Coinoculation of Pantoea phytobeneficialis PF55 and Trichoderma harzianum ESALQ 1306 enhances soil microbial activity and agronomic performance in onion

Coinoculation with growth-promoting microorganisms has proven to be an efficient strategy for enhancing the agronomic performance of onion (Allium cepa L.). This study evaluated the effect of inoculating Pantoea phytobeneficialis PF55 and Trichoderma harzianum ESALQ 1306, applied individually and in combination, on agronomic, biochemical, and microbiological variables of the Valessul cultivar. The experiment was conducted in a randomized block design with four treatments (non-inoculated, PF55, ESALQ 1306, and PF55 + ESALQ 1306) and 12 replications in Florianópolis, SC, Brazil. Inoculation was performed 14 days after seedling transplant. Inoculation with PF55 resulted in a measurable increase in productivity. The results indicate that PF55 application increased productivity, biomass, and nutrient accumulation, while coinoculation with T. harzianum ESALQ 1306 promoted specific effects, such as higher carotenoid contents and soil microbial activity. Isolated inoculation with T. harzianum ESALQ 1306 increased chlorophyll b and total contents, as well as soluble solids levels. These results confirm that the bacterium acts as the primary growth-promoting agent, while the fungus plays a modulating role, influencing physiological and edaphic processes in a more restricted manner.