Tropical and subtropical agroecosystems

Background: Corn is a cereal of great importance in human and animal food; which, guarantees food security and global economy. In Peru, corn is cultivated under conventional agriculture that is dependent on agrochemicals. Objective: To evaluate the combined effect of different foliar doses of hydrogen peroxide and compost on the initial development of corn seedlings. Methodology: Commercial hydrogen peroxide (CHP) (H2O2 at a concentration of 3 g 100 mL-1) and compost-C were evaluated in the treatments:  T0 (control-conventional), T1 (C-2.5% CHP), T2 (C-5% CHP), T3 (C-10% CHP). The morphometric variables were: plant height (PH), root length (RL), number of leaves (NL) and stem diameter (SD) and biomass: aerial fresh weight (AFW), aerial dry weight (ADW), root fresh weight (RFW), root dry weight (RDW) at 26 and 39 DAP (days after planting), Brix grades (°B) were evaluated on the last date. Results: T2 and T3 treatments significantly improved RL and NL at 26 DAP; however, at 39 DAP, T2 increased PH, AFW, RFW, ADW, RDW and °B; and T3 increased RL. The highest positive correlation between variables was present at 39 DAP with respect to 36 DAP. Implications: The combined effect of “CHP” and “C” improves plant performance through a good distribution of organic carbon (glucids) obtained from carbon dioxide fixation and reduces fertilizer use. Conclusion: Treatments T2 and T3 significantly increased the variables under study at 39 DAP. Likewise, the positive correlation between the variables improved.

Background: Comalcalco stands out as one of the municipalities with the largest number of oil facilities in the state of Tabasco, Mexico. The expansion of human settlements, along with the growing demand for food, housing, services, and other needs in recent years, has exerted significant pressure on natural resources, leading to land-use changes that often have negative impacts on them. Objective: To analyze the dynamics of land use changes in the municipality during the periods 1986–2003 and 2023. Methodology: Landsat satellite images were classified and analyzed using the Land Change Modeler module in TerrSet. Results: The main findings indicate that land cover changes have been driven primarily by two transformative forces: government policies that strongly shape land use and the oil industry, which has been present in the municipal territory since the 1970s. Implications: Projections for 2035 reveal a continuous process of territorial transformation in the municipality, characterized by the expansion of human settlements and the reduction of natural cover. The significant loss of hydrophytic vegetation, grasslands, and arboreal vegetation implies a deterioration of ecosystem services and greater socio-environmental vulnerability. Although some gains are expected in mangroves and hydrophytic vegetation, these do not offset the pressure from urban growth. Consequently, the future territorial configuration points to a predominance of livestock and urban land uses, highlighting the need for public policies that balance socioeconomic development with the conservation of natural resources. Conclusion: The development of public policies is essential to ensure the sustainable use and management of natural resources in harmony with socioeconomic activities, thereby fostering regional development while conserving them.

Background: Water is an essential natural resource for the survival of living organisms on Earth. However, recently, both anthropogenic and natural activities have contaminated water bodies in the Andes with metals and other pollutants. Objective: To characterize the water physicochemical and to determine the concentration of metals in water and sediments, as well as the relationship between them, in the tributaries of a reservoir in the southeastern Peruvian Andes. Methodology: We selected 19 sampling points (affluents). Two types of samples were taken at each sampling point: (1) water samples were taken for physicochemical analysis and to find out the concentration of 15 metals; and (2) sediment samples were taken to find out the concentration of 16 metals. We used Spearman's correlation coefficient to analyze the relationship between water physicochemical properties and metal concentrations in water and sediments. Results: For most of the metals (As, Ba, Be, Cd, Cu, Fe, Mn, Pb, Sb and Zn) analyzed in water, concentrations higher than the Peruvian environmental quality standards (EQS) were found. The pH was inversely related to aluminium, beryllium, chromium, copper, iron, manganese, nickel and zinc. Conductivity was directly related to aluminium, beryllium, copper, nickel, lead, uranium and zinc. On the other hand, only positive and significant correlations were found between the concentrations of arsenic, boron, cadmium, lead and antimony found in water and sediments. Implications: It is important to adequately assess, manage, and monitor water resources to ensure their quality for human consumption. This is because we found that the physicochemical characteristics and metal concentrations in water exceed EQS and may represent a risk to human health. Conclusion: The study demonstrates the existence of acid rock drainage in the studied affluents. In most of the tributaries, pH, dissolved oxygen, and most of the metals in the water exceeded the EQS. In addition, an interaction process was evidenced between the concentration of metals in water and sediments.

