الفهرس 
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Abstract
This study was undertaken during two seasons of 2017-2018 and 2018-2019 to evaluate the impact of preharvest treatments through using some amino acids (tryptophan, arginine, glycine solely at the concentration of 100 ppm per each and the mixture of them at the same concentration), besides the control one (distilled water) as foliar spraying on the vegetative growth, flowering characters and chemical constituents of Dahlia pinnata L. plants. Besides studding the previous preharvest treatments interactions with some preservative solutions [control (sucrose at 1.5%, nano silver at 0.5 cm /L + sucrose 1.5% and silver nitrate at 0.2 g /L + sucrose 1.5%] on vase life and quality of Dahlia pinnata L. cut flowers (local variety). In addition, studying the anatomical effects of some treatments on removing the latex matter which observed at the end of the inflorescences cut stems. The obtained results could be summarized as follows. I- Preharvest experiment (amino acids foliar applications) A- Effect of preharvest treatments (amino acids) on vegetative growth 1. Plants treated with the mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm gave the tallest plants (81.1 and 86.0 cm) followed by (81.1 and 83.9 cm) resulted from plants sprayed by arginine at 100 ppm, respectively in both seasons with significant differences between them. While the shortest plants (48.4 and 50.6 cm) were those which did not receive any treatment of amino acids (control) in both seasons. 2. Maximum number of branches were (11.0 and 13.0 branches/plant) for plants sprayed with the mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm in the two seasons, respectively. While the least number of branches (3.0 and 3.2 branches /plant) were obtained from (control), respectively in both seasons. 3. Application of amino acids mixture significantly affected stem diameter compared with other treatments. The largest stem diameter was (2.28 and 2.72 cm) in case of the plants treated with the mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm, followed by (1.94 and 2.01 cm) from the arginine treatment in the two seasons, respectively. However, the lowest stem diameter was (0.87 and 1.10 cm) obtained from the control plants (untreated plants), respectively in both seasons. 4. The maximum number of leaves was (41.0 and 51.2) for plants sprayed with the mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm followed by (35.0 and 37.6) for plants treated with 100 ppm arginine in both seasons, respectively. While the least number of leaves per plant were obtained from plants which did not receive any amino acids (control) (22.0 and 25.3), respectively in both seasons. B- Effect of preharvest treatments (amino acids) on flowering characters 1. The maximum number of inflorescences/plant (63.0 and 66.6 inflorescence) were those which sprayed with the mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm, respectively in both seasons. On the other hand, plants sprayed with individual amino acid (glycine) came in the second order for number of inflorescences/plant (57.0 and 58.3 inflorescence) during both seasons, respectively. 2. Plants treated with the mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm gave the heaviest inflorescence fresh weight (15.59 and 16.70) in the two seasons, respectively. However, the least inflorescence fresh weight was resulted from untreated plants (control) (7.53 and 7.41 inflorescence) respectively, in both seasons. 3. The highest significant values in inflorescence diameter was (12.3 and 12.6 cm) in case of the plants treated with the mixture of amino acid (tryptophan + arginine + glycine) at 100 ppm, followed by (10.6 and 10.8 cm) from the individual amino acid (arginine) at 100 ppm in both seasons, respectively. However, the least inflorescence diameter (6.5 and 6.7 cm) obtained from the control plants (untreated plants) in both seasons. 4. The highest significant inflorescence stem length (34.6 and 36.5 cm) was obtained from the mixture treatment in the two seasons, respectively. Data showed also that the lowest inflorescence stem length (19.5 and 20.3 cm) was obtained from the control plants (untreated plants), respectively, in both seasons. 5. Maximum inflorescences stem diameter were (0.98 and 1.01 cm) for plants which received the mixture of tryptophan + arginine + glycine at 100 ppm, (0.88 and 0.98 cm) for plants which received tryptophan at 100 ppm then the glycine treatment at 100 ppm which was (0.84 and 0.91 cm), respectively in both seasons. 6. Foliar application of amino acids treatments significantly affected rows number/inflorescence, as the maximum values (5.0 and 5.8) resulted from plants treated with the mixture of amino acids at 100 ppm, followed by arginine treatment at 100 ppm (4.0 and 4.3), respectively in both seasons. 7. The highest number of ray florets (39.3 and 38.7) resulted from using the amino acids mixture in both seasons, respectively, followed by arginine treatment at 100 ppm (34.0 and 33.6) in the two seasons, respectively. 8. Application of amino acids individual or as mixture enhanced length of ray floret petals of dahlia plants in both seasons. The maximum length of petals was (4.6 and 4.8 cm) for plants received the mixture treatment at 100 ppm followed by (4.1 and 4.3 cm) for plants which sprayed with arginine at 100 ppm in the two seasons, respectively. 9. Application of amino acids individual or as mixture enhanced width of ray floret petals of dahlia plants in both seasons. The maximum width of petals was (2.5 and 2.9 cm) for plants received the mixture treatment at 100 ppm followed by (2.5 and 2.8 cm) for plants which received arginine at 100 ppm in the two seasons, respectively. C. Effect of preharvest treatments (amino acids) on chemical composition 1. praying dahlia plants with amino acid treatments enhanced chlorophyll A, chlorophyll B and total chlorophyll contents in the two seasons. Treatment with mixture of amino acids (tryptophan + arginine + glycine) at 100 ppm gave the maximum values of chlorophyll a, b and total chlorophyll, followed by arginine treatment at 100 ppm then the tryptophan treatment. Whereas untreated plants (control plants) gave the minimum values of chlorophyll a, b and total chlorophyll than other treatments in both seasons for that respect, respectively. 2. The mixture treatment of amino acids foliar application at 100 ppm gave the maximum values of carbohydrates percentages (39.15 and 40.81 %) in leaves and (19.63 and 22.77 %) in inflorescence, respectively in both seasons, followed by (38.28 and 39.37 %) and (19.34 and 21.45 %) which resulted from leaves and inflorescence by applying the arginine treatment at 100 ppm in both seasons, respectively.. 3. The highest values of carotenoids content (5.83 and 5.89 mg/100g inflorescences) resulted from the untreated plants (control plants) respectively, in both seasons. Followed by spraying glycine at 100 ppm (5.55 and 5.28 mg/ 100g inflorescences), whereas the least values of carotenoids content (4.76 and 4.87 mg /100g inflorescences) resulted from the mixture of amino acids at 100 ppm in both seasons, respectively. 4. Amino acids application as mixture (tryptophan + arginine + glycine) at 100 ppm resulted higher values of anthocyanin content (138.2 and 146.2 mg/ 100g inflorescences) followed by arginine treatment at 100 ppm (131.9 and 135.3 mg/ 100g inflorescences) in both seasons, respectively.
