Effect of Thinning of Mandarin (Citrus reticulata Blanco. cv. Michal) on Yield and Fruit Quality By Mohammad Abd-El- Jaber Alabdallah Supervisor Prof. Dr. Mostafa Qrunfleh Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Horticulture and Plant Protection Faculty of Graduate Studies The University of Jordan May 2003
i Committee Decision This thesis was successfully defended and approved on May 28, 2003. Examination Committee Signature Prof. Mostafa Qrunfleh, Chairman. --------------------- Professor of Fruit Tree Physiology. Prof. Fahmi Shatat, Committee Member. --------------------- Professor of Pomology / Postharvest Physiology. Dr. Ahmad Ateyyeh, Committee Member. Assistant Professor of Fruit Trees. Dr. Khalid Al-Absi, Committee Member. --------------------- Assistant Professor of Fruit Trees.
ii Dedication To the soul of my father, who fought a good fight To my mother, brothers and sisters
iii Acknowledgement A special word of thanks goes to my supervisor Prof. Mostafa Qrunfleh for his patience. I shall be ever grateful for his untiring efforts, his keen grasp of the subject, and his consummate technical ability. I am grateful, also, to committee members: Prof. Fahmi Shatat, Dr. Ahmed Atteyyeh and Dr. Khalid Al-Absi for their valuable comments. Appreciation and sincere thanks are extended to all of the staff of the Agricultural Research Station in the Jordan Valley, especially Mr. Mostafa Farraj for their help throughout the course of this work. Special thanks are expressed to my family and friends for their continuous support.
iv List of contents Committee Decision...i Dedication...ii Acknowledgement... iii List of contents... iv List of tables... vi List of figures... vii List of appendices...viii Abstract... xi 1. INTRODUCTION...1 2. LITERATURE REVIEW...4 2.1. Thinning... 4 2.2. Alternate bearing and the need for thinning... 7 2.3. Citrus fruit development... 8 2.4. Hand thinning... 9 2.5. Chemical thinning agents for citrus...10 2.5.1. Auxins...10 2.5.1.1. Mechanism of action... 13 2.5.2. Gibberellic acid (GA 3 )...14 2.5.3. Ethephon...15 2.6. Abscission and physiological drop...16 3. MATERIALS AND METHODS... 18 3.1. Location...18 3.2. Plant material...18 3.3. Experimental work...18 3.4. Full bloom determination...19 3.5. Application time...19 3.6. Chemical thinning experiments...20 3.6.1. Experiment one. Effect of NAA...20 3.6.2. Experiment two. Effect of GA 3...20 3.6.3. Thinning percentage determination...20 3.7. Hand thinning experiments...21 3.7.1. Experiment three. Effect of three percentages of hand thinning...21 3.7.2. Experiment four. Effect of five levels of retained fruitlets by hand thinning...21
v 3.8. Parameters measured...22 3.8.1. Fruit fresh weight...22 3.8.2. Peel percentage relative to whole fruit weight...22 3.8.3. Total soluble solids (TSS) percentage...22 3.8.4. Fruit volume...23 3.8.5. Yield per tree...23 3.8.6. Titratible acidity of fruit juice...23 3.8.7. Ascorbic acid content of fruit juice...23 3.9. Statistical analysis...23 4. RESULTS AND DISCUSSION... 24 4.1. Experiment one. Effect of NAA...24 4.1.1. Thinning percentage...24 4.1.2. Physical fruit properties...25 4.1.3. Chemical fruit properties...28 4.2. Experiment two. Effect of GA 3...29 4.2.1. Thinning percentage...29 4.2.2. Physical fruit properties...30 4.2.3. Chemical fruit properties...33 4.3. Experiment three. Effect of three percentages of hand thinning...34 4.3.1. Physical fruit properties...34 4.3.2. Chemical fruit properties...35 4.4. Experiment four. Effect of five levels of retained fruitlets by hand thinning...36 4.4.1. Physical fruit properties...36 4.4.2. Chemical fruit properties...37 5. CONCLUSIONS... 39 6. LITERATURE CITED... 41 APPENDIX... 48 ABSTRACT (In Arabic)... 62
