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VIETNAM ACADEMY OF AGRICULTURAL SCIENCES ***** TONG HOANG HUYEN RESEARCH ON AGRO BIOLOGICAL CHARACTERISTICS AND SOME TECHNICAL MEASURES TO IMPROVE YIELD AND QUALITY OF BO HA KING MANDARIN TREE GROWN I[.]
MINISTRY OF EDUCATION AND MINISTRY OF AGRICULTURE AND RURAL TRAINING DEVELOPMENT VIETNAM ACADEMY OF AGRICULTURAL SCIENCES … .*****…… TONG HOANG HUYEN RESEARCH ON AGRO-BIOLOGICAL CHARACTERISTICS AND SOME TECHNICAL MEASURES TO IMPROVE YIELD AND QUALITY OF BO HA KING MANDARIN TREE GROWN IN THAI NGUYEN Major: Crop Science Code: 62 01 10 THESIS SUMMARY Ha Noi - 2023 The thesis was completed at: VIETNAM ACADEMY OF AGRICULTURAL SCIENCE Supervisors: Prof Dr Ngo Xuan Binh Dr Bui Quang Dang Ph.D thesis Reviewer 1: Dr Nguyen Van Vuong Ph.D thesis Reviewer 2: Dr Ngo Hong Binh The thesis was reported to the Thesis Committee at the Institutional level in the Vietnam Academy of Agricultural Sciences At , The thesis can be found at the libraries: National Library of Vietnam Library of Vietnam Academy of Agricultural Sciences Library of Fruit and vegetable research institute , 2023 LIST OF PUBLISHED SCIENTIFIC WORKS RELATED TO THE THESIS Tong Hoang Huyen , Nguyen Tien Dung, Nguyen Van Duy, Khoang Lu Pha, Bui Quang Dang, Ngo Xuan Binh (2022) " Study on the effect of pruning method on growth and yield of Bo Ha king mandarins grown in Thai Nguyen province ", Journal of Agriculture and Rural Development, Issue May 2022: pp 9-14 Nguyen Tien Dung, Tong Hoang Huyen, Nguyen Van Duy, La Van Hien, Bui Tri Thuc, Khoang Lu Pha, Bui Quang Dang , Ngo Xuan Binh (2022), " Determination of genetic differences between Bo Ha king mandarin and other citrus varieties in the North of Vietnam " Vietnam Journal of Science and Technology , No 03 (136) /2022 : No 11-15 Tong Hoang Huyen , Nguyen Tien Dung, Nguyen Van Duy, Bui Quang Dang, Bui Tri Thuc, Nguyen Thi Tinh, Ngo Xuan Binh (2022), " Research on the origin of the buds in relation to the yield of the Bo Ha King mandarin variety grown in Thai Nguyen " Vietnam Science and Technology Magazine , Volume 64, February 2022 issue: Pages 34-37 INTRODUCTION Necessity of the study The Bo Ha king mandarin tree (Yen The - Bac Giang) has a source origin mount instant with existence face of French since the 19th century According to documents published in the years, 1930-1954 by a number of French agronomists working in Indochina, the Bo Ha king mandarin tree planted by the French has grown well in Yen The area since the 19th century, forming the Bo Ha king mandarin area After peace was established in 1954, Yen The established the Bo Ha king mandarin farm, planting king mandarin varieties for export and domestic consumption The Bo Ha king mandarin was the country's number one orange variety and was famous throughout the region at the national skill competitions held in the ancient capital of Hue, once the pride of the people of the North However, in the period after the 1980s, the most harmful pest and disease were greening, along with outdated farming techniques, which severely damaged orange production areas, such as Phu Quy orange area - Nghe An, Tuyen Quang- Ha Giang orange areas in general and the Bo Ha king mandarin area ( Bac Giang) in particular The orange growers had to cut down and switch to other agricultural crops, therefore the Bo Ha king mandarin tree was almost only left in the memory of consumers and producers alike In the period after 2014-2016, the research team of Nong Lam University - Thai Nguyen University investigated and identified some remaining Bo Ha king mandarin trees in farmer households The age of trees were 40- 50 years but most have suffered from greening disease On the basis of investigation, agro-biological characteristics, and application of molecular markers in pedigree determination, it has been determined that these are Bo Ha king mandarin trees, which have different genetic and biological characteristics compared to Ham Yen king mandarin (Tuyen Quang) Simultaneously, the research team has propagated disease-free Bo Ha king mandarin trees, stored and planted at Nong Lam University - Thai Nguyen University The conservation and development of the Bo Ha king mandarin variety is great significance The conservation and development of the Bo Ha king mandarin variety is great significance with production, contribute to the restoration and development of Bo Ha king mandarin, change the structure of plant varieties for agricultural production From the above practice, the implementation of the topic "Research on agro-biological characteristics and some technical measures to improve yield and quality of Bo Ha king mandarin tree grown in Thai Nguyen" is necessary and high significance in science and practice Objectives of the study Studying some agro-biological characteristics and suitable technical measures to improve the yield and quality of Bo Ha king mandarin, contribute to exploitation, development the valuable gene source in midland and mountainous areas in the North of Vietnam The scientific and practical meanings of the thesis 3.1 Scientific meanings - The results of the study are the premise for future studies about technical measures to improve the yield and quality of Bo Ha king mandarin fruit - The research results are the scientific basis to develop the technical process of taking care of the Bo Ha king mandarin tree for the midland and mountainous areas in the North - The research results of the topic are valuable as documents and materials for teaching and further research on the Bo Ha king mandarin variety in particular and citrus in particular in the North of Vietnam 3.2 The practical meanings The results of the study contribute to the conservation, exploitation and development of genetic resources of Bo Ha king mandarin variety which was almost lost in production, is an important basis in building the process of taking care of Bo Ha king mandarin tree, including optimization of the technical processes of pruning, propagation by marcotting, fertilizer using and foliar fertilizer application for Bo Ha king mandarin tree New contributions in the thesis - The thesis researches a systematic assessment of agro-biological characteristics, which is an important reference source for research on orange trees in the Northern Midlands and Mountains regions, and provides arguments, the scientific basis for the building of the intensive care and cultivation process, as well as the planning of planting Bo Ha king mandarin trees in the mountainous provinces of the North - The research results about bud characteristics, association and origin of buds in Bo Ha king mandarin is the scientific basis to explain the phenomenon biennial bearing, simultaneously, is the basis to suggest solutions for that phenomenon - The research results about nutrient supplementation, growth hormones, are the scientific basis for developing solutions to supplement nutrient and growth stimulants in the production process in order to improve the quality and yield of Bo Ha king mandarin bring high economic efficiency - Research results on propagation techniques, especially the ability of grafting and rootstock grafting to the growth of Bo Ha king mandarin tree, are an important scientific basis for the use of rootstocks to propagate Bo Ha king mandarin trees - The results of the study provide a database, which is an important reference in serving the management and development planning of citrus in general, orange trees in particular, in the Northern Midlands and Mountains region Structure of the thesis The thesis is presented in 136 pages size A4, including the Introduction (3 pages); Chapter Overview of the literature (25 pages); Chapter Materials, contents, and research methods (13 pages); Chapter Results and