Beneficial Soil Microorganisms, an Ecological Alternative for Soil Fertility Management

Wastewater irrigation and Trichoderma colonization in tomato plants: effects on plant traits, antioxidant activity, and performance of the insect pest Macrosiphum euphorbiae

The scarcity of freshwater for agriculture in many regions has led to the application of sewage and saline water for irrigation. Irrigation with non-conventional water sources could become a non-harmful process for plant cultivation, and the effects of their use on crops should be monitored in order to develop optimal management strategies. One possibility to overcome potential barriers is to use biostimulants such as Trichoderma spp. fungi. Tomato is a crop of great economic importance in the world. This study investigated the joint effects of Trichoderma afroharzianum T-22 on tomato plants irrigated with simulated unconventional waters. The experiment consisted of a control and three water treatments. In the control, the plants were watered with distilled water. The three water treatments were obtained by using an irrigation water added with nitrogen, a wastewater effluent, and a mixed groundwater-wastewater effluents. Potted tomato plants (variety Bobcat) were grown in a controlled growth chamber. Antioxidant activity, susceptibility to the aphids Macrosiphum euphorbiae, and tomato plant growth parameters were estimated. Trichoderma afroharzianum T-22 had a positive effect on plant growth and antioxidant defenses when plants were irrigated with distilled water. Instead, no significant morphological effects induced by T. afroharzianum T-22 on plants were observed when unconventional water was used for irrigation. However, inoculation with T. afroharzianum T-22 activated a stress response that made the colonized plants more susceptible to aphid development and increased their fecundity and longevity. Thanks to this study, it may be possible for the first time to open a new discussion on the practical possibility of using reclaimed wastewater for crop irrigation with the addition of a growth-promoting fungal symbiont.

Effect of Bio-Inoculum, Compost, and Humic Acid on NPK Availability in Tomato Soils

The study aimed to determine the influence of biological inoculation and organic fertilizer on the availability of nitrogen, phosphorous, and potassium (N.P.K.) in protected tomato soil. During the 2021 agricultural season, the experiment was conducted in greenhouses in the Al-Azzawiya area / Babylon Governorate (longitude 44.5E and latitude 32.7N). Bacterial bio-inoculum was used and compared with the control (S0 and S1), three levels of compost (C0, C1, C2) tons.ha-1, and three levels of organic fertilizer Humus (H0, H1, H2) and the interaction between them in nitrogen, phosphorous, and potassium were used. The results of the statistical analysis resulted in higher values of the triple interaction treatment (S1 + H2 + C2) than the control by giving it the highest mean concentration of available nitrogen, phosphorous, and potassium in the soil (48.70, 19.71, 255.33) mg.kg-1.soil for each, respectively.

Effect of Colonization of Trichoderma harzianum on Growth Development and CBD Content of Hemp (Cannabis sativa L.)

Trichoderma harzianum, as a natural endophytic biocontrol agent, can ameliorate plant development, nutrient uptake, and resistance to biotic and abiotic stresses. This study aimed to investigate the effect of Trichoderma harzianum inoculation on agronomical and quality characteristics of two monoecious hemp (Cannabis sativa L.) varieties, Fedora 17 and Felina. A greenhouse pot experiment was conducted in a completely randomized design of two treatments of Trichoderma harzianum with a low and high dose of the fungus (T1 and T2). The significance of differences between treatments was estimated by using a Fisher’s test with a significance level p = 0.05. The root density of both varieties was significantly affected by treatments, and higher values were recorded in Fedora 17 (2.32 mm cm⁻³). The Arbuscular Mycorrhizal Fungi (AMF) colonization of the root system and the soil emission of CO₂ were higher after the inoculation of Trichoderma harzianum. The highest values of plant height and dry weight were noticed for T2, especially in variety Felina. Trichoderma harzianum positively influenced characteristics of inflorescences such as their number, fresh weight moisture, and compactness in both varieties, while the dry weight, length, and dry yield of inflorescences were not improved. Finally, the fertigation of Trichoderma harzianum in hemp plants was beneficial by increasing the cannabidiol (CBD) content, especially in T2 treatment (4 × 10¹² CFU kg⁻¹).

