Soybean Response to 1-Aminocyclopropane-1-Carboxylate Deaminase-Producing Pseudomonas under Field Soil Conditions

Problem Statement: 1-Aminocyclopropane-1-Carboxylate (ACC) deaminase-producing bacteria have been known to promote plant growth by decreasing ethylene inhibition of various plant processes. However, their efficacy under field soil conditions may vary depending on the range and variability of the environmental factors. This study examined the ability of eight promising isolates of ACC deaminase-producing Pseudomonas to enhance soybean growth under acidic and low fertility status of field soil conditions. Approach: The bacteria were formulated into peat-based carrier and used to inoculate soybean seeds. Cell viability in the carrier was evaluated periodically. The number of bacterial population at the time of seed inoculation was above 10⁷ cell g^-1. Treated and untreated seeds were grown in plots (5×4 m²) and set in a randomized complete block design with 3 replicates. Observations were made at 30 d after planting for shoot height and weight, number of nodules and at harvesting for number of pods and yield. Results: Three out of eight isolates significantly increased soybean growth exhibited by higher number of nodules and pod filling and higher seed dry weight than those of untreated control. Those five remaining bacteria, on the contrary, inhibited soybean growth indicating that other unknown external factors influenced or covered the beneficial trait of ACC deaminase. Conclusion: Bacteria having ACC deaminase activities could be truly plant growth promoting bacteria providing that their beneficial effects are consistent at a wide range of environmental conditions.