discussion (82 pages); Conclusion and recommendations (3 pages); List of 113 documents, including 65 Vietnamese documents, and 48 English documents CHAPTER OVERVIEW OF THE LITERATURE 1.1 Some research results on the main agronomical characteristics of citrus Depending on ecological conditions and propagation form, the age of citrus can be long or short In citrus orchards that are seeded or propagated by grafting, under favorable conditions, the lifespan can reach a few dozen to more than a hundred years and still give good yields [ 3] Branches of citrus include the main branches which are mother branches, nutrition branches, and fruit branches This classification is according to the function of each type of branch The relationship between branches and shoots is quite close [ 47 ] 1.2 Some research results on technical measures to improve yield and quality of citrus plants 1.2.1 About foliar fertilizer utilization Foliar fertilizers contain macronutrients, intermediates, and microelements that provide nutrients in a timely manner for plants to grow and develop rapidly Fertilizers containing trace elements, and growth regulators have the effect of increasing the rate of flowering, fruit set, fruit code, and fruit quality and reducing the number of seeds if sprayed at different times with appropriate periods [ 34 ], [ 35 ] 1.2.2 Research on pruning techniques to shape citrus trees Technical art cut trim gives tree yes abs including the internal content main after: Pruning to shape, pruning after harvest, pruning flowers, pruning fruit, and renovating old and weak trees The main types of pruning and shaping usually applied are spherical or hemispherical cutting, but currently, most countries with a developed citrus industry (USA, Australia, Israel, Taiwan, China ) has been gradually transitioning to a Yshaped pattern (initiating style, jar or open heart type ) even in a fan-less style to facilitate harvesting by machine Pruning usually works better when it is done in concert with other techniques such as fertilizer, watering, and pest control Cut trim can not usually present clearly effect in the early years of pruning [23] The removal of flowers, malformed fruits, clusters of flowers, and fruits that are too thick will contribute to reducing the above imbalance According to the author Vu Cong Hau, (1996 ) [21], pruning is more and more widely applied The rule is to cut carefully when the tree is young, cut less when the tree is old, cut more in winter or drying seasons , when the tree in stage which cease born chief cut much, grow strongly cut little 1.2.3 Research on technical measures of bark grafting method for citrus trees Circling the bark has two main effects: promoting flowering and increasing fruit setting rate Therefore, it is possible to apply this technique to the Bo Ha king mandarin variety to promote flowering as well as increase the fruit setting rate and fruit yield of this orange variety 1.3 Some research results on citrus grafting techniques Nowadays, it is possible to graft in vitro (micrograft) to create disease-free plants Microshoot tip grafting was first applied by Murashige in 1972 It was then further improved by Navarro in 1975, 1976, 1980, and 1981 and Hong Ji Su in 1984 The technique of micrografting of meristem includes stages: preparation of the rootstock, preparation of the shoot apexs, grow plants in vitro by micrografting, and then planting in pots [38] There are many trees that are used as rootstocks for citrus trees In the South, honey oranges are used, in the North use pomelo, recently tangerine and some new rootstocks are used According to the research results of Khuat Huu Trung in 2022 [39], the effect of the grafting season of Tay Giang orange trees in Quang Nam When using the eye grafting method on rootstock of Aurantii Fructus (Citrus aurantium) in Thai Binh, it shows that the most suitable time to graft is in February, then is in the mid-August, and the lowest is in mid-October, expressed through survival and germination rate of grafts, growth parameters including length and width of leaves, length, and diameter of grafted branches Bui Quang Dang et al in 2021 [12], when performing eye grafting of Xa Doai and CS1 oranges on the rootstocks of Aurantii Fructus in the North Central region, it was found that the most suitable time to graft is Summer (mid-June), then Autumn ( midAugust), and the lowest is in the winter season (mid-December) The rate of germination the first time (after 30 days) and the rate of germination the second time (after 100 days) when grafted in the summer crop reached 80.0% and 82.5% Regarding to the growth of grafted trees, Xa Doai grafted orange trees’s height is about 72.5 cm The diameter of the rootstock is 0.91 cm The length of the graft is 45.7 cm The diameter of grafted branches is 0.71cm; The number of level branches is about 2-3 branches; and CS1 grafted orange tree’s height of 75.7 cm; rootstock’s diameter is 0.92 cm; length of grafted branches 47.2 cm; the diameter of grafted branches 0.72 cm, the number of level branches is 2-3 branches CHAPTER RESEARCH MATERIALS, CONTENTS, AND METHODS 2.1 Research site and materials 2.1.1 Research site Research location at University of Agriculture and Forestry, Thai Nguyen University, Quyet Thang Commune, Thai Nguyen City, Thai Nguyen Province 2.1.2 Research objects and materials - Research objects: years old Bo Ha king mandarins; Planting density is about 400-800 trees/ha - Control: Ham Yen king mandarin variety ( provided by Ham Yen Fruit Seed Center, Tuyen Quang province ) 2.1.3Research time The study period was conducted from 2017 to 2020 2.2 Research contents 2.2.1 Research on some agro-biological characteristics of Bo Ha king mandarin variety - Research on morphological characteristics of Bo Ha king mandarin variety: Stems, branches, leaves, flower, fruit, ability to give yield and quality of the Bo Ha king mandarin fruit - Research on genetic diversity of Bo Ha king mandarins by molecular markers - Research on the phylogenetic origin and the relationship between the buds in the Bo Ha king mandarin tree - Research on the growth characteristics of the buds and the correlation between the growth of fruit branches and fruit yield in the Bo Ha king mandarin variety 2.2.2 Research on the influence of some technical measures on growth, yield, and quality of the Bo Ha king mandarin - Research on the effect of pruning on growth and yield of the Bo Ha king mandarin tree - Research on the effect of bark grafting method on yield and quality of the Bo Ha king mandarin tree - Research on the effects of some foliar inoculants products on the yield and quality of Bo Ha king mandarins - Research on the effects of some foliar inoculants products combined with pruning on the yield and quality of the Bo Ha king mandarin - Research on the influence of rootstock and grafting time on the growth of the Bo Ha king mandarin 2.3 Research methods 2.3.1 Research methods on some agro-biological characteristics of Bo Ha king mandarin variety 2.3.1.1 Research on morphological characteristics of the Bo Ha king mandarin The research was conducted on a 4-year-old Bo Ha king mandarin garden, randomly selected trees to experiments, times repeated Experimental plants were evaluated for canopy form, morphological characteristics of stems, leaves, flowers, fruits * Targets and tracking methods: - Evaluation of shape canopy - Stem diameter (cm): Measure with Palmer ruler at the point which is ten cm from the ground - Tree height (cm): Measured with a long ruler from the ground and measured to the highest point of the canopy tree - Canopy diameter (cm): Measured with a tape measure, measure the tree canopy’s projection in the orientation from East-West and South-North directions, then take the average