Colonization Efficacy of the Endophytic Insect-Pathogenic Fungus, Beauveria bassiana, Across the Plant Kingdom: A Meta-Analysis

The insect-pathogenic fungus Beauveria bassiana (Bb) colonizes several plant species as an endophyte. However, the diversity of plants colonized and the extent of colonization by this fungus have not been summarized comprehensively across all plant species. To fill this knowledge gap, a meta-analysis of published studies (years 2002-2018) on the percentage of B. bassiana plant colonization across the plant kingdom was conducted. We collected 232 published papers from which 1,051 studies (individual treatments) were extracted and analyzed with Comprehensive Meta-Analysis, Version 3 (CMA) software. Factors (n = 26) influencing plant colonization by B. bassiana were identified. Across all studies, the mean endophytic colonization of B. bassiana was 29% in different plant taxa. Plant colonization by B. bassiana was highest for isolates collected from insects. Most studies applied B. bassiana at 1 x 10(8) conidia/ml; however, plant colonization was greatest with an application rate of 1 x 10(12) conidia/ml. Among all plant hosts, colonization percentage was highest in faba bean, plants in the family Brassicaceae, angiosperms (eudicots, annuals), plants classified with a forb/herb/vine growth habit, and plants with fibrous or tap root systems. As an inoculant, B. bassiana was most frequently applied to the whole plant after true leaves had developed. The foliar spray was the most studied inoculation method, but the application of solid grain substrate to foliage gave higher plant colonization. Studies conducted in controlled environments resulted in higher endophytic colonization with B. bassiana than field studies. Endophytic B. bassiana presence was confirmed primarily with microscopy, rather than molecular methods. High heterogeneity (I (2) = 97%) across studies was identified with large variability in endophytic B. bassiana colonization across a diversity of plant species. These findings increase our understanding and knowledge of the endophytic lifestyle of B. bassiana, which will facilitate the development of novel, sustainable, and eco-friendly disease management strategies with B. bassiana.