الفهرس 
The active role of cobalt in plant lifeOnly 14 pages are availabe for public view
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Abstract
This study was carried out during 2012 and 2013 seasons on 7 years old Washington Navel orange trees (C. sinensis) budded on sour orange rootstock (Citrus aurantium, L.) and planted at 5 x 5 meters under basin irrigation system. The study included the following three experiments as follows:
1- The first experiment: Impact of spraying cobalt sulphate on vegetative growth, fruit set%, fruit drop%, productivity, fruit quality, leaf mineral concentrations and enzymes activity of Navel orange trees.
This experiment studied the effect of cobalt levels (0, 5, 10, 20 and 40 ppm cobalt) as foliar application, on the vegetative growth, fruit set %, fruit DROP %, yield, fruit quality, leaf and fruit mineral concentrations and enzymes activity in fruit pedicels. selected trees were sprayed two times in each season (in the first week of Mar. and in the first week of Sept.) The experiment was arranged in a randomized complete block design with four replicates each of one tree.
The obtained results could be summarized as follows:
1-1- Vegetative growth:
Number of shoots/branch and Number of leaves/ shoot were increased significantly by foliar spray with cobalt at 5 ppm. Shoot length and leaf area showed inconstant trend in both seasons.
1-2- Fruit set:
Spraying trees with 5 ppm cobalt gave the highest initial fruit set increase in two seasons. Final retained fruits significantly increased by spraying trees with 20 ppm cobalt in the two seasons.
1-3- Fruit drop:
Spraying with 5 ppm cobalt gave the highest final fruit DROP % in the first season only. On the other hand, spraying with different cobalt treatments did not affect fruit DROP %.
1-4- Tree yield:
Yield as number and weight of fruits/tree was increased significantly by spraying 20 ppm cobalt.
1-5- Fruit quality:
1-5-1- Physical properties:
Spraying trees with 5 and 10 ppm cobalt gave the highest values of fruit volume, fruit height, fruit diameter, peel thickness, peel weight, pulp weight but there were no significant effect on pulp percentage.
1-5-2- Chemical properties:
The highest significant increases in total soluble solids, total acidity, TSS/acid ratio and ascorbic acid were obtained by spraying trees with 20 and 40 ppm cobalt in both seasons.
1-6- Macro and micronutrients in leaves:
Leaf content of N, P, K, Ca, Mg, Fe, Zn, Mn and Co in leaves were the highest by spraying cobalt at 20 and 40 ppm in both seasons.
1-7- Cobalt content in fruit pulp:
Cobalt content in fruit pulp was increased by spraying 40 ppm cobalt in both seasons.
1-8- Enzymes activity in fruit pedicels:
1-8-1 Pectinase activity:
Spraying trees with zero and 20 ppm cobalt gave the highest values of pectinase activity on the first date but in the second date, spraying trees with zero, 5 ppm, 10 ppm and 20 ppm cobalt gave the highest pectinase activity. But spraying trees with 40 ppm cobalt gave the least pectinase activity on both dates. Whereas, decreasing pectinase activity decreased fruit drop% and increased yield as number of fruits/tree.
1-8-2 Cellulase activity:
Spraying trees with water and 5 ppm cobalt gave the highest cellulase activity on the first date but on the second date, spraying trees with zero, 5 ppm and 10 ppm cobalt gave the highest cellulase activity. But spraying trees with 40 ppm cobalt gave the least cellulase activity on both dates. Therefore, reducing cellulose activity decreased fruit drop% and increased yield as number of fruits/tree.
Finally, it could be concluded that the vegetative growth, yield/tree, fruit quality, leaf mineral concentration and fruit cobalt concentration were increased and get the highest values by treatment (cobalt spray at 20 ppm). Also, reducing enzymes activity in fruits pedicels.
2- The second experiment: Impact of spraying sodium selenite on vegetative growth, fruit set%, fruit drop%, productivity, fruit quality, leaf mineral concentrations and enzymes activity of Navel orange trees.
This experiment studied the effect of selenium levels (0, 20, 40, 80 and 160 ppm selenium) as foliar application, beside the control treatment which sprayed with water, on the vegetative growth, fruit set %, fruit DROP %, yield, fruit quality, leaf and fruit mineral content and enzymes activity in fruit pedicels. selected trees were sprayed two times during the season (in the first week of Mar. and in the first week of Sept.). The experiment was arranged in a randomized complete block design with four replicates each of one tree.
The obtained results could be summarized as follows:
2-1- Vegetative growth:
Number of shoots/branch, Shoot length, number of leaves/ shoot and leaf area recorded the highest increase by foliar spray with selenium at 80 ppm in both seasons.
2-2- Fruit set:
There were no significant differences between treatments. However, spraying trees with 40 ppm and 160 ppm selenium gave a slightly increase in initial fruit set % in the first season but in the second season, spraying trees with 20 ppm selenium gave a slightly increase initial fruit set %. On the other hand, final retained fruits percentage were significantly increased by all Se treatments in both seasons.
2-3- Fruit drop:
Spraying with selenium did not significantly affect fruit DROP % in the two seasons. However, control treatment gave a slightly increase of final fruit DROP % in both seasons.
