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Pre and Postharvest Management to Improve Yield and Quality of ‘Kinnow’ Mandarin
By
MEHWISH LIAQUAT
M.Sc. (Hons.) Horticulture
2007-ag-2454
A thesis submitted in the fulfillment of the
requirements for the degree of
DOCTOR OF PHILOSOPHY
IN
HORTICULTURE
INSTITUTE OF HORTICULTURAL SCIENCES
FACULTY OF AGRICULTURE
UNIVESITY OF AGRICULTURE,
FAISALABAD-PAKISTAN
2018
DEDICATION
This humble effort
the fruit of studies and thoughts
dedicated to
my Beloved
Mother
Shamim Akhter
who strongly believes that
her prayers are always with me
and
to my worthy father
Rana Liaquat Ali
who always inspired and encouraged
me to get the higher ideas of life.
ACKNOWLEDGEMENTS
I indebted to Almighty Allah, the propitious, the benevolent and sovereign whose blessing and glory flourished my thoughts and thrived my ambitions, giving me talented teachers, affectionate parents, and family members and unique friends. Trembling lips and wet eyes praise for Holy Prophet Muhammad (P.B.U.H.) for enlightening our conscience with the essence of faith in Almighty Allah, converging all His kindness and mercy upon him.
I have no appropriate words to express my deep gratitude to my supervisor, Dr. Saeed Ahmad Associate Professor, Institute of Horticultural Sciences, who, in spite of his busiest schedule, acted as a real spiritual teacher and provided his dexterous guidance and valuable suggestions throughout my research efforts and write up of this manuscript. Under his able guidance, skillful suggestions, constructive criticism and kind supervision this work was converted into a novel write up getting its present shape.
I am grateful to respectable members of my supervisory committee, Dr. Ahmad Sattar Khan, Associate Professor, Institute of Horticultural Science and Dr. Rashid Ahmad, Professor, Department of crop physiology, for their incentive teaching, insightful comments, sympethic attitude, valueable suggestions, cooperation and kind behavior.
I am beholden to my Father, Rana Liaquat Ali due to whose prays and wishes, today I am at this position and I do not have words at my command to express my heartiest thanks, gratitude and profound admiration to my esteemed affectionate Mother, Shamim Akhter, my loving husband Hafiz Muhammad Qasim Ashraf ,my aunty Naseem Akhter , sweet czns, Sobia Khizer, Sumeria yasir and all members in-laws family for their encouragement, immense orisons, mellifluous moral support, patience, spiritual and intellectual inspirations who have always wished to see me glittering high on the skies of success and whose hands always rise in prayer for my success. It is day and night prayers, endurance and ambitious training of my family that brought such a fruit to me.
All of my University friends Anam Noor, Sana Shahzad, Noshi Parveen, Sabiha Abbas,, Aliya Hanif and special thanks to Mr. Abdul Rahim Khan (PHRC-AARI), my senior Dr. Maryam Nasir and Dr. Sakeena-tul-Ain Haider for their help and guidelines, I can never forget the sweet memories of the time passed with them. May Allaha Almighty infuse with the energy to fulfill their inspirations and expectations and further modify my competence May Allah bless us all with long happy and peaceful lives (Aameen).
Mehwish Liaquat
ii
2.5
Zinc Sulphate
15
2.5.1
Causes and management strategies for fruit drop
15
2.5.2
Effect of zinc sulphate on yield and quality of fruit
16
2.5.3
Benefits of foliar applied Zn sulphate than soil application
17
2.5.4
Effects on TSS, sugars and ascorbic acid contents of fruit
18
2.5.5
Deficiency symptom of zinc
18
2.6
Effects of gibberellic acid on different fruit corps
19
2.6.1
Role of gibberellic acid to prevent fruit drop
20
2.6.2
Effects of gibberellic acid on yield and quality of fruit
21
2.6.3
Role of gibberellic acid in fruit growth and development
21
2.6.4
Effects of GA3 on biochemical fruit quality parameters
22
Chapter 3
Materials and Methods
24
3.1
Plant material
24
3.2
Experimental detail
24
3.3.1
Study 1
24
3.3.1.1
Experiment 1: Foliar application of calcium chloride (CaCl2) to improve yield and fruit quality of ‘Kinnow’ mandarin”
24
3.3.1.2
Experiment 2: Foliar application of Zinc sulfate (ZnSO4) to improve yield and fruit quality of ‘Kinnow’ mandarin
25
3.3.2
Study 2
26
3.3.2.1
Experiment 1: Effect of pre harvest spray of gibberellic acid (GA3) on yield and fruit quality of ‘Kinnow’mandarin
26
3.3.2.2
Experiment 2: Effect of pre harvest spray of salicylic acid (SA) on yield and fruit quality of ‘Kinnow’ mandarin
26
3.3.3
Study 3
27
3.3.3.1
Experiment 1: Dose optimization of salicylic acid (SA) to maintain fruit quality during storage of ‘Kinnow’ mandarin
27
3.3.3.2
Experiment 2: Dose optimization of calcium chloride (CaCl2) to maintain fruit quality of ‘Kinnow’ mandarin
27
3.4
Parameters
28
3.4.1
Reproductive Parameters
28
3.4.1.1
Pre harvest fruit drop (%)
28
3.4.1.2
Fruit yield per tree (Kg)
28
3.4.1.3
Total number of fruits per plant
28
3.4.2
Physical and physiological parameters
29
3.4.2.1
Fruit weight (g)
29
3.4.2.2
Weight loss (%)
29
3.4.2.3
Fruit rot (%)
29
3.4.2.4
Peel weight (g)
29
3.4.2.5
Pulp weight (%)
30
3.4.2.6
Peel: pulp ratio
30
3.4.2.7
Juice contents (%)
30
3.4.3
Bio-chemical parameters
30
3.4.3.1
Total soluble solids (ºBrix)
30
3.4.3.2
Titratable acidity (%)
30
3.4.3.3
TSS: TA ratio
30
3.4.3.4
Ascorbic acid (mg 100g-1)
30
3.4.3.5
Total sugars (%)
32
3.4.3.6
Reducing sugars (%)
32
3.4.3.7
Non-reducing sugars (%)
32
3.4.3.8
Method for sugar preparation
33
3.4.4
Phytochemical Parameters
34
3.4.4.1
Determination of total antioxidants and total phenolic contents
34
3.4.4.2
Total antioxidants
34
3.4.4.3
Total phenolic contents
36
3.4.5.
Fruit quality enzyme
37
3.4.5.1
Determination of activities of anti-oxidative enzymes
37
3.4.5.2
Catalase (CAT)
37
3.4.5.3
Peroxidases (POD)
38
3.4.5.4
Superoxide dismutase (SOD)
38
3.5
Statistical Analysis
39
Chapter 4
Results and Discussion
40
4.1
Study 1
40
4.1.1
Experiment 1: Foliar application of calcium chloride (CaCl2) to improve yield and fruit quality of ‘Kinnow’ mandarin”
40
4.1.1.1
Reproductive Parameters
40
4.1.1.1.1
Pre harvest fruit drop (%)
40
4.1.1.1.2
Total number of fruit per tree
41
4.1.1.1.3
Yield (Kg)
41
4.1.1.2
Physical and physiological parameters
42
4.1.1.2.1
Fruit weight (g)
42
4.1.1.2.2
Peel weight (g)
43
4.1.1.2.3
Pulp weight (g)
43
4.1.1.2.4
Peel: pulp ratio
44
4.1.1.2.5
Juice weight (%)
45
4.1.1.3
Bio-chemical parameters
45
4.1.1.3.1
Total soluble solids (ºBrix)
45
4.1.1.3.2
Titratable acidity (%)
46
4.1.1.3.3
TSS: TA ratio
47
4.1.1.3.4
Ascorbic acid (mg 100g-1)
47
4.1.1.3.5
Total sugars (%)
48
4.1.1.3.6
Reducing sugars (%)
48
4.1.1.3.7
Non-reducing sugars (%)
48
4.1.1.3
Phytochemical Parameters
49
4.1.1.3.1
Total Antioxidants (% Inhibition)
49
4.1.1.3.2
Total phenolic contents (mg GAE 100g-1)
49
4.1.1.4
Fruit quality enzyme
51
4.1.1.4.1
Catalase (CAT) (U mg-1 protein)
51
4.1.1.4.2
Peroxidases (POD) (U mg-1 protein)
51
4.1.1.4.3
Superoxide dismutase (SOD) (U mg-1 protein)
52
4.1.1
Discussion
53
4.1.1
Conclusion
56
4.1.2
Experiment 2: Foliar application of Zinc sulfate (ZnSO4) to improve yield and fruit quality of ‘Kinnow’ mandarin
57
4.1.2.1
Reproductive Parameters
57
4.1.2.1.1
Pre harvest fruit drop (%)
57
4.1.2.1.2
Number of fruit per tree
58
4.1.2.1.3
Yield (Kg)
58
4.1.2.2
Physical and physiological parameters
59
4.1.2.2.1
Fruit weight (g)
59
4.1.2.2.2
Peel weight (g)
59
4.1.2.2.3
Pulp weight (g)
60
4.1.2.2.4
Peel: pulp ratio
61
4.1.2.2.5
Juice weight (%)
62
4.1.2.3
Bio-chemical parameters
62
4.1.2.3.1
Total Soluble solids (ºBrix)
62
4.1.2.3.2
Titratable acidity (%)
63
4.1.2.3.3
TSS: TA ratio
64
4.1.2.3.4
Ascorbic acid (mg 100g-1)
65
4.1.2.3.5
Total sugars (%)
65
4.1.2.3.6
Reducing sugars (%)
65
4.1.2.3.7
Non-reducing sugars (%)
65
4.1.2.4
Phytochemical Parameters
66
4.1.2.4.1
Total Antioxidants (% Inhibition)
66
4.1.2.4.2
Total phenolic contents (mg GAE 100g-1)
67
4.1.2.5
Fruit Quality Enzyme
68
4.1.2.5.1.2.3
Anti-oxidative Enzyme (CAT, POD and SOD)