value jar - Number of branch levels: Count the number of levels of branches currently on the tree - Thorn’s Density - Measure leaf’s length and width (mm) - Measure the length and width of the leaf’s waist (mm) (if) - Characteristics about flowering, fruiting, and yielding capacity: - Fruit ripening period: When there are more than 20% of the fruits ripe - Theoretical yield/tree (kg/tree): Number of fruits/tree × weight of fruit (g/plant) - Actual yield: Weigh the total number of fruits of each tree from which to calculate the average yield (kg/tree) - Average fruit weight, edible portion (g/fruit) - Fruit shape, fruit size, peel thickness, number of segments, and number of seeds Parts ratio: peel, seed, segments Each tree was measured 10 fruits on the average - Sensory assessment: Directly observing and tasting, evaluating fruit color, pulp, and taste fruit - Composition analysis of Fruit: Measure Brix, Total Sugar (%), Total Acid ( % ), Vitamin C (mg/100g fresh fruit) 2.3.1.2 Research on genetic diversity of Bo Ha king mandarins by molecular markers The research was conducted on 32 citrus samples including samples of Bo Ha king mandarins, sample of Bo Ha citrus, 11 samples of Ham Yen king mandarins, and some other citrus varieties being grown in the North of Vietnam - The primers used in the study were designed based on the author's research Oliveira et al (2010) [89], * Research methods Genetic diversity analysis of some local citrus varieties in Vietnam by RAPD (Random Amplified Polymorphic DNA) and ISSR (Inter-Simple Sequence Repeat) markers - Extraction of total DNA: - RAPD and ISSR reactions were conducted with random primers according to Malik's method [88] ( Malik et al , 2012) - Polymorphism analysis 2.3.1.3 Research on the growth of the buds in the Bo Ha king mandarin variety *Experimental setup: In the experimental garden, plants were randomly selected, and canopy horizontal branches were selected on tree, all spread on sides, with a diameter >1.0 cm, mark the experimental branch On each experimental branch, when flowering in the Spring, Summer, Autumn, and Winter crops, Select buds for each experiment branch with average growth strength, without pests and diseases to evaluate the growth criterias * Targets and tracking methods: - The shoots growing from the experimental branches are marked with dates so that the growth criteria can be followed - Number of batches to track: Spring crop, Summer crop, Autumn crop, Winter crop - The growing time is counted from the time of buds formation to the mature branches in Spring, Summer, Autumn, and Winter, and compared - The growth behavior of Spring, Summer, Autumn, and Winter crops are tracked and compared Measure the length of the bud once every days Measure until the length of the buds does not change at the last measurements, then it is considered that the buds have stopped growing in length at the first measurement of the last measurements The bud is called mature when it no longer increases in length and the young leaves have turned dark green - Determine the number of leaf nodes and the number of mature leaves/branches/spring, summer, autumn, and winter crops and compare (conducted on buds to monitor growth in length) Determine the mature branch length and mature branch diameter/Spring, Summer, Autumn, and Winter and compared 2.3.1.4 Research on the correlation between fruit branch growth and fruit yield in the Bo Ha king mandarin tree *Experimental setup: In a 4-year-old orchard, 10 plants were randomly selected for the experiment The uniform experimental plants represent the normal growth of the plants in the experimental garden, the plants are not damaged by pests and diseases On every tree choose from horizontal branches spread evenly on sides - branches over 1-yearold Select a branch with a diameter of about ≥ 1.0 cm, mark the branch close to the main stem, and monitor the ability to produce buds, the growth of the mother branch, the age of the mother branch in the marked part or more, and when the branch has buds, proceed to mark the buds which clearly state the date of the buds, and continuously monitor the buds growing on the experimental branches throughout the experimental period The total number of experimental branches initially monitored was 40 branches On the basis of the branches marked in year, to monitor the growth criteria of the fruit branches and fruit yield, on that basis, use mathematics to analyze the correlation between the biological criterias of branch growth and fruit yield *Criteias and methods according to track: The growth criterias of fruit branches include length, diameter, and the number of leaves The above parameters were measured separately on experimental branches The yield parameters of fruiting branches were also measured separately for each fruit-bearing branch The above data will be analyzed to determine the relationship between fruit tree growth and yield capacity 2.3.1.4 Research on the phylogenetic origin and the relationship between the buds in the Bo Ha king mandarin tree * Experimental setup: The experimental garden was years old and randomly selected 10 trees for monitoring and evaluation (according to the method of Ngo Xuan Binh et al in 1998 ) The shoots on the monitored branches were observed and recorded continuously for years (2019, 2020, and 2021) * Tracking criterias: The number of buds in a year, and the rate of branches forming according to the season The origin of the buds formation of the year Determine the origin of the mother branch (the branch that produces the fruit branch) and the origin of the fruit branch (the branch that produces flowers and fruits) Determine the relationship between the buds formations of the year flowers bloom, Spray 2: spray when flowers are in full bloom, Spray 3: spray 10 days after flowers bloom The way to spray: spray wet all flower clusters, and flower buds at the end of the afternoon session * Criterias and tracking methods: Fruiting rate; Number of fruits/tree; Fruit weight (kg); Yield/plant (kg); Fruit quality criterias 2.3.2.3 Research methods on the effects of some foliar fertilization inoculants in combination with pruning on the yield and quality of Bo Ha king mandarin * Select plants for the experiments: The tree is years old, is at the stage of business, and is most vigorous, choose trees that are relatively uniform in terms of initial growth and development The formulations were studied under the same growing and growing conditions * Experimental design: The experiment was arranged in a fully random design on an orange garden which is from years old, with treatments, replicates, and trees each time with different treatments are as follow: + Formula 1: Control: Water spray combined with the best pruning method + Formula 1: Spray inoculant in combination with the best pruning method + Formula 2: Spray inoculant combined with the best pruning method + Formula 3: Spray inoculant in combination with the best pruning method The formulations were carried out under the same growing and care conditions Only for the best pruning method, all the recipes were pruned according to the method of the Fruit and Vegetable Research Institute in the year with good number of fruits and all recipes are pruned according to the initiation method in little fruit year - Method of spraying inoculants in different periods: Spray 10 days before flowers bloom, spray when flowers are in full bloom, and spray 10 days after flowers bloom The way to spray: spray wet all flower clusters, and flower buds at the end of the session afternoon * Monitoring criterias : Fruiting rate and yield factors, fruit quality criterias 2.3.2.4 Research on the influence of fertilizer to yield and fruit quality criterias of Bo Ha king mandarin - Research on the