Emerging salt marshes as a source of Trichoderma arenarium sp. nov. and other fungal bioeffectors for biosaline agriculture

AIMS

Sustainable agriculture requires effective and safe biofertilizers and biofungicides with low environmental impact. Natural ecosystems that closely resemble the conditions of biosaline agriculture may present a reservoir for fungal strains that can be used as novel bioeffectors.

METHODS AND RESULTS

We isolated a library of fungi from the rhizosphere of three natural halotolerant plants grown in the emerging tidal salt marshes on the south-east coast of China. DNA barcoding of 116 isolates based on the rRNA ITS1 and 2 and other markers (tef1 or rpb2) revealed 38 fungal species, including plant pathogenic (41%), saprotrophic (24%) and mycoparasitic (28%) taxa. The mycoparasitic fungi were mainly species from the hypocrealean genus Trichoderma, including at least four novel phylotypes. Two of them, representing the taxa Trichoderma arenarium sp. nov. (described here) and T. asperelloides, showed antagonistic activity against five phytopathogenic fungi, and significant growth promotion on tomato seedlings under the conditions of saline agriculture.

CONCLUSIONS

Trichoderma spp. of salt marshes play the role of natural biological control in young soil ecosystems with a putatively premature microbiome.

SIGNIFICANCE AND IMPACT OF THE STUDY

The saline soil microbiome is a rich source of halotolerant bioeffectors that can be used in biosaline agriculture.

Habitat filtering shapes the differential structure of microbial communities in the Xilingol grassland

The spatial variability of microorganisms in grasslands can provide important insights regarding the biogeographic patterns of microbial communities. However, information regarding the degree of overlap and partitions of microbial communities across different habitats in grasslands is limited. This study investigated the microbial communities in three distinct habitats from Xilingol steppe grassland, i.e. animal excrement, phyllosphere, and soil samples, by Illumina MiSeq sequencing. All microbial community structures, i.e. for bacteria, archaea, and fungi, were significantly distinguished according to habitat. A high number of unique microorganisms but few coexisting microorganisms were detected, suggesting that the structure of microbial communities was mainly regulated by species selection and niche differentiation. However, the sequences of those limited coexisting microorganisms among the three different habitats accounted for over 60% of the total sequences, indicating their ability to adapt to variable environments. In addition, the biotic interactions among microorganisms based on a co-occurrence network analysis highlighted the importance of Microvirga, Blastococcus, RB41, Nitrospira, and four norank members of bacteria in connecting the different microbiomes. Collectively, the microbial communities in the Xilingol steppe grassland presented strong habitat preferences with a certain degree of dispersal and colonization potential to new habitats along the animal excrement- phyllosphere-soil gradient. This study provides the first detailed comparison of microbial communities in different habitats in a single grassland, and offers new insights into the biogeographic patterns of the microbial assemblages in grasslands.

Trichoderma-Azotobacter biofilm inoculation improves soil nutrient availability and plant growth in wheat and cotton

Microbial biofilms are gaining importance in agriculture, due to their multifaceted agronomic benefits and resilience to environmental fluctuations. This study focuses on comparing the influence of single inoculation-Azotobacter chroococcum (Az) or Trichoderma viride (Tv) and their biofilm (Tv-Az), on soil and plant metabolic activities in wheat and cotton grown under Phytotron conditions. Tv-Az proved superior to all the other treatments in terms of better colonisation, plant growth attributes and 10-40% enhanced availability of macronutrients and micronutrients in the soil, over control. Confocal and scanning electron microscopy showed that the cells attached to the root tips initially, followed by their proliferation along the surface of the roots. Soil polysaccharides, proteins and dehydrogenase activity showed several fold enhancement in Tv-Az biofilm inoculated samples. Time course studies revealed that the population of Az and Tv in the rhizoplane and rhizosphere was significantly higher with a 0.14-0.31 log colony-forming unit (CFU) increase in the biofilm-inoculated treatment in both crops. Enhancement in soil biological activities was facilitated by the improved colonisation of the biofilm, due to the synergistic association between Tv and Az. This demonstrates the utility of Tv-Az biofilm as a multifunctional plant growth promoting and soil fertility enhancing option in agriculture.

