Arsenic and mercury exposure in different insect trophic guilds from mercury mining areas in Mexico.

The exposure to arsenic and mercury in various insect trophic guilds from two mercury mining sites in Mexico was assessed. The two study sites were La Laja (LL) and La Soledad (LS) mines. Additionally, a reference site (LSR) was evaluated for LS. The terrestrial ecosystem was studied at LL, whereas both the terrestrial ecosystem and a stream called El Cedral (EC) were assessed at LS. The study sites are situated in the Biosphere Reserve Sierra Gorda (BRSG). Mercury vapor concentrations were measured with a portable analyzer, and concentrations of arsenic and mercury in environmental and biological samples were determined through atomic absorption spectrophotometry. Both pollutants were detected in all terrestrial ecosystem components (soil, air, leaves, flowers, and insects) from the two mines. The insect trophic guilds exposed included pollinivores, rhizophages, predators, coprophages, and necrophages. In LS, insects accumulated arsenic at levels 29 to 80 times higher than those found in specimens from LSR, and 10 to 46 times higher than those from LL. Similarly, mercury exposure in LS was 13 to 62 times higher than LSR, and 15 to 54 times higher than in LL. The analysis of insect exposure routes indicated potential exposure through air, soil, leaves, flowers, animal prey, carrion, and excrement. Water and sediment from EC exhibited high levels of arsenic and mercury compared to reference values, and predatory aquatic insects were exposed to both pollutants. In conclusion, insects from mercury mining sites in the BRSG are at risk.

Analysis of Bacterial Microbiota of Aerated Compost Teas and Effect on Tomato Growth.

Mature composts and their water-based extracts, known as aerated compost teas (ACTs), are biofertilizers that share bioactive effects like soil restoration and plant health promotion, widely used for sustainable agriculture. Bioactive effects of compost and ACTs could be associated with their physicochemical and biological characteristics, like carbon/nitrogen (C/N) ratio and microbiota structure respectively. In our study, we elaborated ACTs using mature homemade compost, wheat bran, and grass clippings, following the C/N ratio criteria. Irrigation of tomato plantlets with ACT whose C/N ratio was close to the expected C/N ratio for mature compost evidenced plant growth promotion. Exploring the bacterial microbiota of elaborated ACTs and origin compost revealed significant structural differences, including phyla involved in N mineralization and free-living N-fixing bacteria. Therefore, ACTs harbor diverse bacterial microbiota involved in the N cycle, which would enrich plant and soil bacterial communities at the taxonomic and functional levels. Furthermore, ACTs are considered a part of agroecological and circular economy approaches.

Mercury entomotoxicology.

Mercury is an industrial pollutant of global concern. Currently entomofauna is disappearing and chemical pollution is one cause, however, it is unknown whether mercury is an additional threat. Therefore, it is necessary to know the entomotoxicology of mercury. The aim of the present work was to perform a comprehensive literature review on the entomotoxicology of mercury. The toxicokinetics and toxicity of mercury in insects, the participation of insects in the mercury cycle and the fact that this element is a threat to entomofauna are characterized. Insects can be exposed to mercury through ingestion, tracheal respiration, and gill respiration. Organic forms of mercury are better absorbed, bioaccumulated and distributed than inorganic forms. In addition, insects can biotransform mercury, for example, by methylating it. Metal elimination occurs through feces, eggs and exuvia. Toxicity molecular mechanisms include oxidative stress, enzymatic disruptions, alterations in the metabolism of neurotransmitters and proteins, genotoxicity, cell death and unbalances in the energetic state. Moreover, mercury affects lipid, germ, and gut cells, causes deformations, disturbs development, reproduction, behavior, and locomotion, besides to alters insect populations and communities. In terrestrial ecosystems, entomofauna participate in the mercury cycle by bioaccumulating mercury from soil and air, predating, being predated and decomposing organic matter. In aquatic ecosystems insects participate by accumulating mercury from water and sediment, predating, being predated and transporting it to terrestrial ecosystems when they emerge as winged adults. There are still information gaps that need to be addressed.

First report of Athelia rolfsii (= Sclerotium rolfsii) causing southern blight on Pachyrhizus erosus in Mexico.

