Tài liệu Nghiên cứu yếu tố gây xì mủ bên trong trái măng cụt (garcinia mangostana l.) (tt)

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MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY LE BAO LONG “STUDY ON FACTORS CAUSING INNER GAMBOGE DISORDER IN MANGOSTEEN (Garcinia mangostana L.)” Maior: Crop Science Code: 62-62-01-10 SUMMARY OF DOCTORAL DISSERTATION Can Tho - 2015 The dissertation was completed at: College of Agriculture and Applied biology – Can Tho University Scientific supervisors: Ass. Prof. LE VAN HOA Ass. Prof. NGUYEN BAO TOAN Opponent 1: Opponent 2: Opponent 3: The dissertation will be presented at university level Time……………………………………Date………………………………… Further information of the dissertation could be found at: 1. Learning Resource Center – Can Tho University 2. National library of Vietnam 1 OVERVIEW OF THE THESIS 1.1 The necessity Mangosteen is called “the Queen” of fruits because of its qualities such as delicous, nutritious, popular and having great export potential, etc. However, through the experience of cropping mangosteen of farmers in Cho Lach district – Ben Tre province and Cau Ke district – Tra Vinh province, it showed that high yield and good quality are necessary to gain high profits from mangosteen fruits; but the investigation and survey results of Nguyen Minh Hoang and Nguyen Bao Ve (2008) showed that the gamboge disorder ratio in mangosteen was rather high, fruit harvested early in the beginning of the season rarely had gamboge disorder but the ratio of gamboge disorder highly increased at the end of the season, it was up to 100% when it was excess rain and it was one of the most interest problems of farmers cropping mangosteen fruit trees in Vietnam as well as in all over the world. Therefore, it is essential to study on factors causing inner gamboge disorder and to suggest possible practices. 1.2 Research objectives The study aims to determine factors that lead to the fruit gamboge phenomenon and suggest possible practices to reduce inner gamboge disorder in mangosteen fruits. 1.3 Subjects and scope Study subjects are mainly mangosteen fruit trees of different ages grown from seeds at farmers’ orchards in Cho Lach district – Ben Tre province and Cau Ke district – Tra Vinh province. Major scope of the study are some factors related to and practices to prevent the incidences of inner gamboge disorder in mangosteen fruits. 1.4 New contributions Inner gamboge disorder fruits had lower Ca2+ and pectin of cell-wall content in fruit-flesh than those in the normal ones; CaCl2 as foliar spraying reduced inner gamboge disorder ratio since Ca2+ increased pectin composition in cell-wall. 2 Internal pressure of fruit caused by growing segments (especially for the uneven growing segments) or the formation of seed containing apomictic embryos was not even. It caused damages and broke latex secretory ducts at the core of fruit and aril; GA3 as foliar spraying increased inner gamboge disorder ratio by increasing the thickness of fruit peel and reducing pectin content in cell-wall of fruit-flesh when harvest Sudden increase of soil moisture before harvesting increased inner gamboge disorder ratio due to water absorption of fruit and latex; Minimizing sudden increase of soil moisture before harvesting reduced inner gamboge disorder ratio. 1.5 Practical and scientific significances Scientific significances: the study results provided specific scientific basis about causes of inner gamboge disorder in mangosteen fruits. The results can be used as additional material of coursebook and reference for further studies of fruit trees. Practical significances: effective application in production, contribute to improve mangosteen fruit’s yield and quality, increase farmers’ income. Chapter 3 MATERIALS, CONTENT AND METHODOLOGIES 3.1 Research materials Mangosteen fruit trees of different ages were experimented at farmers’ orchards in Cho Lach district – Ben Tre province and Cau Ke district – Tra Vinh province, all were grown from seeds. Measuring and analysis instruments: refractometer (model ATAGO, Japan), pH meter (model ORION 420A, USA), spectrometer (model Shimadzu UV-1201, Japan), ...Chemical application on flowering: HVP super (Thiourea 99%, Technical Services Joint Stock Company in Ho Chi Minh City), KClO3 (99,5%; China), Paclo 10WP (Paclobutrazol 10%, Dong Thap Agricultural Service Company Limited),…Foliar fertilizer and plant groưth regulators: CaCl2 (96%, China), Bioted 603 (Vinh Long Technological Development Company), gibberellic and naphthalene acetic acid (China),…Analysis 3 chemicals: CH3OH, EDTA-Na4 (C10H12N2Na4O8.2H2O), NaBH4, (C2H5)2,... (China and Germany), …. 