Genomic characterization of Trichoderma atrobrunneum (T. harzianum species complex) ITEM 908: insight into the genetic endowment of a multi-target biocontrol strain

BACKGROUND

So far, biocontrol agent selection has been performed mainly by time consuming in vitro confrontation tests followed by extensive trials in greenhouse and field. An alternative approach is offered by application of high-throughput techniques, which allow extensive screening and comparison among strains for desired genetic traits. In the genus Trichoderma, the past assignments of particular features or strains to one species need to be reconsidered according to the recent taxonomic revisions. Here we present the genome of a biocontrol strain formerly known as Trichoderma harzianum ITEM 908, which exhibits both growth promoting capabilities and antagonism against different fungal pathogens, including Fusarium graminearum, Rhizoctonia solani, and the root-knot nematode Meloidogyne incognita. By genomic analysis of ITEM 908 we investigated the occurrence and the relevance of genes associated to biocontrol and stress tolerance, providing a basis for future investigation aiming to unravel the complex relationships between genomic endowment and exhibited activities of this strain.

RESULTS

The MLST analysis of ITS-TEF1 concatenated datasets reclassified ITEM 908 as T. atrobrunneum, a species recently described within the T. harzianum species complex and phylogenetically close to T. afroharzianum and T. guizhouense. Genomic analysis revealed the presence of a broad range of genes encoding for carbohydrate active enzymes (CAZYmes), proteins involved in secondary metabolites production, peptaboils, epidithiodioxopiperazines and siderophores potentially involved in parasitism, saprophytic degradation as well as in biocontrol and antagonistic activities. This abundance is comparable to other Trichoderma spp. in the T. harzianum species complex, but broader than in other biocontrol species and in the species T. reesei, known for its industrial application in cellulase production. Comparative analysis also demonstrated similar genomic organization of major secondary metabolites clusters, as in other Trichoderma species.

CONCLUSIONS

Reported data provide a contribution to a deeper understanding of the mode of action and identification of activity-specific genetic markers useful for selection and improvement of biocontrol strains. This work will also enlarge the availability of genomic data to perform comparative studies with the aim to correlate phenotypic differences with genetic diversity of Trichoderma species.

Green manure and long-term fertilization effects on soil zinc and cadmium availability and uptake by wheat (Triticum aestivum L.) at different growth stages

Zinc (Zn) deficiency in human populations depending on cereals as a main source of Zn is a global malnutrition problem. In this field study, we investigated the potential of green manure application to increase soil Zn availability and wheat grain Zn concentrations (biofortification) on a Luvisol with different long-term fertilizer management. We also studied cadmium (Cd), as wheat is a major contributor of this undesired non-essential element to human diets. Clover (Trifolium alexandrinum L.), mustard (Sinapis alba L.) or no green manure was grown on field plots which had been managed with farmyard manure or mineral fertilizers for 65years in Switzerland. After green manure incorporation into the soil, spring wheat (Triticum aestivum L.) was grown on all plots. The "diffusive gradients in thin films" (DGT) method and DTPA extraction were used to compare soil Zn and Cd availability among the treatments. In contrast to mustard, clover increased soil mineral nitrogen concentrations and wheat biomass; however, neither increased grain Zn concentrations. DGT-available Zn and Cd increased temporarily after both farmyard manure and mineral nitrogen fertilizer application. Higher DTPA-extractable soil Zn and Cd, lower wheat grain yields, but higher grain Zn concentrations were obtained with farmyard manure compared to mineral fertilizers, independent of the green manure treatment. Farmyard manure added Zn, Cd and organic matter that increased the soil binding capacity for Zn and Cd. The decomposition of clover residues caused higher wheat grain yields, but only marginally lower grain Zn concentrations. The absence of a stronger dilution of grain Zn was probably due to organic acid and nitrogen release from decomposing clover, which facilitated Zn uptake by wheat. The study revealed that both long- and short-term field management with organic matter alters soil Zn and Cd concentrations but that the long-term effects dominate their uptake by wheat, in Zn sufficient soil.

