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Cinnamon is a tree introduced to the lowlands of Mexico in the mid-16th century, but it spread to other places at the beginning of the 20th century due to its important commercial value as an aromatic spice. In the state of Veracruz, symptoms of dieback have been observed in 12-year-old cinnamon plantations cultivated in an agroforestry system, causing concern among producers. For this reason, the present investigation was carried out to determine the causal agent of these symptoms observed in cinnamon trees. Fifty symptomatic plants were recovered from established plantations. One hundred cinnamon root fragments showing dieback were selected and separated; isolates were made from tissue showing crown and root rot on clarified juice V-8 agar medium. After eight days, the growth of whitish coralloid mycelium with characteristics similar to the Phytophthora oomycete was consistently observed. Subsequently, the identity corresponding to P. cinnamomi was confirmed by morphological, taxonomic studies and Bayesian inference of the rDNA internal transcribed spacer. The pathogenicity test was performed on 20 6-month-old cinnamon plants grown in pots by inoculating 2.5 × 104/mL of zoospores around the roots. Control plants were inoculated with sterile distilled water and kept in a greenhouse under conditions controlled. After five weeks, symptoms of root rot were observed in the inoculated plants; however, the control group plants remained healthy. The results showed that P. cinnamomi subclade 7c was responsible for the symptoms observed in lowland cinnamon plantations in Mexico. Our findings suggest that this phytopathogen is a new threat for cinnamon growers; likewise, it is recommended that growers implement management strategies to avoid its introduction into nurseries or new plantations that could be susceptible to this pathogen.

Avocado root rot caused by the oomycete Phytophthora cinnamomi is a severe disease that affects avocado production in Mexico and worldwide. The use of biological control agents such as Trichoderma species isolated from places where the disease is always present, represents an efficient alternative to reduce losses. Thus, the objective of this research was to evaluate the biocontrol ability of 10 endophytic Trichoderma spp. strains against P. cinnamomi tested both in vitro and in the greenhouse. The endophytic Trichoderma spp. were recovered from Persea americana and Cinnamomum verum roots, isolated and purified on potato–dextrose–agar medium. Ten strains were identified by phylogenetic reconstruction of the internal transcribed spacer region of rDNA sequences as T. asperellum (T-AS1, T-AS2, T-AS6, and T-AS7), T. harzianum (T-H3, T-H4, and T-H5), T. hamatum (T-A12), T. koningiopsis (T-K8 and T-K11), and P. cinnamomi (CPO-PCU). In vitro dual-culture assay, the percentage of inhibition of radial growth (PIRG) between Trichoderma spp. and P. cinnamomi strains was measured according to the Bell’s scale. PIRG results indicated that T-AS2 reached the highest value of 78.32%, and T-H5 reached the lowest value of 38.66%. In the greenhouse, the infection was evaluated according to the percentage of disease incidence. Plants with the lowest incidence of dead by avocado root rot were those whose seedlings were inoculated with T-AS2 and T-AS7, resulting in only 5% death by root rot caused by P. cinnamomi. The disease incidence of seedlings with wilt symptoms and death decreased more than 50% in the presence of Trichoderma spp. Relying on the results, we conclude that T. asperellum and T. harzianum contribute to the biocontrol of soil-borne pathogenic oomycete P. cinnamomi.

The husk tomato (Physalis philadelphica Lam.) is an important Solanaceae native to Mesoamerica that is grown for its green fruit used as an important ingredient in domestic and international cuisine. Nevertheless, husk tomato plants with symptoms resembling those caused by ‘Candidatus Liberibacter solanacearum’ (CLso) have been observed during the last decade in plantations located in the State of Mexico, Michoacan and Sinaloa in Mexico. These areas are located near other solanaceous crops where Bactericera cockerelli the well-known psyllid transmitter of CLso is frequently present. Thus, the goal of this study was to determine if CLso haplotypes are present in husk tomato varieties in commercial fields in Mexico. From 2015 to 2016, plants and fruit showing evident symptoms of CLso infection, as well as psyllids were collected in these states and assayed by PCR for CLso using primer sets OA2/OI2c and LpFrag 1-25F/427R. Phylogenetic reconstruction was performed with Bayesian analysis and maximum likelihood methods using amplicon sequences obtained in this work along with those deposited in the GenBank database corresponding to the CLso detected in Solanaceae, Apiaceae, and Convolvulaceae host families. In addition, all the sequences were subjected to haplotype determination through an analysis of DNA polymorphisms using the DnaSP software. Furthermore, quantitative PCR (qPCR) was performed using CLso-specific primers and probes. Phylogenetic reconstruction and qPCR confirmed the presence of CLso in plants, seeds and insect-vectors, and CLso sequences from plants and seeds completely matched haplotype B, whereas CLso haplotypes A and B were detected in B. cockerelli psyllids. Polymorphism analysis identified a novel Convolvulaceae-associated CLso haplotype, which was named haplotype H. The results of this study will enable the dissemination of infected seeds to new husk tomato production areas to be avoided.

