Endophytic colonization of tomato plants by Beauveria bassiana Vuillemin (Ascomycota: Hypocreales) and leaf damage in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae

Background The endophytic capacity of Beauveria bassiana Vuillemin isolates in 2 tomato varieties and their effects on damage and survival of the tomato fruit worm Helicoverpa armigera Hubner larvae were studied. The bioassays consisted of sowing seeds of 2 tomato cultivars soaked for 24 h in B . bassiana conidial suspension at the concentration of 1 × 10 7 and 1 × 10 9 conidia/ml for the isolates Bb 115 and Bb 11, respectively. Ten leaf, stem, and root segments were cut and incubated for assessing the endophytic growth of the fungus. Percentage of leaf consumption and pathogenicity of B . bassiana on H . armigera larvae were estimated. Main body The fungus B . bassiana developed endophytically in the 2 tomato varieties and was detected in tomato leaf, stem, and root. However, higher colonization rates were observed in roots than in leaves and stems. The B . bassiana isolate Bb 115 had a greater negative effect on the mean survival times (MSTs) of H . armigera larvae and on leaf consumption for local and improved tomato varieties. In fact, the lowest MSTs were recorded at the concentration of 1 × 10 9 conidia/ml for Bb 115 in 1.5 ± 0.2 days, i.e., 7 days less than the surviving larvae of the control group, which MSTs were 8.4 ± 0.9 days. Consumed leaf areas by larvae averaged (89.17 ± 10.33 mm 2 ) at a fungal concentration of 1 × 10 9 conidia/ml for Bb115. It was the best compared to that of untreated control (820.3 ± 92.77 mm 2 ). The colonization rate of the different plant parts increased with conidia concentration in both tomatoes varieties. Conclusion This study reported the effect of endophytic colonization of tomato by B . bassiana on the survival of H . armigera larvae and showed that the isolates Bb 115 and Bb 11 could be considered as useful microorganisms for the integrated control of H . armigera .