Development of a Metarhizium-based biostimulant for the sugarcane crop: effects on pests and crop yield

• Autor(a) principal: Siqueira, Ana Carolina Oliveira
• Data de Publicação: 2020
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11146/tde-15022021-181820/
• topic: Metarhizium; Metarhizium; Bioestimulante; Biostimulant; Cana-de-açúcar; Endophytic fungi; Fungos endofíticos; Growth promotion; Interação planta-inseto-fungo; Plant-insect-fungus interaction; Promoção de crescimento; Sugarcane

The entomopathogenic fungus Metarhizium anisopliae has been used efficiently for decades in the sugarcane crops for biological pest control. Some Metarhizium species can colonize a wide variety of plant species endophytically, providing protection against arthropod pests, accelerating plant development, and acting as antagonists of phytopathogens. This project\'s general objective was to evaluate the potential of Metarhizium species as inoculants, aiming to promote sugarcane growth and, consequently, increase crop production yields and control important insect and nematodes pests. We conducted in vivo and in vitro bioassays using native Brazilian isolates of Metarhizium robertsii, M. humberi, and M. anisopliae to better understand the possible mechanisms related to plant growth promotion traits and colonization of the root system in the model pot-grown tomato (Solanum lycopersicum L.) miniature cultivar \'Micro-Tom\'. The production of compounds that could be involved in stimulating plant growth promotion was assessed in vitro by measuring the production of the hormone auxin (3-indole-acetic acid), phosphatase, phytase, siderophores, and chitinases. The effects of sugarcane inoculation using two types of propagules, two fungal concentrations, and the combined inoculation of two fungal species in promoting plant growth were evaluated at the greenhouse. Effects on populations of the nematode Meloidogyne javanica and Pratylenchus zeae were assessed in vivo and in vitro. We also evaluated the development and food preference of the insect Diatraea saccharalis under laboratory conditions. Finally, field studies were carried out in five commercial sugarcane areas in Iracemápolis-SP, Batatais-SP, and Sertãozinho-SP. Sugarcane plants were inoculated, and their development and pest incidence were evaluated until harvest. In vivo trials revealed that M. robertsii (ESALQ 1635) or M. humberi (ESALQ 1638) inoculated in tomato seedlings improved vegetative and reproductive traits. Inoculation with M. robertsii yielded taller plants, longer roots, and more shoot and root dry mass than M. humberi. Plants inoculated with either M. robertsii or M. humberi increased auxin-induced GUS expression in the roots for up to 30 days after inoculation, confirming that Metarhizium induces auxin-regulated gene expression. The three Metarhizium species grown with or without exogenous tryptophan could produce indole-3-acetic acid (IAA) at different titers. All Metarhizium isolates secreted phosphatases, phytases, siderophores, and chitinases. Of particular importance, the M. robertsii and M. humberi isolates exhibited similar in vitro biochemical profiles, whereas M. anisopliae and Trichoderma harzianum isolates demonstrated distinct traits from the others. Both types of propagules, conidia, and blastospores, M. robertsii and M. humberi, colonized sugarcane tissues; however, higher colonization was observed for conidia. The inoculation of sugarcane with 108 conidia/mL (corresponding to an application of 1012 con/ha) conidia suspensions of M. robertsii and M. humberi was more efficient to increased plant growth compared to 107 conidia/mL and the uninoculated control. The inoculation M. robertsii and M. humberi contributed to reducing M. javanica (up to 45%), P. zeae (up to 33%), compared to the control. Mortality of D. saccharalis larvae on plants colonized of M. robertsii and M. humberi was as high as 91.7% after 30 days of inoculation. In host-choice assays, D. saccharalis larvae preferred the uninoculated control than the fungi inoculated plants. In the field studies, notably, both fungal isolates significantly enlarged stalk length (in 4 out of 5 locations) and markedly boosted stalk volume (m3) in comparison to control plots. As a result, greater sugarcane yield (tons/ha) was achieved with Metarhizium inoculation, mainly at locations A, D, and E, and the farmers\' profit was raised by up to 22.9%. Overall, Metarhizium inoculation significantly reduced key insect pests in most tested plots. Altogether, these findings prove the multiple benefits promoted by M. robertsii and M. humberi when employed as bio-inoculants of sugarcane crop by boosting yields as well as alleviating attacks of root and stalk insect pests. The promising results obtained here culminated in the request for commercial registration of a product based on the M. robertsii and M. humberi isolates and bring a unique perspective on the use of entomopathogenic endophytic fungus as biostimulants and biopesticide.