68
4.1.2
Discussion
69
4.1.2
Conclusion
71
4.2
Study 2
72
4.2.1
Experiment 1: Effect of pre harvest spray of gibberellic acid (GA3) on yield and fruit quality of ‘Kinnow’ mandarin
72
4.2.1.1
Reproductive Parameters
72
4.2.1.1.1
Pre harvest fruit drop (%)
72
4.2.1.1.2
Total number of fruit per tree
72
4.2.1.1.3
Yield (Kg)
72
4.2.1.2
Physical and physiological parameters
74
4.2.1.2.1
Fruit weight (g)
74
4.2.1.2.2
Peel weight (g)
74
4.2.1.2.3
Pulp weight (g)
74
4.2.1.2.4
Peel: pulp ratio
76
4.2.1.2.5
Juice weight (%)
76
4.2.1.3
Bio-chemical parameters
77
4.2.1.3.1
Total soluble solids (ºBrix)
77
4.2.1.3.2
Titratable acidity (%)
77
4.2.1.3.3
TSS: TA ratio
77
4.2.1.3.4
Ascorbic acid (mg 100g-1)
77
4.2.1.3.5
Total sugars (%)
79
4.2.1.3.6
Reducing sugars (%)
79
4.2.1.3.7
Non-reducing sugars (%)
80
4.2.1.4
Phytochemical Parameters
80
4.2.1.4.1
Total Antioxidants (% Inhibition)
80
4.2.1.4.2
Total phenolic contents (mg GAE 100g-1)
80
4.2.1.5
Fruit Quality Enzyme
82
4.2.1.5.1
Catalase (CAT) activity (U mg-1 protein)
82
4.2.1.5.2
Peroxidases (POD) activity (U mg-1 protein)
82
4.2.1.5.3
Superoxide dismutase (SOD) activity (U mg-1 protein)
82
4.2.1
Discussion
84
4.2.1
Conclusion
87
4.2.2
Experiment 2: Effect of pre harvest spray of salicylic acid (SA) on yield and fruit quality of ‘Kinnow’ mandarin
88
4.2.2.1
Reproductive Parameters
88
4.2.2.1.1
Pre harvest fruit drop (%)
88
4.2.2.1.2
Total number of fruit per tree
89
4.2.2.1.3
Yield (Kg)
89
4.2.2.2
Physical and physiological parameters
90
4.2.2.2.1
Fruit weight (g)
90
4.2.2.2.2
Peel weight (g)
91
4.2.2.2.3
Pulp weight (g)
91
4.2.2.2.4
Peel: pulp ratio
91
4.2.2.2.5
Juice weight (%)
92
4.2.2.3
Bio-chemical parameters
92
4.2.2.3.1
Total Soluble solids (TSS) (ºBrix)
92
4.2.2.3.2
Titratable acidity (%)
93
4.2.2.3.3
TSS: TA ratio
94
4.2.2.3.4
Ascorbic acid (mg 100g-1)
94
4.2.2.3.5
Total sugars (%)
95
4.2.2.3.6
Reducing sugars (%)
95
4.2.2.3.7
Non-reducing sugars (%)
95
4.2.2.4
Phytochemical Parameters
96
4.2.2.4.1
Total Antioxidants (% Inhibition)
96
4.2.2.4.2
Total phenolic contents (mg GAE 100g-1)
97
4.2.2.5
Fruit Quality Enzyme
97
4.2.2.5.1
Catalase (CAT) (U mg-1 protein)
97
4.2.2.5.2
Peroxidases (POD) (U mg-1 protein)
98
4.2.2.5.3
Superoxide dismutase (SOD) (U mg-1 protein)
99
4.2.2
Discussion
100
4.2.2
Conclusion
102
4.3
Study 3
103
4.3.1
Experiment 1: Dose optimization of salicylic acid (SA) to maintain fruit quality during storage of ‘Kinnow’ mandarin
103
4.3.1.1
Physical and physiological Characteristics
103
4.3.1.1.1
Weight loss (%)
103
4.3.1.1.2
Fruit rot (%)
104
4.3.1.1.3
Peel weight (g)
105
4.3.1.1.4
Juice weight (%)
107
4.3.1.1.5
Peel: pulp ratio
108
4.3.1.2
Bio-chemical parameters
110
4.3.1.2.1
Total soluble solids (ºBrix)
110
4.3.1.2.2
Titratable acidity (%)
111
4.3.1.2.3
TSS: TA ratio
112
4.3.1.2.4
Ascorbic acid contents (mg 100g-1)
113
4.3.1.2.5
Total sugars (%)
114
4.3.1.2.6
Reducing sugars (%)
115
4.3.1.2.7
Non-reducing sugars (%)
116
4.3.1.3
Phytochemical parameters
117
4.3.1.3.1
Total antioxidants (% inhibition)
117
4.3.1.3.2
Total phenolics contents (mg GAE 100g-1)
118
4.3.1.4
Fruit quality enzymes
119
4.3.1.4.1
Catalase (U mg-1 protein)
119
4.3.1.4.2
Peroxidase (U mg-1 protein)
120
4.3.1.4.3
Superoxide dismutase (U mg-1 protein)
121
4.3.1
Discussion
122
4.3.1
Conclusion
126
4.3.2
Experiment 2: Dose optimization of calcium chloride (CaCl2) to maintain fruit quality of ‘Kinnow’ mandarin
127
4.3.2.1
Physical and physiological Characteristics
127
4.3.2.1.1
Weight loss (%)
127
4.3.2.1.2
Fruit rot (%)
128
4.3.2.1.3
Peel weight (g)
129
4.3.2.1.4
Juice weight (%)
130
4.3.2.1.5
Peel: pulp ratio
131
4.3.2.2
Bio-chemical parameters
132
4.3.2.2.1
Total soluble solid (ºBrix)
132
4.3.2.2.2
Titratable acidity (%)
133
4.3.2.2.3
TSS: TA ratio
134
4.3.2.2.4
Total sugars (%)
135
4.3.2.2.5
Reducing sugars (%)
136
4.3.2.2.6
Non-reducing sugars (%)
137
4.3.2.2.7
Ascorbic acid (mg 100g-1)
138
4.3.2.3
Phytochemical parameters
139
4.3.2.3.1
Total antioxidants (% inhibition)
139
4.3.2.3.2
Total phenolic contents (mg GAE 100g-1)
140
4.3.2.4
Fruit quality enzymes
141
4.3.2.4.1
Catalase (U mg-1 protein)
141
4.3.2.4.2
Peroxidase (U mg-1 protein)
143
4.3.2.4.3
Superoxide dismutase (U mg-1 protein)
144
4.3.2
Discussion
147
4.3.2
Conclusion
148
Chapter 5
Summary
150
General Conclusions
150
Future recommendations and directions
150
Literature Cited
152
LIST OF FIGURES
Figure No.
Description
Page No.
3.1
Flow chart for determination of titratable acidity in Kinnow mandarin fruit juice
31
3.2
Flow chart for determination of ascorbic acid contents in Kinnow mandarin fruit juice
32
3.3
Flow chart for determination of reducing sugars and total sugars in Kinnow mandarin fruit juice
33
3.4
Flow chart for extraction of TPC and total antioxidants in juice of Kinnow fruit
34
3.5
Flow chart for determination of total antioxidants in Kinnow mandarin fruit juice
35
3.6
Flow chart for determination of total phenolic contents in Kinnow mandarin fruit juice
36
3.7
Standard curve of gallic acid for determination of TPC in Kinnow mandarin fruit juice
36
3.8
Flow chart for extraction of anti-oxidative enzymes in Kinnow mandarin fruit juice
37
3.9
Flow chart for determination of CAT activity in Kinnow mandarin fruit juice
37
3.10
Flow chart for determination of POD activity in Kinnow mandarin fruit juice
38
3.11
Flow chart for determination of SOD activity in Kinnow mandarin fruit juice
38
4.1.1.1
Effect of foliar application of CaCl2 on preharvest fruit drop of Kinnow mandarin. Vertical bars represent ± S.E of means
40
4.1.1.2
Effect of foliar application of CaCl2 on total number of fruit per tree of Kinnow mandarin. Vertical bars represent ± S.E of means
41
4.1.1.3
Effect of foliar application of CaCl2 on yield of Kinnow mandarin. Vertical bars represent ± S.E of means
42
4.1.1.4
Effect of foliar application of CaCl2 on fruit weight of Kinnow mandarin. Vertical bars represent ± S.E of means
42
4.1.1.5
Effect of foliar application of CaCl2 on peel weight of Kinnow mandarin. Vertical bars represent ± S.E of means
43
4.1.1.6
Effect of foliar application of CaCl2 on pulp weight of Kinnow mandarin. Vertical bars represent ± S.E of means
44
4.1.1.7
Effect of foliar application of CaCl2 on peel: pulp ratio of Kinnow mandarin. Vertical bars represent ± S.E of means
44
4.1.1.8
Effect of foliar application of CaCl2 on juice weight of Kinnow mandarin. Vertical bars represent ± S.E of means.
45
4.1.1.9
Effect of foliar application of CaCl2 on TSS of Kinnow mandarin. Vertical bars represent ± S.E of means
46
4.1.1.10
Effect of foliar application of CaCl2 on titratable acidity of Kinnow mandarin. Vertical bars represent ± S.E of means.
46
4.1.1.11
Effect of foliar application of CaCl2 on TSS: Acid ratio of Kinnow mandarin. Vertical bars represent ± S.E of means
47
4.1.1.12
Effect of foliar application of CaCl2 on ascorbic acid of Kinnow mandarin. Vertical bars represent ± S.E of means
48
4.1.1.13
Effect of foliar application of CaCl2 on total sugars, reducing sugars and non-reducing sugars of Kinnow mandarin. Vertical bars represent ± S.E of means
49
4.1.1.14
Effect of foliar application of CaCl2 on total antioxidants of Kinnow mandarin. Vertical bars represent ± S.E of means
50
4.1.1.15
Effect of foliar application of CaCl2 on total phenolics of Kinnow mandarin. Vertical bars represent ± S.E of means
50
4.1.1.16
Effect of foliar application of CaCl2 on catalase of Kinnow mandarin. Vertical bars represent ± S.E of means
51
4.1.1.17
Effect of foliar application of CaCl2 on peroxidase of Kinnow mandarin. Vertical bars represent ± S.E of means
52
4.1.1.18
Effect of foliar application of CaCl2 on superoxide dismutase of Kinnow mandarin. Vertical bars represent ± S.E of means.
52
4.1.2.1
Effect of foliar application of ZnSO4 on preharvest fruit drop of Kinnow mandarin. Vertical bars represent ± S.E of means.
57
4.1.2.2
Effect of foliar application of ZnSO4 on total number of fruits of Kinnow mandarin. Vertical bars represent ± S.E of means.