Tomato below ground-above ground interactions: Trichoderma longibrachiatum affects the performance of Macrosiphum euphorbiae and its natural antagonists

Below ground and above ground plant-insect-microorganism interactions are complex and regulate most of the developmental responses of important crop plants such as tomato. We investigated the influence of root colonization by a nonmycorrhizal plant-growth-promoting fungus on direct and indirect defenses of tomato plant against aphids. The multitrophic system included the plant Solanum lycopersicum ('San Marzano nano'), the root-associated biocontrol fungus Trichoderma longibrachiatum strain MK1, the aphid Macrosiphum euphorbiae (a tomato pest), the aphid parasitoid Aphidius ervi, and the aphid predator Macrolophus pygmaeus. Laboratory bioassays were performed to assess the effect of T. longibrachiatum MK1, interacting with the tomato plant, on quantity and quality of volatile organic compounds (VOC) released by tomato plant, aphid development and reproduction, parasitoid behavior, and predator behavior and development. When compared with the uncolonized controls, plants whose roots were colonized by T. longibrachiatum MK1 showed quantitative differences in the release of specific VOC, better aphid population growth indices, a higher attractiveness toward the aphid parasitoid and the aphid predator, and a quicker development of aphid predator. These findings support the development of novel strategies of integrated control of aphid pests. The species-specific or strain-specific characteristics of these below ground-above ground interactions remain to be assessed.

Bacterial siderophores efficiently provide iron to iron-starved tomato plants in hydroponics culture

Iron is one of the essential elements for a proper plant development. Providing plants with an accessible form of iron is crucial when it is scant or unavailable in soils. Chemical chelates are the only current alternative and are highly stable in soils, therefore, posing a threat to drinking water. The aim of this investigation was to quantify siderophores produced by two bacterial strains and to determine if these bacterial siderophores would palliate chlorotic symptoms of iron-starved tomato plants. For this purpose, siderophore production in MM9 medium by two selected bacterial strains was quantified, and the best was used for biological assay. Bacterial culture media free of bacteria (S) and with bacterial cells (BS), both supplemented with Fe were delivered to 12-week-old plants grown under iron starvation in hydroponic conditions; controls with full Hoagland solution, iron-free Hoagland solution and water were also conducted. Treatments were applied twice along the experiment, with a week in between. At harvest, plant yield, chlorophyll content and nutritional status in leaves were measured. Both the bacterial siderophore treatments significantly increased plant yield, chlorophyll and iron content over the positive controls with full Hoagland solution, indicating that siderophores are effective in providing Fe to the plant, either with or without the presence of bacteria. In summary, siderophores from strain Chryseobacterium C138 are effective in supplying Fe to iron-starved tomato plants by the roots, either with or without the presence of bacteria. Based on the amount of siderophores produced, an effective and economically feasible organic Fe chelator could be developed.

Harnessing plant-microbe interactions for enhancing farm productivity

Declining soil fertility and farm productivity is a major global concern in order to achieve food security for a burgeoning world population. It is reported that improving soil health alone can increase productivity by 10-15% and in combination with efficient plant traits, farm productivity can be increased up to 50-60%. In this article we explore the emerging microbial and bioengineering technologies, which can be employed to achieve the transformational increase in farm productivity and can simultaneously enhance environmental outcomes i.e., low green house gas (GHG) emissions. We argue that metagenomics, meta-transcriptomics and metabolomics have potential to provide fundamental knowledge on plant-microbes interactions necessary for new innovations to increase farm productivity. Further, these approaches provide tools to identify and select novel microbial/gene resources which can be harnessed in transgenic and designer plant technologies for enhanced resource use efficiencies.