Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1999
Publication Date: N/A
Interpretive Summary: The silverleaf whitefly attacks over 600 plants in warm climates worldwide. In the United States, whitefly infestations cause 250-500 million dollars in crop loss annually. The rapid development of resistance to chemical pesticides and a lack of natural enemies has made the silverleaf whitefly a serious pest in Texas, California, and Florida. Molds which infect and kill whiteflies, such as Paecilomyces fumosoroseus (Pfr) and Beauveria bassiana, are promising microbial pesticides for controlling this pest. It is envisioned that microbial biocontrol agents will play a crucial role in integrated pest management strategies by effectively infecting and killing this pest and by slowing down the whitefly's development of resistance to effective chemical control measures. Commercial acceptance of these microbial pesticides requires low-cost production methods which yield a stable, effective biopesticide. In this study, we describe the nutritional loptimization of a liquid culture fermentation media for rapidly producing high concentrations of Pfr spores. Sources of carbohydrate and nitrogen were identified which supported the production of high concentrations of desiccation tolerant spores. Vitamins were found to be an unnecessary media component. The development of a cost-effective liquid culture fermentation medium for rapidly producing high concentrations of desiccation-tolerant Pfr spores enhances the commercial potential of this microbial biopesticide. Field trials and large-scale fermentation and drying studies are currently in progress to further evaluate the potential of Pfr spores produced under these nutritional conditions.
Technical Abstract: Field application of the entomopathogenic fungus Paecilomyces fumosoroseus for the commercial control of whiteflies in cotton and vegetable crops requires a production method which provides high yields of desiccation tolerant blastospores. In this study, we evaluated the impact of 13 amino acids, 7 carbohydrates, trace metals (cobalt, iron, manganese and zinc), and vitamins on the hyphal growth and sporulation of P. fumosoroseus cultures and on the freeze-drying tolerance of blastospores produced under these conditions. A comparison of various amino acids as sole nitrogen sources showed that glutamic acid supported highest biomass accumulation (14-16 mg/ml) and sporulation (2-3 x 10**8 blastospores/ml). Tests with various carbohydrates showed that P. fumosoroseus grew best on sucrose (17 mg biomass/ml) but produced more spores when grown on glycerol (4-5 x 10**8 blastospores/ml). Cultures grown in defined media without zinc produced significantly less biomass (<4 mg/ml) and fewer spores (<1.6 x 10**7 blastospores/ml) than cultures grown in zinc-supplemented media. The vitamins tested were shown to be unnecessary for growth or sporulation. Freeze-drying tolerance was not related to the initial water potential of the medium nor to the amount of intracellular trehalose or glucose accumulated within blastospores. Blastospore survival after drying was significantly increased when blastospores were produced in media containing sodium citrate or galactose (80-100% survival) as the sole carbon source. The amount of glucose present in the suspension medium was also shown to affect blastospore survival after freeze drying.