vi List of tables Table 1.Percentage of opened florets of 'Michal' mandarin... 19 Table 2. Effect of thinning by NAA on fruit weight, volume, peel percentage and yield of 'Michal' mandarin... 26 Table 3. Effect of thinning by NAA on fruit chemical properties of 'Michal' mandarin.... 29 Table 4.Effect of thinning by GA 3 on fruit weight, volume, peel percentage and yield of 'Michal' mandarin.... 31 Table 5. Effect of different GA 3 concentrations on fruit chemical properties of 'Michal' mandarin... 34 Table 6. Effect of different hand thinning percentages on fruit physical properties of 'Michal' mandarin.... 35 Table 7. Effect of hand thinning percentages on fruit chemical properties of 'Michal' mandarin.... 36 Table 8. Effect of retaining different numbers of fruitlets by hand thinning on fruit physical properties of 'Michal' mandarin.... 37 Table 9. Effect of retaining different numbers of fruitlets by hand thinning on fruit chemical properties of 'Michal' mandarin.... 38
vii List of figures Figure 1.Effect of differnet NAA concentrations on thinning of Michal mandarin.... 25 Figure 2.Effect of differnet GA 3 concentrations on thinning of 'Michal' mandarin.... 30
viii List of appendices 7.1. Appendix A: Statistical analysis for experiment one... 48 Table 7.1.1 Analysis of variance for effect of different NAA concentrations on average ascorbic acid content of 'Michal' mandarin....48 Table 7.1.2. Analysis of variance for effect of different NAA concentrations on average peel percentage of 'Michal' mandarin...48 Table 7.1.3. Analysis of variance for effect of different NAA concentrations on average titratible acidity of 'Michal' mandarin....49 Table 7.1.4. Analysis of variance for effect of different NAA concentrations on average total soluble solids percentage of 'Michal' mandarin...49 Table 7.1.5. Analysis of variance for effect of different NAA concentrations on average fruit weight of 'Michal' mandarin....50 Table 7.1.6. Analysis of variance for effect of different NAA concentrations on average fruit volume of 'Michal' mandarin....50 Table 7.1.7. Analysis of variance for effect of different NAA concentrations on average yield per tree of 'Michal' mandarin....51 Table 7.1.8. Analysis of variance for effect of different NAA concentrations on average thinning percentage of 'Michal' mandarin....51 7.2. Appendix B: Statistical analysis for experiment two... 52 Table 7.2.1. Analysis of variance for effect of different GA 3 concentrations on average ascorbic acid content of 'Michal' mandarin....52 Table 7.2.2.Analysis of variance for effect of different GA 3 concentrations on average peel percentage of 'Michal' mandarin....52 Table 7.2.3. Analysis of variance for effect of different GA 3 concentrations on average titratible acidity of 'Michal' mandarin....53 Table 7.2.4.Analysis of variance for effect of different GA 3 concentrations on average total soluble solids percentage of 'Michal' mandarin...53
ix Table 7.2.5. Analysis of variance for effect of different GA 3 concentrations on average fruit weight of 'Michal' mandarin....54 Table 7.2.6. Analysis of variance for effect of different GA 3 concentrations on average fruit volume of 'Michal' mandarin...54 Table 7.2.7. Analysis of variance for effect of different GA 3 concentrations on average yield per tree of 'Michal' mandarin...55 Table 7.2.8. Analysis of variance for effect of different GA 3 concentrations on average thinning percentage of 'Michal' mandarin...55 7.3. Appendix C: Statistical analysis for experiment three... 56 Table 7.3.1. Analysis of variance for effect of different percentages of hand thinning on average ascorbic acid content of 'Michal' mandarin...56 Table 7.3.2. Analysis of variance for effect of different percentages of hand thinning on average peel percentage of 'Michal' mandarin...56 Table 7.3.3. Analysis of variance for effect of different percentages of hand thinning on average titratible acidity of 'Michal' mandarin...57 Table 7.3.4. Analysis of variance for effect of different percentages of hand thinning on average total soluble solids percentages of 'Michal' mandarin...57 Table 7.3.5. Analysis of variance for effect of different percentages of hand thinning on average fruit weight of 'Michal' mandarin...58 Table 7.3.6. Analysis of variance for effect of different percentages of hand thinning on average fruit volume of 'Michal' mandarin...58 Table 7.3.7. Analysis of variance for effect of different percentages of hand thinning on average yield per tree of 'Michal' mandarin...58 7.4. Appendix D: Statistical analysis for experiment four... 59 Table 7.4.1. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average ascorbic acid content of 'Michal' mandarin...59
