Assessing the efficacy of exogenous auxin and indole-3-acetic acid-producing bacteria in promoting growth of Vigna radiata (L.) R. Wilczek. in used engine oil-contaminated soil

This study aimed to compare the activity of synthetic phytohormones (naphthalene-acetic acid (NAA) and indole-butyric acid (IBA)) and indole-3-acetic acid-producing bacteria (Bacillus stercoris B.PNR1, Bacillus stercoris B.PNR2, and Paenibacillus sp. BSR1-1) to stimulate the growth of mung bean (Vigna radiata (L.) R. Wilczek) planted in used engine oil-contaminated soil. The results revealed that both synthetic phytohormones significantly stimulated mung bean growth in soil contaminated with used engine oil. Mung beans treated with IBA or NAA showed a 76.25±2.63 and 81.25±3.50% survival rate, compared to a survival rate of only 66.25% in the absence of seed treatment. Furthermore, the shoot length (20.54-20.84 cm), shoot fresh weight (0.276-0.279 g), shoot dry weight (0.025-0.025 g), and shoot dry weight per pot (0.190-0.204 g) of mung beans grown in used engine oil with seeds treated with IBA or NAA were higher than those of mung bean seedlings without seed treatment. In contrast with the shoot, NAA did not stimulate the growth of the mung bean root as much as the shoot. Paenibacillus sp. BSR1-1 tended to promote root growth to the best extent because the root length (7.61±0.25 cm) of mung bean grown in used engine oil was higher than that grown with receiving other bacterial isolates or NAA and IBA; however, root dry weight per pot of mung bean with seed treated with Paenibacillus sp. BSR1-1 was not significantly different from those treated with IBA and NAA.