Pseudopestalotiopsis elaeidis associated with leaf spots on Cycas revoluta in Brazil

Cycas revoluta (Cycadaceae) is commonly cultivated as an ornamental tree in several countries. In April 2015, C. revoluta leaves showing brownish spots with a yellow halo that progressed to leaflet necrosis were observed in Belém, Pará state, Brazil. This study aimed to determine the aetiology of this disease on sago palm in Brazil. Based on DNA sequence-based phylogeny, morphology, and colony characterization, the fungus was identified as Pseudopestalotiopsis elaeidis. To the best of our knowledge, this is the first report of P. elaeidis associated with leaf spots on C. revoluta worldwide.     

Searching for bioactive compounds from Solanaceae: lethal and sublethal toxicity to Spodoptera frugiperda and untargeted metabolomics approaches

Journal of Pest Science - The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major pest of maize crops and others row crops on the American continent, and this...     

Impact of fungicide application volume on ASIAN rust control and soybean crop yield

European Journal of Plant Pathology - Multisite fungicides are an anti-resistance strategy to control Phakopsora pachyrhizi. Among the protective fungicides, mancozeb is a fungicide that has been...     

Mineralogy and nutrient desorption of suspended sediments during a storm event

Purpose

This study investigated desorption of potassium (K) and phosphorus (P) from soil and river suspended sediments sampled during a storm event in a Brazilian watershed traditionally used for tobacco plantations.

Material and methods

Suspended sediment samples were collected automatically at the outlet of the watershed and were grouped into three phases: beginning (phase a), middle (phase b) and final stages (phase c) of the storm event. Granulometric and mineralogical characterisation of soils (0 to 0.20 m depth) and suspended sediments was determined, and K and P extractions were performed using a cation and anion exchange resin (CAER) membrane. A kinetic modelling approach was used to estimate the amount of K and P desorbed.

Results and discussion

Clay-sized (<2 μm) content of the soils were all <21 %. Kaolinite, smectite (partially with hydroxy-Al interlayer) and a small amount of illite were found in the clay fraction of the different soils. The clay-sized fractions in sediments of phases a, b and c of the storm event were 49, 52 and 72 %, respectively. Smectite (>90 %) and kaolinite (<10 %) were the dominant clay minerals in the suspended sediments. The values of labile P and potentially available P of suspended sediments were higher than those for soils. In sediments, the highest values of labile P (325 mg kg^?1) and labile K (4,458 mg kg^?1) were found in phase c and in phase a, respectively.

Conclusions

Particle size distribution and clay mineralogy of soils differed from those of suspended sediments collected during the storm event. By comparison with the watershed soils, suspended sediments collected during the storm event were enriched in fine particles composed mainly of smectite, and this may explain their P and K desorption behaviour. This suggests particle size and clay species selectivity processes during the transfer of sediment particles from soils to aquatic systems. The amounts of P and K desorbed from the suspended sediments in the three phases of the storm event were much larger than those desorbed from soils. This indicates that rainfall promoted the transfer of these nutrients to the watercourses.     

Mineralogical changes caused by grape production in a regosol from subtropical Brazilian climate

Purpose

Inadequate soil use and management practices promote commonly negative impacts on the soil constituents and their properties, with consequences to ecosystems. As the soil mineralogy can be permanently altered due to soil use, this approach can be used as a tool to monitor the anthropogenic pressure. The objective of the present study was to assess the mineralogical alterations of a Brazilian regosol used for grape production for 40?years in comparison with a soil under natural vegetation (forest), aiming to discuss anthropogenic pressure on soils.

Material and methods

Soil samples were collected at depths of 0?C0.20 and 0.20?C0.40?m from vineyard production and natural vegetation sites. Physical and chemical parameters were analysed by classic approaches. Mineralogical analyses were carried out on <2?mm, silt and clay fractions. Clay minerals were estimated by the relative percentage of peak surface area of the X-ray patterns.