x Table 7.4.2. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average peel percentage of 'Michal' mandarin...59 Table 7.4.3. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average titratible acidity of 'Michal' mandarin...60 Table 7.4.4. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average total soluble solids percentages of 'Michal' mandarin...60 Table 7.4.5. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average fruit weight of 'Michal' mandarin...61 Table 7.4.6. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average fruit volume of 'Michal' mandarin...61 Table 7.4.7. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average yield per tree of 'Michal' mandarin...61
xi Effect of Thinning of Mandarin (Citrus reticulata Blanco. cv. Michal) on Yield and Fruit Quality By Mohammad Abd-El- Jaber Alabdallah Supervisor Prof. Dr. Mostafa Qrunfleh Abstract Effect of various concentrations of naphthaleneacetic acid (NAA), gibberellic acid (GA 3 ), and two methods of hand thinning namely: three percentages of hand thinning and five levels of retained fruitlets on yield and fruit quality of 11 year old mandarin (Citrus reticulata Blanco. cv. Michal) trees grown at the Agricultural Research Station in the Jordan Valley was tested. Thinning experiments were performed 40 days after fullbloom during the year 2002. The results indicated that all NAA concentrations (100, 200, 300, 400 and 500 ppm) were significantly effective in thinning fruitlets of Michal mandarin as compared to the control, and the severity of thinning increased with increasing NAA concentration. In addition, all NAA concentrations significantly increased average fruit weight and volume, and peel percentage as compared to the control. Moreover, all NAA concentrations caused a significant reduction in average yield per tree. On the other hand, all NAA concentrations had no significant effect on fruit ascorbic acid content, fruit juice acidity and fruit TSS percentage.
xii With respect to the use of GA 3, all the concentrations (50, 100, 150, 200 and 250 ppm) were significantly effective in fruitlet thinning compared to the control, and the severity of thinning increased with increasing GA 3 concentration. In addition, all GA 3 concentrations caused a significant increase in average fruit weight, and average fruit volume. Moreover, only the 250 ppm significantly increased the peel percentage over the control, and the other concentrations (50, 100, 150 and 200 ppm) were ineffective in this respect. Furthermore, all GA 3 concentrations significantly reduced average yield per tree as compared to the control. On the other hand, all GA 3 concentrations were significantly ineffective in influencing fruit juice acidity, and fruit TSS percentage. However, the 250 ppm GA 3 significantly increased fruit ascorbic acid content over the control, and the other concentrations (50, 100, 150, and 200 ppm) were ineffective in this respect. The 30% and 60% fruitlet removed by hand significantly increased average fruit weight, and average fruit volume over the control with no influence on peel percentage, fruit ascorbic acid content, fruit juice acidity and fruit TSS percentage. In addition, both hand thinning treatments significantly reduced average yield per tree as compared to the unthinned trees. Retaining one, three, five and seven fruitlets per shoot significantly increased average fruit weight, and average fruit volume as compared to shoots containing more than 10 fruitlets. These treatments were significantly ineffective on peel percentage, fruit ascorbic acid content, fruit juice acidity, and fruit TSS percentage, and caused at the same time a significant reduction in average yield of tree.
