Potential for Biological Control of Early Leafspot of Peanut Using Bacillus cereus and Chitin as Foliar Amendments

Chitin applied as an amendment to peanut leaves increased the populations of indigenous chitinolytic epiphytes from < 1% to > 40% of the total microflora. The total epiphytic bacterial populations increased by up to 0.3 log with the addition of chitin. When the chitinolytic Bacillus cereus strain 304 isolated from chitin-amended leaves was reapplied to peanut foliage with chitin, its populations were sustained as actively growing vegetative cells for a longer period than when applied to nonamended leaves. Eight days after application, B. cereus populations were > 1 log higher on chitin-amended leaves than on nonamended leaves. In two of three field trials, significant reductions in the severity of early leafspot caused by Cercospora arachidicola were seen on chitin-amended leaves, and a trend toward additional control (P < 0.10) was obtained on leaves treated with chitin plus the chitinolytic B. cereus. Scanning electron microscopy revealed chitin deposits, fungal hyphae, and spores colonized by bacilliform bacteria. Colonized fungal hyphae and spores were pitted and distorted, indicating a potential for biological control of chitin-containing fungal pathogens by chitinolytic bacterial antagonists. (c) 1992 Academic Press, Inc.