Pachyrhizus erosus, commonly named jicama, is native to Mexico and is cultivated for its tuberous roots which are edible. In November 2021, field sampling was carried out in municipality of Huaquechula (18.748640N, 98.550817W, 1,580 m above sea level), state of Puebla, México. The disease had an incidence between 20 and 30% in approximately 10 ha. Infected plants showed wilting, yellowing foliage, rotting with white mycelium, abundant sclerotia were observed in the roots and tuber. Tuber splits transversely over time. Twenty plants with symptoms of disease were carried out to isolate the fungus. The sclerotia found in the tubers were disinfected with 3% NaOCl, rinsed twice with sterile distilled water, and excess moisture was removed and, transferred on Potato Dextrose Agar (PDA) culture medium and incubated at 28°C. Mycelial fragments from symptomatic tubers, were plated directly to PDA. Twenty representative isolates were obtained by hyphal-tip method, one for each diseased plant sampled (10 isolates from sclerotia and the other 10 from fragments of mycelium). After 10 days, colonies showed fast-growing, dense, cottony-white aerial mycelium, forming globoid to irregular sclerotia, measuring 1.0-1.7 mm in diameter (mean = 1.42 mm; n=100). The number of sclerotia produced per Petri dish ranged from 54 to 542 (mean = 274, n = 50). These sclerotia were initially white and gradually turned brown. Microscopic examination showed septate hyphae with some cells having clamp connections. Based on morphological characteristics, the fungal isolates were identified as Athelia rolfsii (Curzi) CC Tu & Kimbr (Syn: Sclerotium rolfsii Sacc) (Mordue 1974). For molecular identification, a representative isolate (Sr.1), the ITS region was amplified (650 bp) using primers ITS1/ITS4 (White et al. 1990). The obtained sequence (GenBank: ON206899) was subjected to BLAST analysis, where it had 100% identity with A. rolfsii isolates (GenBank: MG836252 and MH517363). Phylogenetic analysis with the neighbor-joining method in MEGAX, grouped the Sr.1 isolate into a common clade with different A. rolfsii isolates. Pathogenicity was confirmed by inoculating 20 tubers detached from healthy P. erosus variety "Criolla de Morelos", into which a portion of mycelium from the Sr.1 isolate was inserted with a sterile wooden stick at one point per tuber. In five tubers, only a sterile wooden stick was inserted as negative controls. The tubers were placed under laboratory conditions with relative humidity close to 100% and a temperature of 28°C. Symptoms like those observed in the field were observed after five days. Control tubers showed no symptoms. Additional pathogenicity tests were performed on 50 plants of 100-day-old P. erosus of the variety "Criolla de Morelos", grown in pots with sterile soil. Ten sclerotia of 10 days old were deposited at the base of the stem, 10 mm below the soil surface; as control treatment only, sterile distilled water was deposited on 20 plants. The plants were placed in a greenhouse (Center for Technological Innovation in Protected Agriculture of the Popular Autonomous University of the State of Puebla), at 28 ± 1°C and 90% of temperature and relative humidity, respectively. After 15 days, all inoculated plants showed symptoms similar to those observed in the field. Control plants showed no symptoms. A. rolfsii was re-isolated from inoculated tubers and stem, fulfilling Koch's postulates. Previously, A. rolfsii was reported in Mexico, causing southern blight on sesame (Hernández-Morales et al. 2018). To our knowledge, this is the first report of Athelia rolfsii causing southern blight on P. erosus in Mexico (Farr and Rossman 2022). This research is important to design management strategies and prevent its spread to other P. erosus-producing areas.

Genome analysis of Pseudomonas sp. 14A reveals metabolic capabilities to support epiphytic behavior.

The surface of aboveground plant parts, known as the phyllosphere, is a habitat for various microorganisms called epiphytes establishing biotrophic interactions with their hosts. However, these communities can be affected by environmental and anthropogenic variations such as the application of agrochemicals. Thus, epiphytes have the capacity to survive in such environments. In this study, we obtained the genome of Pseudomonas sp. 14A, an epiphyte isolated from the pepper phyllosphere. The phylogenomic analyses suggested that Pseudomonas sp. 14A may be novel species closely related to P. moraviensis R28-S. Notably, the metabolic pathways proposed consistent with epiphytic lifestyle in Pseudomonas sp. 14A, were shared with other species displaying a different degree of phylogenetic relatedness. Furthermore, variations in configuration of metabolic gene clusters were observed, that could expand microbial metabolic diversity in close relatedness species, highlighting the relevance of microbial diversity associated with plants.

Raman Spectroscopy and Machine-Learning for Early Detection of Bacterial Canker of Tomato: The Asymptomatic Disease Condition.

Bacterial canker of tomato is caused by Clavibacter michiganensis subsp. michiganensis (Cmm). The disease is highly destructive, because it produces latent asymptomatic infections that favor contagion rates. The present research aims consisted on the implementation of Raman spectroscopy (RS) and machine-learning spectral analysis as a method for the early disease detection. Raman spectra were obtained from infected asymptomatic tomato plants (BCTo) and healthy controls (HTo) with 785 nm excitation laser micro-Raman spectrometer. Spectral data were normalized and processed by principal component analysis (PCA), then the classifiers algorithms multilayer perceptron (PCA + MLP) and linear discriminant analysis (PCA + LDA) were implemented. Bacterial isolation and identification (16S rRNA gene sequencing) were realized of each plant studied. The Raman spectra obtained from tomato leaf samples of HTo and BCTo exhibited peaks associated to cellular components, and the most prominent vibrational bands were assigned to carbohydrates, carotenoids, chlorophyll, and phenolic compounds. Biochemical changes were also detectable in the Raman spectral patterns. Raman bands associated with triterpenoids and flavonoids compounds can be considered as indicators of Cmm infection during the asymptomatic stage. RS is an efficient, fast and reliable technology to differentiate the tomato health condition (BCTo or HTo). The analytical method showed high performance values of sensitivity, specificity and accuracy, among others.

The Avocado Sunblotch Viroid: An Invisible Foe of Avocado.

This review collects information about the history of avocado and the economically important disease, avocado sunblotch, caused by the avocado sunblotch viroid (ASBVd). Sunblotch symptoms are variable, but the most common in fruits are irregular sunken areas of white, yellow, or reddish color. On severely affected fruits, the sunken areas may become necrotic. ASBVd (type species Avocado sunblotch viroid, family Avsunviroidae) replicates and accumulates in the chloroplast, and it is the smallest plant pathogen. This pathogen is a circular single-stranded RNA of 246-251 nucleotides. ASBVd has a restricted host range and only few plant species of the family Lauraceae have been confirmed experimentally as additional hosts. The most reliable method to detect ASBVd in the field is to identify symptomatic fruits, complemented in the laboratory with reliable and sensitive molecular techniques to identify infected but asymptomatic trees. This pathogen is widely distributed in most avocado-producing areas and causes significant reductions in yield and fruit quality. Infected asymptomatic trees play an important role in the epidemiology of this disease, and avocado nurseries need to be certified to ensure they provide pathogen-free avocado material. Although there is no cure for infected trees, sanitation practices may have a significant impact on avoiding the spread of this pathogen.