الفهرس 
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Abstract
SUMMARY AND CONCLUSION
This investigation was conducted during two successive seasons
(2019 /2020 and 2020/2021) on two young mango cultivars namely,
“Sediek” and “Ewais” to determine the effect of foliar spraying with
different levels of silicone which applied in the form of potassium
silicate “25% SiO 2 +10% k 2 O.” (0.0%, 0.1% and 0.2%) and α-
tocopherol “vitamin E” (0 ppm, 200 ppm and 400 ppm) to mitigate the
harmful effect of low, high temperatures and negative impact of soil
salinity on young mango trees. The trees were about 2 years old at the
beginning of study, planted at 5*6 m apart, each cultivar was grafting
on Sukkary rootstock "tolerant to salinity" and grown on a sandy loam
"newly reclaimed lands and the soil salinity was 4.55 dSm -1 " at the
experimental farm of the Fac. of Agric. at Demo, Fayoum, Egypt.
The experiment comprised the following treatments:
1: Control sprayed with distilled water only.
2: Sprayed with 0.1% potassium silicate (P.S. 1 ).
3: Sprayed with 0.2% potassium silicate (P.S. 2 ).
4: Sprayed with 200 ppm α-tocopherol (α-Toc. 1 ).
5: Sprayed with 400 ppm α-tocopherol (α-Toc. 2 ).
6: Sprayed with 0.1 potassium silicate (P.S. 1 ) + 200ppm α-tocopherol(α-Toc. 1 ).
7: Sprayed with 0.1 potassium silicate (P.S. 1 ) + 400ppm α-tocopherol (α-Toc. 2 ).
8: Sprayed with 0.2 potassium silicate (P.S. 2 ) + 200ppm α-tocopherol (α-Toc. 1 ).
9: Sprayed with 0.2 potassium silicate (P.S. 2 ) + 400ppm α-tocopherol (α-Toc. 2 ).
SUMMARY AND CONCLUSION 2
Our results could be summarized as follow:
1-The obtained results revealed that the growth characteristics
like tree height, scion and rootstock diameters, number of
leaves/shoot, leaf area and shoot length for mango trees of Sediek
and Ewais mange cvs. were negatively influenced by abiotic stresses.
This might be due to severe cold of winter and/or summer heat as
well as soil salinity which decrease physiological and biochemical
processes like nutrient metabolism, ion uptake, carbohydrate
assimilation and growth promoters, thus reducing plant growth and
development. Consequently, the lowest significant values of growth
parameters were detected by young mango trees grown under abiotic
stresses conditions without spraying with potassium silicate and/or α-
tocopherol.
2-Results showed that tree height increased by increasing
application rates of potassium silicate and/or α-tocopherol in the two
studied seasons. This may be due to foliar application of P.S. and/or
α-Toc. stimulated vegetative growth of mango trees due to the
positive effects of silicone on vegetative growth of trees especially
under adverse conditions by improving nutrient uptake, mechanical
properties of the plant parts and stimulating active roots. Also,
silicon and α-tocopherol inhibits oxidative degradation by enhancing
the activity of antioxidant enzymes that reduce reactive oxygen
SUMMARY AND CONCLUSION 3
species caused by stress conditions and toxic metals. Therefore, the
highest values of the tree height (160.67and167.30 cm during April
and October 2020, respectively were achieved by tree sprayed with
0.2% Potassium silicate plus 400 ppm α-tocopherol. Meanwhile,
foliar application by the lower levels of P.S. (0.1%) and α-Toc.
(200ppm) alone or combined gave the lowest values on this respect.
3-The obtained data indicate beneficial influence of spraying
with α-tocopherol alone than spraying with potassium silicate
individually. Also, trees which were sprayed with α-tocopherol alone
gave higher values of tree height, leaf area, scion and rootstock
diameters comparing with those sprayed with potassium silicate
alone especially at higher level of treatments.
4-The data clearly showed that leaf area was significantly
enhanced by foliar application of potassium silicate and α-tocopherol
alone or in combination. Trees of Ewais cultivar grown under abiotic
stresses and sprayed with foliar application of potassium silicate
and α-tocopherol alone or combined produced the largest leaf area
comparing with the trees of Sediek cultivar grown under the same
conditions.
5- Young mango trees sprayed with a higher concentration of
P.S. (0.2%) plus 400 ppm α–Toc. together gave the highest
significant values of shoot length (38.01cm and 59.32cm during
April and October, respectively (average of the two studied seasons).
SUMMARY AND CONCLUSION 4
Followed in descending order by those sprayed with 0.1% Potassium
Silicate + 400 ppm α–Toc., 0.2% potassium silicate + 200 ppm α-
tocopherol and then by 0.1% P.S. + 200 ppm α-Toc., respectively.
6- Number of leaves per shoot of Sediek and Ewais mango
cvs. was affected significantly by spraying with potassium silicate
and α-tocopherol alone or in combination. Consequently, the lowest
number of leaves/shoot was observed for young mango trees grown
under environmental stresses conditions. Also, number of leaves per
shoot was increased by increasing levels of potassium silicate and α-
tocopherol alone or in combination.