2-4- Tree yield:
Yield as number and weight of fruits/tree was significantly increased by spraying 40 ppm selenium in both seasons.
2-5- Fruit quality:
2-5- 1- Physical properties:
Spraying trees with 40 and 80 ppm selenium gave a significant increase of fruit volume, fruit height, fruit diameter, peel thickness, weight and percentage of pulp than the control in both seasons. 2-5-2- Chemical properties:
The highest significant increases of total soluble solids, total acidity, TSS/acid ratio and ascorbic acid were found by spraying trees with 20 ppm selenium in both seasons.
2-6- Macro and micronutrients in leaves:
Leaf mineral of N, P, K, Ca, Mg ,Fe, Zn, Mn and Co in leaves were increased by spraying selenium at 40 and 80 ppm.
2-7- Selenium content in fruit pulp:
Selenium content in fruit pulp was increased significantly by 160 ppm selenium spray in both seasons.
2-8- Enzymes activity in fruit pedicels:
2-8-1 Pectinase activity:
Spraying trees with 80 ppm selenium gave the highest pectinase activity on both dates. But the control treatment gave the least pectinase activity on both dates which increased fruit set% and decreased fruit drop%.
2-8-2 Cellulase activity:
Spraying trees with 20 ppm selenium gave the highest cellulase activity on both dates. But spraying trees with 160 ppm selenium gave the least cellulase activity in both dates which increased fruit set% and decreased fruit drop%.
Finally, it could be concluded that the vegetative growth, yield/tree, fruit quality, leaf mineral content, fruit selenium content and enzymes activity in fruits pedicels were increased significantly by treatment with selenium spraying at 40 ppm.
3- The Third experiment: Impact of spraying silicon on vegetative growth, fruit set%, fruit drop%, productivity, fruit quality, leaf mineral concentrations and enzymes activity of Navel orange trees.
This experiment studied the effect of silicon levels (0, 25, 50, 100 and 200 ppm silicon) as foliar application, beside the control treatment which sprayed with water, on the vegetative growth, fruit set %, fruit DROP %, yield, fruit quality, leaf and fruit mineral concentration and enzymes activity in fruit pedicels. selected trees were sprayed two times during the season (in the first week of Mar. and in the first week of Sept.). The experiment was arranged in a randomized complete block design with four replicates each of one tree.
The obtained results could be summarized as follows:
3-1- Vegetative growth:
Number of shoots/branch and, shoot length, number of leaves/ shoot and leaf area were increased significantly by foliar spray with silicon at 50 ppm in both seasons.
3-2- Fruit set:
There were no significant differences between treatments in the first season. However, spraying trees with zero and 200 ppm silicon gave slightly increase of initial fruit set % in the first season. In the second season, spraying trees with 200 ppm silicon gave the highest significant increase of initial fruit set %. The final retained fruits % was the highest by spraying 100 ppm silicon in both seasons.
3-3- Fruit drop:
Spraying silicon with 100 ppm in both seasons had reduced final fruit DROP % significantly.
3-4- Tree yield:
Yield as number of fruits/tree was the highest by spraying silicon at 200 ppm while fruit weight was increased significantly with 100 ppm silicon in the two seasons. Weight of fruits /tree was increased significantly with 100 and 200 ppm silicon in the two seasons.
3-5- Fruit quality:
3-5- 1- Physical properties:
Spraying trees with 50 and 100 ppm silicon gave the highest values of fruit volume, fruit height, fruit diameter, peel weight, and weight and percentage of pulp than these of the control in both seasons.
3-5-2- Chemical properties:
The highest values of total soluble solids, were found by spraying trees with 25 and 50 ppm silicon in both seasons. Ascorbic acid was increased significantly with 100 and 200 ppm silicon when compared with the control in the two seasons.
3-6- Macro and micronutrients in leaves:
Leaf mineral in leaves varied from season to season as affected by silicon spraying. Generally, the mineral level in leaves of all treatments were in the optimum level.
3-7- Silicon concentration in fruit pulp:
Silicon percentage in fruit pulp was the highest by spraying 50 or 200 ppm silicon and 100 or 200 ppm silicon spray in the first and second seasons, respectively.
3-8- Enzymes activity in fruit pedicels:
3-8-1 Pectinase activity:
In the second season spraying trees with control and 50 ppm silicon gave the highest pectinase activity on both dates. But spraying trees with 100 and 200 ppm in the first date and 200 ppm silicon on the second date gave the least pectinase activity. Thus, the reduction in pectinase activity decreased fruit drop% and increased number of fruits/tree.
3-8-2 Cellulase activity:
Spraying trees with zero ppm silicon gave the highest cellulase activity in both dates. However, spraying trees with different silicon concentrations gave the least cellulase activity in both dates. Whereas, the reduction in cellulase activity decreased fruit drop% and increased number of fruits/tree.
Finally, it could be concluded that the vegetative growth, yield/tree, fruit quality, leaf mineral content and fruit selenium content were increased by spraying with 50 ppm silicon. Moreover, it reduced pectinase and cellulase activity in fruits pedicels.