The aim of this paper was to determine in 32 patients from 4 different Mexican hospitals the frequency of opportunistic bacteria in the 2010 to 2011 time period. The patients were divided in 4 groups. Group 1 included 21 HIV positive patients with acute respiratory syndrome. Four HIV positive patients with tuberculosis symptoms were included in Group 2; two patients with tuberculosis symptoms and one asymptomatic person formed Group 3. Reference Group 4 included 4 patients from whom 4 strains of Mycobacterium spp. had been reported. The strains were isolated and identified by 16S rRNA gene amplification, API 20E and 50CH, biochemical test, and antibiotic sensitivity. The strains found were 10 Pantoea agglomerans, 6 Mycobacterium spp., 6 Pseudomonas spp. and 10 strains of normal floral species: Thermoactinomycetes bacterium (1), Enterococcus faecium (2), Bacillus licheniformis (1), Lactobacillus rhamnosus (2), Streptococcus oralis (2), Streptococcus anginosus (1), and Enterobacter hormaechei (1).

Stenocarpella maydis and Stenocarpella macrospora are the causal agents of ear rot in corn, which is one of the most destructive diseases in this crop worldwide. These fungi are important mycotoxin producers that cause different pathologies in farmed animals and represent an important risk for humans. In this work, 160 strains were isolated from soil of corn crops of which 10 showed antifungal activity against these phytopathogens, which, were identified as: Bacillus subtilis, Pseudomonas spp., Pseudomonas fluorescens, and Pantoea agglomerans by sequencing of 16S rRNA gene and the phylogenetic analysis. From cultures of each strain, extracellular filtrates were obtained and assayed to determine antifungal activity. The best filtrates were obtained in the stationary phase of B. subtilis cultures that were stable to the temperature and extreme pH values; in addition they did not show a cytotoxicity effect against brine shrimp and inhibited germination of conidia. The bacteria described in this work have the potential to be used in the control of white ear rot disease.

A rapid, eco-friendly, and simple method for the synthesis of long-lasting (2 years) silver nanoparticles (AgNPs) is reported using aqueous leaf and petal extracts of Tagetes erecta L. The particles were characterized using UV-Visible spectrophotometry and the analytical and crystallographic techniques of transmission electron microscopy (TEM). The longevity of the AgNPs was studied using UV-Vis and high-resolution TEM. The antibacterial activity of the particles against Erwinia amylovora was evaluated using the Kirby–Bauer disk diffusion method. The results were analyzed using ANOVA and Tukey’s test (p ≤ 0.05). Both the leaf and petal extracts produced AgNPs, but the leaf extract (1 mL) was long-lasting and quasi-spherical (17.64 ± 8.87 nm), with an absorbance of UV-Vis λmax 433 and a crystalline structure (fcc, 111). Phenols, flavonoids, tannins, and terpenoids which are associated with -OH, C=O, and C=C were identified in the extracts and could act as reducing and stabilizing agents. The best antibacterial activity was obtained with a nanoparticle concentration of 50 mg AgNPs L−1. The main contribution of the present research is to present a sustainable method for producing nanoparticles which are stable for 2 years and with antibacterial activity against E. amylovora, one of most threatening pathogens to pear and apple productions.

