Molecular Characterization and Endophytic Colonization of a Native Beauveria bassiana Isolate in Maize: Effects on Plant Growth and Spodoptera frugiperda Herbivory

Beauveria bassiana (Balsamo-Crivelli) Vuillemin can colonize plant tissues as an endophyte, promoting plant growth and defense against pathogens and insect herbivory. Understanding the endophytic behavior of native isolates is important for developing pest management strategies in maize, a crop affected by Spodoptera frugiperda (J. E. Smith). This study aimed to genetically characterize a Mexican B. bassiana isolate (Bb-IIAF1-24) collected in Los Reyes, Michoacán, using the β-tubulin gene. The phylogenetic relationships showed that this isolate formed a well-supported clade with other B. bassiana isolates from different countries; however, a low divergence among them was observed. In a second part of this study, the influence of foliar and soil inoculation (1 × 108 conidia mL−1) of Bb-IIAF1-24 isolate on endophytic colonization in maize plants, as well as the effects on plant growth and herbivory by S. frugiperda were evaluated. This fungus was detected in roots, stems, and leaves, but no significant differences were found between root and stem colonization or between foliar and soil inoculation methods. Beauveria bassiana treatment resulted in increased stem diameter in plants when applied to soil compared to foliar application and the control. In contrast, plants subjected to foliar application were significantly taller than those receiving soil application or the control plants. Plants from both application methods experienced lower leaf damage compared to the control. These findings demonstrate the potential of the Bb-IIAF1-24 isolate as an endophytic fungus to promote maize growth and reduce herbivory by S. frugiperda.