Comparison of wheat growth-response to endophytic Beauveria bassiana (hypocreales: Cordycipitaceae) derived from an insect versus plant host

Abstract

Beauveria bassiana (Hypocreales) is a cosmopolitan entomopathogen, infecting >700 insect species. Although traditionally associated with insects, endophytic colonisation of plants is also known. Endophytism may protect plants against insects/diseases and enhance plant growth. Both insect- and plant-derived (endophytic) ‘sources’ of B. bassiana may be present in an agroecosystem, both of which may be in contact with plants. Here, growth response, viz., root length, shoot height, fresh root biomass, fresh and dry shoot biomass of wheat, Triticum aestivum L. (Poaceae), is reported following inoculation with B. bassiana (strain PPRI 7598). The strain was passaged and re-isolated from an insect (IN) versus plant (PL) substrate. When five wheat cultivars were inoculated with either B. bassiana PPRI 7598IN or -PL isolates through seed imbibition, a significantly higher level of endophytism (roots, stems and leaves, combined) was recorded with 7598IN (29.74%) compared to 7598PL (26.13%). Cultivar Baviaans responded best to endophytic colonisation (plant parts combined) at 33.54%, followed by Tugela (31.34%), Kariega (27.87%), Gariep (25.67%) and Elands (21.28%). On average, B. bassiana-treated plants showed a 71% growth increase over control plants. In topically sprayed bioassays, 7598IN caused 57% mortality to D. noxia, compared with 50% by 7598PL; also recording a significantly shorter mean time to aphid mortality (4.14 days) versus 7598PL (4.58 days). A significantly higher level of overt mycosis (58.2%) was noted with 7598IN compared with 7598PL (47.9%). Results underscored several positive aspects associated with endophytic B. bassiana in wheat, creating new and exciting IPM possibilities