Induced host plant resistance in cauliflower by Beauveria bassiana

Abstract

Endophytic fungi, whichrnlive within host plant tissues asymptomatically, are important mediators ofrnplant-herbivore interactions. We tested whether Beauveria bassianarn(Balsamo) Vuillemin (Ascomycota: Hypocreales), an entomopathogenic fungus couldrncolonize the cauliflower (Brassica oleracea L. var. botrytis)rnafter fungal spores suspension applied as foliar spray. Further, we assessedrnwhether the oviposition behavior and development of Plutella xylostellarnL. (Lepidoptera: Plutellidae) was affected by endophytic B. bassiana.rnAfter inoculation, re-isolation of fungus on selective media revealed thatrncolonization of cauliflower by B. bassiana increased consistently withrnthe time but after reaching a threshold level of 70%, rate of colonizationrnbecame constant. Sequence characterized amplified region (SCAR) marker assayrnwas used to identify the presence of B. bassiana in treated plantrnsamples and a nucleotide BLAST search of the endophytic fungus showed 100 %rnsimilarity with the B. bassiana sequence. Scanning electron microscopern(SEM) images of the treated leaf surface revealed that although numerousrnconidia were present only few actually germinated. SEM and light microscopy ofrninner surface of treated leaf epidermis showed the random and crisscross growthrnof fungal hyphae. The secondary metabolite profiles of treated, control andrnpure fungus culture from ethyl acetate extracts were investigated using gasrnchromatography-mass spectrometry. Chromatographic separation yielded 9, 9 andrn12 compounds in treated, control and pure culture of B. bassianarnextracts respectively. In the laboratory experiments, P. xylostella didrnnot show any preference in laying eggs on the treated and untreated cauliflowerrnplants. However, no larvae were able to develop on treated leaf.