Physiological response of onion plants to foliar application of putrescine and glutamine

Two field experiments were carried out in Egypt during two successive seasons (2007/2008 and 2008/2009). This study aimed to investigate the response of growth, yield quality and some metabolic constituents of onion (Allium cepa L. cv. ‘Giza 20’) to foliar application of putrescine (Put; 25, 50 and 100 mg L⁻¹) and glutamine (Glut; 50, 100 and 200 mg L⁻¹), the former a diamine and the latter an amino acid, either alone, or in combination. Foliar application of Put and Glut, either alone or in combination, significantly increased plant height, number of leaves, fresh weight of leaves/plant, fresh and dry weight/plant, leaf area, leaf area/plant, bulb length, bulb diameter and weight, as well as yield of onion and quality of bulbs. Total soluble sugars, sulfur compounds, total soluble phenols, total free amino acids and total photosynthetic pigment content in leaves were increased by increasing Put and/or Glut concentrations up to 100 and 200 mg L⁻¹, respectively. Generally, foliar application of Put at 100 mg L⁻¹ and Glut at 200 mg L⁻¹ singly, or combined, effectively increased bulb yield and quality. In conclusion, the yield-contributing characters and quality of onion could be improved by application of Put and/or Glut.