3.3 Research content 3.3.1 Survey of the incidences inner gamboge disorder in mangosteen fruits 3.3.1.1 Morphological characteristics and physical - biochemical characteristics of mangosteen fruits in growing process The experiments began in 3/2011 when mangosteen fruit trees were completely flowering and finished in 6/2011. Fruit samples were collected randomly from 30 trees aged from 20 - 25 years in one orchard in Long Thoi commune – Cho Lach district – Ben Tre province. The survey aimed to find out about inner gamboge disorder time and relationship between morphological and physiological-biochemical characteristics with the incidences of inner gamboge disorder in fruits. 3.3.1.2 Physical-biochemical characteristics of normal mangosteen and inner gamboge disorder fruit Fruit samples were collected randomly from 35 trees of different ages (from 15 to 25 years) in a orchard in Long Thoi commune – Cho Lach district – Ben Tre province in 2011 crop season. The survey aims to determine the differences of physical-biochemical characteristics between normal mangosteen and inner gamboge disorder fruits. 3.3.1.3 Ability to identify inner gamboge disorder fruits The survey was carried out in Cho Lach district – Ben Tre province in 2012 crop season. Four groups of the survey subject consisted of traders, orchard owners, sellers, and customers. Each participating subject was required to sellect 30 inner gamboge disorder fruits. The survey aims to find out about the relationship between external morphological characteristics and the incidenes of inner gamboge disorder through ability to identify of each group. 4 3.3.1.4 Relationship between plant age and the incidences of inner gamboge disorder It included two experiments: the first experiment to investigate the correlation of plant age with the ratio of inner gamboge disorder in fruit was carried out on 6 orchards with trees of different ages (10 - 15, 20 – 25, 30 – 35, 40 – 45, 50 - 55, and over 60 years old), the second experiment to investigate physical–biochemical characteristics of mangosteen fruits from young and old trees was carried out on 5 trees aged 10 – 15 years old and on 5 trees over 50 years old in one orchard under the same care regime. Both experiements were executed in Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season. The survey aims to find out the relationship between plant age and the incidences of inner gamboge disorder. 3.3.2 Survey on factors caused inner gamboge disorder in mangosteen fruit 3.3.2.1 The relationship between fruit physical characteristics and the incidences of inner gamboge disorder The survey aims to find out about the relationship between physical characteristics of fruit and the incidences of inner gamboge disorder, including two eperiments as follows: * Correlation of physical characteristics with the incidences of inner gamboge disorder Fruit samples were collected to survey physical-biochemical characteristics of normal and inner gamboge disorder fruits, at the same time the sample were used to survey the correlation with the incidences of inner gamboge disorder in fruits * Effect of gibberellic and naphthalene acetic acid as foliar spraying on the incidences of inner gamboge disorder The experiment was carried out in the orchard had stable fruit production (20 - 25 years old) in Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season. The experiment design was completely randomized, including 7 treatments with six replications for each 5 treatment, and each of which equal to one tree. The treatments included no chemical application (water spraying), GA3 or NAA from 25 to 100 ppm. Foliar spraying with GA3 and NAA were applied after completed flowering in 1 month with 8 liters.tree-1, spraying 4 times with 15-day invervals. 