5. Plants sprayed with amino acids mixture (tryptophan + arginine + glycine) at 100 ppm gave the highest values of NPK % (2.42 and 2.46 % N), (0.29 and 0.29 %P) and (2.79 and 2.84 % K), followed by the arginine treatment at 100 ppm (2.30 and 2.33 % N), (0.27 and 0.27 % P) and (2.58 and 2.64 % K). While the lowest values of NPK % in dahlia plants (1.89 and 1.92 % N), (0.21 and 0.24 % P) and (2.15 and 2.17 % K) resulted from untreated plants with amino acids respectively, in both seasons. Postharvest experiments Part 1: The anatomical studies of reducing latex in inflorescence cut stems Holding inflorescence stems in ethyl alcohol for two minutes resolved that problem of dahlia inflorescence stems comparing with the other treatments as appeared in the anatomical studies which proved that latex substance disappeared after that treatment. Since, treatment of ethyl alcohol for two minutes showed wide xylem vessels, dissolution the tyloses in the xylem vessels, the cortex and pith parenchymatic cells were fully turgid and intact as well as the tissue had few intercellular spaces. Part two: Postharvest treatments 1. The longest vase life was obtained from inflorescences of the plants which sprayed with the mixture of amino acids at 100 ppm and held in nano silver at 0.5 cm/L + sucrose 1.5% vase solution and or AgNO3 at 0.2 g/L + sucrose 1.5% (7.0 days for each) in both seasons of the study. While inflorescences of the untreated plants (control) which held in sucrose 1.5% only gave the shortest vase life (4.2 days) during both seasons of study. 2. Change in fresh weights of inflorescences from plants treated with amino acids mixture at 100 ppm and held in nano silver at 0.5 cm/L + sucrose 1.5% vase solution, increased until the third day of vase life and started to decline thereafter in both seasons of study, while that of control started to decline after the first day of the vase life with lesser values than the other treatments in both seasons. 3. The combined treatment of preservative solution (AgNo3 at 0.2 g/L + sucrose 1.5 %) plus amino acid arginine (100 ppm) resulted in the highest value of maximum increase in fresh weight compared with all the other treatments in the first season. Whereas the highest value of maximum increase in fresh weight (2.80 g) in the second season resulted from silver nitrate 0.2 g/L + sucrose 1.5 % plus the mixture of amino acid at 100 ppm. 4. Maximum total water uptake was obtained from inflorescences of the plants which sprayed with the mixture of amino acids at 100 ppm and held in nano silver at 0.5 cm /L + sucrose 1.5 % (87.00 and 87.17 ml/ inflorescence) in both seasons, respectively. Whereas inflorescences of the unsprayed plants (control) and held in sucrose at 1.5 % solely showed the lowest total water uptake (12.83 and 13.33 ml/ inflorescence) in both seasons, respectively. 5. Combined treatment of amino acids mixture at 100 ppm and preservative solution nano silver 0.5 cm /L + sucrose 1.5 % gave the highest values of change in water uptake compared with other treatments and the control. Since, the previous treatment caused an increase in values of change in water uptake till the last day of vase life duration. On contrast, the control gave the lowest values of change in water uptake compared with all other cases. 6. The interaction between the amino acid mixture and the preservative solution (AgNo3 at 0.2 g /L + sucrose 1.5 %) resulted in the lowest values of change in water loss compared with all other treatments in both seasons of study. Whereas the highest values of change in water loss resulted from nano silver at 0.5 cm /L + sucrose 1.5 %. 7. Plants which sprayed with amino acids mixture at 100 ppm and held in vase solution containing nano silver at 0.5 cm/L + sucrose 1.5% had better water balance as compared with control and other holding solutions under study. Since, this treatment has positive values of water balance until the 4th day; thereafter decreased gradually. 8. The highest percentages of fructose, sucrose and glucose in ray floret petals of dahlia cut inflorescences resulted from inflorescences held in nano silver at 0.5 cm/L + sucrose 1.5 % were (0.81, 1.83 and 0.41 %), respectively at the end of vase life duration. While the lowest percentages of fructose, sucrose and glucose in petals of dahlia cut inflorescences held in sucrose 1.5% alone were 0.78, 1.80 and 0.38 %, respectively. 9. Nano silver at 0.5 cm/L + sucrose 1.5% and AgNO3 at 0.2 g /L+ sucrose 1.5 % had superior effects on eliminating bacterial growth in vase solution. In that, vase solution containing Nano silver or AgNO3 recorded zero bacterial count. While vase solution containing sucrose solely recorded the highest bacterial count (11.49 x 104cfu mL-1).