effect of the dose of potassium fertilizer on the yield of Bo Ha king mandarin tree The experiment was arranged in a fully random design with treatments, replicates, and trees each time are as follow: Formula 1: Control- manure; Formula 2: kg potassium chloride; Formula 3: 0,2 kg potassium chloride; Formula 4: 0,4 kg potassium chloride; Formula 5: 0,6 kg potassium chloride; Formula 6: 0,8 kg potassium chloride; Formula 2: kg potassium chloride Fertilizer recipes are used on the background with 0.8 kg of superphosphate + 20 kg of manure - Study on the effect of nitrogen fertilizer dosage on the yield of Bo Ha king mandarin The experiment was arranged in a fully random design with treatments, replicates, and trees each time are as follow: Formula 1: manure; Formula 2: kg urea fertilizer; Formula 3: 0,25 kg urea 10 fertilizer; Formula 4: 0,5 kg urea fertilizer; Formula 5: 0,75 kg urea fertilizer; Formula 6: kg urea fertilizer; Formula 7: 1,2 kg urea fertilizer The dose of potassium fertilizer used from the best results from the potassium fertilizer experiment; General fertilizer background for the experiments was: 0.8 kg superphosphate + 20 kg manure Tracking criterias: - Fruiting rate and yield relating factors, quality indicators, pest and disease activvities in different fertilizer formulations 2.3.2.5 Research on the influence of rootstock and grafting time on the growth of Bo Ha king mandarin * Experimental design: The experiment was arranged in a completely randomized design with treatments, replicates, and 10 plants each time with the following formulas: Formula 1: Using rootstock is a Citrus hystrix tree; Formula 2: Using rootstock is sour pomelo; Formula 3: Using the rootstock is Dien pomelo Grafting method used: eye grafting * Targets to track: - Evaluation of the ability of grafted eyes to adapt and grow on rootstocks - Evaluation of pests and diseases - Determine the percentage of grafted plants that pass and not meet the standards for garden release 2.3.3 Data processing methods The aggregated data are processed by statistical processing software: IRISART 4.0 and Microsoft Excel CHAPTER RESEARCH RESULTS AND DISCUSSION 3.1 3.1 Research results on some agro-biological characteristics of Bo Ha king mandarin 3.1.1 Research results on morphological characteristics of Bo Ha king mandarin 3.1.1.1 Characteristics of stems and branches Bo Ha king mandarins tree has a relatively good growth ability, years old trees have the height from 212.13 cm to 229.27 cm, with an average of 218.66 cm The tree branch is inclined, there are almost no thorns on the branches The root diameter ranges from 4.88 cm to 5.23 cm, with an average of 5.10 cm; Foliage is hemispherical, canopy diameter ranges from 176.72 cm to 203.20 cm, averaging 189.26 The tree has a large branching ability, the number of level I branches is from 3.00 to 3.83, the average is 3.44 branches, the average diameter is 3.26 cm, the average height of branching is 15.60 cm The number of level II branches ranges from 12.60 to 15.74 branches, with an average of 13.87 branches The ratio of level II branches / level I branches ranged from 3.89-4.20, with an average of 4.04 Comparing the morphological characteristics of the Bo Ha king mandarin tree with that of the Ham Yen king mandarin tree in the 11 study, it was found that the morphological characteristics of Bo Ha king mandarin are quite similar to the morphological characteristics of Ham Yen king mandarin trees when planted in Thai Nguyen and with the same care regime 3.1.1.2 Leaves morphological characteristics The set of Bo Ha king mandarin leaves has oval shape, dark green color, the leaf edge is wavy, blade length ranges from 8.79 to 8.85 cm (mean 8.83 cm), blade width ranges from 4.71 to 4.76 cm (mean 4.74 cm), leaves have no waist The petiole has a length of 0.48 - 0.62 cm (mean 0.57 cm) When compared with Ham Yen king mandarins, the leaf morphology of Bo Ha king mandarins is quite similar to Ham Yen king mandarin But it has a slightly larger length/width ratio (1.86 versus 1.75) 3.1.1.3 Morphological characteristics of the flower The results of observing flower morphology showed that most flowers of Bo Ha king mandarins are clustered or self-flowering, flowers are self-sufficient with leaves or no leaves Large flower buds, corolla, and petals are white, and thick, with many male stamens but There is only female pistil In which, the female pistil has parts of the stigma head, style, and ovary The female pistil is usually higher than the anther, under the flower bulb there is a nectar disk, the nectar disc is larger than the flower bulb, which can secrete nectar to attract insects to suck nectar for pollen transmission In general, the Bo Ha king mandarin tree has the same shape, color, and number of petals as the Ham Yen king mandarin tree The criterias of petal length, number of stamens/flowers, length of stamens, and pistil length are lower than that of the Ham Yen king mandarin tree 3.1.1.4 Morphological characteristics of the fruit The Bo Ha king mandarin fruit has a flat spherical shape, the bottom is flat, and the essential oil vesicle is clearly visible This feature is different from Ham Yen king mandarin (concave bottom, floating essential oil vesicle) The peel, pulp, and shrimp have a dark yellow color similar to Ham Yen king mandarins Bo Ha king mandarin crockery is juicy, crispy, and delicious to eat Bo Ha king mandarin tree grows well when planted in Thai Nguyen, the tree gives good yield and quality of fruit Our research results show that Bo Ha king mandarins have many common characteristics of orange varieties in general, the most obvious difference being that compared with other orange varieties, it is shown in canopy morphology and color of fruit pulp 3.1.2 Research results on genetic diversity of Bo Ha king mandarin by molecular markers ISSR and RADP 3.1.2.1 Extraction of total DNA from leaf samples Thirty-two citrus samples were collected for total DNA extraction from young leaves, the results of electrophoresis testing the extracted product on 1.0% agarose gel are shown in Figure 12 Figure 3.1 Electrophoresis results of total DNA testing of citrus samples collect The results of electrophoresis testing of total DNA extraction products in Figure showed that all 32 samples analyzed gave a bright, clear, unbroken DNA band The results of total DNA analysis indicate that DNA concentrations of samples ranged from 27.5 - 35.5 ng/µL, the OD 260 /OD 280 ratio ranged from 1.85 to 1.95 Thus, it can be concluded that the total DNA has been successfully extracted from the collected citrus samples, and the total DNA has sufficient content and purity enough to carry out studies on genetic diversity analysis by analytical markers 3.1.1.2 Results of PCR product polymorphism analysis with RAPD and ISSR primers In this study, we used 13 DNA markers including 10 RAPD markers and ISSR markers to evaluate the genetic diversity of collected citrus samples The obtained results are summarized in Table The results of electrophoresis of PCR products with primer OPA-08 and primer ISSR-T1 are shown in Figure 3.2 Figure 3.2 Electrophoresis images of PCR products with primers OPA-08 (top) and primers ISSR-T1 (bottom) Note: M: 1kb DNA standard scale, running from 1-30: are 30 research samples The analysis results of each pair of primers in Table 3.6 showed that all 13 used markers giving 100% polymorphism No homomorphic segments appeared in all 32 samples analyzed The analysis results also showed that the RAPD markers for the total number of polymorphic segments ranged from 10 segments (primer OPQ-18 and OPT-01) to 14 segments (primer OPB-18), ISSR markers for the number of polymorphic segments ranging from - segments From the results of polymorphism analysis using 10 RADP and