Growth Enhancement and Disease Reduction of Soybean by 1-Aminocyclopropane-1-Carboxylate Deaminase-Producing Pseudomonas

Problem statement: 1-Aminocyclopropane-1-Carboxylate (ACC) deaminase-producing bacteria have been known to ameliorate the inhibition-effect of increase concentration of ethylene in higher plants, which can be triggered by high concentration of indole-3-Acetic Acid (IAA) and/or by the presence of plant pathogens. This study examined the potential use of Pseudomonas isolates producing ACC deaminase as well as IAA to enhance soybean growth and reduce disease incidence in soil containing pathogenic fungi. Approach: Eleven promising ACC deaminase-producing isolates of Pseudomonas were retested in vitro for their ACC deaminase activity and IAA production and evaluated their potential antagonist against root-nodule bacteria. Non antagonist isolates were further tested for their ability to enhance soybean growth and reduce disease incidence in sterile and non-sterile soils containing root-pathogenic fungi Fusarium oxysporum, Sclerotium rolfsii and Rhizoctonia solani. Results: All isolates produced ACC deaminase as well as IAA, but 3 out of 11 isolates inhibited at least one strain of rhizobia which limit their use for soybean. The isolates increased some aspects of soybean growth, but most of the increases were not significantly different from untreated control. Most isolates significantly increased the survival rates of soybean in soil containing pathogenic fungi although their ability to reduce plant weight loss varied across pathogen treatments. Conclusion: The ability of Pseudomonas producing ACC deaminase as well as IAA to increase plant growth was less significant than that of the isolates to reduce disease incidence. The higher the destructive effect of the pathogens, the better was the ability of the isolates to reduce the disease.