3.3.2.2 Effect of soil moisture on the incidences of inner gamboge disorder The survey aims to determine the relationship between soil moisture before harvesting and the incidences of inner gamboge disorder, including three experiments: * Relationship between changes of soil moisture before harvesting with the incidences of inner gamboge disorder The experiment started in 3/2011 when mangosteen trees were completely flowering and ended in 6/2011 on 6 mangosteen trees aged from 20 – 25 years in one orchard in Long Thoi commune – Cho Lach district – Ben Tre province. * Effect of timing of artificial water stress The experiment started in 3/2011 when mangosteen trees were completely flowering and ended in 6/2011 in the orchard of 23-year-old mangosteen trees had stable fruit production in Long Thoi commune – Cho Lach district – Ben Tre province. The experiment design was completely randomized, including 4 treatments with four replications for each treatment, each of which equal to one tree. The treatments were timing of artificial water stress after completed flowering 0.5; 1.5; 2.5; and as soon as fruit achieved level-0 color index according to the standard of MOA (2002). * Effect of the frequency of artificial water strees The experiment started in 3/2012 when mangosteen trees were completely flowering and ended in 6/2012 in the orchard of 24-year-old mangosteen trees had stable fruit production in Long Thoi commune – Cho Lach district – Ben Tre province. The experiment design was completely randomized, including 5 treatments with four replications for each treatment, each of which equal to one tree. The treatments were the number of water 6 stress times when the trees were completely flowering 2.5 months: control (without treating artificial water stress), 1, 2, 3 and 4 times. The first water stress when completed flowering 2.5 months, for multiple treatments of water stress, the next treatment will be conducted after 7 days. 3.3.2.3 Survey on the relationship of calcium content in soil and fruit with inner gamboge disorder ratio The experiment was conducted on 30 mangosteen orchards had stable fruit production (20 - 25 years old) in Long Thoi commune – Cho Lach district – Ben Tre province in 2013 crop season. The survey aims to find out about the correlation of calcium conten in soil and fruit with the incidences of inner gamboge disorder. 3.3.3 Survey on practices to prevent the incidences of inner gamboge disorder 3.3.3.1 Survey on inducing early flowering The experiment was carried out on 14-year-old mangosteen orchard in Phu Tan commune – Cau Ke district – Tra Vinh province in 2010/2011 crop season. The experiment design was completely randomized, including 7 treatments with 3 replications for each treatment, each of which equal to one tree. The treatments: control (water spraying), time of spraying thiourea (1, 2, and 3 months) after drenching PBZ 2 g a.i./m or KClO3 40 g a.i./m in canopy diameter. The experiment aims to determine the effect of flowering time on the incidences of inner gamboge disorder 3.3.3.2 Study on additional organic fertilizer application The experiment was carried out on mangosteen orchard (24 years old) had stable fruit production in Phu Tan commune – Cau Ke district – Tra Vinh province in 2010/2011 crop season. The experiment design was completely randomized, including 5 treatments with 4 replications for each treatment, each of which equal to one tree. Each treatment corresponded with the dosages of organic fertilizer for each tree: 0, 10, 20, 40, và 80 kg.tree-1. The experiment aims to determine the effect organic fertilizers on the incidences of inner gamboge disorder. 7 3.3.3.3 Study on irrigation regime The experiment was carried out on mangosteen orchard (20 – 25 years old) had stable fruit production in Long Thoi commune – Cho Lach district – Ben Tre province in 2012/2013 crop season. The experiment design was completely randomized, including 3 treatments with 5 replications for each treatment, each of which equal to one tree. The treatments included: nontreated, transparent plastic cover after completed flowering 2 months, and non-treated - watering 2 days/once – 50 liters/tree/time. The experiment aims to determine the effect of irrigation regime on the incidences of inner gamboge disorder. 