الفهرس 
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Abstract
SUMMARY AND CONCLUSION
In the present study, the aim was to investigate the effect of foliar application of tryptophan, indole-3-acetic acid, and melatonin on vegetative growth, mineral content of vegetative growth, SPAD readings, yield and quality of potato (Solanum tuberosum L.) plants cv. Spunta imported from Holand.
This work was carried out at the Experimental Farm of Horticulture Department, Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima, Qalubia Governorate, Egypt during the summer seasons of 2021 and 2022.
The experiment included ten treatments which were: tryptophan was used at three concentrations (1, 2 and 4 mM), indole acetic acid at three levels (0.3, 0.6 and 1.2 mM), and melatonin at three concentrations (50, 100 and 200 μM), plus water served as a control treatment. The foliar treatments were applied three times; 35, 49, and 63 days after planting.
The experiment was conducted according to a randomized complete block design (RCBD) with three replicates.
The vegetative growth characteristics, i.e., plant length, number of stems and leaves per plant, shoot fresh and dry weight per plant, and leaf area. Furthermore, SPAD readings and mineral analysis of vegetative growth were recorded such as N, P, K, Ca, Mg percentages and Zn content in the vegetative growth of plant. Also, yield components and tuber quality were recorded, i.e., tuber number per plant, average tuber weight, tuber weight per plant, total yield per hectare, dry matter, tuber specific gravity, and starch content.
The obtained results could be summarized as follows:
1. Effect of tryptophan, melatonin and IAA foliar application on vegetative growth parameters of potato
All applied treatments caused significant increases in plant length, except IAA treatment at 1.2 mM, while melatonin at 100 μM and IAA at 0.6 mM gave the highest values of plant length in both growing seasons. There were no significant differences between 100 μM melatonin and 0.6 mM IAA in both seasons. On the other hand, all treatments significantly increased number of leaves/plant, leaf area/plant and shoot dry weight except tryptophan at 1 mM, while melatonin at 100 and 200 μM gave the highest values of these parameters without significant differences in both seasons. In addition, all treatments caused significant increases in number of branches/plant, except tryptophan at 1 mM and IAA at 0.3 and 1.2 mM, while tryptophan at 4 mM, melatonin at 100 and 200 μM and IAA at 0.6 mM gave the highest values of this character without significant differences in both growing seasons. Additionally, all applied treatments significantly increased shoot fresh weight, while melatonin at 100 and 200 μM and IAA at 0.6 and 1.2 mM gave the highest values of this parameter in both growing seasons. However, the lowest significant values of all vegetative growth parameters were acquired by the control treatment in both seasons.
2. Effect of tryptophan, melatonin and IAA foliar application on SPAD readings of potato
Results indicate that the foliar sprayings of tryptophan, melatonin, and IAA had no significant effect on the SPAD readings of the potato plants as compared to control treatment in both growing seasons.
3. Effect of tryptophan, melatonin and IAA foliar application on mineral analysis of vegetative growth of potato
All tested treatments significantly increased nitrogen percentage, except tryptophan at 1 mM and melatonin at 50 μM, while melatonin at 100 and 200 μM and IAA at 0.6 and 1.2 mM gave the highest values of nitrogen without significant differences in both growing seasons. Additionally, all used treatments caused significant increases in phosphorus percentage, however tryptophan treatment at 4 mM and IAA at 1.2 mM gave the highest values of phosphorus in both growing seasons. There were no significant differences between tryptophan at 4 mM and IAA at 1.2 mM in phosphorus percentage in both seasons. In addition, all foliar treatments resulted in significant increases in potassium percentage, except IAA treatment at 0.3 mM while tryptophan at 2 and 4 mM, melatonin at 200 μM and IAA at 1.2 mM gave the highest values of potassium without significant differences in both growing seasons. Also, all treatments significantly increased magnesium percentage, except tryptophan at 1 mM, melatonin at 50 μM and IAA at 0.3 and 0.6 mM, however tryptophan at 4 mM, melatonin at 100 and 200 μM and IAA at 1.2 mM gave the highest values of magnesium without significant differences in both seasons. Also, all treatments significantly increased calcium percentage, while tryptophan at 4 mM, melatonin at 100 μM and IAA at 0.6 mM gave the highest values of calcium without significant differences in both growing seasons. Additionally, all treatments caused significant increases in zinc content, except tryptophan at 1 mM, while tryptophan at 2 and 4 mM and melatonin at 100 μM gave the highest values of zinc in both growing seasons. Furthermore, the lowest significant values of all determined minerals were recorded with the control treatment in both seasons.
4. Effect of tryptophan, melatonin and IAA foliar application on tuber yield components and quality of potato
Treatments of tryptophan at 4 mM and melatonin at 100 and 200 μM gave the highest significant values of number of tubers/plant in both seasons. No significant differences between the tested treatments in number of tubers/plant in both growing seasons. In addition, all foliar applications caused significant increases in average tuber weight, except tryptophan at 1 mM, melatonin at 50 μM and IAA at 0.3 mM, while tryptophan at 2 and 4 mM and IAA at 0.6 and 1.2 mM gave the highest values of average tuber weight without significant differences in both growing seasons. Additionally, all treatments significantly increased tubers weight/plant and total tuber yield, except tryptophan at 1 mM and IAA at 0.3 mM, however tryptophan at 4 mM, melatonin at 100 and 200 μM and IAA at 0.6 and 1.2 mM gave the highest values of these parameters without significant differences in both seasons. Additionally, the lowest significant values of all parameters were recorded with the control treatment in both growing seasons.
Exogenous applications of tryptophan at 2 and 4 mM, melatonin at 100 μM, and IAA at 1.2 mM significantly increased dry matter percentage, while tryptophan at 2 mM, melatonin at 100 μM, and IAA at 1.2 mM gave the highest significant values of dry matter in both seasons. There were no significant differences between the tested treatments in this character in both seasons. In addition, tryptophan at 2 mM, melatonin at 100 and 200 μM and IAA at 1.2 mM gave the highest and significant values of tuber specific gravity and starch percentage in both growing seasons without significant differences between the tested treatments. However, the lowest significant values of all cases were recorded with the control treatment in both growing seasons.
In conclusion, the precent study concludes that foliar applications of tryptophan, melatonin, and indole-3-acetic acid can be used to enhancing and increase the plant productivity. from this study, we can recommend applying foliar applications of tryptophan at 4 mM or melatonin at 100 μM or indole-3-acetic acid at 1.2 mM were the most effective treatments, which enhanced growth, yield, and quality of potato plants cv. Spunta under Qalubia Governorate, Egypt conditions. In addition, we can recommend using tryptophan instead of melatonin and indole-3-acetic acid because it seem to be more safety on human health.