations in the first centimeters of soil depth. The total porosity of the soil was above 0.50 m3 m-3, but the proportion of the volume of macropores, micropores, and cryptopores resulted in soils with resistance to penetration to the roots. Microbial biomass was higher on the soil surface when compared to deeper soil layers, however, the metabolic quotient was higher in soil depth, showing that microorganisms in depth have low ability to incorporate carbon into microbial biomass. Root growth occurred in a greater proportion in the first centimeters of soil-depth, possibly because the soil attributes that favor the root growth is concentrated on the soil surface.

Soybean Plant Metabolism under Water Deficit and Xenobiotic and Antioxidant Agent Application.

The aim was to evaluate the interactive effects on biochemistry and physiology of soybean plants exposed to simultaneous xenobiotic and water deficit stresses, and the possible attenuation of plant damage by an antioxidant agent. Soybean plants were submitted to eight different soil water potentials, in two experiments (first experiment: -0.96, -0.38, -0.07, -0.02 MPa, and second experiment: -3.09, -1.38, -0.69, -0.14 MPa), xenobiotic, and antioxidant agent applications. Was observed a reduction in water status, gas exchange, photosynthetic pigments, photosystem II quantum yield, and increased leaf temperature in plants under low water availability. Water deficit also induced oxidative stress by the increased production of reactive oxygen species, cellular and molecular damage, and induction of the antioxidant defense metabolism, reduction of gas exchange, water status, and photosynthetic efficiency. The xenobiotic application also caused changes, with deleterious effects more pronounced in low soil water availability, mainly the reactive oxygen species production, consequently the antioxidant activity, and the oxidative damages. This indicates different responses to the combination of stresses. Antioxidant enzyme activity was reduced by the application of the antioxidant agent. Principal Component Analysis showed a relation with the antioxidant agent and reactive oxygen species, which is probably due to signaling function, and with defense antioxidant system, mainly glutathione, represented by thiols.