ISSR molecular markers, NTSYSpc 2.1 software was used to build a tree diagram of genetic clustering and genetic distance Trees showing genetic groups of 32 analyzed orange and mandarin samples are shown in Figure 3.3 13 Figure 3.3 Tree diagram of genetic relationship of 32 samples of citrus varieties studied (coefficient: genetic similarity coefficient) The diagram depicting the genetic relationship of 32 samples of citrus varieties in Figure 3.3 shows that the genetic similarity coefficient between the studied orange samples ranges from 0.64 to 1.00; demonstrating that the orange samples had a high genetic polymorphism From the above results, it is shown that Bo Ha king mandarins and Ham Yen king mandarins, and Ha Giang king mandarins belong to two different phylogenetic groups with a genetic similarity coefficient of 0.75 The study to evaluate the genetic diversity of 36 samples of Vietnamese local orange varieties using the SSR indicator of Le Thi Thu Trang and collaborators ( 2021 ) [57] also identified Bo Ha king mandarin as a separate subgroup compared with other orange varieties in Vietnam 3.1.3 Research results on the growth characteristics of the buds of the Bo Ha king mandarin variety The results of research on the relationship between the buds of Bo Ha king mandarins show that: In a year, the Bo Ha king mandarin tree produces four main crops of buds in Spring, Summer, Autumn, and Winter Spring crop branches mainly produce fruit branches (the branches bear flowers and fruits) and autumn branches (source of mother branches produce fruit branches next year) are two important types of branches that determine the yield of the tree Compared with Ham Yen king mandarin is planted and care in the same condition, the time presents the buds crops of the Bo Ha king mandarin are earlier than Ham Yen king mandarin Under the same ecological conditions, Bo Ha king mandarin bloom flower and ripening earlier than Ham Yen king mandarins 14-27 days, and Bo Ha king mandarins are relatively early ripening, the first ripe fruits can be harvested in early November every year, while Ham Yen king mandarins can only be harvested from December to the Lunar New Year, this is an important feature to distinguish the difference between 14 two varieties of Ham Yen and Bo king mandarin The comparison between Bo Ha king mandarins and Ham Yen king mandarins shows that the buds crops of Bo Ha king mandarins appear earlier than Ham Yen king mandarins when grown at the same location, with the same care density Bo Ha king mandarins bloom flower and ripen early, the first ripe fruit crop can be harvested in early November every year, this is an important feature to make clear the difference between the two varieties of Ham Yen and Bo Summer The Bo Ha king mandarin grown in Thai Nguyen has crops of fortune tỷ lệ chồi vụ năm giống với giống cam khác However, the appearance time of the early buds and the flowering time are similar to the time of the first flowering crop of Tay Giang oranges 3.1.4 Research results on phylogenetic origin and relationship between buds crops in Bo Ha king mandarin tree 3.1.4.1 The origin and formation of branches according to the fruit-bearing function of the spring crop in 2019 The research results in figure 3.4 have shown that the spring crop in 2019 formed two main types of branches: flower-bearing branches (often called fruit branches) accounted for 81.1 % of the total number of Spring crop branches, and nutrient branches (which not bear flowers) accounted for 18.9% Figure 3.4 The diagram about the origin of branches of the Spring crop in 2019 and the proportion of spring branches according to fruit bearing function Phylogenetic origin and relationships between summer, autumn, and winter buds crops in Bo Ha king mandarin tree in 2019 Research results show that: in 2019 (the year of harvest), the tree produces many flowers and bears many fruits, the spring branch is the type of branch that flowers and bears fruit in the year ( the determining factor for the yield of the Bo Ha king mandarin tree) was formed mainly from the branches of the autumn crop last year (2018) (Hình 3.6) 3.1.4.2 15 Phylogenetic origin and relationship between summer, autumn, and winter buds crops in Bo Ha king mandarin tree in 2020 The year 2020 is the year of failure crop, plants produce few flowers and give low yields The results of years follow-up (2019 and 2020) show that: The 1-year growth cycle of the Bo Ha king mandarin tree has clear rules, spring branches are mainly differentiated into fruit branches, and annual autumn branches are the mother branches of the following year's fruit branches This is a very important factor related to the impact of farming techniques to promote the emergence and growth of the Autumn buds to have a high and stable annual yield 3.1.3.3 The ratio of branches according to the growth cycle of the year and the correlation analysis between the ratio of branches in the autumn crop and the yield of fruit The year 2019 and 2021 are the years the tree produces many fruits (bumper year) and the year 2020 is the year the tree produces little fruit (the year of failure crop) In the years when the tree produces a lot of fruit (with a good crop), the percentage of Spring branches is very high, in the years the tree produces few fruits (lost the crop), the rate of spring branches is very low, but the rate of Autumn branches is very high This phylogenetic rule can serve as a basis to explain the phenomenon biennial bearing in citrus trees in general and Bo Ha king mandarin trees in particular It can be concluded that: The origin of the buds is closely related, the previous one is the mother branch of the next one In particular, Spring buds mainly form branches bearing flowers and fruits, Autumn branches are the mother branches that produce fruit branches next year, so Spring branches and Autumn branches are two important types of branches that determine the yield of the tree In the years when the tree bears a lot of fruit (with a good crop), the ratio of spring branches to the total number of branches growing in the whole year is very high, while the rate of autumn branches is very low In the years of low fruit trees (lost the crop), the rate of Spring branches is very low, but the rate of Autumn branches is very high The linear correlation between the ratio of Autumn branches and fruit yield in the next year of orange trees shows a very close correlation (correlation coefficient r = 0.81) 3.2 Research results on the effects of some technical measures on growth, yield, and quality of the Bo Ha king mandarin 3.2.1 Research results on the effect of pruning on growth and yield of Bo Ha king mandarin tree 3.2.1.1 Research results on the effect of the pruning method on the growth of buds and the rate of seasonal buds in the Bo Ha king mandarin variety In this study, we use the pruning method according to the method of the Fruit and Vegetable Research Institute and the initiation method With the Bo Ha king mandarin variety, Spring and Autumn buds account for a higher ratio of Summer and Winter buds with the trend: with a good crop, the Spring bud plays the dominant role and in the year when the tree produces less fruit, the autumn buds are dominant Overall, pruning measures in both methods have positive effects in regulating the 3.1.3.2 16 rate of spring buds and increasing the annual rate of autumn buds, affect seriously to the process of flowering and fruiting, creating a premise to improve crop productivity The results also show that, in 2019 (the year of low fruit), the pruning method according to the Fruit and Vegetable Research Institute was more effective than pruning according to the initiation method in increasing the percentage of Autumn branches In 2020, the initiation