Mayra Santiago Velasco

The transition toward sustainable agriculture has driven the use of plant growth-promoting microorganisms as viable alternatives to conventional agrochemicals. Among these, species of the genus Trichoderma have emerged as pivotal players due to their ability to establish beneficial and complex interactions with plants that extend far beyond their traditional role as biocontrol agents. This review integrates recent advances in understanding the mechanisms by which Trichoderma promotes plant growth and development. Specifically, the evolutionary transition of Trichoderma from a mycoparasitic lifestyle to beneficial plant associations is examined, together with the molecular processes involved in plant recognition, root colonization, and establishment within the rhizosphere and plant tissues. Furthermore, the mechanisms through which Trichoderma enhances plant performance are addressed, including metabolite production (both volatile and non-volatile), phytohormone modulation, nutrient acquisition and mobilization, and enhanced photosynthetic capacity. Finally, current agricultural applications, the technical challenges of formulation and field implementation, and future perspectives on Trichoderma-based microbial consortia and precision agriculture tools are analyzed. Overall, this review provides a comprehensive framework highlighting the potential of Trichoderma as a premier biostimulant for modern sustainable farming.

Some actinobacterial species have been reported to improve plant growth due to their roles as biostimulants and biological control agents. In this study, the effect of actinobacterial isolate 27, obtained from the rhizospheric soil of melon plants and identified as Streptomyces calvus, was evaluated on the growth of Arabidopsis thaliana and tomato plants. In Arabidopsis, in vitro assays showed that after seven days of interaction, isolate 27 increased fresh weight by 1.4-, 1.5-, and 2.3-fold and lateral root number by 1.7-, 1.3-, and 2.5-fold under physical contact and split-plate systems (MS and ISP2 media), respectively, compared with non-inoculated plants. An increased β-glucuronidase (GUS, encoded by the uidA gene) signal was observed in primary and lateral roots of the Arabidopsis DR5::uidA reporter line during both interaction types, suggesting the activation of auxin-responsive pathways. In addition, isolate 27 rescued the rhd6 (root hair defective 6) mutant phenotype, restoring root hair formation. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that isolate 27 emitted volatile organic compounds (VOCs), including an alcohol and several sesquiterpenes, and that this profile changed during interaction with Arabidopsis plantlets. In soil-based pot assays, inoculation with isolate 27 significantly enhanced the development of Arabidopsis plants after 23 days, both when applied alone and in co-inoculation with Trichoderma atroviride. Furthermore, isolate 27 stimulated tomato plant growth, leading to significant increases in fresh and dry biomass, as well as shoot and root lengths after 28 days. Overall, these results demonstrate that S. calvus isolate 27 promotes plant growth and development through the production of bioactive compounds that modulate plant growth pathways, including hormonal responses, highlighting its potential as a bioinoculant for sustainable and productive agricultural systems.