58
4.1.2.3
Effect of foliar application of ZnSO4 on yield of Kinnow mandarin. Vertical bars represent ± S.E of means.
58
4.1.2.4
Effect of foliar application of ZnSO4 on fruit weight of Kinnow mandarin. Vertical bars represent ± S.E of means.
59
4.1.2.5
Effect of foliar application of ZnSO4 on peel weight of Kinnow mandarin. Vertical bars represent ± S.E of means.
59
4.1.2.6
Effect of foliar application of ZnSO4 on pulp weight of Kinnow mandarin. Vertical bars represent ± S.E of means.
60
4.1.2.7
Effect of foliar application of ZnSO4 on peel: pulp ratio of Kinnow mandarin. Vertical bars represent ± S.E of means.
61
4.1.2.8
Effect of foliar application of ZnSO4 on juice weight of Kinnow mandarin. Vertical bars represent ± S.E of means.
62
4.1.2.9
Effect of foliar application of ZnSO4 on TSS of Kinnow mandarin. Vertical bars represent ± S.E of means.
63
4.1.2.10
Effect of foliar application of ZnSO4 on titratable acidity of Kinnow mandarin. Vertical bars represent ± S.E of means.
63
4.1.2.11
Effect of foliar application of ZnSO4 on TSS: Acid ratio of Kinnow mandarin. Vertical bars represent ± S.E of means.
63
4.1.2.12
Effect of foliar application of ZnSO4 on ascorbic acid of Kinnow mandarin. Vertical bars represent ± S.E of means.
64
4.1.2.13
Effect of foliar application of ZnSO4 on total sugars, reducing sugars and non-reducing sugars of Kinnow mandarin. Vertical bars represent ± S.E of means
66
4.1.2.14
Effect of foliar application of ZnSO4 on total antioxidants of Kinnow mandarin. Vertical bars represent ± S.E of means
67
4.1.2.15
Effect of foliar application of ZnSO4 on total phenolics of Kinnow mandarin. Vertical bars represent ± S.E of means
68
4.2.1.1
Effect of GA3 on preharvest fruit drop, number of fruits per tree and yield of Kinnow mandarin. Vertical bars represent ± S.E of means
73
4.2.1.2
Effect of GA3 on fruit weight, peel weight and pulp weight of Kinnow mandarin. Vertical bars represent ± S.E of means
75
4.2.1.3
Effect of GA3 on peel: pulp ratio and juice weight of Kinnow mandarin. Vertical bars represent ± S.E of means
76
4.2.1.4
Effect of GA3 on TSS and TA of Kinnow mandarin. Vertical bars represent ± S.E of means
78
4.2.1.5
Effect of GA3 on TSS: TA ratio and ascorbic acid of Kinnow mandarin. Vertical bars represent ± S.E of means
78
4.2.1.6
Effect of GA3 on total sugars, reducing sugars and non-reducing sugars of Kinnow mandarin. Vertical bars represent ± S.E of means
79
4.2.1.7
Effect of GA3 on total antioxidant and total phenolic contents of Kinnow mandarin. Vertical bars represent ± S.E of means
81
4.2.1.8
Effect of GA3 on catalase, peroxidase and superoxide dismutase of Kinnow mandarin. Vertical bars represent ± S.E of means
83
4.2.2.1
Effect of exogenous application of SA on preharvest fruit drop of Kinnow mandarin. Vertical bars represent ± S.E of means
88
4.2.2.2
Effect of exogenous application of SA on total number of fruits per tree of Kinnow mandarin. Vertical bars represent ± S.E of means
89
4.2.2.3
Effect of exogenous application of SA on yield of Kinnow mandarin. Vertical bars represent ± S.E of means.
92
4.2.2.4
Effect of exogenous application of SA on fruit weight per tree of Kinnow mandarin. Vertical bars represent ± S.E of means.
92
4.2.2.5
Effect of exogenous application of SA on juice weight of Kinnow mandarin. Vertical bars represent ± S.E of means.
93
4.2.2.6
Effect of exogenous application of SA on TSS of Kinnow mandarin. Vertical bars represent ± S.E of means.
94
4.2.2.7
Effect of exogenous application of SA on TA of Kinnow mandarin. Vertical bars represent ± S.E of means.
94
4.2.2.8
Effect of exogenous application of SA on TSS: TA ratio of Kinnow mandarin. Vertical bars represent ± S.E of means.
94
4.2.2.9
Effect of exogenous application of SA on ascorbic acid ratio of Kinnow mandarin. Vertical bars represent ± S.E of means.
94
4.2.2.10
Effect of exogenous application of SA on total sugars, non-reducing sugars and reducing sugars of Kinnow mandarin. Vertical bars represent ± S.E of means
95
4.2.2.11
Effect of exogenous application of SA on total antioxidant of Kinnow mandarin. Vertical bars represent ± S.E of means
97
4.2.2.12
Effect of exogenous application of SA on total phenolic contents of Kinnow mandarin. Vertical bars represent ± S.E of means
98
4.2.2.13
Effect of exogenous application of SA on catalase of Kinnow mandarin. Vertical bars represent ± S.E of means
98
4.2.2.14
Effect of exogenous application of SA on peroxidase of Kinnow mandarin. Vertical bars represent ± S.E of means
98
4.2.2.15
Effect of exogenous application of SA on superoxide dismutase of Kinnow mandarin. Vertical bars represent ± S.E of means
99
LIST OF TABLES
Table No.
Description
Page No.
4.1.2.1
Effect of foliar application of ZnSO4 on fruit quality enzymes of Kinnow mandarin.
68
4.2.2.1
Effect of exogenous application of SA on peel weight, pulp weight and peel: pulp ratio of Kinnow mandarin.
91
4.3.1.1
Effects of different SA treatments on weight loss (%) of Kinnow mandarin during cold storage
104
4.3.1.2
Effects of different SA treatments on fruit rot (%) of Kinnow mandarin during cold storage
105
4.3.1.3
Effects of different SA treatments on peel weight (g) of Kinnow mandarin during cold storage
106
4.3.1.4
Effects of different SA treatments on juice weight (%) of Kinnow mandarin during cold storage
107
4.3.1.5
Effects of different SA treatments on peel: pulp ratio of Kinnow mandarin during cold storage
109
4.3.1.6
Effects of different SA treatments on TSS (ºBrix) of Kinnow mandarin during cold storage
110
4.3.1.7
Effects of different SA treatments on TA (%) of Kinnow mandarin during cold storage
11
4.3.1.8
Effects of different SA treatments on TSS: TA ratio of Kinnow mandarin during cold storage
112
4.3.1.9
Effects of different SA treatments on ascorbic acid contents (mg 100 g-1) of Kinnow mandarin during cold storage
113
4.3.1.10
Effects of different SA treatments on total sugars (%) of Kinnow mandarin during cold storage
114
4.3.1.11
Effects of different SA treatments on reducing sugars (%) of Kinnow mandarin during cold storage
115
4.3.1.12
Effects of different SA treatments on non-reducing sugars (%) of Kinnow mandarin during cold storage
116
4.3.1.13
Effects of different SA treatments on total antioxidants (% inhibition) of Kinnow mandarin during cold storage
117
4.3.1.14
Effects of different SA treatments on total phenolics (mg GAE 100 g-1) of Kinnow mandarin during cold storage
118
4.3.1.15
Effects of different SA treatments on CAT (U mg-1 protein) of Kinnow mandarin during cold storage
119
4.3.1.16
Effects of different SA treatments on POD (U mg-1 protein) of Kinnow mandarin during cold storage
120
4.3.1.17
Effects of different SA treatments on SOD (U mg-1 protein) of Kinnow mandarin during cold storage
21
4.3.2.1
Effects of CaCl2 concentration on weight loss (%) of Kinnow mandarin during cold storage
127
4.3.2.2
Effects of CaCl2 concentration on fruit rot (%) of Kinnow mandarin during cold storage
128
4.3.2.3
Effects of CaCl2 concentration on peel weight (g) of Kinnow mandarin during cold storage
129
4.3.2.4
Effects of CaCl2 concentration on juice weight (%) of Kinnow mandarin during cold storage
130
4.3.2.5
Effects of CaCl2 concentration on peel: pulp ratio of Kinnow mandarin during cold storage
131
4.3.2.6
Effects of CaCl2 concentration on TSS (ºBrix) of Kinnow mandarin during cold storage
132
4.3.2.7
Effects of CaCl2 concentration on TA (%) of Kinnow mandarin during cold storage
133
4.3.2.8
Effects of CaCl2 concentration on TSS: TA ratio of Kinnow mandarin during cold storage
134
4.3.2.9
Effects of CaCl2 concentration on total sugars (%) of Kinnow mandarin during cold storage
135
4.3.2.10
Effects of CaCl2 concentration on reducing sugars (%) of Kinnow mandarin during cold storage
137
4.3.2.11
Effects of CaCl2 concentration on non-Reducing sugars (%) of Kinnow mandarin during cold storage
137
4.3.2.12
Effects of CaCl2 concentration on ascorbic acid contents (mg 100 g-1) of Kinnow mandarin during cold storage
138
4.3.2.13
Effects of CaCl2 concentration on total antioxidants (% inhibition) of Kinnow mandarin during cold storage
139
4.3.2.14
Effects of CaCl2 concentration on total phenolic contents (mg GAE 100g-1) of Kinnow mandarin during cold storage
140
4.3.2.15
Effects of CaCl2 concentration on catalase (U mg-1 protein) of Kinnow mandarin during cold storage
141
4.3.2.16
Effects of CaCl2 concentration on peroxidase (U mg-1 protein) of Kinnow mandarin during cold storage
142
4.3.2.17
Effects of CaCl2 concentration on SOD (U mg-1 protein) of Kinnow mandarin during cold storage
143
LIST OF SYMBOLS AND ABBREVIATIONS
Abbr. Full name
≤ Less than or equal to
ºC Degree Celsius
% Percent
∆ Changes of
µL L Microliter (s)
µM Micro molar (s)
AA Acetyl aldehyde
AARI Ayub Agriculture Research Institute
ACC Acetyl-CoA carboxylase
ACO ACC oxidase
ANOVA Analysis of variance
AOX Alternative oxidase
APX Ascorbate peroxidase
CAT Catalase
CI Chilling injury
CRD Completely Randomized Design
CaCalcium
CaCl2 Calcium chloride
Cv Cultivar (s)
DPPH 2, 2 diphenyl-1-picrylhydrazyl
et al et alia
FAO Food and Agriculture Organization of United
Nations
FC Folin- Ciocalteu
G Gram
GAE Gallic acid equvilanet
GOPGovernment of Pakistan
GA3Gibberellic acid
H2O2Hydrogen peroxide
KgKilogram (s)
LLiter (s)
L-1Per liter
LSDLeast significant difference
Mg Milligram (s)
mLMilliliter (s)
mMMillimolar (s)
PProbability
PEPectin esterase
PGPolyglacturanase
pH hydrogen ion in a solution
PHRCPostharvest Research Center
PODPeroxidases
RCBDRandomized complete block design
RH Relative humidity
ROS Reactive oxygen species
SASalicylic acid
S.E.Standard error
SODSuperoxide dismutase
SSCSoluble solids contents
TA Titratable acidity
TPC Total phenolic contents
UK United Kingdom
US$ United States dollar
V Volume
Vit.C Vitamin C
Zn Zinc
ZnSO4 Zinc Sulphate
LIST OF CHEMICALS
Chemicals Company
For Pre and Postharvest application
Zinc sulphateRiedel-deHaen
Calcium chlorideMerck
Gibberellic acid Uni-Chem
Salicylic acidMerck
For Biochemical analysis
2, 6-dichlorophenol indophenolFluka
AcetonMerck
Copper sulphateApplichem
Hydro chloric acid Merck
Lead acetateRiedel-de Haen
Oxalic acidApplichem
PhenolphthaleinMerck
Sodium bicarbonateRiedel-deHaen
Sodium hydroxideMerck
Sodium potassium tartrateRiedel-deHaen
Sulphuric acid Merck
Antioxidative enzymes
Di-potassium hydrogen phosphate Applichem
Ethylene diamine tetra-acetic acid Applichem
Guaiacol Across Organic
Hydrogen peroxideMerck
MethionineMerck
Nitro blue tetrazolium Bio-Basic Inc.