method (formula 2) helped the highest rate of Autumn, get a raise from 57.2% in control treatment without pruning to 61.2% This has implications for the next year's productivity formation (in 2021) This result also gives permission to determine that: In the year that the Bo Ha king mandarin is fruitful, the pruning method of the Fruit and Vegetable Research Institute is suitable, the years of Bo Ha king mandarins have few fruits, the pruning method of initiation is suitable 3.2.1.2 Effect of pruning methods on fruit setting rate and yield building factors of Bo Ha king mandarin It is possible to conclude: Two pruning methods are meaningful and effective on increasing fruit yield in the studied Bo Ha king mandarin trees However, It should be applied under specific conditions each year according to the growth and flowering situation of the tree In fruitful years, the pruning method according to the Fruit and Vegetable Research Institute is more effective than pruning by the initiation method, in the years of low fruit, the initiation pruning method is suitable 3.2.2 Research results on the effect of rind removal method on yield and quality of the Bo Ha king mandarin 3.2.2.1 Effect of rind removal method on flowering time of the Bo Ha king mandarin tree In this study, we have determined that rind removal method has the effect of helping flowers bloom earlier, the appropriate time for the Bo Ha king mandarin tree planted in Thai Nguyen is November 15 last year The early flowering and short blooming time have important meaning in the production of fruit trees in general and Bo Ha king mandarin trees in particular help fruit ripening time is early, even, and concentrated The early ripening time of Bo Ha king mandarins helps reduce competition with other orange varieties, increasing product costs The concentrated ripening time of Bo Ha king mandarin s makes the care and harvesting more convenient and reduces production costs 3.2.2.2 Effect of rind on the fruiting rate of the Bo Ha king mandarin tree The time of shelling on November 15, 2018, has the highest fruit setting rate The difference in fruit set rate between the experimental treatments was completely statistically significant at the 95% level Tracking results in 2020 (the year that Bo Ha's oranges in this study had few fruits) also give the same result as in 2019 The time of shelling on November 15, 2019 (CT3) for the highest fruit set rate in 2020 ( reaching 11.06 % ) and higher than the rest of the formulas (significant at the 95% level) Thus, from the tracking results in 2019 and 2020, it can be confirmed that shelling on November 15 every year is the most suitable to help improve the fruit setting rate in Bo Ha king mandarin 17 Effect of rind removal time on yield components of Bo Ha king mandarin tree The Bo Ha king mandarins are grown in Thai Nguyen, the most suitable time to peel the skin is on November 15 every year Rind removal method is a technical measure to help plants flower early, flowering time is concentrated, increase fruit setting rate and increase fruit yield on trees and help limit the phenomenon biennial bearing 3.2.3 Research results on the effects of some foliar fertilization products on the yield and quality of Bo Ha king mandarins 3.2.3.1 Research results on the effect of some foliar fertilization inoculants on the fruiting rate of Bo Ha king mandarins grown in Thai Nguyen Using inoculant 2, spraying 10 days after flowers bloom gave the highest fruit set rate in Bo Ha king mandarin in the study 3.2.3.2 Research results on the effects of some foliar fertilization inoculants on yield and quality components of Bo Ha king mandarins grown in Thai Nguyen Spraying inoculant gave the highest quality of Bo Ha king mandarins and was statistically significant when compared to the control at 95%, except the edible rate of the fruit When spraying inoculant 2, the dry matter ratio of the fruit was 14.88%, the total sugar, reducing sugar, total acid content and Brix of the fruit were 8.03%, 6.89%, 0.74%, and 9.29%; The vitamin C content of the fruit is 39.16 mg/100g of fresh fruit However, when spraying different inoculants, the edible rate of the fruit was lower than the controls 3.2.4 Results of research on the effects of some foliar fertilization inoculants combined with pruning on the fruit set rate and yield and quality components of Bo Ha king mandarin fruit 3.2.4.1 Research results on the effect of some foliar fertilization inoculants combined with pruning on the fruit set rate of Bo Ha king mandarin s grown in Thai Nguyen Research results show that, when spraying different inoculants in combination with pruning, the fruit set rate is higher than the control which use only pruning according to the corresponding method In which, the rate of fruit set after 60 days of flowering was highest when using inoculant 3.2.4.2 Research results on the effects of some foliar fertilization inoculants combined with pruning on some yield and quality components of Bo Ha king mandarins grown in Thai Nguyen Spraying inoculant gave the best results and the difference was statistically significant compared with the control at 95% When spraying inoculant 2, the average number of fruits /plant was 131.9 fruits, the average weight of fruit was 217.30 g, and the average yield/tree was 28.66 kg 2020 is a year of few fruits, using the initiation pruning method, spraying inoculants after 10 days of flowering gives the highest results and is statistically significant at 95% higher than the control The average number of fruits /plant was 59.8 fruits, the average fruit weight of fruit was 217.35 g, and the average yield/tree was 13.00 kg Spraying inoculant combined with pruning gave the best fruit quality parameters and this difference was statistically significant at 95% compared to the control When spraying inoculant 2, the percentage of dry matter, total sugar, reducing sugar, total acid, 3.2.2.3 18 and Brix of Bo Ha king mandarin were 15.78, reaching 7.92% and 6.98%, 0.82%, and 9.22% The vitamin C content of the fruit, when sprayed with inoculant in combination with pruning according to the method of the Fruit and Vegetable Research Institute, was 39.16 mg/100g of fresh fruit Thus, using the combined method of pruning and providing appropriate nutrition will contribute to improving yield and quality, limiting the biennial bearing phenomenon in oranges in general and Bo Ha king mandarin in particular This is the scientific basis for building the process of taking care of Bo Ha king mandarins in particular and citrus in general 3.2.4.3 Research results on the effect of fertilizer formula on yield of Bo Ha king mandarin Research results on the effect of potassium fertilizer dosage on fruit yield of Bo Ha king mandarin tree The experiment arranged different doses of potassium chloride (KCl) (0 kg; 0.2 kg; 0.4 kg; 0.6 kg; 0.8 kg and kg) on the background of manure used is 0.5 kg Urea + 0.8 kg superphosphate + 20 kg manure Experimental results showed that: different doses of potassium fertilizer affected the number of fruits/tree, average fruit weight and fruit yield/tree of Bo Ha king mandarin variety The number of fruits per tree of the treatments was from 87.4 to 130.9 fruits, of which the potassium fertilizer formulas were higher than the control, formula (0.4 kg Potassiumchloride) and (0.6 Potassiumchloride) are highest Formula and are also the two formulas with the highest average fruit weight (203.2 g/fruit and 202.8 g/fruit) significantly higher than the control (reached 195.4 g/fruit), fruit yield is from 17.1 kg - 26.6 kg/tree, of which the highest are CT4 (26.6 kg) and CT5 (26.1 kg), definitely higher than the control at the confidence level 95% The correlation between the dose of potassium fertilizer and fruit yield