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Soybean ( Glycine max) is the most important crop in Argentina. At present Fusarium graminearum is recognized as a primary pathogen of soybean in several countries in the Americas, mainly causing seed and root rot and pre- and post-emergence damping off. However, no information about infections at later growth stages of soybean development and pathogenicity of F. graminearum species complex is available. Therefore, the objectives of this study were to compare the pathogenicity of F. graminearum and F. meridionale isolates towards soybean under field conditions and to evaluate the degree of pathogenicity and trichothecene production of these two phylogenetic species that express different chemotypes. Six isolates of F. graminearum and F. meridionale were evaluated during 2012/13 and 2013/14 soybean growing seasons for pod blight severity, percentage of seed infected in pods and kernel weight reduction. The results showed a higher aggressiveness of both F. graminearum and F. meridionale species during the 2013/14 season. However, the differences in pathogenicity observed between the seasons were not reflected in a distinct trichothecene concentration in soybean seeds at maturity. Fusarium meridionale isolates showed similar pathogenicity to F. graminearum isolates but they were not able to produce this toxin in planta during the two field trials. [ABSTRACT FROM AUTHOR]

Aims: The aims of this study were to determine the occurrence of Fusarium graminearum species complex (FGSC) on soybean pods, seeds and roots, including rhizoplane, during the period of soybean crop in rotation with wheat and to evaluate the FGSC dynamics on wheat and soybean residues during two soybean growing seasons in rotation with wheat, particularly F. graminearum sensu stricto (FGss)., Methods and Results: Soybean roots, pods and seeds were analysed during 2012/13 and 2013/14 seasons. The morphological identification of FGSC and mycotoxin analysis was done. Crop residues were taken in both soybean season in wheat rotation and FGss were quantificated by real-time PCR. The results showed that Fusarium species, mainly FGSC, survive in a soybean crop in rotation with wheat. Isolation frequency of these species was higher on soybean pods than on seeds at R6 stage. Deoxynivalenol contamination on soybean seeds was higher in the 2013/14 season in comparison with the 2012/13 season. Low isolation levels of Fusarium species and species that did not belong to FGSC were observed in soybean root, whereas in rhizoplane a higher level was observed. Fusarium species inoculum on residues remained stable during crop succession and the FGSC were recovered from both wheat and soybean residues. Real time PCR data showed a higher DNA concentration of FGss in wheat residues in the first developmental stages of soybean plants, being the levels more significant during 2012/13 season. With regard to soybean residues collected during the wheat growing stages, an increase in DNA from anthesis until wheat harvest was observed., Conclusions: In a no-till production system, the populations of FGSC can colonize wheat and soybean residues to become an inoculum source., Significance and Impact of the Study: This study provides new data on the occurrence of FGSC populations in soybean plant and FGss on residues in soybean-wheat rotation, a cultural practice commonly used in in Argentina., (© 2020 The Society for Applied Microbiology.)

Fusarium meridionale has been frequently isolated from soybean in Argentina and showed similar pathogenicity as F. graminearum sensu stricto. However, no data on their growth and mycotoxin production under different environmental conditions are yet available. The aims of this study were: to determine the effect of temperature, water activity (a W ) and strain on growth of F. meridionale and to evaluate deoxynivalenol (DON) and nivalenol (NIV) production in a soybean based medium. The results showed that optimal conditions for F. meridionale growth were at 25 °C and 0.98-0.99 a W . Deoxynivalenol production was favored at 25 °C and 0.96 a W while NIV production was strain-dependent, being 30 °C and 0.98 a W optimal conditions for F. meridionale B2300 strain and 20 °C and 0.98 a W for F. meridionale F5043 and F. meridionale 5048 strains. These conditions are similar to those observed at pre-harvest stage in soybean crop, thus control strategies need to be considered to reduce the risk of the occurrence of DON and NIV in harvested grains., (Copyright © 2018. Published by Elsevier B.V.)

Fusarium head blight (FHB) is a devastating disease that causes extensive yield and quality losses to wheat and other small cereal grains worldwide. Species within the Fusarium graminearum complex are the main pathogens associated with the disease, F. graminearum sensu stricto being the main pathogen in Argentina. Biocontrol can be used as part of an integrated pest management strategy. Phytohormones play a key role in the plant defense system and their production can be induced by antagonistic microorganisms. The aims of this study were to evaluate the effect of the inoculation of Bacillus velezensis RC 218, F. graminearum and their co-inoculation on the production of salicylic acid (SA) and jasmonic acid (JA) in wheat spikes at different periods of time under greenhouse conditions, and to evaluate the effect of B. velezensis RC 218 and Streptomyces albidoflavus RC 87B on FHB disease incidence, severity and deoxynivalenol accumulation on Triticum turgidum L. var. durum under field conditions. Under greenhouse conditions the production of JA was induced after F. graminearum inoculation at 48 and 72 h, but JA levels were reduced in the co-inoculated treatments. No differences in JA or SA levels were observed between the B. velezensis treatment and the water control. In the spikes inoculated with F. graminearum, SA production was induced early (12 h), as it was shown for initial FHB basal resistance, while JA was induced at a later stage (48 h), revealing different defense strategies at different stages of infection by the hemibiotrophic pathogen F. graminearum. Both B. velezensis RC 218 and S. albidoflavus RC 87B effectively reduced FHB incidence (up to 30%), severity (up to 25%) and deoxynivalenol accumulation (up to 51%) on durum wheat under field conditions.