Effects and Persistence of Endophytic Beauveria bassiana in Tomato Varieties on Mite Density Tetranychus evansi in the Screenhouse

Abstract

The tomato red spider mite (RSM), Tetranychus evansi Baker and Pritchard, is an important exotic pest in the production of tomatoes and other sola naceous plants in Africa. Isolates of Beauveria bassiana ICIPE 273, ICIPE 279, ICIPE 283, ICIPE 10, and ICIPE 35 were previously tested for their endophytic activity in tomato in a screenhouse assay. ICIPE 35 was able to colonise leaves, stems and roots of the tomato varieties Cal J, Kilele and Anna F1, whereas the other four isolates were undetectable in all plant parts of the varieties tested, thus confirm ing no colonisation. Colonisation was assessed after every two-week period by plat ing the various plant parts on selective media. Persistence was examined by comparing colonisation from week 2, 4 and 6, since there was no colonisation detected after this time, for all the tested tomato varieties. There were no significant differences in levels of colonisation in the various parts of tomato varieties, i.e. stem (F = 1.7, DF = 2, P = 0.186), roots (F = 2.0, DF = 2, P = 0.127), and leaves (F = 0.28, DF = 2, P = 0.752). The density of T. evansi was lower in endophyte-colonised plants than the controls. In conclusion, this study revealed that B. bassiana can colonise and persist in the tested tomato varieties for a period of 6 weeks in the screenhouse and reduce adult RSM populations.