Production of thermotolerant entomopathogenic fungal conidia on millet grain

Abstract

Thermotolerance of entomopathogenic (insect-killing) fungi should be seriously considered before industrialization. This work describes the feasibility of millet grain as a substrate for production of thermotolerant Beauveria bassiana (Bb) GHA and ERL1170 and Metarhizium anisopliae (Ma) ERL1171 and ERL1540 conidia. First, conidial suspensions of the Bb isolates, produced on millet grain in polyethylene bags, were exposed to five temperatures (43-47 °C) at 15-min intervals for up to 120 min (experiment I). Agar-based quarter-strength (¼) Sabouraud dextrose agar supplemented with yeast extract (SDAY) and whey permeate media served as controls. Millet-grain-based culture was superior in producing the most thermotolerant Bb conidia, followed by whey permeate agar and ¼SDAY-based cultures. Secondly, to compare the thermotolerance of conidia produced at the same conditions, the Bb isolates were then produced on agar-based millet powder medium, with ¼SDAY and whey permeate agar media as controls, and the two Ma isolates were added (experiment II). They were then exposed to the same temperatures as above. More thermotolerant Bb and Ma conidia were produced on millet powder agar than on whey permeate agar and ¼SDAY overall. These results suggest that millet grain can be used as a substrate to produce thermotolerant conidia in a mass production system.

Improving mycoinsecticides for insect biological control

“…Although not addressed in this review, while formulation, e.g., inclusion of UV-protectants (absorbers), heat/humidity stabilizers, etc., has a strong potential for addressing some of these problems, costs and unanticipated effects associated with formulation compounds can outweigh benefits (Behle et al 2009;Inglis et al 1995). Growth substrate for the production of the infectious conidia has been shown to influence pathogenesis and stress resistance, with millet grain and/or inclusion of salicylic acid promising candidates for the production of thermotolerant conidia (Kim et al 2011a;Rangel et al 2012) and inclusion of hydrocarbons resulting in more virulent spores (Crespo et al 2002). Although requiring further confirmation, strains with increased virulence have been developed via protoplast fusions of B. bassiana with a toxinogenic strain of B. sulfurescens that produced somatic hybrids that were stable at least for one passage through an insect host (Viaud et al 1998), and hyphal fusions occurring during pairings of B. bassiana isolates have been used to generate thermotolerant varieties .…”

Use of a Solid Formulation ofBeauveria bassianafor Biocontrol of the Red Palm Weevil (Rhynchophorus ferrugineus) (Coleoptera: Dryophthoridae) Under Field Conditions in SE Spain*

“…Most common substrates for fungal entomopathogens include primary products from agriculture (Alves & Pereira 1989;Moore & Prior 1993;Zimmermann 1993). Some simple and cheap methods for production of biocontrol fungi have been developed using agricultural waste products (Steinmetz & Schönbeck 1994;Leite et al 2005;Kassa et al 2008;Sahayaraj et al 2008;Machado et al 2010;Kim et al 2010).…”

A novel approach: Beauveria bassiana granules applied to nursery soil for management of rice water weevils in paddy fields

“…When the fungal grains were applied to nursery soil, the conidia encountered high‐humidity conditions from the watering and germinated rapidly, and extensive mycelial masses formed. The fungal mycelial mass on the nursery soil might have resulted from nutrients in the millet and/or from the soil, including nitrogen, phosphorous, potassium and others . Once the young rice plants were transplanted to the paddy field, fungi on the nursery soil and rice plants could be exposed to contact with rice water weevils, followed by their infection and death of weevils, although colonization of the applied fungi was not fully investigated in the nursery soil for paddy fields.…”