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 Russian wheat aphid, Diuraphis 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.
The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is one of the main pests of small-grain cereal crops, including bread wheat, Triticum aestivum (Poaceae). In a series of glasshouse experiments, we evaluated the systemic effect of endophytic Beauveria bassiana strain PPRI 7598 on D. noxia biotype RWASA1 using three South African wheat cultivars, Gariep, Molopo, and Kariega. The objectives of the study were: (a) to determine the effect of endophytism on RWA reproduction and population growth, and (b) to assess the effect of the endophyte on aphid biomass and T. aestivum response to D. noxia herbivory using a damage rating index. Plant endophytic colonisation was confirmed before each trial using a B. bassiana-selective medium. Three independent trials were performed 10 days apart under glasshouse conditions. The effect of the endophyte-treated versus non-treated plants varied significantly in terms of net reproductive rate (R0) and the intrinsic rate of increase (rm) of the D. noxia population. Overall, the endophyte significantly reduced D. noxia R0 by approximately 14 nymphs/female and decreased the aphid mass by 13% in treated plants, whereas the mean aphid mass increased by 17% in control plants in all pooled cultivars. These findings demonstrated the endophytic potential of B. bassiana strain PPRI 7598 for suppression of D. noxia populations in RWASA1-susceptible cultivars. The integration of B. bassiana endophytism with host plant resistance may counteract biotype development and support a more sustainable approach towards RWA control in integrated pest management programmes.
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