Encapsulation of Metarhizium brunneum enhances endophytism in tomato plants

Biocontrol of insect pests using fungal entomopathogens has been promoted as a promising alternative to chemical pesticides. Apart from their direct mode of action against insect pests, several fungal entomopathogens have been reported as natural endophytes, paving the way for novel plant protection measures. In this study, we aimed at the selective propagation of finely dispersed Metarhizium brunneum strain BIPESCO5 mycelium in submerged culture and encapsulation in calcium alginate/starch beads to protect the fungus during drying, enable growth on different soils and promote endophytism in tomato plants. We found that a combination of osmotic pressure and increased medium viscosity promoted selective formation of finely dispersed mycelium reflected by 34.1-fold decreased pellet diameters, 1.8-fold increased mycelial biomass concentrations and low blastospore contents of 40.4 × 105 mL−1 after 48 h. Encapsulation of mycelium enhanced drying survival by 31.5%. Co-encapsulated starch was degraded by 24.8% after 21 days and served as a nutrient source for growth on soils with best results on sterile and non-sterile potting substrate with 8.7 mm and 4.4 mm radial mycelial growth, respectively, compared to water agar with 7.6 mm. When applied to the soil, encapsulation significantly increased endophytism 3.8–7.0-fold compared to plants treated with non-formulated fungal biomass. This study provides the first evidence of endophytic establishment of M. brunneum in the stem of tomato plants after application of mycelium to roots as well as on increased endophytism by encapsulation. These results might provide the basis for future work on increasing endophytism by formulation technologies.