EFFECT OF GIBBERELLIC ACID AND CHEMICAL FERTILIZERS ON GROWTH AND CHEMICAL COMPOSITION OF Cryptostegia grandiflora, R. Br. PLANTS

Abstract

This study was conducted in the Experimental Nursery of the Ornamental Horticulture Department, Faculty of Agriculture, Cairo University, during the two successive seasons of 2006/2007 and 2007/2008. The aim of the study was to investigate the response of Cryptostegia grandiflora,R. Br.plants to gibberellic acid spray treatments and NPK fertilization (using conventional and slow-release NPK fertilizers). The plants were fertilized monthly with a conventional NPK fertilizer (18 N – 6 P2O5 – 6 K2O) at rates of 5 and 7 g/plant, or were supplied every 4 months with a commercial slow release fertilizer (Regal Nursery, 24 N -8 P2O5 -8 K2O) at rates of 15 and 21 g/plant. In addition, unfertilized plants were used as the control. Plants receiving each of the NPK fertilization levels were sprayed monthly with gibberellic acid at concentrations of 50 or 100 ppm. Control plants were sprayed with tap water. Results showed that GA3 and/or chemical fertilization treatments increased the values recorded for most of the different vegetative growth parameters (vine length, number of internodes of main vine, average internode length, stem diameter, number of branches/plant, leaf area, fresh and dry weights of leaves, stems and roots/plant), as well as the N and K percentages in leaves, compared to the untreated plants. In most cases, increasing GA3 concentration resulted in steady increases in these parameters. Total chlorophylls, total carbohydrates and P concentrations were decreased by GA3 treatments and increased by chemical fertilization treatments. Raising the application rate of each type of chemical fertilizer resulted in steady increases in the values of most of the studied growth parameters. In most cases, at the same fertilization rate, the slow-release fertilizer Regal Nursery gave higher values for most of the vegetative growth and chemical characteristics, compared to the conventional NPK fertilizer. In most cases, combining GA3 at 50 ppm with the highest rate of Regal Nursery (21 g/plant/4 months) gave values that were insignificantly different than the highest values recorded for most of the vegetative characteristics, which were obtained in plants sprayed with GA3 at 100 ppm and supplied with the highest rate of Regal Nursery. From the obtained results, is recommended that, for the best vegetative growth of Cryptostegia grandiflora, the plants may be sprayed with GA3 at 50 ppm and supplied with 21 g/plant/ 4 month of the slow- release fertilizer Regal Nursery (24 N -8 P2O5 -8 K2O).