الفهرس 
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Abstract
The purpose of this study was elucidating the effect of different sources, concentrations and frequencies of application of silicon as well as the use of chitosan on growth, tree nutritional status, yield and fruit quality of Zebda mango trees.
The nearly same obtained during both seasons could be summarized under the following main items:
1- Vegetative growth aspects
The three growth aspects namely shoot length , number of leaves on it , and leaf area were positively affected by using silicon in potassium and calcium forms at 0.05% to 0.2% twice or thrice and chitosan at 0.1% alone or in combined application and this effect was in proportional to the increase in concentrations and frequencies of application of silicon. Combined application of silicon and chitosan was materially superior than using each alone. Treating the trees with potassium silicate and chitosan together at 0.1% gave the highest values.
2- Leaf chemical composition
There was a remarkable promotion on chlorophyll a,b, total chlorophylls , total carotenoids, N, P, K , Mg, Ca, Zn , Fe and Mn with using silicon and / or chitosan relative to the control. The promotion was associated with increasing concentrations and frequencies of application of silicon. Using silicon via K was considerably superior than using it via Ca. The highest values were recorded on the trees that received both materials together at 0.1%.
3- Flowering aspects
Panicle length , number of panicle / tree and number of flowers / panicle were positively affected by application of silicon in both sources (K or Ca) at 0.05 to 0.2% twice or thrice and chitosan at 0.1% singly or in combinations relative to the control treatment. Using silicon in potassium source was materially superior than using it through calcium source in improving all flowering aspects. Combined application of silicon and chitosan was preferable than using each alone in this aspects.
4- Percentage of fruit retention
Percentage of fruit retention was remarkably enhanced in response to treating the trees with silicon in both forms at 0.05% to 0.2% twice or thrice and chitosan at 0.1% singly or in combined use relative to the control. Using silicon in K form was materially superior than using it via Ca in enhancing fruit retention %. Treating the trees with K- silicate plus chitosan each at 0.1% gave the maximum values.
5- Yield / tree
There was a remarkably promotion on the yield expressed in number of fruits / tree and weight (Kg) by using potassium or calcium silicate twice or thrice at 0.05% to 0.1% and chitosan at 0.1% either alone or in combined applications relative to the control. Using silicon in K form was superior than using it via Ca in improving the yield. Also, using silicon and chitosan was preferable than using each alone in this respect. from economical point of view it is recommended to use silicon in the form of potassium silicate thrice and chitosan thrice each at 0.1%.
6- Physical and chemical characteristics of the fruits
Single and combined applications of silicon and chitosan were beneficial in enhancing fruit quality of the fruits in terms of increasing weight, height, diameter and thickness of fruit , flesh % , edible to non- edible portions, T.S.S % , total and reducing sugars % and vitamin C and decreasing total acidity % and total fiber % relative to the control treatment. Non- reducing sugars was unaffected by the present treatments.
Using silicon in the form of potassium silicate was materially superior than using it via calcium silicate in enhancing fruit quality. The most effective treatment in this respect was the application of silicon in the form of potassium silicate thrice and chitosan thrice each at 0.1%.
Conclusion:
According to the obtained data, it is recommended to spray Zebda mango trees three times (growth start, just after fruit setting and 21 days later) with a mixture of potassium silicate and chitosan each at 0.1% for improving quantity and quality of the fruits.