7- Abiotic stresses, including salinity, cold and extreme
temperature caused a harmful effect on relative water content
(RWC) and membrane stability index (MSI) for young mango trees
under study. Young mango trees exposed to the adverse
environmental conditions had the lowest significant values of RWC
and MSI. On the other hand, foliar application with P.S. and α-Toc.
alone or together enhanced significantly these parameters.
The negative impacts of abiotic stresses on relative water
content and the membrane stability index of young mango trees may
be due to the accumulation of reactive oxygen species that causes
membrane damage, lipid peroxidation, and hindered physiological
and biochemical processes such as nutrient metabolism, ion uptake,
and loss of cell water content.
SUMMARY AND CONCLUSION 5
Furthermore, silicon protects trees against oxidative damage
by maintaining water uptake, forming antioxidant defense, increasing
photosynthesis activity and root growth. In addition, antioxidants
like alpha-tocopherol play an essential role in protecting the cell
membrane from the harmful effects of abiotic stresses by increasing
membrane stability, stimulating photosynthesis and decreasing
reactive oxygen species and lipid peroxidation.
8-Results reveal that Chlorophyll fluorescence (F v /F m ) and
SPAD chlorophyll differed significantly by foliar application of
potassium silicate and α-tocopherol alone or together. Leaves of trees
sprayed with the higher levels of P.S. +α-Toc. together had the
highest significant values of F v /F m and SPAD chlorophyll. Moreover,
the effect of spraying with α-tocopherol alone on F v /F m and SPAD
chlorophyll was more noticeable than spraying with potassium
silicate individually particularly at higher concentration of
treatments.
9- The obtained results show that total carbohydrate contents
increased by increasing appellation rates of potassium silicate or α-
tocopherol alone. Furthermore, total carbohydrate content of young
mango trees spraying with α-tocopherol alone was higher than that of
trees spraying with potassium silicate alone. Young mango trees
sprayed with the higher level of potassium silicate (2%) + 400 ppm
α-tocopherol had the highest significant values of total carbohydrate
(25.78 % in April and 26.27 in October). Meanwhile, total
SUMMARY AND CONCLUSION 6
carbohydrate content of trees sprayed with the lower level of this
mixture (1% potassium silicate + 200 ppm α-tocopherol were 23.42
% in April and 23.95 % in October "averages of the two studied
seasons".
10- Negative relationships was detected among free proline
content in leaves of young mango trees grown under adverse
environmental conditions and foliar application of potassium silicate
and α-tocopherol singular or together. Consequently, leaves of young
mango trees exposed to abiotic stresses without any treatments had
the highest significant values of free proline content. Spraying with
potassium silicate alone was more noticeable than spraying with α-
tocopherol alone especially at higher levels of treatments on free
proline content.
11- Phenol content differed significantly by foliar application
of potassium silicate and -tocopherol separately or together. As
demonstrated by the obtained results, the lowest significant values of
phenols (1.05 and 1.07 mg g1 DW in April and October, respectively
"averages of the two studied seasons") were detected by untreated
trees. In addition, phenol content was raised by increasing the
application rate of potassium silicate and/or –tocopherol.
12- In general, leaf minerals content like N, P, K, and Ca as
well as the K/Na ratio of young mango trees grown under abiotic
stress were enhanced significantly by foliar application of potassium
SUMMARY AND CONCLUSION 7
silicate and/or α-tocopherol alone or together comparing to control
treatment especially at higher levels. On the other hand, leaf Na
content showed an opposite trend under the same condition.
Therefore, young mango trees grown under abiotic stress without
any treatments had the highest significant values of Na percent.
In addition, leaf minerals content like N, P, K, and Ca of
young mango trees sprayed with α-tocopherol singularly was the
most promising than those sprayed with potassium silicate alone.
In the end. It can be concluded that heat, cold and salinity
stresses were characterized by inducing a dramatic decline of all
physiological responses of young mango trees. Meanwhile, foliar
application of potassium silicate and/or α-tocopherol alone or in
combination significantly improves morphological, physiological
characteristics and leaf mineral content.
Foliar application of α-tocopherol alone was more noticeable
comparing spraying with potassium silicate alone particularly at the
higher rates and maintained the growth and trees performance under
abiotic stresses.
potassium silicate or α-tocopherol plays a vital role in
inhibiting oxidative degradation by enhancing the activity of
antioxidant enzymes that reduce reactive oxygen species caused by
abiotic stresses and ion toxicity. They also improved cell water status
SUMMARY AND CONCLUSION 8
through ameliorating phenolic content, membrane stability index and
relative water content, reflecting its vital role as anti-oxidant.
According to our results, we recommend foliar spraying with
either P.S. at 0.2% or α-Toc. at 400pp alone or combined for four
times in winter season (on the first of December, 1 st of January, 1 st of
February and then on the first of March). And for four times during
summer season (on the 1 st May and after one month later till up the
first of August) to alleviate adverse effects of salinity, low and high
temperatures on young mango trees.