Net Assimilation Rate and Growth Behavior of Beans as Affected by Gibberellic Acid Urea and Sugar Sprays

Abstract

Bean plants, 2 weeks old, grown in nutrient solution, were sprayed with the following solutions: (a) 10% sucrose; (b) 2% urea; (c) 50 ppm gibberellic acid; (d) 10% sucrose and 2% urea; (e) 10% sucrose and 50 ppm gibberellic acid; (f) 2% urea and 50 ppm gibberellic acid; (g) 10% sucrose, 2% urea and 50 ppm gibberellic acid; (h) check without treatment. Gibberellic acid was sprayed once; sucrose and urea were sprayed 3 times at intervals of 3 days. The following results were obtained after 10 days: Gibberellic acid increased net assimilation rate, relative growth rate, stem dry weight, leaf area, and plant height. Root dry weight was reduced and leaf dry weight was not significantly altered. Reduction in root dry weight induced by gibberellic acid could be effectively controlled by 10% sucrose sprays. Increase in net assimilation rate caused by gibberellic acid seemed to result from a more rapid translocation of photosynthates from the leaves to the stem. Urea sprays increased stem elongations of plants receiving gibberellic acid. Urea sprays increased stem elongations of plants receiving gibberellic acid. Urea caused severe leaf burning when applied alone. Gibberellic acid and sucrose were both very effective to protect against injury by 2% urea sprays.