Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 1996
Publication Date: N/A
Interpretive Summary: The sweetpotato (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. Resistance to chemical pesticides and a lack of natural enemies has made the sweetpotato 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. Commercial acceptance of these microbial pesticides requires low-cost production methods which yield a stable, effective microbial agent. In this study, we describe the development of a liquid culture fermentation process for rapidly producing high concentrations of Pfr spores. More than 80% of the Pfr spores produced using this process survived air- or freeze-drying. Twenty different Pfr isolates were tested using this method dand all sporulated rapidly and produced high spore concentrations. Efficacy tests with air-dried Pfr spores showed that these spores were effective in infecting and killing sweetpotato whiteflies. The development of this cost-effective liquid culture fermentation process for rapidly producing high concentrations of desiccation-tolerant Pfr spores enhances the commercial potential of this microbial pesticide. Field trials and large-scale fermentation and drying studies are currently in progress to further evaluate the potential of this process.
Technical Abstract: A submerged culture technique for producing high concentrations of desiccation tolerant Paecilomyces fumosoroseus blastospores was developed by testing media with differing carbon concentrations and carbon-to- nitrogen ratios. While all media tested produced spores in submerged culture, maximal blastospore concentrations were produced in media containing 80 gl**-1 glucose and 13.2 gl**-1 Casamino acids (MS medium), and a significantly higher percentage of these blastospores survived air drying. Liquid cultures of Pfr isolate ARSEF 4491, grown in MS medium, produced 5 X 10**8 blastospores ml**-1 after 72 h growth. When blastospore suspensions obtained from cultures grown in MS medium were air-dried (30-40% r.h.) overnight at room temperature, 79% of the dried Pfr ARSEF 4491 blastospores germinated. Lyophilization studies with these blastospores showed that 86% survived drying. In a survey of 22 other Pfr isolates, MS media supported the rapid production of high concentrations o desiccation tolerant blastospores in all the isolates tested. When stored at 4 deg, more than 60% of the lyophilized blastospores produced in MS medium were still viable after 7 months' storage while less than 25% of the air dried blastospores survived after 90 d storage. Lyophilized and air-dried Pfr blastospores stored at 22ø lost viability rapidly. Standard whitefly bioassays were performed with air-dried blastospores of Pfr ARSEF 4491 and solid substrate produced conidia of Beauveria bassiana ARSEF 252. Air-dried, liquid culture produced Pfr blastospores gave LD50s of 56.6 and 115.6 blastospores mm**-3 for the silverleaf whitefly Bemisia argentifolii in 2 different bioassays with potency ratios (LD50 B. bassiana/LD50 P. fumosoroseus) of 4.11 and 3.77, respectively.