1 1. INTRODUCTION Citrus is a major fruit tree crop grown in the Jordan Valley. There was a steady increase with respect to area and production of citrus in Jordan. For example, citrus occupied (5950) hectare, and produced (167.4) thousand tons in 1996, while in the year 2000 it occupied (6650) hectare, and produced (181.6) thousand tons (Ministry of Agriculture, 2000). Commercial Citrus species and related genera are primarily evergreens of subtropical and tropical origins belonging to the family Rutaceae (Davies and Albrigo, 1994). Thinning refers to the removal of excess numbers of fruits from a tree, so the remaining fruits will become larger (Hartmann, et al, 1988). The three general methods of thinning are hand, mechanical, and chemical. Flowers and fruits naturally thin themselves, often at distinct time periods. Blossoms that were not pollinated turn yellow and drop off just after flowering. Small, immature fruits often drop naturally during what is known as June drop'. Fruits that are diseased or infested with insects, such as apples or pears infested with codling moth, may drop prematurely. In some types of trees, natural thinning is sufficient; other species need additional thinning to produce high-quality fruit (Ingels et al, 2001). The importance of fruit size as a parameter of quality of citrus fruits has increased markedly in recent times to a point that the income obtained from small-sized fruits is often lower than the production and handling costs (Guardiola and Garcia-Luis, 1997). In addition, fruit size has become as important as yield in the determination of the profitability, and an
2 economic premium is usually obtained through the increase in fruit size even at the expense of a reduction in crop yield. Fruit trees often set more fruit than they can support or develop adequately, especially if the trees were not properly pruned during the previous season. Excessive fruits compete with each other for carbohydrates (stored energy) and remain small. This carbohydrate drain, or sink, can also weaken the tree and make it more susceptible to pests and sunburn damage. Leaving too much fruit on a tree can also lead to alternate bearing (a cycle in which the tree bears excessively in one year and little the next year) or limb breakage. Thinning the fruit helps prevention of these problems from developing (Ingels et al, 2001). Most commercially important citrus cultivars bloom prolifically producing as many as 100,000-200,000 flowers on mature tree; however, fewer than 1-2% of these flowers will produce harvestable fruit (Davies and Albrigo, 1994). For example, orange trees tend to flower heavily, the number of flowers per tree usually ranging between 25,000 and 100,000, with numbers as high as 200,000 being reported (Agusti et al, 1982). According to Ingels et al (2001), thinning immature fruit at the appropriate time allows each remaining fruit to develop to its maximum size, with little reduction of tree vigor. Less-crowded fruit receive more sunlight, so fruit color and flavor may be improved. Fruit thinning can also reduce the spread of some diseases. For example, if the fruit are touching each other, brown rot can quickly spread from one fruit to another just before harvest. Air movement around tightly clustered fruit is minimal, so the surface of unthinned fruit does not dry quickly, allowing disease organisms to multiply and spread. Fruit thinning is done to stimulate floral initiation for next year crop (Westwood, 1993).
60 Table 7.4.3. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average titratible acidity of 'Michal' mandarin S.V. df Mean square F value Replicate 3 1.14 0.82 Treatment 4 0.86 0.62 Experimental error 12 1.38 41.2 Sampling error 580 0.03 Table 7.4.4. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average total soluble solids percentages of 'Michal' mandarin S.V. df Mean square F value Replicate 3 21.67 1.93 Treatment 4 8.66 0.77 Experimental error 12 11.22 15.53 Sampling error 380 0.72
61 Table 7.4.5. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average fruit weight of 'Michal' mandarin S.V. df Mean square F value Replicate 3 163.02 5.9 Treatment 4 39314.75 1423.22 Experimental error 12 27.62 0.32 Sampling error 380 87.44 Table 7.4.6. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average fruit volume of 'Michal' mandarin S.V. df Mean square F value Replicate 3 1019 5.88 Treatment 4 23425.87 135.12 Experimental error 12 173.37 1.37 Sampling error 80 127 Table 7.4.7. Analysis of variance for effect of retaining different numbers of fruitlets per shoot on average yield per tree of 'Michal' mandarin S.V. df Mean square F value Replicate 3 83.83 2.98 Treatment 4 5168.84 183.64 Error 12 28.14
62 (Citrus reticulata Blanco. cv. Michal).. : (GA 3 ) (NAA) 'Michal ' ١١.. ( ٥٠٠ ٤٠٠ ١٠٠,٢٠٠,٣٠٠) NAA 'Michal'.NAA NAA