Potassium chloride Applichem
Potassium di-hydrogen phosphate Applichem
Riboflavin Applichem
Triton XMerck
Total Phenolic and total antioxidant contents
2, 2-diphenyl-1-picrylhydrazyl (DPPH) Sigma
Folin- Ciocalteu (FC)Merck
Sodium carbonate (Na2CO3)Riedel-deHaen
Protein Content
2-Mercaptoethanol sigmaMerck
Ethanol 95% Merck
Phosphoric acid 85% (w/v)Riedel-deHaen
Sodium dodecyl sulfateMerck
Note:
Riedel-deHaen Riedel-deHaen, Laborchemikalien GmbH and CO. KG, USA
Chem Alert Chem Alert, Ventnor Avenue, West Perth, Australia
Bio Basic Inc. Bio Basic Inc. Markham, Ontario, Canada
Applichem Applichem, Missouri, USA
Fluka Fluka, Buchs, Switzerland
Across Across organics, New Jersey, USA
Merck Merck Pty, Ltd., Lahore, Pakistan
MP Biomedical MP Biomedicals India Pty. Ltd, India
Sigma Sigma-Aldrich Pty. Ltd., Lahore, Pakistan
ABSTRACT
Citrus is one of the most important fruit crops in Pakistan. Kinnow mandarin is the leading citrus cultivar of Pakistan. The yield is lower as compared to other advanced citrus producing countries. Poor tree health and nutritional deficiencies are the major causes of lower yield. Poor management practices before and after harvesting cause serious problems regarding the yield and quality of Kinnow. Heavy losses can occur due to poor pre and postharvest management. To overcome these problems, different experiments were planned and executed. The study was divided into three subcategories such as study 1, study 2 (preharvest) and study 3 (postharvest). In 1st two studies foliar sprays of calcium chloride, zinc sulphate, gibberellic acid and salicylic acid were applied on the Kinnow trees, four months before fruit harvest to check their effects on preharvest fruit drop and other fruit quality related parameters. In third study, two experiments were conducted to optimize the doses of salicylic acid (2, 3 and 4 mM) and calcium chloride (2, 3 and 4%) as pre-storage treatments to increase the storage life and maintain the fruit quality during cold storage at 5ºC. The results showed that 0.5% calcium chloride was found best to minimize the preharvest fruit drop (16.48%) as compared to control where preharvest fruit drop was 49.70%. Maximum yield (110.03 kg per tree), fruit weight (264.29 g), juice weight (51.53%), TSS (13.13 ºbrix), ascorbic acid contents (43.84 mg100 g-1)), total sugars (16.98%), reducing sugars (6.23%), phenolic contents (341.82 mg GAE100g-1), total antioxidants (91.14% inhibition) were also noted from the fruit of same treatment. Among the zinc sulphate doses 0.6% zinc sulphate exhibited the lowest preharvest fruit drop (10.08%) and maximum yield (120.89 kg) with maximum juice weight (42.23%) and higher TSS (9.50 ºbrix), total sugars (17.37%), reducing sugars (5.99%), ascorbic acid contents (35.46 mg 100g-1), total antioxidants (53.25 %inhibition) and total phenolics (205.33 mg GAE100g-1). Gibberellic acid (30 mgL1) performed best to minimize the preharvest fruit drop (11.82%) and improve the yield up to 1015.77 kg with good eating quality parameters. Salicylic acid of 4mM exhibited best results to reduce the preharvest fruit drop (26.16%) and maximize the yield (195.26 kg), fruit weight (232.55 g), juice weight (50.94%), TSS (13.47 ºbrix), total sugars (14.96%), reducing sugars (5.84%) and ascorbic acid contents (47.66 mg 100g-1). The results of postharvest treatments (study 3) indicated that 3mM salicylic acid was performed best to minimize the weight loss from 15.46 to 8.52% and to reduce the fruit rot from 16.12 to 1.40% with higher values of juice weight (48.16%), ascorbic acid contents (42.19 mg 100 g-1), total phenolic contents (207.10 mg GAE 100 g-1), total antioxidants (64.95 % inhibition) after storage. The antioxidative enzyme such as CAT (22.76 U mg-1protein), POD (0.63 U mg-1protein) and SOD (124.54 U mg-1protein) activity were greater at higher dose treatment (4mM SA) after 90 days storage. Moreover, 4% calcium chloride played a very effective role in controlling the weight loss from 14.59 to 7.39% and reducing the decay percentage from 11.68 to 1.33%, Maximum TSS (9.41 ºbrix), TA (1.66%), ascorbic acid contents (50.95 mg 100g-1), sugars [total sugars (14.90%) and reducing sugars (8.32%)] were also more at same treatment. However, 3% calcium chloride treatment showed best results in juice weight (53.24%) total phenolic (63.17 mg GAE 100 g-1), total antioxidants (218.44 % inhibition), and fruit quality enzymes [(CAT (25.66 U mg-1 protein), POD (0.55 U mg-1 protein) and SOD (128.26 U mg-1 protein). It was concluded that preharvest fruit drop can be minimized with maximum quality related attributes by the foliar spray of 0.5% calcium chloride, 0.6% zinc sulphate, 30 mgL-1 gibberellic acid and 4 mM salicylic acid when applied on Kinnow trees four month before fruit harvest. Moreover, treatments of 3, 4 % calcium chloride and 3 mM salicylic acid before storage is best to maintain the quality related parameters of Kinnow fruit during 90 days storage at 5ºC
i
Chapter-1 INTRODUCTION
Citrus are the most widely cultivated fruit crops and rank first in the world fruits production. Total production of World Citrus industry possess 12,257 thousand tons on an area of 8712 thousand hectares whereas currently in Pakistan different citrus fruits are cultivated on an area of 206,569 hectares with production of 2.36 million tonns in 2016. Currently, leading Citrus producing countries in the world are Brazil, China, United States, Mexico, India and Spain which contribute about 2/3 of worldwide Citrus production (FAOSTAT, 2017).
Citrus fruit are also containing a good quantity of vitamin C, minerals, nutrients, phytochemicals and carbohydrates, which are basically essential for human health. Citrus fruit has been pronounced to inhibit liver, lungs and skin cancers, heart diseases, birth problems and influences to a stable and strong life style (Ghirdharilal, 2000).
Citrus is divided into various categories such as Sweet oranges, Mandarin, Grape fruit, Lemon and Lime which are being cultivated commercially. Citrus fruit is cultivated in all provinces of Pakistan but Punjab produces over 98% of the crop and 70% of it’s share is under Kinnow mandarin due to its large population, suitable growing conditions and sufficient water supply. Pakistan is the 12th biggest producer of citrus in the world (Asi et al., 1989).
The citrus yield in Pakistan is low as compared to other advanced citrus growing countries due to lack of several factors such as inadequate nutritional management, non-availability of disease free planting material, excessive premature fruit drop, abnormal fruit growth, inconsistency in yield, less organic matter in soil, non-availability of better quality water and insects pest and disease attack (Davies and Albrigo, l994; Iglesias et al., 2007). The citrus fruit quality and production can be enhanced through suitable practices and management of proper nutrition in the tree (Lahey et al., 2004; Saleem et al., 2005; Chen and Dekkers, 2006; Modise et al., 2009).
Kinnow is most important exportable commodity between all citrus fruit and a mean of foreign exchange. Kinnow may be stored at 4-5ºC with 85-90% relative humidity for 8-12 weeks without chilling injury. Kinnow mandarin is a delicate in nature because 20-30% postharvest losses happened during the storage due to bacterial and fungal contamination on the fruit, mismanagement of diseases, low quality fruit, unsuitable weather condition, delay in harvesting, lack of proper roads and improper cold storage facilities, surplus supply in the market and other comparable factors are responsible for these losses (Singh et al., 2004). Pakistani soils have unavailability of essential nutrients and cannot maintain the crop productivity (Rafiq, 1996; Ahmed and Rashid, 2003). Citrus plantation facing problem of essential macro and micro nutrients that plants take up from the soil (Ibrahim et al., 2007; Ashraf et al., 2010; Razi et al., 2011). Citrus is very nutrient demanding fruit crop (Wang et al., 2006). The combination of proper plant growth regulators, macro and micro nutrients could enhance yield and quality of citrus plants.
