INFLUENCE OF L-TRYPTOPHAN AND AUXINS APPLIED TO THE RHIZOSPHERE ON THE VEGETATIVE GROWTH OF ZEA-MAYS L

Glasshouse experiments were conducted to evaluate the influence of L-T RP in comparison with indole-3-acetamide (IAM), tryptophol (TOL) and i ndole-3-acetic acid (IAA) on the growth of Zea mays L. var. Early Sung low. L-TRP (25 to 2.5 x 10(-5) mg kg-1 soil), IAM (22 to 2.2 x 10(-5) mg kg-1 soil), TOL (20 to 2.0 x 10(-5) mg kg-1 soil), and IAA (22 to 2 .2 x 10(-5) mg kg-1 soil) were applied as a soil drench to established uniform seedlings. All treatments were applied in a completely random ized design with 10 replicates. IAM had no significant effect on the p lant growth parameters. Shoot height, uppermost leaf collar base dista nce, internodal distance, and shoot dry and fresh weights were signifi cantly improved upon the addition of TOL (2.0 x 10(-2) mg kg-1 soil), however, the highest concentration (20 mg kg-1 soil) caused a 14.6% re duction in leaf width. L-TRP (2.5 x 10(-3) mg kg-1 soil) also had a si gnificant influence on shoot height, uppermost leaf collar base distan ce, internodal distance and fresh weight of shoot compared with the co ntrol. The highest concentration of L-TRP (25 = mg kg-1 soil) had a ne gative effect on leaf width and dry weight of the shoot. The most pron ounced response on the corn growth parameters was observed with the ap plication of IAA at lower concentrations (2.2 x 10(-5) to 2.2 x 10(-2) mg kg(-1) soil) specifically improving root growth. The highest conce ntration (22 mg kg-1 soil) of IAA had a significant negative effect on plant height, leaf width, stem diameter, shoot fresh and dry weight. These findings indicate that L-TRP applied at the appropriate concentr ations can have positive effects on corn growth comparable to pure aux ins (TOL and IAA).