3.3.3.4 Additional of calcium chloride as foliar spraying The experiment was carried out on mangosteen orchard with trees aged 20 - 25 years old in Long Thoi commune – Cho Lach district – Ben Tre province in 2013/2014 crop season. The experiment design was completely randomized, including 9 treatments with 4 replications, each of which equal to one tree. Calcium chloride was sprayed over the leaf canopy with the dosage of 8 liters.tree-1 beginning at flowering and 8 weeks after flowering, spray 4 times with 15-day interval. Control treatment was conducted without chemical application (water spraying), other treatments had CaCl2 content from 0.25% - 2.0%. The experiment aims to determine the effect of calcium chloride as foliar spraying on the incidences of inner gamboge disorder. 3.4 Research methodologies 3.4.3 Data analysis and statistics Microsoft Excel was used to analyze data and draw graphs. Analysis of variance and independent sample T-Test were used to find out the differences between treatments and analysis the correlation by the use of SPSS version 20.0; means were compared by verification of LSD and Duncan. 8 Chapter 4 RESULTS AND DISCUSSION 4.1 Survey on the incidences of inner gamboge disorder in mangosteen fruits 4.1.1 Morphological characteristics, physiological–biochemical characteristics in growing process 4.1.1.1 Exterior and inner morphological characteristics of mangosteen fruits Large and small segments together appear inside the fruit, large segments with or without apomictic embryo, the number of stigma lobes corresponds exactly with the number of fruit segments (Fig. 4.2). Fig. 4.2 Inner morphology of mangosteen fruit (1: large segment containing embryo, 2: large segment containing embryo, 3: small segment) Latex secretory ducts moved from stalk to inside fruit (Fig. 4.4A), yellow latex secretory ducts arranged in peel, fruit-flesh, the core of fruit, and around aril (Fig. 4.4B), ducts were branched as canal-like type without specific structure (Fig. 4.4C). The results showed that latex secretory ducts were easily influenced. Fig. 4.4 The distritution of latex vessels inside fruit (A: longitudinal section, B: cross-section, C: latex secretory ducts) 9 4.1.1.3 Inner gamboge disorder time The inner gamboge disorder appeared 8 weeks after completed flowering (Fig. 4.13). Growth segments (embryos) and heavy rain were factors related to the inner gamboge phenomenon. Inner gamboge disorder ratio (%) 50 No. seed contain embryo1 (seed) 1.6 40 1.2 30 0.8 20 0.4 10 0 0 2 4 6 8 10 12 Inner gamboge disorder1 ratio (%) No. embryo 2 TH Time after full flowering (week) Fig. 4.13 The formation of seed containing apomictic embryo and inner gamboge disorder in growing process ( : ± standard deviation) Fig. 4.18 showed that growing segment affected latex vessels at the core of fruit, after completed flowering until 6 weeks showed that the core of fruit was normal (Fig. 4.18A), the core of fruit was affected by a slight impact after 8 weeks (Fig. 4.18B), after 10 weeks the core of fruit was curved (Fig. 4.18C) and this broke latex secretory ducts. Dorly et al. (2008) and Poerwanto et al. (2009) also had similar consideration. Fig. 4.19 showed that there were great changes of rainfall in growing period; Limpawiphagorn (1998) and Chutimunthakun (2001) also stated that excess water during preharvest usually caused the incidences of inner gamboge disorder. Fig. 4.18 Longitudinal section of mangosteen in various growing period (A: the core of normal fruit, B: wristed core of the fruit, C: curvature of the fruit core) Rainfall (mm) 10 Growth stage Developing Growth and harvesting Fig. 4.19 Daily rainfall and growing period of mangosteen fruits in Long Thoi commune – Cho Lach district – Ben Tre province in 2011 crop season 4.1.2 The incidences of gamboge disorder, physical – biochemical characteristics of inner gamboge disorder and normal developed mangosteen fruits at harvest 4.1.2.2 Physical–biochemical characteristics of inner gamboge disorder and normal mangosteen fruits at harvest The weight of inner gamboge disorder fruits were higher and peel thicker than those of normal developed, significant difference (Tab. 4.2). The level of pectin in cell-wall of fruit-flesh of the inner gamboge disorder fruits were 1.33 folds lower than those in the normal ones (Tab. 4.3). Tab. 4.2 Physical – biochemical characteristics of inner gamboge disorder and normal mangosteen fruits from trees of different ages (15 to 25 years) in Long Thoi commune – Cho Lach district – Ben Tre province in 2011 crop season. Parameters Weight Size Quality Fruit weight (g) PTV (%) Peel thickness (mm) CCCR ODNM1 o Brix Fruit Inner gamboge disorder 71.6±0.88 75.2±0.25 8.6±0.06 0.223±0.01 15.1±0.1 Normal 67.7±0.52 71.6±0.18 8.0±0.04 0.242±0.06 16.1±0.1 T-test ** ** ** * ** Data were expressed as mean ±SE; * significant difference 5% by T-Test; **: significant difference 1% by T-Test; PTV: the percentage of peel weight, CCCR ODNM1: the ratio of latex secretory duct height/width in large segment position. 