In Pakistan Citrus Plantations are dealing with issue of fruit colour, size, quality and extreme preharvest fruit drop that’s because of the shortages of important hormones and nutrients (Ibrahim et al., 2007). Lack of nutrients disrupts the production of plant growth regulators such as fruit color, size and early fruit dropping. Excessive preharvest fruit drop is also depends on several factors likewise high temperatures, water shortages, insect/pest attack, and wind speed of the area (Ibrahim et al., 2007; Razi et al., 2011; Ashraf et al., 2012).
Different approaches have been introduced to minimize pre and postharvest losses in citrus fruits such as application of nutrients (Zn and CaCl2) and growth regulators (GA3 and SA) can inhibit the excessive preharvest fruit drop, enhance the yield and quality (Doberman and Fairhurst, 2000; Rodriguez et al., 2005; Saleem et al., 2005) and prolong storage life of citrus fruits (Bhardwaj et al., 2010). Among the different essential mineral nutrients, zinc (Zn) is an essential micronutrient and play important role in enzymatic systems required for synthesis of protein and maturity rate in plants (Swietlik, 1999 and 2002). It is essential for tryptophan synthesis, which is a precursor of indole-3 acetic acid. It also perform significant role in metabolism of starch (Alloway, 2008). It is well recognized that Zn acts as a co-factor of different enzymes and influences various biological function within the plants such as photosynthesis, nucleic acids metabolism, proteins and carbohydrates biosynthesis (Marschner, 1995). However, foliar application of ZnSO4 can enhance the citrus fruit yield, quality and minimize the preharvest fruit drop (Rodriguez et al., 2005; Ashraf et al., 2012).
Calcium is one of the fundamental components in plant nourishment. It plays an essential role in enhancing fruit yield and quality (EL-Shobaky and Mohamed, 2000). Both pre and postharvest CaCl2 application have been utilized to delay maturing or aging, to decrease postharvest rot and prevent disease attack in horticultural crops (Conway et al, 1984; Poovaiah, 1986).
Calcium chloride has been recognized to the maintenance of membrane system and the development of Ca-pectates within the cell wall which improve the rigidity of the central lamella and cell wall of fruit (Grant et al., 1973; Jackman and Stanley, 1995). It inhibits the cell wall degradation (Buescher and Hobson, 1982) and increases the skin strength (Mignani et al., 1995). Calcium chloride plays important role in maintaining the postharvest quality of citrus fruit with no detrimental effect on consumer liking (Poovaiah et al., 1988; Lester and Grusak, 1999; Hossain et al., 2005; Abdi et al., 2006; Misra and Gupta, 2006; Singh et al., 2006; Hosseini and Thengane, 2007; Naeem et al., 2009) and stabilizing the cell membrane. Pre and postharvest CaCl2 application can delay the ripening and senescence process within the plants. Dipping treatments of CaCl2 enhance the Ca contents within strawberry plants and prolong shelf life of fruit as compared to foliar spray of CaCl2 without causing chilling injury (Picchioni et al., 1998). Foliar applications of CaCl2 maintain the cell wall of the plants and prevent it from cell wall degrading enzymes (White and Broadley, 2003).
Exogenously applied growth regulator (PGR) such as gibberellic acid (GA3) and salicylic acid (SA) when used in suitable amount can provide significant advantages to citrus cultivators, these chemicals have recognized as effective role to improve fruit quality and maintain the fruit colour, increase in size and delay in senescence (Coggins Jr and Hield, 1968). Exogenous applications of GA3 enlarge the fruit development in citrus fruit and endogenous gibberellin status within the fruit also involved in the initiation of fruit development (Talon et al., 1990). Different doses of GA3 (5, 50, 100 and 500 mg L-1) to young fruit at fruit setting stage have been stated to enhance the fruit weight, peel thickness, juice content with increased flavor of grapefruit (Berhow, 2000). Foliar application of GA3 and CaCl2 on ‘Baldy’ mandarin trees increases fruit weight, juice contents, total soluble solids, acidity, TSS/ acid ratio and vitamin C contents in juice were observed to be affected after mid-November spray (El-Hammady et al., 2000).
Salicylic acid (SA) is simple phenolic compound which usually produced in large quantity within the plants (Abdelal, 1983). SA play an essential role to enhance pathogenic resistance in plants, reduce postharvest decay, inhibit ethylene biosynthesis, reduce transpiration rate and delay the fruit senescence in horticultural fruits and vegetables crops (Hayat, 2010). Many plants physiological and biochemical processes are also stimulated by SA application (Arberg, 1981). Application of SA also increased the antioxidant activity of the plants to stimulate the plants growth in oxidative stress (Senaratna et al., 2000). Exogenously applied SA enhanced the endogenous level of polyamines in ‘Ponkan’ mandarin and lower the antioxidants degradation in ‘Cara Cara’ navel orange fruit (Zheng and Zhang, 2004; Huang et al., 2008).
Little information's are available in literature but not a complete answer regarding the effects of pre and post harvest application of nutrients and growth regulator to reduce the fruit drop, improve the fruit quality and shelf life of Kinnow especially relating to antioxidant and enzymatic activity.
Pre and postharvest treatments of fungicides is extremely important in Pakistan but unfortunately, almost no consideration is paid to use of non-chemical techniques which can avoid from the harmful effects on human health. Keeping in view above review, the present study was conducted to pursue the following objectives:
1- To reduce the pre harvest fruit drop and improve the fruit quality by foliar application of nutrients (CaCl2 and ZnSO4) and growth hormons (GA3 and SA).
2- To extend shelf and storage life of ‘Kinnow’ mandarin by dipping application of SA and CaCl2.
Chapter-2 REVIEW OF LITERATURE
2.1 Introduction
‘Kinnow’ was developed as a result of cross between ‘King’ (Citrus nobilis) and ‘Willow-leaf’ (Citrus deliciosa). Both of parents belong to Indo-China regions. H. B. Frost, a citrus breeder at the Citrus Research Center, University of California, USA, evolved ‘Kinnow’ in 1915. It was named mandarin and released as a marketable selection in 1935 (Webber and Batchler, 1948). The name Kinnow was developed by joining the first and last digit of two parents i.e. ‘KIN’ originated from King and ‘OW’ from Willow combined by the word ‘N’ in the middle to form the complete word ‘Kinnow’(Sharif and Burhan, 2005). It was presented from California to the Punjab Agriculture and Research Institute Lyallpur, which is now called as Agriculture University, Faisalabad in 1943-44 (Malik, 1992). Pakistan weather has been demonstrated well for its better quality with enhanced value of fruit (Saunt, 1990). The province Punjab is the foremost region delivering better quality fruit with large production (GOP, 2010).
2.2 Pre and postharvest problem in citrus fruit
Losses in citrus are affected by pre and postharvest factors. Preharvest factors comprise climatic conditions particularly temperature, relative humidity, rain, tree health, management practices, fruit drop and stage of fruit harvest. Postharvest applications for example harvesting, treatments, handling, packaging, and marketing significantly affect fruit losses. Losses happen at different phases of management, from collecting until the point that fruit reaches consumers. Typically higher losses are experienced in mechanically harvesting citrus fruits (Reckham and Grierson, 1971).
2.3 Pre and postharvest effect of calcium chloride on quality of citrus fruit
2.3.1 Role of calcium chloride in fruit physiology
The role of Ca2+ in the physiology of plant tissue is well-known. Calcium enhances inflexibility of cell walls and hinders the enzymes for example polygalcturonase from reaching their active sites, thus delaying tissue softening and ripening (John, 1987). Postharvest application of CaCl2 maintain the cell turgor pressure, firmness of tissue, membrane integrity and delays membrane lipid catabolism therefore increase shelf life of produces (Chaplin et al., 1980).
Calcium (Ca2+) has been broadly considered as both an important component and play essential function in retaining quality of horticultural crops such as fruits and vegetables (Bangarth, 1979; Kirkby and Pilbeam, 1984). Calcium plays functional role as an intracellular ‘secondary messenger ‘in cell membranes and plant cell wall (Zocchi and Mignani, 1995) in addition to the relationships among pectic substances inside the cell wall. Ca2+ions build the attachment of cell walls (Demarty et al., 1984). It is also involved in delay the rate senescence and fruit ripening (Ferguson, 1984).
2.3.2 Role of calcium chloride to maintain fruit firmness
Calcium is also an important plant nutrient that has a major part in cell functions, such as decreasing softening and senescence of fruits (Barker and Pilbeam, 2015). It is additionally viewed as the most vital mineral component defining quality of fruit (El-Badawy, 2012). Calcium is involved with preserving the textural quality of products because of its role to the linkages between pectic substances inside the cell wall. Calcium ions form cross-links among free carboxyl groups of the pectin chains, resulting in firming of the cell wall (Garcia et al., 1996). Calcium developments to cell wall and central lamella polygalacturonic acid, enhancing structural integrity (Van-Buren, 1979).
Pre and post-harvest CaCl2 applications reduce the postharvest decay and control the physiological disorders and extend storage life of Kinnow mandarin (Poovaiah et al., 1988). Foliar application CaCl2 enhance calcium substances within fruit cell wall was very effective in delaying senescence, ensuing in firmer and good eating quality of fruit (Serrano, 2004). CaCl2 is similarly used to prolong the shelf-life of harvest produces (Martin-Diana et al., 2007). The use of CaCl2 retains the inflexibility of cell walls, delays membrane lipid catabolism and senescence (Ferguson, 1984). Therefore, tissues remain strong because of the hindrance of several enzymes such as polygalacuturonase which is engaged with softening thus ripening is delay and shelf-life prolonged (Pila et al., 2010; Mahajan et al., 2011). Numerous examinations have been showed on the postharvest treatment of CaCl2 to increase the postharvest life of crops. These have demonstrated that CaCl2 decrases physiological weight reduction and delays softening of mangoes (Mootoo, 1991) and decay of apples (Nayital, 1990) during storage.
The calcium movement in trees is slow and tree root take-up calcium from fertilized soils in this way tree is ineffective in improving the endogenous level of calcium contents in fruits. Ghani et al. (2011) stated that the direct dipping application of CaCl2 increase the Ca contents on leaves and fruits. Postharvest application of CaCl2 may have also a potential use as an integrated insect pest and disease management (Biggs et al., 2000).
