Infection of Helicoverpa armigera by endophytic Beauveria bassiana colonizing tomato plants

Abstract

Beauveria bassiana was isolated from leaf tissue of a wild tomato plant. This isolate (reference WG-40) and a further two isolates of B. bassiana from soil (reference WG-14 and WG-19) were evaluated for their ability to endophytically colonize tomatoes and subsequently infect Helicoverpa armigera larvae. The three isolates were inoculated on to tomato plants using root dip, injection, solid substrate and direct foliar application methods. A detached leaf assay was used to evaluate B. bassiana-induced mortality of second and fourth instar larvae of H. armigera at 1, 3 and 5weeks post plant inoculation with B. bassiana. Isolate WG-40 was the most effective at colonizing tomato plants compared to WG-14 and WG-19 that originated from soil. Root dipping was the most successful inoculation method. Larval mortality of H. armigera was significantly affected by the larval stage and the application method used to establish the fungus. Second instar larvae were more susceptible than fourth instar at all time intervals evaluated. Isolate WG-40 was the most pathogenic and achieved the highest insect mortality. Pupation and adult emergence were inversely correlated to the fungal infection. A few adverse growth effects on the tomato plants were observed as a consequence of endophytic colonization by B. bassiana, although the response was related to application method and fungal isolate. These findings suggest that endophytic colonization of B. bassiana has potential as an effective strategy to control H. armigera in tomatoes.