Genetic diversity and effect of temperature and pH on the growth of Macrophomina phaseolina isolates from sunflower fields in Hungary

Impact of climate change on the potential global prevalence of Macrophomina phaseolina (Tassi) Goid. under several climatological scenarios

Introduction

Climate change forms one of the most dangerous problems that disturb the earth today. It not only devastates the environment but also affects the biodiversity of living organisms, including fungi. Macrophomina phaseolina (Tassi) Goid. is one of the most pervasive and destructive soil-borne fungus that threatens food security, so predicting its current and future distribution will aid in following its emergence in new regions and taking precautionary measures to control it.

Methods

Throughout this work, there are about 324 records of M. phaseolina were used to model its global prevalence using 19 environmental covariates under several climate change scenarios for analysis. Maximum Entropy (MaxEnt) model was used to predict the spatial distribution of this fungus throughout the world while algorithms of DIVA-GIS were chosen to confirm the predicted model.

Results

Based on the Jackknife test, minimum temperature of coldest month (bio_6) represented the most effective bioclimatological parameter to fungus distribution with a 52.5% contribution. Two representative concentration pathways (RCPs) 2.6 and 8.5 of global climate model (GCM) code MG, were used to forecast the global spreading of the fungus in 2050 and 2070. The area under curve (AUC) and true skill statistics (TSS) were assigned to evaluate the resulted models with values equal to 0.902 ± 0.009 and 0.8, respectively. These values indicated a satisfactory significant correlation between the models and the ecology of the fungus. Two-dimensional niche analysis illustrated that the fungus could adapt to a wide range of temperatures (9 °C to 28 °C), and its annual rainfall ranges from 0 mm to 2000 mm. In the future, Africa will become the low habitat suitability for the fungus while Europe will become a good place for its distribution.

Discussion

The MaxEnt model is potentially useful for predicting the future distribution of M. phaseolina under changing climate, but the results need further intensive evaluation including more ecological parameters other than bioclimatological data.

Geostatistical Modeling Improves Prediction of Macrophomina phaseolina Abundance and Distribution in Soybean Fields

Charcoal rot, caused by the soilborne fungus Macrophomina phaseolina (Mp) poses a serious threat to soybean health and harvests at a global scale. Mp exhibits varying distribution patterns across fields, which complicates our ability to predict disease occurrences and outbreaks. Therefore, determining the spatial distribution of Mp abundance and its relationship with soil physicochemical properties would help to inform precision management decisions for mitigating charcoal rot. To achieve this, Mp colony-forming units (CFU) and edaphic properties were evaluated in 297 soybean fields located in the main soybean-growing regions across seven departments of Paraguay. A pattern of decreasing CFU density was observed from the southeastern to the western part of the country. Whereas several edaphic factors are positively correlated with Mp CFU, pH showed a significant negative correlation with CFU. Both spatial and nonspatial models suggest that cation exchange capacity, percentage of clay, and pH could be potential predictors of Mp CFU abundance. Including the spatial dependence of edaphic factors improved the prediction of Mp CFU more effectively than classical statistical models. We demonstrated that the occurrence of Mp shows a significant spatial clustering pattern, as indicated by Moran's I. Our findings will help growers and policymakers make informed decisions for managing Mp by improving our ability to predict which agricultural fields and soils are at greatest risk for charcoal rot.

Phenotypic Variability and Genetic Diversity of the Pathogenic Fungus Macrophomina phaseolina from Several Hosts and Host Specialization in Strawberry

Macrophomina phaseolina, is a pathogenic soil-borne fungus that affects more than 500 plant species, causing various types of disease to several crops, among which is the crown and root rot disease in strawberry. Its wide variability has been characterized reiteratively in the literature, but little is known about its virulence mechanisms. Morphological, physiological, genetic and phytopathogenic parameters were evaluated among 32 isolates of Macrophomina from different hosts occurring in Argentina and Spain. Colony characteristics, average size of microsclerotia, chlorate phenotype and mycelial growth at different temperatures (5º-40 °C), and pH (3.0-8.0) were recorded. The morphological and physiological traits were heterogeneous and did not show any association with the genetic structure nor with their pathogenicity. Most of the isolates (71.9%) exhibited chlorate-sensitive phenotype. The optimal growth temperature range was between 25 °C and 35 °C, and the optimal pH varied between 4.0 and 6.0. The genetic structure analyzed with four DNA markers (EF-1α, ITS, CAL and TUB) showed little diversity among isolates of M. phaseolina, with no clear association with the country of origin, but a significant association with the host. Based on their phylogenetic affinity, one isolate was reclassified as M. pseudophaseolina and another one as M. tecta. It is the first report of M. pseudophaseolina causing charcoal rot on beans, in Argentina, and the first report of M. tecta outside Australia. Pathogenicity tests on strawberry plants revealed marked host specialization, being the isolates obtained from strawberry more virulent than those from other hosts.

In vitro growth and cell wall degrading enzyme production by Argentinean isolates of Macrophomina phaseolina, the causative agent of charcoal rot in corn

Macrophomina phaseolina is a polyphagous phytopathogen, causing stalk rot on many commercially important species. Damages caused by this pathogen in soybean and maize crops in Argentina during drought and hot weather have increased due its ability to survive as sclerotia in soil and crop debris under non-till practices. In this work, we explored the in vitro production of plant cell wall-degrading enzymes [pectinases (polygalacturonase and polymethylgalacturonase); cellulases (endoglucanase); hemicellulases (endoxylanase) and the ligninolytic enzyme laccase] by several Argentinean isolates of M. phaseolina, and assessed the pathogenicity of these isolates as a preliminary step to establish the role of these enzymes in M. phaseolina-maize interaction. The isolates were grown in liquid synthetic medium supplemented with glucose, pectin, carboxymethylcellulose or xylan as carbon sources and/or enzyme inducers and glutamic acid as nitrogen source. Pectinases were the first cell wall-degrading enzymes detected and the activities obtained (polygalacturonase activity was between 0.4 and 1.3U/ml and polymethylgalacturonase between 0.15 and 1.3U/ml) were higher than those of cellulases and xylanases, which appeared later and in a lesser magnitude. This sequence would promote initial tissue maceration followed by cell wall degradation. Laccase was detected in all the isolates evaluated (activity was between 36U/l and 63U/l). The aggressiveness of the isolates was tested in maize, sunflower and watermelon seeds, being high on all the plants assayed. This study reports for the first time the potential of different isolates of M. phaseolina to produce plant cell wall-degrading enzymes in submerged fermentation.