2.3.3 Postharvest dipping treatments with calcium chloride
Dipping CaCl2 treatments support the spreading of the solution on the exterior surface of the Kinnow mandarin fruit. This technique has an additional advantage it is because they released enzymes and substrates from the damaged cells. By using dipping treatment oxidation reduction reactions prevents the browning and off-flavors (Soliva-Fortuny and Martin-Belloso, 2003). Different factors (temperature, pH, dipping time and concentration) can influence product quality. Dipping time could be different for different fruit crops it is because different scientist reports 1 to 15 min dipping. Luna-Guzman et al. (1999) stated that dipping time periods 5 min for soaking of melon. Martin-Diana et al. (2005a) reported that treated carrots and lettuce for 1-5 min. Manganaris et al. (2007) used a time interval of 5 min for soaking of peach fruit. Long time periods 15 min for dipping application were used by Suutarinen et al. (1998) on strawberry fruit.
2.3.4 Role of calcium to improve yield and fruit quality
Calcium is one of the fundamental components in plant nourishment. It play an essential role in enhancing fruit yield and quality (EL-Shobaky and Mohamed, 2000). Postharvest CaCl2 application involved to reduce the weight loss of fruit during storage due to lower loss of protein, phospholipids and decreased ion leakage in treated fruit such as plum. CaCl2 treatment was powerful to retain the membrane functionality, integrity maintenance (Lester and Grusak., 1999) and the development of Ca-pectates within the cell wall which increase the rigidity of the central lamella and fruit cell wall (Grant et al., 1973; Jackman and Stanley, 1995). It inhibits the cell wall degradation (Buescher and Hobson, 1982) and increases the skin strength (Mignani et al., 1995).
Pre and postharvest CaCl2 applications have been utilized to delay maturing or aging, to decrease postharvest rot and prevent the development of numerous physiological disorders in fruits and vegetables (Conway et al., 1984; Poovaiah, 1986). Exogenous application of CaCl2 improved the yield and quality of mango due to the decrease of abscission layer and maintains the central lamella cells and increase fruit firmness (Kumar et al., 2006). Treatment with CaCl2 and Ca (NO3)2 @ 0.6-2.0% delayed ripening after harvest, decreased weight loss and reduced rate of respiration (Bender, 1998). Fruits storability was enhanced after CaCl2 application during storage (Wahdan et al., 2011). Gill et al. (2005) reported that pre and postharvest CaCl2 application affect the quality and storage life of fruits during cold storage.
CaCl2 treated fruit decrease TSS were possibly due to reduction in metabolic process, respiration rate, and slow conversion from starches to sugars; hence delay the ripening method (Rohani et al., 1997). The sugar contents continuously increase with increase storage period and that this increase was delayed after CaCl2 application (Cheour et al., 1991).
TA of the fruit is associated to the application of organic acids in the fruit. Application with CaCl2 inhibits the breakdown of organic acids during respiration process (Ibrahim, 2005). Postharvest CaCl2 treatment extended the storage life of strawberry fruit by delay conversion of sugars, reduction in organic acids and rise of color saturation index (Cheour et al., 1991). Fruits treated with CaCl2 retaining the acidity may be due to decrease in metabolic changes of organic acid into carbon dioxide and water (Ibrahim, 2005).
Andrea et al. (1999) who reported that the postharvest treatment of CaCl2 lower the pH in strawberry fruits during cold storage. The variations of pH may be because of the changes in TA or storage temperature. The decrease of acidity due to improved activity of citric acid glyoxylase throughout ripening process or transformation into sugars and increased in metabolic activities during storage (Lam et al., 1987).
2.3.5 Pre and postharvest application of calcium chloride in disease management of different fruit crops
Poovaiah et al. (1988) observed that pre and postharvest CaCl2 application reduced the postharvest deterioration in fruits and vegetables and delay the aging or maturation process to prevent the growth of numerous` physiological disorders. Postharvest application of CaCl2 improved tissue resistance to bacterial and fungal attack by maintaining the cellular walls, in this way CaCl2 provide more resistance to destructive enzymes formed by fungi that is also involved to reduce the rate of respiration and ethylene production in fruit.
Dipping application of CaCl2 reduced decay (Hernandez-Munoz et al., 2006). It also prohibited postharvest disorders and decreased total soluble solids during storage (Garcia et al., 1996). Dipping in CaCl2 solution did not influence titratable acidity (Manganaris et al., 2007).
Due to deficiency of calcium a wide range of physiological disorders that occur in fruits and vegetables are associated with cell death in tissues. The main cause of cell death is loss of membrane integrity with subsequent damage of cell compartmentalization (Christiansen and Foy, 1979; Poovaiah, 1979). Loss of quality due to lack of calcium in cell walls might be associated to structural failure of tissues. During ripening there are significant changes in the pectin-rich central lamella portion of cell wall where calcium ions have a part in connecting nearby acidic pectin polymers (Seymour et al., 1993). Fruit treated with calcium chloride enhanced resistance to fungal attack in strawberry was related to maintence of cell wall and center lamella structure (Lara et al., 2004).
CaCl2 treatments have been used as firming and antimicrobial agent in the fruit and vegetables production. Sams et al. (1993) and Chardonnet et al. (2003) stated that CaCl2 effect on fruit decay and firmness after the harvest of entire apples. Saftner et al. (2003) work was also focused on the firming result of CaCl2 application on fresh-cut honeydew. Luna-Guzman and Barrett (2000) reported that when dipping solution of CaCl2 used in fresh-cut cantaloupe increase the fruit firmness, decrease bacterial load and respiration rate. Other scientiest used CaCl2 as firming agent (Morris et al., 1985; Main et al., 1986; Rosen and Kader, 1989; Garcia et al., 1996; Suutarinen et al., 1998) in strawberries. Wills and Mahendra (1989) studied the influence of CaCl2 on peaches fruit quality.Treatment of strawberries fruit with CaCl2 solution (Conway and Sams, 1984). The application of CaCl2 in other fruits and vegetables were considered an important improvement in the quality of the produce such as grapefruit (Baker, 1993), tomatoes (Floros et al., 1992) and hot peppers (Mohammed et al., 1991).
The postharvest treatment with CaCl2 can help to increase the storage life of fruits and vegetables by preventing the process of browning. Tissue browning has been detected in fruits after various examinations such as in pineapple (Hewajulige et al., 2003) and peaches fruits (Manganaris et al., 2007). Saftner et al. (2003) found that CaCl2 applications prohibited color variations and increase of flesh translucency in honeydew.
Calcium is not leachable nutrients in the soil (Cheung, 1990). Various soils comprise large amount of insoluble calcium such as CaCl2 and CaCO3 however produces grown in these soils will regularly show a calcium deficiency symptoms (Boyonton et al., 2006). Calcium must be provided in the xylem sap (Banath et al., 1966). Large amount of different cations for example magnesium, aluminum, iron, ammonium and particularly potassium lessen the calcium take up in few crops because of their antagonistic influence for their assimilation (Kulkarni et al., 2010).
2.4 Salicylic Acid (SA)
2.4.1 Introduction
Salicylic acid (SA) is an abundant plant phenolic compound which controls various processes within plants (Raskin, 1992). Salicylates are a key element in the signal transduction pathways of plants performs a significant role in disease resistance (Park et al., 2007). SA is similarly associated with local and systemic acquired resistance to pathogens (Meena et al., 2001). It is recognized that SA as a plant growth hormones can involved in disease resistance of a little developing plants or separate plant organs (Qin et al., 2003). When defense reactions of the plants are stimulated at the place of contamination (LAR), a systemic defense response is frequently activated in distal plant parts to secure the uncontaminated tissues against following attack by the pathogen.
SA acts as a signal molecule that play essential role in plant defense system. A naturally happening defense system of plant is triggered at the point when a pathogen attack on plant and this system induce systemic acquired resistance (SAR) in uncontaminated tissues to restrict disease infection (Tsuda et al., 2008; Aman et al., 2013). Exogenously applied SA improved the endogenous level of SA in plants. The pathogenesis related genes (PR-genes) were also stimulated at positions of pathogen attack and inducing disease infection or pathogenic resistance in plant (Van Loon et al., 2006). This SAR system is activated a specific set of pathogen related PR-genes, several of the genes which encode for antimicrobial proteins activity (Durrant and Dong, 2004; Van Loon et al., 2006).
2.4.2 SA prevents oxidative stress, diseases and reduces chilling injury during storage
The defense system of the plant framework against oxidative stress comprises of two parts; The first part of defense is named as ROS avoidance genes consist of alternative oxidase (AOX) and the second part is named as ROS scavenging genes comprises of CAT, SOD, thioredoxin system, the ascorbate cycle and the glutathione peroxidase system (Buchanan et al., 2000).
SA has been stated to induce protection against various abiotic stresses, contaminations and pathogen occurrence (Hayat et al., 2010). SA is basic phenolic compound which usually supply in large quantity by the plants (Abdelal, 1983). Nearly all physiological and biochemical actions of plants are controlled after pre and postharvest SA treatments (Arberg, 1981). SA enhanced the antioxidant activities of plants to prevent the growth of plants in oxidative stress condition (Senaratna et al., 2000). Foliar application of SA improves the endogenous polyamines in ‘Ponkan’ mandarin and decrease the degradation of antioxidants in ‘Cara Cara’ navel orange fruit (Zheng and Zhang, 2004; Huang et al., 2008). SA application reduces the rate of respiration and ethylene production in various fruit. Zhang et al. (2003) reported that kiwifruit softening was delayed after acetylsalicylic acid treatments.
Chilling injury (CI) is a critical disorder which occurs at low and non-freezing temperatures. It is specifically identified with time of exposure and storage temperature (Henriod et al., 2005). The SA presence as bioactive compounds is identified as nontoxic for human health (Hooper and Cassidy, 2006). It is also reported that foliar treatment of SA decreases chilling injury in pomegranates and peaches fruit (Wang et al., 2006; Sayyari et al., 2009).
Recently, some other researcher worked on the postharvest treatment of SA on different fruit crops and reported their results that postharvest application of SA could be applied to decrease chilling injury and decay symptoms in fruit during storage (Wang et al., 2006 and Sayyari et al., 2009). Both pre and post harvest SA application have been effective in fruit quality preservation and extend shelf life of strawberry fruit during storage (Babalare et al., 2007). Exogenous SA application has increased defense against pathogens in pear fruit (Jiankang et al., 2006) and in cherry fruit reduced the disease progress (Yao and Tian, 2005).
SA use at safe level to susceptible plants could improve their protection against pathogens attack (Murphy et al., 2000). Moreover, exogenously applied SA has been establish to increase the adequacy of the biocontrol of yeast in pear fruit and inhibits the maturation of fruit (Wang et al., 2006). SA influence on fruit ripening, softening and senescence due to fluctuations in some quality characteristics for example fruit softening, rise in sugar substances and reduction in titratable acidity, color changes and production of aroma (Nemeth et al., 2002).
