Pomology
S.M Gholami; M. Hadadinejad; H. Moradi; H. Sadeghi
Abstract
Introduction
Bud dormancy is one of the important issues in planting and cultivation of fruit trees that needs to be addressed in many trees such as orange (Citrus sinensis). Bud dormancy involves cessation of horizontal and vertical growth, lack of budbreak, and reduction in plant activity during cold ...
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Introduction
Bud dormancy is one of the important issues in planting and cultivation of fruit trees that needs to be addressed in many trees such as orange (Citrus sinensis). Bud dormancy involves cessation of horizontal and vertical growth, lack of budbreak, and reduction in plant activity during cold weather. One of the commercial orange cultivars is Tarocco blood orange which compared to older blood cultivars, is larger in size and with lower alternate bearing has higher marketability. The nursery trees of this cultivar are grafted on sour orange, citrange, and vigorous rootstock of citrumelo (a hybrid between trifoliate orange and grapefruit) (Talon et al., 2020). One of the major problems of nurserymen in spring grafting of Tarocco cultivar on vigorous citrumelo rootstock is the failure of about 50 percent of buds to break compared to other cultivars on the same rootstock and other similar rootstocks. This unwanted dormancy leads to a one-year delay in the nursery tree production process and unnecessary occupation of nursery space. Given the commercial importance of blood orange and the adverse effects of bud dormancy on yield and fruit lifetime, solutions are used to control and overcome this problem. One of the effective solutions is the application of cytokinins which can stimulate the growth of graft buds (Yadav & Saini, 2018).
Materials and Methods
This research was conducted in a citrus nursery at the University of Agricultural Sciences and Natural Resources of Sari, in late May 2022. Citrumelo seedlings were grown in 5.3 liter pots containing a loamy-silt soil mix in the nursery location. Tarocco cultivar buds were prepared from a seven-year-old mother orchard and T-budding was performed in June (during rootstock bark slipping). All hormone treatments were applied after graft union and before bending the branch using a soft brush on the graft buds. The applied treatments included hormone treatment (control, 5000 mg.l-1 benzyladenine, 1000 mg.l-1 kinetin, and 50 mg.l-1 thidiazuron) and treatment time (13, 15, and 17 days after grafting). After two months, some traits related to budbreak and growth of the grafted buds were evaluated.
Results and Discussion
The results showed that thidiazuron and benzyladenine treatments had better effects compared to kinetin treatment on spring budbreak and initial growth of Tarocco grafted buds. In a way that 50 mg.l-1 thidiazuron treatment had the highest number of sprouted buds (67.91), largest leaf area (118.04 cm2), highest number of leaves (16.50), especially when applied 13 days after grafting. Also, in leaf size related traits, leaf area indices, graft growth rate as well as chlorophyll and carotenoid content of Tarocco graft leaves were significantly affected by different hormonal treatments and application times, with 50 mg.L-1 thidiazuron being more effective than other treatments. Cytokinins can promote division and expansion of leaf cells and thereby result in increased cell numbers and improvement of different leaf parameters. Also, cytokinins regulate important physiological processes like photosynthesis. Application of these materials provides cell division especially in areas like buds and growth points and also possibly more buds may form on the spring graft by using these treatments during the grafting process which can lead to increased bud break and faster plant growth (Cook & Bahar, 2017). Increasing cytokinin levels can stimulate the photosynthesis process which results in increased food production, leaf growth and ultimately increased leaf area. On the other hand, cytokinins affect plant metabolism and can regulate production and accumulation of different growth factors. This may lead to a better balance in nutrient distribution and metabolic activities which in turn aids leaf area increase (Hodchek et al., 2023). Finally, according to the obtained results, it can be recommended to nurserymen of this cultivar to use 50 mg.L-1 thidiazuron 13 days after grafting as a practical and effective strategy for increasing spring budbreak, growth and development of Tarocco buds grafted on citrumelo.
Conclusions
In general, based on the results, the application of 50 mg.l-1 of thidiazuron 13 days after grafting can be considered a practical and effective strategy to enhance bud awakening, as well as the growth and development of Tarocco spring shoots on citronmelo. This practice is recommended for producers of seedlings of this cultivar.
