Physiological responses to fluroxypyr, fenoxaprop-p-ethyl and their combinations on shoot tip tissues of soybean and maize

Abstract

Effects of the herbicides; fluroxypyr (F) [4-amino-3,5-dichloro-6-fluoro-2-pyridyloxyacetic acid], fenoxaprop-p-ethyl (Fp) [(R)-2-{4-(6-chlorobenzoxazol-2-yloxy) phenoxy} propionic acid] and their combinations on growth and development of soybean (Glycine max) and maize (Zea mays) shoot tips were evaluated in vitro. Both herbicides were used at two concentrations (10 and 100 µM ) for post-emergence control of weeds. F control broadleaf weeds and Fp is used for grasses. Normal growth was inhibited in soybean shoot tips by F treatments, resulted in stem malformation and bending in case of 100 µM treatment. Furthermore, reduced leaves number, inhibited completely the growth and development of adventitious roots. F increased fresh and dry weights (f.wt. & d.wt.) of maize but the higher concentration (100 µM) gave an opposite trend with soybean. Fp at 10 µM (in maize) and 100 µM (in maize and soybean) inhibited shoot tip growth. Individual treatments of Fp and their combinations with F mostly decreased f.wt. & d.wt. in both plants. Often, chlorophyll and carotenoids contents were negatively influenced by herbicides treatments in both plants. F and Fp treatments increased total soluble carbohydrates in soybean. Similar trends were observed with all herbicides treatments in maize. Fp treatments increased phenol content in maize. Individual treatments of Fp at 100 µM in both plants and their combinations with F in maize caused a significant increase in indole content. The different combinations of F and Fp increased free amino acids and proline in maize while their effects on soybean were variable. Protein breakdown, accumulation of phenols and proline were recorded as characteristic features for a state of stress which are primarily an expression of the degree of severity of the disturbance.