It is also well recognized that SA perform significant role against diseases (Singh, 1978; Rainsford, 1984). Mycorrhizal fungi increase stress tolerance of orange (Zou et al., 2011). Preharvest spray of acetyl salicylic acid (100 mg L-1) and phosphorus acid (100 mg L-1) is effective to control the phytophthora root-rot disease of citrus (Walker, 1988). SA application destroy the postharvest mango diseases (Zainuri et al., 2001), pear (Cao et al., 2006) and sweet cherry (Chan and Tian, 2008).
2.4.3 Role of salicylic acid in plant growth and development
Exogenously applied SA considerably improved overall growth and development of the plant such as fresh and dry weights of root and shoot, shoot size, leaf area, (Amborabe et al., 2002; Khodary, 2004; Eraslan et al., 2007; Karlidag et al., 2009b; Niakan et al., 2010). SA also involve to enhance the flowering and fruit setting (MartinMex et al., 2005a, 2005b) in various plants. SA doses also increase the fruit weight, number of fruit per tree and fruit yield (Fariduddin et al., 2003; Larque-Saavedra and Martin-Mex, 2007). It enhances the biochemical quality parameters such as total soluble solids, fruit firmness and vitamin C contents but did not influence on the titratible acidity in strawberry fruit (Karlidag et al., 2009a; Shafiee et al., 2010).
SA is enormously extended in plant domain (Raskin et al., 1990) and incorporated into plant hormones (Raskin, 1992). It is assumed to have different regulating roles within plant metabolism (Popova et al., 1997) and belongs to plant phenolics group. Phenolic compounds are well recognized for utilizing their influence on physiological and biochemical methods such as enzymatic activities, membrane permeability, flowering, heat production, photosynthesis, ion uptake, plant growth and development. SA being a usual compound also perform role in plant growth regulation (Arberg, 1981).
Exogenous treatment of SA inhibits the ripening and softening of kiwifruit (Zhang et al., 2003) and banana fruit (Srivastava and Dwivedi, 2000). SA application decrease lipid peroxidation of navel orange (Huang et al., 2008) and enhance protection against storage diseases of sweet cherry (Qin et al., 2003). Application of SA and methyl salicylate (MeSA) enhance protection to chilling injury symptom in horticultural crops such as mango (Ding et al., 2007), peach (Wang et al., 2006; Cao et al., 2010) pineapple (Lu et al., 2010), loquat (Cai et al., 2006), pomegranate (Sayyari et al., 2009) and tomato (Ding et al., 2001). Both pre and postharvest SA application (Yao and Tian, 2005) decrease deterioration in sweet cherry through activation of the antioxidant enzymes (Xu and Tian, 2008) and defense resistance system (Chan and Tian, 2006).
2.4.4 Role of salicylic acid enhancing the fruit quality parameter
SA has been described to increase the fruit quality by decreased the respiration rate in many fruits. SA as an indication that activates the stimulation of cyanide resistance to respiration in plant system by influencing the AOX enzyme activity (Raskin et al., 1989). In horticultural crops effect of SA on AOX enzyme movement leading to reduce in the dangerous impacts of oxidative stresses such as chilling injury, reduced fruit ripening and rate of senescence, inhibits fermentation and retains low respiration rates. Respiration rate also dependent on ethylene production. By increasing the ethylene production may leads to rises in respiration rate and subsequently increases the senescence rate. Postharvest SA application reduced the rate of respiration due to its adverse effects on 1- aminocyclopropane-1-carboxylic acid (ACC), Acyl-COA oxidase (ACO), polygalacturonase (PG), polygalacturonase (PG), pectin methyl esterase (PME), cellulose and antioxidative enzymes leading to decline in ethylene.
SA is a plant growth hormone preventing biosynthesis of ethylene and the rate of senescence (Ozeker, 2005). SA has been inhibiting the transformation of ACC enzyme into ethylene (Leslie and Romani, 1988) by suppressing ACC oxidase enzyme activity (Fan et al., 1996). SA is also involved in local and systemic acquired resistance to pathogens (Yalpani et al., 1994).
SA may involve to lessening respiration rate and reduction in weight loss by closing stomata (Zheng and Zhang, 2004). Postharvest dipping treatment of SA also reduce the total soluble solids (TSS) value in comparison to untreated fruit which demonstrating that SA inhibits the fruit softening and starch degradation (Yiwei et al., 2008). The loss of the firmness during storage due to cell wall carbohydrates metabolism which has been related with increase susceptibility to infection by fungal pathogens (Conway et al., 1987). The treated fruits with SA decrease the fungal decay in apple fruit (Yiwei et al., 2008).
Srivastava and Dwivedi (2000) reported that application of SA has been found to inhibit banana fruit ripening. Treated fruit with SA decrease the rate of fruit softening, pulp: peel ratio, reducing sugar contents, invertase activities and respiration rate as compared to the untreated fruit. SA application reduced the cell wall degrading enzymes such as polygalacturonase, cellulose and xylanase. SA trestments reduced the activity of antioxidative enzyme such as CAT, POD and SOD during ripening of banana fruit.
Elwan and El-Hamahmy (2009) stated that SA application (10-6M) decreased the peroxidase enzyme activity and improved invertase activities in paper leaves. SA concentration improved superoxide free radical and lipoxygenase (LOX) activity in kiwifruit. Hence, fruit ripening and senescence inhibited due to delayed in ethylene production. Exogenously applied SA on kiwifruits inhibits the process of softening, retained vitamin C and firmness during five months cold storage (Zhang et al., 2003).
TSS and sugars contents may increase during fruit maturation due to the activity of sucrose-phosphate synthase (SPS), an important enzyme in sucrose biosynthesis (Hubbard et al., 1991). Both ripening and the ethylene process is stimulated by this enzyme during storage (Langenkamper et al., 1998). A decrease in sucrose synthase activity due to an increase in sucrose-phosphate synthase and invertase activities have been described during ripening of some fruits (Cordenunsi and Lajolo, 1995). Application of SA (32 ml L -1) retained a lower value of TSS contents in kiwifruits than the untreated fruit during cold storage (Aghdam et al., 2009). SA decreased ethylene production may results to reduced SPS enzyme activity leading to reduce in sucrose synthesis.
2.5 Zinc sulphate
Amongst the diverse important mineral nutrients, zinc (Zn) is a significant micronutrient play important role in enzymatic systems essential for protein synthesis, seed production and maturity rate in plants (Swietlik, 1999, 2002). It is alos involved in synthesis of tryptophan, which is a precursor of indole acetic acid (IAA). It also performs a key part in plant metabolism of starch (Alloway, 2008). Zinc also play role in the plants nitrogen metabolism. It is identified that Zn acts as a co-factor of numerous enzymes and influence several biological developments for example nucleic acids metabolism, photosynthesis, carbohydrates and protein biosynthesis (Marschner, 1995).
2.5.1 Causes and management strategies for fruit drop
In Pakistan, Kinnow continue its unique taste and quality when ideally grown under natural environmental conditions. In developing countries like Pakistan Citrus plantation are facing problem of fruit colour, poor quality, small size fruit and extreme preharvest fruit drop due to deficits of necessary nutrients (Ibrahim et al., 2007). The deficiency of nutrients disrupts the production of plant growth hormones. The factors which contributes the excessive premature fruit dropping in fruit crops such as high temperatures and inadequate water supply, wind velocity of the area, insect-pest and disease attack (Razi et al., 2011; Ashraf et al., 2012). Citrus fruit trees produce abundant flowers which change into fruits. The above stated factors cause of preharvest fruit drop and treatment of plant growth regulators or nutrients is mentioned to minimize preharvest fruit drop (Modise et al., 2009; Ashraf et al., 2010; 2012). Fruit drop was noted at the time of anthesis which continuous up to the harvesting period (Modise et al., 2009). The early fruit drop is due to weak abscission layer of fruit after anthesis. Abscission level is formed at the stem zone causing in fruit drop due to imbalance of growth regulators such as auxins, cytokinins and gibberellins (Lahey et al., 2004; Chen and Dekkers, 2006; Balal et al., 2011). At an early stage the fruit size is very small, the fruit drop is negligible. However, fruit drop is very severe when size of the fruit is medium and entire area underneath citrus trees is enclosed with fruit drop (Saleem et al., 2005). Exogenous application of plant growth regulators is very effective in decreasing the extreme premature fruit drop (Lahey et al., 2004; Saleem et al., 2005; Chen and Dekkers, 2006; Modise et al., 2009).
Plant growth hormones like SA and 2,4-dichlorophenoxyacetic acid (2,4-D), naphthalene acetic acid (NAA) and gibberellic acid (GA3) (Michael et al., 1999) have been reported to play essential role in inhibiting the citrus fruit drop (Ashraf et al., 2012). Also, micronutrients deficiency (Zn, Cu, Fe and Mn) in the soils of citrus plantations also influence the fruit quality, fruit yield and fruit drop (Ibrahim et al., 2007; Ashraf et al., 2012).
2.5.2 Effect of zinc sulphate on yield and quality of fruit
Zn is one of the micronutrient essential for regular plant growth (Hafez and El- Metwally, 2007). Extreme inadequacy of Zn nutrient was observed in the citrus orchard of Punjab, Pakistan (Rehman et al., 1999). However, preharvest application of ZnSO4 may enhance the yield, quality of citrus fruit and inhibit the prharvest fruit drop (Rodriguez et al., 2005; Ashraf et al., 2012). The foliar spray of both macro- and micro-nutrients and growth hormones increases the citrus fruit yield and quality and can control the preharvest fruit drop (Doberman and Fairhurst, 2000).
Shawky et al. (1993) indicated that Zn spray may produce a physiological influence which directed to increase the fruit number for every tree due to increase in fruit set percentage. Foliar spray of ZnSO4 before harvesting on citrus trees could be ascribed to enhance the endogenous level of auxins which improved the fruit setting and prevent the fruit drop. The Balady mandarin trees was attained maximum yield after Zn application (250 mgL-1) due to increases in fruit weight and fruit number per tree (El-Baz, 2003). The increase in fruit set percentage, fruit retention, reduced fruit drop and increased the fruit yield, physical and chemical characteristics of fruit after foliar application of 0.6% ZnSO4 only or with GA3 (20 mgL-1 ) (Eman et al., 2007).
