Submitted to: Mycopathologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2007
Publication Date: April 17, 2007
Citation: Dorner, J.W., Horn, B.W. 2007. SEPARATE AND COMBINED APPLICATIONS OF NONTOXIGENIC ASPERGILLUS FLAVUS AND A. PARASITICUS FOR BIOCONTROL OF AFLATOXIN IN PEANUTS. Mycopathologia. 163(40;215-223. Interpretive Summary: Aflatoxin contamination of peanuts is a serious food safety issue, and it threatens the economic viability of the U. S. peanut industry. Aflatoxin contamination results from growth in peanuts by Aspergillus flavus and A. parasiticus, fungi that occur naturally in soils. Application of strains of A. flavus and A. parasiticus that cannot make aflatoxin (nontoxigenic strains) to peanut soils has proven effective in significantly reducing aflatoxin contamination of peanuts. In many of our previous studies, a mixture of nontoxigenic strains of A. flavus and A. parasiticus has been used to reduce aflatoxin contamination. The purpose of this study was to determine the effectiveness of nontoxigenic strains of A. flavus and A. parasiticus when applied separately and as a mixture for controlling aflatoxin contamination in peanuts. Results showed that the nontoxigenic A. flavus alone was just as effective as the A. flavus/A. parasiticus mixture and more effective than A. parasiticus alone for reducing aflatoxin in peanuts. Results also showed that toxigenic strains of A. flavus that are naturally present in peanut soils are more aggressive in colonizing peanuts than nontoxigenic strains of A. flavus or A. parasiticus. Therefore, for nontoxigenic strains that are applied for biological control to be effective, they must greatly outnumber toxigenic strains in soil.
Technical Abstract: Peanut is typically sown in single or twin rows centered on 91 cm beds. A planter capable of sowing 8 rows of peanuts on a 182 cm bed was developed at NPRL. This planter spaces seed evenly in a diamond pattern in order to optimize plant spatial relationships. A diamond-pattern seed placement usually results in achieving ground cover 10 to 14 days sooner than peanuts planted in single or twin rows. This benefit will decrease soil moisture loss, the survivability of competitive plant species, and improve yield. Reducing early competition for resources between peanut plants may further contribute to earliness. Management of soil borne diseases in peanut may be affected by planting patterns. Three disease strategies were factored over single row, twin row, and diamond planting patterns, for a total of 9 treatments. The first disease strategy was on a 10 to 14 day schedule starting with three chlorothalanil applications followed by four tebuconazole applications. The second disease management strategy followed AUPnut using chlorothalanil when recommended during the first 49 DAP, tebuconazole between 50 and 100 DAP, and chlorothalanil after 101 DAP. The third disease management strategy incorporated AUPnut recommendations with minimum soil temperature to determine product selection for disease control from July until harvest. Tebuconazole was selected when minimum soil temperature was below 21.1 C and above 23.8 C to target Rhizoctonia solani and Sclerotium rolfsii, which are more prevalent with lower and higher minimum soil temperatures, respectively. Chlorothalanil, which is a more affordable product, was selected to maintain suppression of Cercospora arachidicola and Cercosporidium personatum when minimum soil temperature was between 21.1 and 23.8 C. Replicated field experiments were conducted in 2002, 2003, and 2004 at two locations each year on Americus and Faceville soil types in Terrell county Georgia. Peanut cultivar ‘Georgia Green’ was sown at 124 kg/ha to establish single row, twin row, and diamond pattern plots establishing a uniform number of plants per linear unit of row. Acephate was applied in furrow at planting in all treatments because a system for delivering granular insecticides has not been incorporated with the diamond planter. A two-row KMC digger/inverter was modified in order to effectively handle peanuts evenly spread over a 182 cm bed for the diamond planted plots. Disease index, yield components, and grade are recorded.