Sepideh Taghizadeh; Hossein Sadeghi; Mehdi Hadadinejad
Abstract
Introduction: Influx of Siberian cold air masses into the northern parts of Iran causes severe decrease in temperature, heavy snowfall and freezing of citrus every few years. Depending on the temperature drop, in some years only fruits and in some years, citrus trees suffer severe damage too. One of ...
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Introduction: Influx of Siberian cold air masses into the northern parts of Iran causes severe decrease in temperature, heavy snowfall and freezing of citrus every few years. Depending on the temperature drop, in some years only fruits and in some years, citrus trees suffer severe damage too. One of the sudden drops in temperature was in January 2007, when the temperature dropped from -7 degrees Celsius to -13 degrees Celsius. Consecutive damage to citrus trees and crops in the north of the country has caused citrus gardeners to despair of its economic viability and to refrain from rehabilitating destroyed orchards. The mechanisms of frost resistance and relative tolerance to cold in citrus include physiological adaptation and metabolic changes. These changes will lead to the production of various cellular osmolytes, the accumulation of soluble substances, changes in lipid metabolism (with an increase in unsaturated fatty acids), an increase in supercooling temperature, and ultimately an increase in plant resistance. The use of passive and active methods can also partially prevent frost damage or reduce the severity of the injury, but spraying with compounds that may provide physical protection of trees against freezing or spraying chemicals that reduce the freezing point of the cellular fluid by altering the concentration of the cell sap could be more promising.
Materials and Methods: Experimental factors include freezing temperatures at three levels (-5, -8 and -11° C) and spraying with two types of experimental material including carnauba wax in two concentrations of zero and four percent (manufactured by Orange Saft SL, Spain) and glycol potash in two concentrations of zero and 10% (prepared by Pooshesh sabze Company, Iran), carnauba + glycol potash (carnauba wax in 4% concentration and 10% glycol potash concentrate) and control (distilled water solution).
Results: Electrolyte leakage is the uncontrolled leakage of organic ions from the cell membrane due to stress and damage to the membrane. The lowest electrolyte leakage was observed at -5° C and the highest one was at -8° C. As a messenger molecule, proline is effective in regulating mitochondrial activity, cell proliferation, and cell death. Proline also expresses certain genes that are essential for improving plant conditions under stress. Proline concentration increased with decreasing temperature but it decreased again at -8 ° C. Using carnauba wax at -5 ° C has reduced the concentration of total soluble sugars (66.92 micro g / g by weight) but did not significantly differ from the control treatment (83/23) and -11 ° C. Frost tolerance and frost resistance vary in different organs of citrus trees. Young shoots and twigs are very sensitive to cold and frost, so their tissues change color due to the cold. If the intensity of cold and frost increases, it will cause the shoots to dry out. freezing temperature has a significant effect on Shoot dying back, so that the highest dryness of the shoots was observed at -11 ° C (91.66%) and the lowest at -5° C (10.41%). The highest percentage of leaf abscission was observed at -11 and the lowest with significant difference at -5° C. Symptoms of freezing such as leaf abscission and tree Shoot dying back are not seen up to -5 ° C but they are well visible at -8 ° C. Experimental treatments also failed to prevent shoots from drying out at -11° C.
Conclusion: Thomson navel orange young trees do not suffer much damage up to -5° C, but as the temperature decreases, the damage caused by frost increases in the form of leaf abscission and Shoot dying back of branches. Carnauba wax has a positive role in this experiment by preventing leaf abscission at -8 ° C, but glycol potash has a negative role by increasing leaf abscission and Shoot dying back. Increasing leaf potassium levels through potash glycol not only did not increase cold resistance but also increased susceptibility to frost. Potassium must be supplied from other sources. The results of this experiment showed that the use of carnauba wax up to 48 hours before the possible cold, which is announced through meteorology, with a concentration of 4%, can keep it alive up to -8 ° C, which normally destroys the plant, but with passing through this temperature, for example at -11 degrees Celsius, is not able to maintain the plant.
