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Previously, severe green mould infections could be attributed mainly to Trichoderma aggressivum Samuels & W. Gams, as well as T. pleuroti S.H. Yu & M.S. Park and T. pleuroticola S.H. Yu & M.S. Park in the case of Agaricus bisporus (J.E. Lange) Imbach (button mushroom) and Pleurotus ostreatus (Jacq.) P. Kumm. (oyster mushroom), respectively. The purpose of our study was the examination of green mould agents deriving from the growing facilities of button mushroom, oyster mushroom and shiitake (Lentinula edodes (Berk.) Pegler) located in various countries of Europe, and initially classified into the Trichoderma harzianum Rifai species complex (THSC). Species identification was carried out using the multilocus sequence typing analysis of the internal transcribed spacer regions, as well as translation elongation factor 1-alpha, calmodulin and RNA polymerase B subunit II gene sequences. In vitro confrontation assays were applied to test the aggressiveness of the isolates towards mushrooms, while the effect of commercial fungicides on the growth of the strains was examined by the macrodilution method. Six Trichoderma species, namely T. afroharzianum P. Chaverri, F.B. Rocha, Degenkolb & Druzhin., T. atrobrunneum F.B. Rocha, P. Chaverri & Jaklitsch, T. guizhouense Q.R. Li, McKenzie & Yong Wang, T. harzianum sensu stricto, T. pollinicola F. Liu & L. Cai and T. simmonsii P. Chaverri, F.B. Rocha, Samuels, Degenkolb & Jaklitsch were detected in the different samples, with T. harzianum, T. pollinicola and T. simmonsii being the most aggressive. Prochloraz was found to have strong in vitro inhibitory effect on mycelial growth on most strains, however, T. simmonsii isolates showed remarkable tolerance to it. Our data suggest that T. harzianum and T. simmonsii may also be considered as potential causal agents of mushroom green mould.

The cultivation and consumption of sweet potato (Ipomoea batatas) are increasing globally. As the usage of chemical fertilizers and pest control agents during its cultivation may lead to soil, water and air pollution, there is an emerging need for environment-friendly, biological solutions enabling increased amounts of healthy crop and efficient disease management. Microbiological agents for agricultural purposes gained increasing importance in the past few decades. Our goal was to develop an agricultural soil inoculant from multiple microorganisms and test its application potential in sweet potato cultivation. Two Trichoderma strains were selected: Trichoderma ghanense strain SZMC 25217 based on its extracellular enzyme activities for the biodegradation of plant residues, and Trichoderma afroharzianum strain SZMC 25231 for biocontrol purposes against fungal plant pathogens. The Bacillus velezensis strain SZMC 24986 proved to be the best growth inhibitor of most of the nine tested strains of fungal species known as plant pathogens, therefore it was also selected for biocontrol purposes against fungal plant pathogens. Arthrobacter globiformis strain SZMC 25081, showing the fastest growth on nitrogen-free medium, was selected as a component with possible nitrogen-fixing potential. A Pseudomonas resinovorans strain, SZMC 25872, was selected for its ability to produce indole-3-acetic acid, which is among the important traits of potential plant growth-promoting rhizobacteria (PGPR). A series of experiments were performed to test the selected strains for their tolerance to abiotic stress factors such as pH, temperature, water activity and fungicides, influencing the survivability in agricultural environments. The selected strains were used to treat sweet potato in two separate field experiments. Yield increase was observed for the plants treated with the selected microbial consortium (synthetic community) in comparison with the control group in both cases. Our results suggest that the developed microbial inoculant has the potential to be used in sweet potato plantations. To the best of our knowledge, this is the first report about the successful application of a fungal-bacterial consortium in sweet potato cultivation.

The utilization of microorganisms with biocontrol activity against fungal and bacterial pathogens of plants is recognized as a promising, effective, and environment-friendly strategy to protect agricultural crops. We report the glyphosate-tolerant Pseudomonas resinovorans SZMC 25872 isolate as a novel strain with antagonistic potential towards the plant pathogenic bacterium Agrobacterium tumefaciens. In our studies, the growth of the P. resinovorans SZMC 25872 and A. tumefaciens SZMC 14557 isolates in the presence of 74 different carbon sources, and the effect of 11 carbon sources utilized by both strains on the biocontrol efficacy was examined. Seven variations of media with different carbon sources were selected for the assays to observe the biocontrol potential of the P. resinovorans strain. Also, 50% concentrations of the cell-free culture filtrates (CCF) obtained from medium amended with L-alanine or succinic acid as sole carbon source were found to be effective for the growth suppression of A. tumefaciens by 83.03 and 56.80%, respectively. The effect of 7 media on siderophore amount and the activity of extracellular trypsin- and chymotrypsin-like proteases, as well as esterases were also evaluated. Significant positive correlation was found between the siderophore amount and the percentage of inhibition, and the inhibitory effect of the CCFs obtained from medium amended with succinic acid was eliminated in the presence of an additional iron source, suggesting that siderophores produced by P. resinovorans play an important role in its antagonistic potential. The metabolic profile analysis of the P. resinovorans SZMC 25872 strain, performed by high performance liquid chromatography - high resolution mass spectrometry (HPLC-HRMS), has identified several previously not reported metabolites that might play role in the antagonistic effect against A. tumefaciens. Based on our findings we suggest that the possible inhibition modes of A. tumefaciens SZMC 14557 by P. resinovorans SZMC 25872 include siderophore-mediated suppression, extracellular enzyme activities and novel bioactive metabolites.

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