Harnessing root exudates for plant microbiome engineering and stress resistance in plants.

A wide range of abiotic and biotic stresses adversely affect plant's growth and production. Under stress, one of the main responses of plants is the modulation of exudates excreted in the rhizosphere, which consequently leads to alterations in the resident microbiota. Thus, the exudates discharged into the rhizospheric environment play a preponderant role in the association and formation of plant-microbe interactions. In this review, we aimed to provide a synthesis of the latest and most pertinent literature on the diverse biochemical and structural compositions of plant root exudates. Also, this work investigates into their multifaceted role in microbial nutrition and intricate signaling processes within the rhizosphere, which includes quorum-sensing molecules. Specifically, it explores the contributions of low molecular weight compounds, such as carbohydrates, phenolics, organic acids, amino acids, and secondary metabolites, as well as the significance of high molecular weight compounds, including proteins and polysaccharides. It also discusses the state-of-the-art omics strategies that unveil the vital role of root exudates in plant-microbiome interactions, including defense against pathogens like nematodes and fungi. We propose multiple challenges and perspectives, including exploiting plant root exudates for host-mediated microbiome engineering. In this discourse, root exudates and their derived interactions with the rhizospheric microbiota should receive greater attention due to their positive influence on plant health and stress mitigation.

New opportunities in plant microbiome engineering for increasing agricultural sustainability under stressful conditions.

Plant microbiome (or phytomicrobiome) engineering (PME) is an anticipated untapped alternative strategy that could be exploited for plant growth, health and productivity under different environmental conditions. It has been proven that the phytomicrobiome has crucial contributions to plant health, pathogen control and tolerance under drastic environmental (a)biotic constraints. Consistent with plant health and safety, in this article we address the fundamental role of plant microbiome and its insights in plant health and productivity. We also explore the potential of plant microbiome under environmental restrictions and the proposition of improving microbial functions that can be supportive for better plant growth and production. Understanding the crucial role of plant associated microbial communities, we propose how the associated microbial actions could be enhanced to improve plant growth-promoting mechanisms, with a particular emphasis on plant beneficial fungi. Additionally, we suggest the possible plant strategies to adapt to a harsh environment by manipulating plant microbiomes. However, our current understanding of the microbiome is still in its infancy, and the major perturbations, such as anthropocentric actions, are not fully understood. Therefore, this work highlights the importance of manipulating the beneficial plant microbiome to create more sustainable agriculture, particularly under different environmental stressors.

Endophytic Fungi Assures Tropical Forage Grass Growth by Water Stress Tolerances.

Forage plants is the base of beef and dairy cattle production. While water stress limits agricultural production worldwide, endophytic fungi can play a beneficial role for plants, such as tolerance to biotic and abiotic stresses. The objective of this work was to evaluate the effect of inoculation of the endophytic fungi Paraconiothyrium estuarinum (CML 3695, CML 3696, CML 3699) and Paraconiothyrium cyclothyrioides (CML 3697, CML 3698) on agronomic characteristics of two forage species, Brachiaria brizantha (A. Rich) Stapf. cv. Marandu and Megathyrsus maximus Jacq. cv. BRS Mombaça, under different available water capacities. The treatments simulated a long drought period (LDH) equivalent to 10% of the available water capacity (AWC) and simulated 7 (7 DH) and 14 days of drought (14 DH) without water supply. The grasses were evaluated for length and dry weight of shoots and roots. All treatments reached humidity below the permanent wilting point (PWP) and the highest variation in soil moisture was observed at 14 DH, for both grass species. The endophytic fungi promoted an average 15% increase in shoot length (SL) for B. brizantha and an increase of 34% for SL, 266% for Dry Shoot Mass (SDM), and 340% for Dry Root Mass (RDM) for M. maximus treated with P. estuarinum (CML 3699) at 7 DH. Paraconiothyrium estuarinum (CML 3699) guaranteed the highest tolerance to water deficit and sustainable growth performance to both tested grasses.

Optimizing mass production of Trichoderma asperelloides by submerged liquid fermentation and its antagonism against Sclerotinia sclerotiorum.

Commercial products based on Trichoderma are obtained mainly from solid-state fermentation. Submerged liquid fermentation is the most appropriate method compared to the solid medium for large-scale production of Trichoderma spp. The present study aimed to optimize the combination of key variables that influence the liquid fermentation process of Trichoderma asperelloides LQC-96 for conidial production coupled with its efficiency in the control of Sclerotinia sclerotiorum. In addition, we verified whether the optimized culture conditions can be used for the conidial production of Trichoderma erinaceum T-12 and T-18 and Trichoderma harzianum T-15. Fermentation studies were performed in shake flasks following a planned experimental design to reduce the number of tests and consumable costs. The effect of temperature, pH, photoperiod, carbon:nitrogen ratio and water activity on conidial production were assessed, which of pH was the only meaningful factor contributing to increased conidial production of T. asperelloides LQC-96. From the five variables studied initially, pH and C:N ratio were further used in the second design (rotational central composite design-RCCD). Hence, the best conditions for the production of T. asperelloides LQC-96 conidia by liquid fermentation consisted of initial pH of 3.5, C:N ratio of 200:1 at 30 °C, without glycerol, and under 24 h photoperiod. The highest conidial concentration was observed after seven days of fermentation. Under these optimal conditions, T. erinaceum T-12 and T-18, and T. harzianum T-15 were also cultivated, but only LQC-96 efficiently parasitized S. sclerotiorum, precluding sclerotium myceliogenic germination. Our findings propose optimal fermentation conditions that maximize conidial production of T. asperelloides as a potential biofungicide against S. sclerotiorum.