Background: Several fungal species within the genus Pyricularia are associated with blast diseases affecting Poaceae crops, including wheat, rice, oat, barley, triticale, and various grass weeds. Among these, Pyricularia oryzae is recognized as a major pathogen due to its significant impact on cereal production worldwide. The fungus can survive on weed hosts, potentially serving as inoculum reservoirs. Objective: To characterize grass weed species acting as alternative hosts for Pyricularia spp. in rice agroecosystems in Paraguay. Methodology: During the 2020/2021 rice season, symptomatic weed samples exhibiting elongated or elliptical lesions with reddish-brown margins and lighter centers were collected across major rice-producing regions. Samples were processed at the Microbiology and Biotechnology laboratories of the Facultad de Ciencias y Tecnología, Universidad Nacional de Itapúa, and the Instituto Paraguayo de Tecnología Agraria (IPTA). Results: Morphological characterization of isolates cultured on oat agar revealed grayish to dark-gray colonies, with conidia hyaline, pyriform to obclavate, and containing two transverse septa. Molecular identification based on ITS region sequencing confirmed isolates from Cynodon dactylon as Pyricularia grisea (99.8% similarity) and from Echinochloa sp. as Pyricularia oryzae (100% similarity). Pathogenicity assays in rice seedlings (cv. IRGA 424) reproduced typical blast symptoms for the rice-derived isolate, whereas the Cynodon dactylon- and Echinochloa-derived isolates elicited differential reactions, including hypersensitive, incompatible, and mild blast-like symptoms. Implications: These findings underscore the epidemiological role of grass weeds as alternative hosts and potential inoculum reservoirs of Pyricularia spp., emphasizing the need to integrate weed monitoring and management into comprehensive blast disease control strategies in rice cultivation systems. Conclusion: Grass weed species present in rice agroecosystems of Paraguay were identified as reservoirs for Pyricularia spp., highlighting their potential role in pathogen survival and dissemination within rice fields.

Background: Temperature and atmospheric CO₂ concentration strongly influence the biological cycle of plants, particularly during the reproductive stage. These environmental factors have been altered by anthropogenic activity, affecting flower morphology and fertility. Objective: To evaluate the floral morphology of Capsicum annuum and C. chinense under high temperature and elevated CO₂ conditions. Methodology: Plants were grown in four controlled-environment chambers: T1 = control (30 °C, 400 µmol mol⁻¹), T2 = 30 °C and 1200 µmol mol⁻¹, T3 = 40 °C and 400 µmol mol⁻¹, and T4 = 40 °C and 1200 µmol mol⁻¹. Morphometric traits of sepals, petals, androecium, and gynoecium were recorded throughout flower development. Results: In C. annuum, flowers from T2 were larger from the earliest stages, significantly surpassing the other treatments after day 13 and reaching their maximum size on day 19 (19.1 ± 0.27 mm). In C. chinense, the same treatment reached its largest size on day 17 (13.3 mm). Elevated CO₂ increased petal and ovary area in both species, whereas high temperature reduced filament length, style width, ovary diameter, and the number of ovules per ovary. It also decreased pollen quantity and viability. In all treatments, flower temperature was higher than ambient air temperature. Implications: Elevated CO₂ partially offset the negative effects of heat stress by promoting floral organ growth; however, high temperature impaired reproductive structures and potential fertility. Conclusion: Elevated CO₂ enhanced floral development in Capsicum species, whereas high temperature reduced pollen viability and reproductive efficiency, potentially limiting fruit set under future climate change scenarios.