Diversity of Physiological and Biochemical Characters of Microdochium Fungi.

The biological characterization of Microdochium majus, M. nivale, and M. seminicola strains with wide geographical origins showed the diversity of their pathogenic properties and metabolite compounds, allowing them to exist in their habitats. Significant differences in the ability of Microdochium fungi to cause lesions on wheat and oat leaves were found. The intensity of symptoms depended on the species and substrate origin of the strains. On average M. seminicola strains were able to cause less leaf necrosis than M. majus and M. nivale. The volatile organic compound (VOC) profile of Microdochium fungi included 29 putative fungal metabolites. The spectrum of the identified VOCs in M. seminicola strains was much richer than that in M. majus and M. nivale strains. In addition, the strains of M. seminicola emitted at least six sesquiterpenes. Mycotoxin analysis by HPLC/MS/MS revealed that the analyzed Microdochium strains did not produce any toxic metabolites typically produced by filamentous fungi.

Natural Occurrence of Alternaria Fungi and Associated Mycotoxins in Small-Grain Cereals from The Urals and West Siberia Regions of Russia.

Alternaria fungi dominate the grain microbiota in many regions of the world; therefore, the detection of species that are able to produce mycotoxins has received much attention. A total of 178 grain samples of wheat, barley and oat obtained from the Urals and West Siberia regions of Russia in 2017-2019 were included in the study. Grain contamination with Alternaria fungi belonging to sections Alternaria and Infectoriae was analysed using qPCR with specific primers. The occurrence of four mycotoxins produced by Alternaria, AOH, AME, TEN, and TeA, was defined by HPLC-MS/MS. Alternaria DNA was found in all analysed grain samples. The prevalence of DNA of Alternaria sect. Alternaria fungi (range 53 × 10-4-21,731 × 10-4 pg/ng) over the DNA of Alternaria sect. Infectoriae (range 11 × 10-4‒4237 × 10-4 pg/ng) in the grain samples was revealed. Sixty-two percent of grain samples were contaminated by at least two Alternaria mycotoxins. The combination of TEN and TeA was found most often. Eight percent of grain samples were contaminated by all four mycotoxins, and only 3% of samples were free from the analysed secondary toxic metabolites. The amounts varied in a range of 2-53 µg/kg for AOH, 3-56 µg/kg for AME, 3-131 µg/kg for TEN and 9-15,000 µg/kg for TeA. To our knowledge, a new global maximum level of natural contamination of wheat grain with TeA was detected. A positive correlation between the amount of DNA from Alternaria sect. Alternaria and TeA was observed. The significant effects of cereal species and geographic origin of samples on the amounts of DNA and mycotoxins of Alternaria spp. in grain were revealed. Barley was the most heavily contaminated with fungi belonging to both sections. The content of AOH in oat grain was, on average, higher than that found in wheat and barley. The content of TEN in the grain of barley was lower than that in wheat and similar to that in oat. The content of TeA did not depend on the cereal crop. The effect of weather conditions (summer temperature and rainfall) on the final fungal and mycotoxin contamination of grain was discussed. The frequent co-occurrence of different Alternaria fungi and their mycotoxins in grain indicates the need for further studies investigating this issue.

Evidence of Microdochium Fungi Associated with Cereal Grains in Russia.

In total, 46 Microdochium strains from five different geographic regions of Russia were explored with respect to genetic diversity, morphology, and secondary metabolites. Based on the results of PCR, 59% and 28% of the strains were identified as M. nivale and M. majus, respectively. As a result of sequencing four genome regions, namely ITS, LSU, BTUB, and RPB2 (2778 bp), five genetically and phenotypically similar strains from Western Siberia were identified as M. seminicola, which, according to our findings, is the prevalent Microdochium species in this territory. This is the first record of M. seminicola in Russia. Attempts were made to distinguish between Microdochium species and to identify species-specific morphological characteristics in the anamorph and teleomorph stages and physiological properties. We examined the occurrence frequency of conidia with different numbers of septa in the strains of Microdochium. The predominance of three-septate macroconidia in M. majus was higher than that in M. nivale and typically exceeded 60% occurrence. Most M. majus and M. nivale strains formed walled protoperithecia on wheat stems. Only three strains of M. majus and one strain each of M. nivale and M. seminicola produced mature perithecia. The growth rate of M. seminicola strains was significantly lower on agar media at 5-25 °C than those of M. majus and M. nivale strains. Multimycotoxin analysis by HPLC-MS/MS revealed that the strains of three Microdochium species did not produce any toxic metabolites.