Sulfur is an essential element in determining the productivity and quality of agricultural products. It is also an element associated with tolerance to biotic and abiotic stress in plants. In agricultural practice, sulfur has broad use in the form of sulfate fertilizers and, to a lesser extent, as sulfite biostimulants. When used in the form of bulk elemental sulfur, or micro- or nano-sulfur, applied both to the soil and to the canopy, the element undergoes a series of changes in its oxidation state, produced by various intermediaries that apparently act as biostimulants and promoters of stress tolerance. The final result is sulfate S⁺⁶, which is the source of sulfur that all soil organisms assimilate and that plants absorb by their root cells. The changes in the oxidation states of sulfur S⁰ to S⁺⁶ depend on the action of specific groups of edaphic bacteria. In plant cells, S⁺⁶ sulfate is reduced to S⁻² and incorporated into biological molecules. S⁻² is also absorbed by stomata from H₂S, COS, and other atmospheric sources. S⁻² is the precursor of inorganic polysulfides, organic polysulfanes, and H₂S, the action of which has been described in cell signaling and biostimulation in plants. S⁻² is also the basis of essential biological molecules in signaling, metabolism, and stress tolerance, such as reactive sulfur species (RSS), SAM, glutathione, and phytochelatins. The present review describes the dynamics of sulfur in soil and plants, considering elemental sulfur as the starting point, and, as a final point, the sulfur accumulated as S⁻² in biological structures. The factors that modify the behavior of the different components of the sulfur cycle in the soil–plant–atmosphere system, and how these influences the productivity, quality, and stress tolerance of crops, are described. The internal and external factors that influence the cellular production of S⁻² and polysulfides vs. other S species are also described. The impact of elemental sulfur is compared with that of sulfates, in the context of proper soil management. The conclusion is that the use of elemental sulfur is recommended over that of sulfates, since it is beneficial for the soil microbiome, for productivity and nutritional quality of crops, and also allows the increased tolerance of plants to environmental stresses.

Selenium is an element that must be considered in the nutrition of certain crops since its use allows the obtaining of biofortified crops with a positive impact on human health. The objective of this review is to present the information on the use of Se and S in the cultivation of plants of the genus Allium. The main proposal is to use Allium as specialist plants for biofortification with Se and S, considering the natural ability to accumulate both elements in different phytochemicals, which promotes the functional value of Allium. In spite of this, in the agricultural production of these species, the addition of sulfur is not realized to obtain functional foods and plants more resistant; it is only sought to cover the necessary requirements for growth. On the other hand, selenium does not appear in the agronomic management plans of most of the producers. Including S and Se fertilization as part of agronomic management can substantially improve Allium crop production. Allium species may be suitable to carry out biofortification with Se; this practice can be combined with the intensive use of S to obtain crops with higher production and sensory, nutritional, and functional quality.

Environmental stress has regulated the function, morphology, and diversity of cells, organs, individuals and plant communities. The interaction of plants with the stress-inducing environments has produced in the plants a set of adaptive responses that can be studied in different description scopes: from organelles and subcellular structures to the level of plant communities. When it occurs for short time or low intensity, environmental stress can induce hardening, followed by induction of tolerance; on the other hand, when the plant´s reaction is for a long time or responding to a significant stress intensity, the response of plants includes decreased growth, depletion of metabolic reserves and loss of productivity and yield, even reaching the death of plants. Current knowledge about these crop responses can be translated into agronomic practices aimed at mitigating the adverse effects of environmental stress. This chapter will present the mechanisms of response and adaptation of crop plants to the environmental factors that most commonly cause crop damage or yield loss: high and low temperature, salinity, water deficit and nutrient deficits. Agronomic practices aimed at modifying or balancing some of the environmental factors involved and the use of tolerance induction techniques are described.

Fusarium oxysporum causes vascular wilt disease in a broad range of crops, including tomato (Solanum lycopersicum). Tomato, a major and important vegetable crop, is susceptible to F. oxysporum f. sp. lycopersici (FOL), a biotrophic pathogen that is the causal agent of tomato wilt resulting in significant yield losses each year. Development of disease in susceptible tomato plants requires FOL to advance through a series of transitions, beginning with spore germination and culminating with establishment of a systemic infection. In addition, many host attributes, including the composition of root exudates, the structure of the root cortex, and the capacity to recognize and respond quickly to invasive growth of a pathogen, can impede the development of FOL. FOL divides into races on the basis of the ability of individual strains to overcome specific genes. This implies the presence of avirulence genes (Avr) in the fungus that is recognized by products of the corresponding genes. In tomato, resistance (R) genes against the wilt-inducing FOL are called immunity genes, and the interaction between these genes will determine the success of the infection.