Results and discussion

Grape production reduced the organic matter content by 28?% and the clay content by 23?% resulting in a decreasing cation exchange capacity. A similar clay fraction was observed in both soils, containing kaolinite, illite/mica and vermiculite with hydroxy-Al polymers interlayered. Neither gibbsite nor chlorite was found. However, in the soil under native vegetation, the proportion of illite (79?%) was higher than vermiculite (21?%). Whereas, in the soil used for grape production during 40?years, the formation of vermiculite was promoted.

Conclusions

Grape production alters the proportions of soil constituents of the regosol, reducing clay fraction and organic matter contents, as well as promoting changes in the soil clay minerals with the formation of vermiculite to the detriment of illite, which suggests weathering acceleration and susceptibility to anthropogenic pressure.

Recommendations and perspectives

Ecosystems in tropical and subtropical climates can be more easily and permanently altered due to anthropogenic pressure, mainly as a consequence of a great magnitude of phenomena such as temperature amplitude and rainfall that occurs in these regions. This is more worrying when soils are located on steep grades with a high anthropogenic pressure, like regosols in Southern Brazil. Thus, this study suggests that changes in soil mineralogy can be used as an important tool to assess anthropogenic pressure in ecosystems and that soil quality maintenance should be a priority in sensible landscapes to maintain the ecosystem quality.     

A study of potassium dynamics and mineralogy in soils from subtropical Brazilian lowlands

Purpose  

The dynamics and availability of potassium (K) in soils depend on many factors, including the mineralogy of fractions and the soil geochemical conditions. The objective of this work is to quantify K in distinct lowland soil compartments in the south of Brazil, relating them to particle size fractions and mineralogical constitution.     

Decoupling structural and environmental determinants of sap velocity: Part I. Methodological development

This paper presents a novel theoretical framework for the study of individual tree sap flow that incorporates both spatial and temporal variability in sap velocities. In this formulation, the instantaneous sap velocity at any point in the radial profile of xylem tissue is defined as the product of a time-invariant sap velocity distribution and a time-varying term which is defined as a stem conductance. We hypothesize that the characteristic distribution of sap velocity is relatively uniform both within individual trees and between trees of the same species if location in the xylem tissue is expressed in normalized units relative to the total xylem depth (i.e. tree size). Experimental evidence confirms our hypothesis in the case of a population of sugar maples in a mixed deciduous forest and dwarf apple trees in an orchard, despite the fact that observations were drawn from a wide range of tree sizes and under varying soil moisture levels and atmospheric conditions that determines water demand. Furthermore, profiles of sap velocity and resulting integrals of total sap flow exhibit significant reduction in bias (by 30–40%) in comparison to prior methods used to extrapolate point observations of sap velocity. The method we describe exhibits the greatest improvement when only a small fraction of the total sapwood is measured, which is the typical scenario for most applications. While these results require further confirmation in order to be generalized, they nevertheless offer the basis to improve both the specific sampling strategies used to estimate whole-tree transpiration using sap velocity probes as well as methods employed to upscale water use of individual trees to larger scales for evaluation of landscape water balance.     

Toxic effects of mercury chloride on silver catfish (Rhamdia quelen) spermatozoa

Heavy metals are highly toxic elements that are present in the environment, especially in water. Mercury chloride (HgCl₂) stands out among these compounds because of its strong ability to induce damage to any tissue with which it comes into contact. The gametes of spawning aquatic animals, such as fish, are susceptible to such damage. Thus, our objective was to evaluate the toxic potential of HgCl₂ in the capacitation and activation of Rhamdia quelen sperm. Semen was collected from seven males and activated in 58 mM sodium chloride (NaCl) containing 0 (control), 4^?10, 7^?10, 7^?9, and 7^?8 M HgCl₂. The evaluated variables included motility, vigor, motility time, morphology, membrane integrity, membrane fluidity, mitochondrial functionality, production of reactive oxygen species (ROS), and DNA fragmentation. All evaluated HgCl₂ concentrations increased primary pathologies and reduced motility, vigor and motility time. Damage to membrane integrity and fluidity began occurring at a concentration of 7^?10 M HgCl₂. These results indicate that HgCl₂ has a toxic effect on different sites of fish spermatozoa and that sperm motility decreases after exposure to HgCl₂, impairing sperm capacitation and activation.