Destruxin A production byMetarhizium brunneumstrains during transient endophytic colonisation ofSolanum tuberosum

Metarhizium spp. are known to produce destruxin A (dtx A) and can act as endophytes. Data regarding the fate and behaviour of secondary metabolites in the environment are necessary for registration. Endophytic colonisation and dtx A production on potato plants were monitored at 24, 48, 72, 96 and 120 h after inoculation with Metarhizium brunneum strains (BIPESCO5 and EAMa 01/58-Su). Both strains were recovered from leaves, stem, tuber and root fragments of fungal-challenged potato plants. Although a similar colonisation was observed for both strains, there were differences in percentages in different parts of the plants, with the higher values occurring in the leaves at 96 h for EAMa 01/58-Su (83.3%) and BIPESCO5 (81.6%), and the lower ones, 10–13.3%, observed in tubers and roots at 72, 96 and 120 h post-inoculation for both strains. For strain EAMa 01/58-Su, dtx A was quantified at 24 h (2.49 ± 1.7 and 2.0 ± 1.4 µg/kg, respectively), and the same concentration was found in both tuber and root at 96 h (2.5 ± 1.7 µg/kg); for BIPESCO5, the concentrations differed in tuber at 24 h and in root at 48 h (6.8 ± 4.8 and 2.1 ± 1.4 µg/kg, respectively). The concentration of dtx A in plant tissues was very low compared to the colonisation levels, suggesting that dtx A production by the fungus may be temporary and that the compound might degrade rapidly.