The ZnSO4 application increase in weight and diameter of fruit can be essential constituent for fruit growth and development which have been affected by tryptophan (Sahota and Arora, 1981). The fruit quality and quantity can be enhance after foliar ZnSO4 spray on trees might be due to its influence on improving formation and translocation of carbohydrates and carbohydrate related enzymes (Yogeratnam and Greenham, 1982).
The exogenous application of ZnSO4 (0.6%) increase the fruit weight, size and peel thickness of ‘Kinnow’ mandarin because of the role of Zinc in the synthesis of tryptophan which is a precursor for the synthesis of indoleacetic acid (IAA) (Cakmak et al., 1989) which regulate the fruit growth and development. Therefore, Zn level increase in tree leaves, the trees starts producing more tryptophan so the fruit growth enhanced. Preharvest treatment of ZnSO4 improved the fruit yield by rise in fruit size and weight in sweet orange (Sahota and Arora, 1981). Eman et al. (2007) also stated that application of ZnSO4 (0.4%) expended the peel thickness in ‘Washington Navel’ oranges.
Citrus trees production relies upon numerous biotic (cultivar, rootstock, insect pest and disease management) and abiotic factors (soil, nutrition, environment, location, and irrigation management system) (Davies and Albrigo, l994; Iglesias et al., 2007). The sufficient supply of micronutrients is most essential to produce better quality fruit (Ioannis et al., 2004; Babu and Yadav, 2005). There is a remarkable effort to increase citrus trees growth, production and good quality via suitable cultural practices and retaining of suitable nutrients level. Irregular fruit growth, variation in yield, vulnerability to diseases and lower fruit quality due to nutritional disorders. Properly supply of mineral nutrients to fruit trees grow more healthy, yield more crop, increase disease resistance and are more tolerant to stresses (Ioannis et al., 2004).
2.5.3 Benefits of foliar applied Zn sulphate than soil application
In developing countries like Pakistan, the Zn deficiency is more common in alkaline and calcareous soils after that of nitrogen (N) and phosphorus (P), where approximately 70% of cultivated soils are Zn deficit (Alloway, 2008). The zinc deficiency may be adjusted by soil or foliar application. When zinc applied in soil is a lesser amount available to plants due to its lower movement and high fixation in soil. Therefore, foliar treatment of ZnSO4 appears to be an effective method. Under extreme Zn deficiency, the foliar applied ZnSO4 has been reported to increase its level in oranges (Boaretto et al., 2002). The positive influence of ZnSO4 (0.6%) sprays on fruit drop, fruit retention, nutritional position, yield and fruit quality have been detected in sweet orange (Dawood et al., 2001; Eman et al., 2007) and sweet lime (Anora and Yamdagni, 1986). Soil applications of zinc are not effective since the fruit crops roots inhibit deep soil layers and zinc does not simply move within the soil. Hence, a foliar spray of Zn is more effective than soil application (Swietlik, 2002).
2.5.4 Effects on TSS, Sugars and ascorbic acid contents of fruit
The foliar treatment of ZnSO4 (0.8%) on ‘Khasi’ mandarin trees has been described to higher juice weight percentage (Babu and Yadav, 2005). ZnSO4 (0.2%) application increase SSC and TA contents of the fruit can be recognized to their influences on various enzymes which are involved in the development of sugars, acids and proteins (Srivastava and Gupta, 1996). The SSC and TA contents can be improved with the preharvest spray of ZnSO4 (0.2%) in ‘Balady’ mandarin (Dawood et al., 2001).
Sahota and Arora (1981) also investigated that SSC: TA ratio was not considerably influenced by ZnSO4 spray both alone or in combination with N in ‘Hamlin’ sweet orange. The zinc perform an essential role in the auxin synthesis and higher production of auxins has been stated to increase the vitamin C contents in ‘Kinnow’ mandarin as claimed by Nawaz et al. (2008). Correspondingly, exogenously applied ZnSO4 (0.6%) has been found to enhance the vitamin C contents in Navel’ orange (Nakhlla, 1998) and ‘Balady’ mandarin (El- Menshawi et al., 1997).
Though, the foliar application of ZnSO4 (0.2%) was decreased reducing sugars contents in compare to the untreated treatment. Total sugar level increased in treatments having Zn can be ascribed to its influence on the actions of aldolase enzyme which is involved in the development of sugars (Alloway, 2008). Use of foliar application of ZnSO4 (0.2%) was enhanced the total sugars percentage of ‘Khasi’ mandarin fruit (Babu and Yadav, 2005).
2.5.5 Deficiency symptom of zinc
Zinc deficient leaves may have low efficacy to condensate sugars into more complex carbohydrates or have fewer efficacy to transport sugars from tree leaves to additional portions of tree (source-sink relationship). Cakmak and Marschner (1988) described that, Zn deficit leaves decreased the sucrose transportation it may be associated to the role of Zn in the structural reliability of bio membranes. Physiological disorders occurs due to deficiency of Zn such as rosetting and small leaf are the most typical symptoms occur in fruit trees (Swietlik, 2002). Zinc is necessary for the functioning of several enzymes, along with the synthesis for tryptophan which is a precursor of IAA. The decrease in IAA synthesis in Zn-deficient plants may be due to inhibited synthesis or improved degradation of IAA (Cakmak et al., 1989). Zinc deficit symptoms are certainly recognized by usually blotchy leaves, more compact leaf size, and frequently dieback of branches and slight malformed fruit (Spiegel-Roy and Goldschmidt, 2008). Tryptophan, the direct precursor of IAA enlarged underneath Zn deficiency, representative that this amino acid was not the limiting effect in IAA production. Also, zinc shows a significant role in numerous biochemical processes inside the plants. Zinc is an important element involved over 300 enzymes (Fox and Guerimot, 1998).
Zinc deficiencies in the plants reduced protein synthesis and accumulation of amino acids (Dickinson et al., 2003). Purohit (2007) described that, the conspicuous symptoms is an inter veinal chlorosis of the mature leaves followed by white necrotic spotting, reduced internodes, lesser leaves and small growth are typical symptoms due to zinc deficiency. Occasionally the leaves are bunched on small branches identified as rosettes.
2.6 Effects of gibberellic acid on different fruit corps
The use of the plant growth regulators (PGRs) in horticultural crops to boost plant growth and increase yield by rising fruit size, set and number of fruit . Plant growth regulators such as growth promoters, growth inhibitors or retardants perform an important part in regulating internal mechanisms of plant growth by relating important metabolic process such as nucleic acid metabolism and protein synthesis. Application of growth regulators (PGR’s) may be a beneficial to extend crop yield and production. GAs belongs to a category of plant hormones that control developmental methods for instance shoot elongation, germination, formation of tuber, fruit set and plant growth in different species. GA3 more extensively existing plant growth regulator which encourages stem and internode enlargement, enzyme production, seed germination (Davies, 1995). GA3 is a significant growth regulator that might have various usages to adjust the plant growth and yield (Rafeeker et al., 2002).
2.6.1 Role of gibberellic acid to prevent fruit drop
The role of GA3 in enhancing citrus fruit quality is well recognized (Pozo et al., 2000; Fidelibus et al., 2002; Saleem et al., 2008). The preharvest use of GA3 (30 mg L-1) was demonstrated very useful in inhibiting preharvest fruit drop in Kinnow mandarin (Tominaga, 1998) and sweet orange (Liao et al., 2006). The main factors which are involved in acceleration of fruit drop such as high light intensity and dry weather conditions. Fruit abscission can cause by the nutritional, environmental and hormonal factors (Gillaspy et al., 1993; Gomez et al., 2000).
Foliar spray of GA3 (25 mg L-1) inhibit the fruit softening, delay peel colour, and lessen the preharvest drop of fruit and puffiness (Kawase et al., 1981; Ladaniya, 1997). Foliar application of GA3 (30 mg L-1) in mandarin inhibited the ripening process and decrease damage of fruit (Chapman and Peacook, 1979). Kher et al. (2005) observed that GA3 was the most active compounds in increasing the fruit weight, fruit number per tree, yield and reducing the titratable acidity in guava fruit. Brahmachari and Rani (2005) suggested that application of GA3 (20 mg L-1) are useful in extend the storage life and maintaining the fruit quality of guava. Bhattacharya (1991) described that the treated fruit with GA3 application prolonged the shelf life of lime fruits via inhibiting in ripening process. Development and color break stage were reduced with 50 mg L-1 application of GA3 treatment in Purple plum (Kaur et al., 2008). The GA3 treatment (20 mg L-1) which delayed the peel color, reduction in TA, increase in juice weight, TSS/acid ratio and vitamin C (Thapa and Gautam, 2002). Preharvest application of GA3 delayed the loss of chlorophyll in citrus fruit (Bakhshi and Chadha, 1968). Exogenously applied growth regulators considerably enhance total number of fruit per tree, fruit weight, juice contents percentage, total soluble solids, acidity and ascorbic acid contents reduce the fruit drop (Nawaz et al., 2008). GA3 treated trees develop fruit color progressively in Kinnow mandarin (Sen et al., 2012). GA3 (30 mg L-1) application delayed the ripening process and decreased the pre and postharvest losses in Kinnow mandarin (Amir et al., 2003).
2.6.2 Effects of gibberellic acid on yield and quality of fruit
GA3 application (5-200 mg L-1) increased the fruit weight, fruit number, tree yield and reduced fruit drop in Clementine mandarin (Garcia-Martinez and Garcia-papi, 1979). The difference in tree yield of sweet orange varieties may be due to their varietal modification and appropriateness or inappropriateness of different cultivars to a specific region. Agusti et al. (1982) described that GA3 (5 mg L-1) significantly increased the fruit set percentage and yield in the ‘Navelate’ sweet orange.
Improved yield due to preharvest application of GA3 or Zn can be ascribed to their influence on increased levels of IAA. Increase in yield may be recognized to the enhancement in the nutritional status. The GA3 play important role in enhancing fruit quantity specifically, fruit weight and fruit size might be owing to its role in increasing cell elongation (Eman et al., 2007). Foliar application of GA3 (30 mg L-1) or ZnSO4 (0.75%) on plants produced elongation in the primary cells in the new tissues and growth centers. The GA3 as a bioregulator might be ascribed to its stimulative effects on cell expansion and cell division (Marschner, 1986).
2.6.3 Role of gibberellic acid in f
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