The production of ornamental plants in Mexico represents a job-generating activity that has grown in recent years; however, it is adversely affected by phytosanitary issues, notably those induced by Phytophthora. Studies of Phytophthora in ornamental nurseries are scarce in Mexico. The aim in this study was to identify Phytophthora species from selected ornamental plant nurseries in Mexico as potential new hosts. Samples of 13 genera diseased plant tissue and soil were collected from eight nurseries in Mexico during 2009–2010. Based on morphology and sequences of ITS rDNA, the 19 isolates obtained were identified as P. cactorum, P. capsici, P. cinnamomi, P. drechsleri, P. kelmanii, P. nicotianae, and P. tropicalis. Additional loci were sequenced to support species determinations within the P. capsici species complex; some of these isolates could not be confirmed as belonging to any described species, and one appeared to be an interspecific hybrid. This is the first report of P. kelmanii in Mexico; this is noteworthy due to being a broad host range, similar to most of the other species encountered. Evidence of nursery-grown plants serving as a Phytophthora vector to a home garden has been reported for the first time in Mexico. Cestrum nocturnum and Solanum ovigerum are new hosts for Phytophthora worldwide.

The ‘Poblano’ pepper crop is economically important in Mexico and throughout the world as it is used as a hot spice in food. The cultivated area of the ‘Poblano’ pepper crop is decreasing yearly for many reasons, among them a wilt disease commonly associated with Fusarium spp. This disease is a problem of field and greenhouse production plants. Moreover, it is not clear whether the pathogens that cause wilt in mature plants are the same as those involved in the damping-off symptoms and death of pepper seedlings in greenhouses. For this reason, the aim of the present study was to identify the causal agent of damping-off in pepper during seedling production, establish its relationship with the causal agent of wilting in mature plants, and determine whether histological damage in seedlings occurs. Isolates were recovered from the crown rot and stem base of 4-month-old infected ‘Poblano’ mature pepper plants and were identified using morphological and phylogenetic approaches. Fusarium oxysporum and F. solani were isolated from the crown rot and base stem, respectively. A pathogenicity test showed that both species caused damping-off in pepper seedlings. Histological studies with inoculated seedlings of both isolates showed several changes in the external cortex, epidermal cells, endodermis, Casparian strips, cell size, and xylem wall. Casparian strip rupture resulted in permeability loss and regulatory activity to maintain the cellular equilibrium inside the vascular bundles. Hence, according to these findings, producers should avoid seedling contamination by infected mature plants because the aggressiveness of Fusarium isolates can cause rapid seedling mortality.

Hemileia vastatrix coffee leaf rust reduces Mexican coffee production by 51%. We aimed to analyze the size and distribution of H. vastatrix urediniospores among coffee plantations, as well as the morphological structures of the uredinium. In 2015, 65 leaf samples with rust symptoms were collected from 17 coffee cultivars grown at various altitudes (229–1649 m) under different environmental conditions in 14 regions of four Mexican states. A total of 30 spores per sample were measured and grouped using the Ward centroid method, and the group distribution was analyzed. Uredinia morphology was examined via electron microscopy, and the identity of the rust was confirmed. We identified eight significant spore groups. Groups 8h and 3a had the smallest and largest spores, respectively, which were distributed in two and one state, respectively, at different altitudes. The spores in groups 1b–7f were variable within the intermediate size range, and their distribution was at least one group per state under temperate, warm, and humid conditions. The uredinium had double-cell walls in the pedicels and urediniospores, a split septum, spores with hilum and protuberances, and an oval spore shape; anastomosis was detected on vegetative hyphae and haustoria. These findings may reflect gaps in knowledge in the biological cycle of this rust.

This review highlights the impact of emerging diseases; emerging diseases and pathogen dispersion; disease spread; and possible causes contributing to the emergence of pathogens. Some plant diseases are caused by potentially dangerous pathogens that have led changes in humanity. Despite our efforts in the fight against these dangerous pathogens; the influences of natural phenomena such as hurricanes or strong winds that disperse pathogens remain. However, some actions such as investment in research priorities that are focused on quarantined pathogens and official regulations can help in disease prevention. We discuss emerging diseases as a threat to crops, identify future research areas, and encourage the establishment of research networks focused on quarantine pathogens to address the problem and minimize risks.