AUTHOR=Siqueira Ana Carolina Oliveira , Mascarin Gabriel Moura , Gonçalves Cassiara R. N. C. B. , Marcon Joelma , Quecine Maria Carolina , Figueira Antonio , Delalibera Ítalo 

TITLE=Multi-Trait Biochemical Features of Metarhizium Species and Their Activities That Stimulate the Growth of Tomato Plants

JOURNAL=Frontiers in Sustainable Food Systems

VOLUME=4

YEAR=2020

URL=https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2020.00137

DOI=10.3389/fsufs.2020.00137

ISSN=2571-581X

ABSTRACT=<p>The interaction between <italic>Metarhizium</italic> spp. and plant roots may induce host plant growth and help control below- and above-ground pests and diseases. We conducted <italic>in vivo</italic> and <italic>in vitro</italic> bioassays using native Brazilian isolates of <italic>Metarhizium robertsii</italic> (ESALQ 1635), <italic>M. humberi</italic> (ESALQ 1638), and <italic>M. anisopliae</italic> (ESALQ 1669) to better understand the possible mechanisms related to plant growth promotion traits and colonization of the root system in the model pot-grown tomato (<italic>Solanum lycopersicum</italic> L.) miniature cultivar “Micro-Tom.” <italic>In vivo</italic> trials revealed that <italic>M. robertsii</italic> (ESALQ 1635) or <italic>M. humberi</italic> (ESALQ 1638) inoculated in tomato seedlings improved vegetative and reproductive traits. Inoculation with <italic>M. robertsii</italic> yielded taller plants, longer roots, and more shoot and root dry mass than <italic>M. humberi</italic>. The number of flowers and the fresh weight of fruits was significantly increased by <italic>M. robertsii</italic> and <italic>M. humberi</italic> inoculation, in relation to uninoculated control plants. Both fungal species endophytically colonized all tomato tissues within 30 days of inoculation. Plants inoculated with either <italic>M. robertsii</italic> or <italic>M. humberi</italic> increased auxin-induced GUS expression in the roots for up to 30 days after inoculation, confirming that <italic>Metarhizium</italic> induces auxin-regulated gene expression. We also explored the production of key compounds including enzymes, hormones, and metabolites involved in plant growth promotion. The three <italic>Metarhizium</italic> species grown with or without exogenous tryptophan were able to produce indole-3-acetic acid (IAA) at different titers. All <italic>Metarhizium</italic> isolates produced phosphatases, phytases, siderophores, and chitinases. Of particular importance, the <italic>M. robertsii</italic> and <italic>M. humberi</italic> isolates exhibited similar <italic>in vitro</italic> biochemical profiles, whereas <italic>M. anisopliae</italic> and <italic>Trichoderma harzianum</italic> isolates demonstrated distinct traits from the others. Taken together, we argue that the <italic>M. robertsii</italic> isolate is more efficient than the <italic>M. humberi</italic> isolate to endophytically colonize tomato plants resulting in improved growth. However, <italic>M. humberi</italic> (ESALQ 1638) yielded a slightly better production of some metabolites <italic>in vitro</italic>. Thus, we propose that the isolates of <italic>M. robertsii</italic> and <italic>M. humberi</italic> could be explored as complementary plant growth promoters.</p>