Pomology
Seyed Mahmud gholami; Hossein Moradi; hossein sadeghi
Abstract
Tarocco cultivar is one of the most popular cultivars of blood orange, which is propagated by grafting on the growing base of citronmelo, but stagnates in spring grafting. Considering the role of cytokinins in the awakening and growth of buds, the present study was conducted in order to investigate the ...
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Tarocco cultivar is one of the most popular cultivars of blood orange, which is propagated by grafting on the growing base of citronmelo, but stagnates in spring grafting. Considering the role of cytokinins in the awakening and growth of buds, the present study was conducted in order to investigate the effect of time (13, 15 and 17 days after grafting) and the concentration of cytokinin compounds (5000 mg/l benzyl adenine, 1000 mg/l kinetin and 50 mg/l thidiazuron) were carried out on the elimination of stagnation and some traits of tarocco spring grafted on citromelo rootstock. The results showed that the time and type of hormone have a significant effect on the elimination of stagnation and the growth of the spring shoots of taraco. So that the application of thidiazuron hormone treatment 13 days after grafting to the elimination of stagnation in more than 90% of grafts. It was also found that thidiazuron and benzyl adenine treatments had better results compared to quintine treatment on bud awakening and early growth of tarocco spring shoots. The treatment of 50 mg/liter of tidiazuron had the highest number of blossomed buds (91.67), leaf area (118.04 cm2) and number of leaves (16.50), especially when applied 13 days after transplanting. In general, according to the obtained results, the use of 50 mg/liter of tidiazuron 13 days after grafting can be considered as a practical and effective strategy to increase bud awakening and the growth and development of tarocco spring shoots on citronmelo for producers seedlings of this cultivar are recommended.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 offered 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 and 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 benzyladenine, 1000 mg/L kinetin, and 50 mg/L 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 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 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 and 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 thidiazuron 13 days after grafting as a practical and effective strategy for increasing spring budbreak, growth and development of Tarocco buds grafted on citrumelo.
