Frosty pod rot disease of cacao (FPR), caused by the fungus Moniliophthora roreri, has severely impacted the production of cocoa in Latin America since its discovery. Prior to the 1950s, FPR was known only from Colombia and Ecuador. However, beginning in the 1970s, its geographical range has dramatically expanded throughout most of the cacao‐producing regions of the Americas. The origin of the pathogen remains unknown. In this study, we evaluated the genetic diversity of M. roreri from areas spanning, as much as possible, its current geographical range using simple‐sequence repeat markers and a publicly available single‐nucleotide polymorphism data set. Two hotspots of genetic diversity were found: coastal Ecuador and the inter‐Andean Magdalena Valley of Colombia, neither of which correspond to the Amazonian origin of the host. However, both areas were early centres of intense cultivation of cacao. Our results indicate that M. roreri was introduced into both areas from its centre of origin, where intensive cacao cultivation probably led to the increase of inoculum and further dissemination of the disease. Current invasions can be traced to two genotypes responsible for all known instances of the pathogen in Central America, the Caribbean, Peru and Bolivia. We also report for the first time M. roreri in Maynas (Peruvian Amazon), which is probably the result of a recent introduction from Colombia.
Traces of cadmium (Cd) have been reported in some chocolate products due to soils with Cd and the high ability of cacao plants to extract, transport, and accumulate it in their tissues. An agronomic strategy to minimize the uptake of Cd by plants is the use of cadmium-resistant bacteria (Cd-RB). However, knowledge about Cd-RB associated with cacao soils is scarce. This study was aimed to isolate and characterize Cd-RB associated with cacao-cultivated soils in Colombia that may be used in the bioremediation of Cd-polluted soils. Diversity of culturable Cd-RB, qualitative functional analysis related to nitrogen, phosphorous, carbon, and Cd were performed. Thirty different Cd-RB morphotypes were isolated from soils with medium (NC, Y1, Y2) and high (Y3) Cd concentrations using culture media with 6 mg Kg-1 Cd. Cd-RB were identified based on morphological and molecular analyses. The most abundant morphotypes (90%) were gram-negative belong to Phylum Proteobacteria and almost half of them showed the capacity to fix nitrogen, solubilize phosphates and degrade cellulose. Unique morphotypes were isolated from Y3 soils where Burkholderia and Pseudomonas were the dominant genera indicating their capacity to resist high Cd concentrations. P. putida GB78, P. aeruginosa NB2, and Burkholderia sp. NB10 were the only morphotypes that grew on 18 up to 90 (GB78) and 140 mg Kg-1 Cd (NB2-NB10); however, GB78 showed the highest Cd bioaccumulation (5.92 mg g-1). This study provides novel information about culturable Cd-RB soil diversity with the potential to develop biotechnology-based strategies.
Physiological processes of plants infected by vascular pathogens are mainly affected by vascular bundle obstruction, decreasing the absorption of water and nutrients and gas exchange by stomatal closure, and inducing oxidative cascades and PSII alterations. Chitosan, a derivative of chitin present in the cell wall of some organisms including fungi, induces plant defense responses, activating systemic resistance. In this study, the effect of chitosan on the physiological and molecular responses of tomato plants infected with Fusarium oxysporum f. sp. lycopersici (Fol) was studied, evaluating the maximum potential quantum efficiency of PSII photochemistry (Fv/Fm), photochemical efficiency of PSII (Y(II)), photochemical quenching (qP), stomatal conductance (gs), relative water content (RWC), proline content, photosynthetic pigments, dry mass, and differential gene expression (PAL, LOXA, ERF1, and PR1) of defense markers. A reduction of 70% in the incidence and 91% in the severity of the disease was achieved in plants treated with chitosan, mitigating the damage caused by Fol on Fv/Fm, Y(II), and chlorophyll contents by 23%, 36%, and 47%, respectively. Less impact was observed on qP, gs, RWC, and dry mass (16%, 11%, and 26%, respectively). Chitosan-treated and Fol-infected plants over-expressed PR1a gene suggesting a priming-associated response. These results demonstrate the high potential of chitosan to protect tomato plants against Fol by regulating physiological and molecular responses in tomato plants.
The two spotted spider mite Tetranychus urticae is an important polyphagous pest worldwide. It is able to adapt to a wide variety of environments and has a high reproduction rate. In practice, farmers try to reduce losses by using synthetic acaricides. However, frequent and inadequate applications of acaricides have made this mite resistant to many active ingredients, creating the need to search for alternative control strategies. The aim of this research was to identify and to evaluate an indigenous strain of a fungus, which eliminated a T. urticae colony in a greenhouse. The isolated fungus was identified through a morphological and molecular characterization as Cladosporium cladosporioides. Thereafter, the mites were treated with five concentrations of C. cladosporioides conidia (2x104, 2x105, 2x106, 2x107, and 2x108 conidia ml-1) and a positive control (commercial Beauveria bassiana strain, 1x106 conidia ml-1). After 10 d, all treatments achieved at least 50% control; the concentrations 2x107 and 2x108 spores ml-1 controlled 73.3% and 81.7%, respectively, surpassing the commercial strain slightly (72.3%). TL50 ranged between 5 (2x108 spores ml-1) and 8 (2x104 spores ml-1) d, and LC50 was 1.95x106. The possible acaricidal effect of this strain on these mites is discussed.
Characterization of acetolactate synthase gene (ALS) in Echinochloa colona (L.) Link., a hexaploid weed species. Adv Weed Sci. 2023;41:e020220067.
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