Isolation of potentially antagonistic bacteria from special composts used by organic farmers.

Fungal diseases are one of the major factors limiting crop production. Protection of plants against fungal infection is dependent mainly on pesticides that are considered hazardous to the environment. Some chemical pesticides have already been proven to cause adverse effects on humans and on natural enemies of pests (Chet and Inbar 1994, Applied Biochemistry and Biotechnology 48: 37-43). This concern has led researchers to develop safer and more environmentally friendly pest-control alternatives. Farmers growing organic food (crops grown without chemical fertilizers and pesticides) use alternatives such as biopesticides and biofertilizers. They generally claim that their crops suffer less damage from diseases and insect-pests than neighboring fields using mainstream agricultural practices. In some cases these alternatives have been developed and promoted by farmers themselves. Some organic farmers in Karnataka and Tamil Nadu states of India, who use six different composts (popularly known as Biodynamic or BD preparations), when visited in 1998, reported lower incidence of diseases and insect pests than neighboring "mainstream" farmers. Further queries revealed that each compost was prepared using a different protocol, all proposed in 1924 by Rudolf Steiner (Proctor, P., Cole, G., Lyons, T., in Grasp the Nettle: Making Biodynamic Farming and Gardening Work , Random House, Ltd., New Zealand, 1997, 176 pages). These preparations were available commercially in Tamil Nadu. We counted microbial population in - different BD preparations after developing a method of counting antagonistic bacteria. Fusarium solani (causes black root rot of chickpea) was used as test organism. The colonies with maximum level of suppression of the fungus on a given culture plate were isolated. A total of 28 potentially antagonistic bacteria were from the BD-preparations. Purified isolates were characterized for Gram reaction, sporulation, and tolerance to desiccation. Twenty-seven of the 28 isolates (96%) from the six BD preparations formed spores. All spore-forming bacteria survived for at least 108 days in a desiccator; some survived for at least 17 months (studies continuing). Antagonists surviving desiccation for long periods could be used in dry formulations as biocontrol agents. Some of the isolates showed suppression of disease causing fungi in plate culture (Figure 1).

Figure 1: A bacterium (BCB 19) isolated as antagonistic to Fusarium solani using Two-Layer Method (see previous submission for NRMP web page for details), suppressed the growth of Sclerotium rolfsii in Dual plate culture. Note some clear zone between the fungus and the bacterium even after 6 days. The fungus grew over most other bacterial colonies within two to three days.

Some others killed larvae of Helicoverpa in laboratory culture conditions (Figure 2).

Figure 2. About 40 to 72% of Helicoverpa larvae died within 10 days when the different BCB isolates were sprayed on to chickpea seeds offered at 3rd instar stage in laboratory tests.

Seven of these spore-forming bacteria were studied for species identification using a kit from BIOLOG, Hayward USA ( www.biolog.com ). None of these matched the 23 spore-forming species in the database of the kit. It is likely that most of the organisms are a new species not identified so far. More studies will be needed to confirm this view. The studies indicated a great potential of accessing potentially useful microorganisms from materials used by organic farmers. Scientists interested in collaborative studies using the bacteria indicated above (now a part of the microbial culture collection at ICRISAT) may contact O. P. Rupela " o.rupela@cgiar.org ".

For More Details Click Here: A new method for identification and enumeration of microorganisms with potential for suppressing fungal plant pathogens

For more information please contact:

Dr Rupela O P
Scientist (Soil Biology),
ICRISAT-Patancheru 502 324.