is shown in a parabolic figure, the correlation between the dose of potassium fertilizer and fruit yield shows a positive correlation when the dose of potassium fertilizer increased gradually and the highest yield was achieved when the dose of potassium fertilizer was 0.4 kg (CT4) and 0.6 kg (CT5) Then showed a negative correlation, when the dose of potassium fertilizer increased higher than 0.6 kg, the fruit yield tended to decrease sharply - Research results on the effect of nitrogen fertilizer dosage on yield and quality of Bo Ha king mandarin tree The experiment arranged different doses of urea nitrogen fertilizer (0 kg; 0.25 kg; 0.5 kg; 0.75 kg and kg) on the background using 0.4 kg potassium chloride + 0.8 kg superphosphate + 20 kg of manure Experimental results show that: The effect of nitrogen dosages on yield is expressed in different rules at different levels of fertilizer dosage Fruit yield was positively correlated when the dose of nitrogen fertilizer increased gradually and fruit yield reached the highest level in the treatment with 0.5 kg Urea/tree (reaching 27.1 kg/tree) higher than the control (reaching 18.6 kg.tree) at the confidence level 95% When the dose of urea fertilizer is higher than the threshold of 0.5 kg/tree, the yield of Bo Ha king mandarin tends to decrease, shows a negative relationship when the dose of urea was increased to 0.75 kg, kg and 1.2 kg, the fruit yield was only: 17.2 kg/tree, 15.9 kg/tree and 14.6 kg/tree, respectively Research results on the effect of fertilizer on yield of Bo Ha king mandarin tree show that: Fertilizer has a significant effect on fruit yield in 19 Bo Ha king mandarin tree, fertilizing at an appropriate and balanced rates has the effect of improving fruit yield in the studied oranges trees When fertilizing is unbalanced, applying too high a dose of potassium fertilizer or a high dose of nitrogen fertilizer will reduce yield and quality of fruit The 4-years-old Bo Ha king mandarin tree, suitable NPK fertilizer combination is: 0.8 kg superphosphate + 20 kg manure, the most suitable dose of potassium fertilizer (KCl) is from 0.4-0.6 kg/plant and the most suitable dose of nitrogen fertilizer (Urea) is 0.5kg/plant 3.2.5 Research results on the effect of rootstock and grafting season on the growth of the Bo Ha king mandarin 3.2.5.1 Effect of grafting season Comparisons between different grafting seasons in the same grafting combination found that the highest survival rate was achieved when grafting in the Autumn crop, then in the Summer, and the lowest when grafted in the Spring crop Comparing the survival rate between the grafting combinations, it was found that grafting Bo Ha king mandarins on Dien pomelo root gave the highest survival rate, followed by sour pomelo; The lowest survival rate when using rootstock is a citrus aurantium The difference in the research results between the combinations is statistically significant at 95% The survival rate of Bo Ha king mandarin eye graft on Dien pomelo root when grafted in summer, autumn and spring after 70 days was 87.8%, 91.1%, and 86.7%, respectively In each grafting combination, the germination rate of grafted eyes was highest during Autumn grafting, then Summer, and lowest when grafting in Spring The results of monitoring the germination rate of grafted eyes between grafting combinations showed that using rootstock of 1-year-old Dien pomelo gave the highest germination rate and the difference was significant at 95 % Summer grafting gave the highest branch diameter when compared with other grafting seasons because within months of follow-up, grafts grew in summer and autumn, this is the time of year with high temperature, intense brightness strong, branches elongate in a short range, nutrients used to raise diameter of trunk and branches, so the diameter of grafted branches is highest When monitoring the growth of grafted cuttings on different rootstocks, it was found that using Dien pomelo rootstock for the growth parameters of the studied cuttings graft of Bo Ha king mandarin give the highest after that is the rootstock from sour pomelo and lowest is the combination between eye grafts of Bo Ha king mandarins on citrus aurantium Thus, the research results show that using Dien pomelo root to graft Bo Ha king mandarins is the most suitable Research results also show that when graft in the Autumn, the long of the branches, diameter of branch graft, number branch level and branch level are not high but number of leaves and number leaves eyes are highest if compare with the grafting in Spring and Summer when the monitor grafted plants at the age of months, the high number of leaf eyes and leaves is very significant, creating a premise for the best growth and development in the next stage From the above research results, it is shown that using Dien pomelo rootstocks to graft Bo Ha king mandarin eyes, in the autumn is the most suitable We continue to evaluate the effect of rootstock on the level of pests and diseases of the Bo Ha king 20 mandarin tree The results are presented in Table 3.33 The monitoring results showed that the combination of Bo Ha king mandarins grafted on the rootstock of citrus aurantium appeared to both pests and diseases, in which the ulcer disease and Tristeza disease are highest When uses sour pomelo as rootstock, grafted plants not appear greening disease but appear others diseases at light degree Using Dien pomelo rootstocks, only citrus leafminer appeared in less than 30% of trees, branches, and leaves, and no other pests and diseases appeared during the monitoring period From the above research results, it is possible to conclude that using Dien pomelo rootstocks is suitable for Bo Ha king mandarin eye grafting The grafted tree on Dien pomelo rootstocks gave the highest survival rate and germination rate The grafted plants grow and resist well to pests and diseases, and the percentage of plants that reach the highest standard for market in the studied grafting combinations, is highest The suitable grafting season is determined as in the Autumn 3.2.5.2 Research on the effect of rootstock age on the ability of grafting branches to integrate and grow After determining the suitable rootstock for Bo Ha king mandarin’s grafting eyes, we conducted a study on the influence of the age of the rootstocks on the integration and growth of the grafted branches In this study, the effect of using Dien pomelo as rootstock for Bo Ha king mandarins is one of the new points of the thesis Statistical monitoring results in table 3.36 show that different rootstock age, different growth parameters of grafted branches, growth parameters increase gradually when using rootstocks from year old to years old in which the 3-year-old rootstock has higher growth monitoring criterias than the 1-year-old and 2-year-old rootstocks with statistical significance at 95% Thus, the 3-year-old Dien pomelo rootstocks showed the highest germination percentage and growth parameters when compared with the 1-year-old and 2-year-old Dien pomelo rootstocks When the age of the rootstocks increases, the diameter of the rootstock is larger, the size of the roots is larger, and the roots are stronger, deeper, and wider, so the ability to provide nutrients to the graft is better, the grafts germinate better and the growth ability is better 3.2.5.3 Research results on the correlation between rootstock diameter and some growth parameters of grafted branches From the results of the analysis of the influence of the diameter of the 1-year-old and 3-year-old Dien pomelo rootstock, it can be concluded that the diameter of the Dien pomelo rootstock has a significant effect on the diameter of the Bo Ha king mandarin graft; The larger the rootstock diameter, the larger the graft diameter The diameter of the