Rural Industries Research & Development Corporation

Research Compendium 1993 - 1994

Research Project

CHEMICAL INDUCTION OF NODULES ON PLANTS FOR PESTICIDE DEGRADATION AND CROP PROTECTION

Objectives

To develop strategies that can both detoxify soil of pesticides and protect plants. Specifically, to extend the promising new technology of chemically-induced nodulation of plants to the following areas:

• the incorporation of pesticide degrading microbes into nodular structures on the roots of plants, with the aim of providing a plant-microbial system capable of accelerated degradation or protection from chemicals; and
• nodulation with microorganisms antagonistic to plant pathogens, such as the 'damping off' fungi or using insecticidally-active agents such as Bacillus thuringiensis.

Background

Biodegradation of certain pesticides in soil is a well known phenomenon but the use of plants inoculated with pesticide-degrading microorganisms had not previously been considered for this purpose. This research was stimulated by successful artificial induction of associations between bacteria and plants for biological nitrogen fixation. Similar associations between pesticide-degrading bacteria and plants with potential value of agriculture might be engineered, allowing the 'clean up' of soils and by providing protection from the effects of residual pesticides. A related goal was to provide plant protection by incorporating protective or antagonistic microorganisms into such systems

Research

The biodegradation of 2,4-dichlorophenoxyacetate (2,4-D) was selected as a suitable model chemical system. This system was chosen because it is well understood genetically, it is possible to transfer the genetic capability between different species of bacteria with reasonable ease, and the activity is capable of fairly straightforward chemical analysis. In future applications of this approach however, it would be necessary to use microbial strains with appropriate pesticide-degrading activity as the situation requires.

Outcome

Using canola and wheat plants as hosts, associations with a soil isolate of Acinetobacter carrying 2,4-D degrading ability have been formed in laboratory systems. These associations accelerated degradation of 2,4-D, and completely destroyed the herbicide within 24 hours. Alcaligenes eutrophus , well known as a 2,4-D degrading organism did not colonise roots as effectively.

The 2,4-D degrading plasmid was transferred by conjugation from Alcaligenes to strains of Rhizobium naturally forming root nodules on subterranean clover and white clover plants. Such transconjugants were stable, retaining their 2,4-D degrading ability indefinitely, and were found to provide protection of the clover plants from the effects of herbicide. These clover plants were also capable of fixing atmospheric nitrogen.

Implications

This area of research has a long way to go before practical benefits will be available to agriculture. The results from this project, however, form an excellent basis for an ongoing bioremediation project within the CRC for Sustainable Cotton Production at Narrabri, funded by The Cotton R & D Corporation.

RIRDC Project No: US-17A

RESEARCHER: Ivan R Kennedy

ORGANISATION: Department of Agricultural Chemistry and Soil Science

PHONE: 02 351 2112

PUBLICATIONS:

Feng, L., B.G., Gartner, E., van Zwieten, L. and Kennedy, I.R. (1994) Expression of the 2, 4-D degrading plasmid pJP4 of Alcaligenes eutrophus in Rhizobium trifolii. Acta Biotecnol. 14, 119-129.

Van Zwieten, L., Feng, L. and Kennedy, I.R. (1995) Plant microbial associations: Their potential for soil decontamination. Acta Biotechnologica In press.

Last updated: 10 October 1996
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