Physiological and morphological characteristics of Phaseolus vulgaris L. grown in soil with picloram residues

Abstract

The long lasting residual effect of some auxin herbicides depends on soil characteristics and may cause phytotoxicity on subsequent crops. Picloram is one of the main herbicides used in pastures, presenting a long lasting residual effect in the soil. This study aimed at determining the physiological and morphological characteristics of common bean plants grown in soil contaminated with picloram, under greenhouse conditions. A complete randomized blocks design, with treatments consisting of picloram doses (0 g ha^-1, 7.5 g ha^-1, 15 g ha^-1, 30 g ha^-1, 60 g ha^-1 and 120 g ha^-1 a.i.), with five replications, was used. Urochloa brizantha was sown in pots, and its height and shoot fresh and dry matter were evaluated. In the same pots, Phaseolus vulgaris was sown as a bio-indicator of picloram, and the following characteristics were measured: plant height, fresh and dry matter, phytotoxicity, leaf area, number of leaves per plant, maximum photosynthetic efficiency and relative electron transport rate. The phytoremediation process occurs in soil with picloram residues (up to 30 g ha^-1) when covered by U. brizantha for 150 days. The common bean plants show a good potential as biological indicator of the presence of picloram residues in the soil.