Endophytic Beauveria bassiana in maize: influence of genotype, fungal source, inoculation methods, and time on colonization and fitness of Fall armyworm

We investigated how Beauveria bassiana isolate origin and maize genotype affect endophytic colonization and suppression of the Fall armyworm (FAW). The objectives were to determine whether isolate origin (insect or soil-derived) influences colonization across maize tissues, assess the role of four genotypes (two landraces and two improved lines), and evaluate FAW fitness on colonized plants. Three indigenous isolates, two insect-derived (Bb11, Bb115) and one soil-derived (DL1.1), were applied to four maize genotypes. These included two landraces (Kokoli Daneri, Ovinonboe) and two improved varieties (Faaba QPM, TZL Composite 4W Benin). Inoculation was performed using foliar spraying and seed coating. Colonization declined over time but varied significantly with isolate, genotype, and tissue type (p < 0.0001). Insect-derived isolates achieved higher colonization, particularly in stems and roots of landraces, indicating genotype-dependent compatibility. Bb115 achieved systemic colonization in Kokoli Daneri leaves at 7 days after inoculation. Feeding assays showed that FAW larvae fed on colonized plants had reduced survival, lower larval and pupal weights, and reduced adult fecundity and emergence. FAW fitness was assessed using corrected larval mortality, larval and pupal weight and size, adult emergence, and reproduction (adult emergence, fecundity). The reduction of fitness remained moderate and was more pronounced in landrace and insect isolate combinations. These results emphasize the importance of fungal isolate, maize genotype, inoculation method, and timing in enhancing endophytic biocontrol.