Guar (Cyamopsis tetragonoloba (L.) Taub.) is an important legume plant used as food and industrial crop. Guar forms nitrogen-fixing symbiosis with nodule bacteria (rhizobia) supplying the plant with this important nutrient element. The ability to form symbiosis with rhizobia of various taxonomic groups of genera Bradyrhizobium and Ensifer is a common trait of guar with cowpea and soybean. Pot experiments were performed to compare nodulation and response of guar, cowpea and soybean to inoculation with nine strains isolated from guar nodules and belonging to the above-mentioned genera. Strains assigned to species Bradyrhizobium archetypum and Bradyrhizobium valentinum were isolated from nodules of guar for the first time. Nodule number and biomass on the inoculated guar roots significantly varied depending on the strain from 15 to 40 nodules per plant and from 20 to 54 mg dry weight (DW)/plant, respectively. Eight strains formed nitrogen-fixing symbiosis with cowpea. Nodule number and biomass on the cowpea roots varied depending on the strain from 19 to 67 nodules per plant and from 3 to 61 mg DW/plant, respectively. Significant differences among strains were also observed in acetylene reduction activity and positive effects of inoculation on shoot biomass and nitrogen content in shoots of plant species. However, symbiosis with soybean was inefficient, since only few small white nodules were observed and no effects were found on plant growth. Correlations between the symbiotic parameters in guar and cowpea dependent on the rhizobia strain were found and discussed in view of mechanisms underlying formation and functioning of nitrogen-fixing symbiosis. Several studied strains offer promise as inoculants for guar and cowpea and recommended for further field trials.

Multi-strain consortia are expected to protect plants more reliably than single strains, yet this is rarely tested directly, and the behavior of introduced strains in the field is difficult to follow. We assembled a consortium of Stenotrophomonas rhizophila MGMM118, Bacillus halotolerans MGMM119, Pseudomonas grimontii MGMM120 and Pseudomonas viciae MGMM121 strains isolated from the winter wheat rhizosphere and characterized their hydrolytic activities, auxin production, and analyzed their genomes. The consortium increased shoot and root length of wheat. In biocontrol experiments on barley, the consortium reduced the root rot disease index caused by Fusarium culmorum by approximately ten-fold (5.6% vs. 59.7%), outperforming each individual strain (11.9–17.9%). The consortium also reduced Fusarium root rot in tomato by two-fold. In a field experiment on wheat, strain-specific qPCR detected all introduced microorganisms in the wheat rhizosphere at up to 106 CFU per gram of soil, demonstrating different dynamics for each individual strain. Metabarcoding showed that community structure depended on plant developmental stage rather than on the consortium application. Since metabarcoding could not reliably identify the introduced strains, we suppose that strain-specific qPCR is a more appropriate tool for monitoring of inoculants, particularly in complex soil microbial communities.

Phytopathogenic fungi of the genus Alternaria cause black spot (helminthosporiasis) disease and therefore apply to develop bioherbicides for controlling weeds and illegal vegetation of narcotic plants such as opium poppy (Papaver somniferum subsp. somniferum). In this report, Alternaria papavericola strain 1.39 was identified using sequencing of the ITS region and characterized. Strain 1.39 produced auxins and abscisic acid, did not produce salicylic, jasmonic, or gibberellic (GA3) acids, and did not metabolize any of these phytohormones. Strain 1.39 produced siderophores but showed no 1-aminocyclopropane-1-carboxylate deaminase activity and did not solubilize phosphates Ca₃(PO₄)₂, Ca-phytate, Al₃PO₄, or Fe₃PO₄. Extracts from the culture liquid of strain 1.39 caused necrosis in leaves of poppy and, to a lesser extent, on creeping thistle, tomato, and wheat leaves. Strain 1.39 inhibited poppy seed germination energy by 80%, reduced shoot biomass by 77%, and resulted in the death of 75% of poppy plants in a pot experiment. The phytotoxin was isolated from the culture liquid of this fungus using chromatographic methods. Detailed study of structure of this phytotoxin by a complex of physicochemical methods revealed that it is (+)-cis-sclerosporide(1S,2S,3S,4R,5S,6R)-2,3,5-trihydroxy-4,6-dimethoxycyclohexyl-(1R,5S,6S)-5-isopropyl-8-methylbicyclo[4.4.0]deca-2,7-diene-2-carboxylate). The results showed possibility for application of A. papavericola 1.39 as bioherbicide against opium poppy.