rootstock has a relatively clear influence on the length of the cuttings, but the effect is not clear on the length of the cuttings and the number of leaves/leaves eyes of the Bo Ha king mandarin tree 3.2.5.4 Correlation analysis results between the age of the rootstock and the flowering time of the grafted branch of the Bo Ha king mandarin Using the rootstocks of 3-year-old Dien pomelo to graft Bo Ha king mandarin's eyes in this research give the highest effect, time for the tree become mature and 21 flowering earlier, improving yield of Bo Ha king mandarins compared to using 1- and 2-year-old rootstocks Using the rootstock of 3-year-old Dien pomelo, the trees flowers after 17 months from the time of grafting, the average weight of the fruit was 193.24, the average number of fruits/tree was 95.36 and the average yield/ dandelion tree 18.43 CONCLUSIONS AND RECOMMENDATIONS CONCLUSIONS 1.1 Agro-biological characteristics of Bo Ha king mandarin - About morphological characteristics: Bo Ha king mandarin grows well when planted in Thai Nguyen, the tree gives good yield and fruit quality Morphologically, the tree branch is inclined, the foliage is hemispherical, The tree is capable of large branching Leaves are oval, dark green, wavy margins, no leaf waist Flowers are hermaphroditic, mostly in the form of inflorescences or self-flowering, sometimes with cheeks or not, with petals, bright white, with many male stamens but only female pistil The peel of the fruit when ripe is dark yellow, the pulp and shrimp are dark, the pulp is berry, crunchy, very delicious to eat In particular, the fruit has a flat spherical shape, the bottom is flat, and the essential oil bag is clearly visible This is a fruit morphological feature that is clearly different between Bo Ha king mandarin and Ham Yen king mandarin (Ham Yen king mandarin has a concave bottom and a floating essential oil bag) - Characteristics of the buds crops: Bo Ha king mandarin gives seasons of buds in the year, including Spring, Summer, Autumn and Winter The number of spring buds, summer buds and autumn buds appear relatively large, and winter buds are less in number Compared with Ham Yen king mandarin planted and cared for under the same conditions, the time of appearance of the buds of Bo Ha king mandarin is earlier than that of Ham Yen king mandarin Under the same growing conditions and care regime, Bo Ha king mandarin bloom and ripen earlier than Ham Yen king mandarin, and Bo Ha king mandarin belong to relatively early ripening group, the first ripe fruit crop can be harvested in early November every year, while Ham Yen king mandarin can only be harvested from December to the Lunar New Year, this is an important feature to distinguish between two varieties of Ham Yen and Bo Ha king mandarin - Genetic diversity: Evaluation of genetic diversity between Bo Ha king mandarin and citrus varieties grown in Vietnam by molecular markers shows that Bo Ha king mandarin has its own phylogenetic branch Bo Ha king mandarin and Ham Yen and Ha Giang king mandarin are two separate phylogenetic branches with a similarity coefficient of 0.73 - About the origin of the buds: Spring buds mainly form flower and fruit-bearing branches, Autumn buds are the mother branches that give birth to fruit branches next year So these are two important branches types that determine the yield of the tree In the years when the tree bears a lot of fruit (bumper crop), the ratio of spring branches to the total number of branches growing in the whole year is very high, while the rate of autumn branches is very low In the years of low fruit trees (years of failure crop), the rate of spring branches is very low, but the rate of autumn branches is very high 22 The linear correlation between the ratio of Autumn branches and fruit yield in the following year of orange trees shows a very close correlation 1.2 About some technical measures to improve yield and fruit quality of Bo Ha king mandarin - About pruning method: The method of the Fruit and Vegetable Research Institute and the method of initiation are both meaningful and effective in increasing fruit yield, limiting biennial bearing phenomenon, and helping to stabilize the yield of Bo Ha king mandarin trees However, it should be applied in specific conditions each year according to the growth and flowering and fruiting situation of the tree In fruitful years, the pruning method of the Fruit and Vegetable Research Institute is more effective than pruning according to the initiation method, in the years of low fruit, the initiation pruning method is more suitable - About the peel circling technique: The technique of circling the peel on the Bo Ha king mandarin tree grown in Thai Nguyen has an important meaning to help the trees flower earlier, flowering time concentrated, and help the fruit ripen early, even and concentrated, thereby increasing product costs, reducing production costs The most suitable time to circle the shell is November 15 every year - About the foliar inoculants spraying: The foliar fertilizers sprayed at different times showed the effect of increasing the fruit set rate, the number of fruits on the tree, the yield, and the quality of the fruit In particular, using products sprayed 10 days after the flowers bloom had the highest effect on Bo Ha king mandarin compared to the remaining inoculants Spraying inoculants after 10 days of flowering combined with appropriate pruning methods (in the year of bumper crop, pruning according to the method of the Fruit and Vegetable Research Institute, in the years of failure crop, pruning according to the initiation method) had the effect of improving the fruit setting rate, increase the number of fruits on the tree, and increase the yield and quality of Bo Ha king mandarins - the use of fertilizer combinations: Fertilizer has a significant effect on fruit yield in Bo Ha king mandarin tree, in which potassium fertilizer with appropriate dosage has the effect of increasing the rate of fruit set, fruits are sweet and flowers bloom earlier Nitrogen fertilizers with appropriate doses increase plant’s growth and yield, Too much nitrogen fertilizer will have negative effects such as reduced fruit setting, the sweetness decreases and especially the plants are more heavily infected with pests and diseases The fertilizer background for 3-4 year old Bo Ha king mandarin tree includes: 0.8 kg superphosphate + 20 kg manure, the most suitable dose of potassium fertilizer (KCl) is from 0.4-0.6 kg/plant and the most suitable dose of nitrogen fertilizer (Urea) is 0, 5kg/tree - About grafting time and rootstocks: grafting on Dien pomelo rootstocks in the Autumn is the most suitable for Bo Ha king mandarin grafting eyes through survival rate, germination rate, and growth of grafted branches The age of the rootstocks is positively correlated with the survival and germination rate of the graft; 3-year-old Dien pomelo rootstocks gave the best about criterias of germination rate and growth criterias of grafted cuttings, including maturity time, earliest flowering time, and highest average yield Plants flower after 17 months from the time of grafting The 23 diameter of Dien pomelo rootstock has a significant effect on the diameter of the Bo Ha king mandarin grafts, a relatively clear influence on the length of the graft, but the effect is not clear on the number of leaves/leaf nodes of the Bo Ha king mandarins RECOMMENDATIONS - Continue to study the effects of GA3 preparations on the growth, yield, and quality of Bo Ha king mandarins - On the basis of the research results of the thesis, continue to study to optimize the planting and care process of the Bo Ha king mandarin tree in the Northern midland and mountainous areas of Vietnam in general and in Thai Nguyen in particular