SELECTION OF STRAINS OF Beauveria bassiana AND Metarhizium anisopliae (ASCOMYCOTA: HYPOCREALES) FOR ENDOPHYTIC COLONIZATION IN COCONUT SEEDLINGS
Beauveria bassiana and Metarhizium anisopliae are considered virulent pathogens of the coconut weevil Rhynchophorus palmarum (Linnaeus). The objective of this study was to determine the ability of B. bassiana (Beauveriplant SBb36) and M. anisopliae (JGVM1) to establish an endophytic relationship with coconut Cocos nucifera (Linnaeus) seedlings. Strains were selected based on the mortality of adults of R. palmarum exposed to these fungi. Three methods of inoculation were used to inoculate the seedlings obtained through seed germination: foliar spray, stem injection and drench to the roots. Immersion of seedlings in a conidial suspension was used to inoculate seedlings obtained from tissue culture. Colonization was determined through the re-isolation of the fungi four weeks after inoculation. Beauveriplant SBb36 and JGVM1 colonized endophytically 100% of the seedlings obtained through tissue culture and 91.6% of seedlings obtained from germinated seeds. For plants inoculated by immersion with B. bassiana, the colonization rate in petioles (43%) was higher than in leaves and roots, 14 and 17%, respectively. Metarhizium anisopliae did not show significant differences in the colonization rate in leaves, petioles and roots. Plants inoculated by foliar spraying showed that colonization was higher in leaves > petioles > stems > roots. Colonization in stem injection was higher in stems than in the roots. Soil drench inoculation was higher in roots > stems. To our knowledge, this is the first report describing the endophytic relationship that B. bassiana and M. anisopliae establish with coconut seedlings obtained through seed germination and tissue culture when targeted inoculations are performed.