11 Tab. 4.3 Cell-wall composition of inner gamboge disorder and normal fruits from mangosteen trees of different ages (15 to 25 years) in Long Thoi commune – Cho Lach district – Ben Tre province in 2011 crop season. Extract ingredients Extract with distilled water (mg.g-1) Pectin (mg.g-1) Sugar type Neutral sugar Acidic sugar Neutral sugar Acidic sugar Hemicellulose (mg.g-1) Neutral sugar Acidic sugar Cellulose (mg.g-1) Total sugar Fruit Inner gamboge disorder 4.05 0.15 0.10 0.00 0.28 0.01 1.08 0.02 1.16 0.04 0.10 0.00 5.1 0.1 T-test Normal 2.32 0.46 0.67 1.63 1.17 0.17 6.2 0.08 0.02 0.04 0.02 0.03 0.00 0.23 ** ** ** ** ns ** ** Data were expressed as mean ±SE; ns: no significance different by T-Test; **: significant difference 1% by T-Test. 4.1.3 Ability to identify inner gamboge disorder fruits Traders attained the highest ability to identify inner gamboge disorder fruits (41.2%), the lowest were of customers (27.4%), ability to indentify inner gamboge disorder fruits of orchards’ owners and sellers were 33.2 and 29.6%, respectively (Fig. 4.23). The diffrerences of the ability to identify were mainly the time, traders identified fruit at harvest while other groups identified when the peel has turned completely into dark purple; Fig. 4.24 showed that when obtained level-2 harvest index according to MOA (2002), the peel of inner gamboge disorder fruits in small segment position often changed color first. Fig. 4.23 Ability to identify inner gamboge disorder fruits of traders, orchards’ owners, sellers and customer ( : ± SE) 12 Fig. 4.24 Characteristics of inner gamboge disorder fruits (A: exterior, B: inner) Inner gamboge disorder ratio1 (%) 4.1.4 Relationship between plant age and the incidences of innder gamboge disorder Fig. 4.25 showed that the frequency of the inner gamboge disorder and plant age had negative correlation at the significance level 1%. The differences of inner gamboge disorder ratio and plant age were the growth, the results in Tab. 4.4 showed the differences of physical-chemical characteristics of mangosteen fruits from young trees (10 – 15 years) and old trees ( > 50 years) at harvest. 50 a 40 30 r = 0,97** b bc c 20 d d 10 0 10 - 15 20 - 25 30 - 35 40 - 45 50 - 55 > 60 Plant age (year) Fig. 4.25 Relationship between inner gamboge disorder ratio and plant age ( : ± SE) Tab. 4.4 Physical –chemical characteristics of mangosteen fruit from young trees (10 – 15 years old) and old trees (> 50 years old) collected at Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season. Item Weight Segment Size Quality Fruit weight (g) Total Height (mm) Width (mm) CCCR Peel thickness (mm) o Brix Plant age 10 – 15 years > 50 years 68.5±1.4 64.0±1.5 5.8±0.05 5.7±0.05 47.5±0.4 46.5±0.4 52.1±0.4 50.0±0.6 0.91±0.01 1.02±0.07 8.7±0.1 8.3±0.1 15.3±0.1 15.1±0.1 Different * ns ns ** ns * ns Data were expressed as mean ±SE; ns: no significance different by T-Test; *: significant difference 5% by T-Test;**: significant difference 1% by T-Test; CCCR: the ratio of fruit height/width 13 gamboge Inner bên trong1 bị xì mủdisorder lệ trái Tỷ (%) ratio(%) 4.2 Survey on factors causing inner gamboge disorder in mangosteen fruits at harvest 4.2.1 Relationship between physical characteristics of fruits with the incidences of inner gamboge disorder 4.2.1.1 Correlation of physical characteristics of fruit and the incidences of inner gamboge disorder Fig. 4.33 showed that there was a positive correlation between the inner gamboge disorder ratio and peel thickness as harvest (r = 0.83**). 50 40 30 20 y = 8,3687x - 38,812 r = 0,83** 10 0 5,0 6,5 8,0 9,5 11,0 12,5 Peel thickness Độ dày vỏ trái (mm) (mm) Fig. 4.33 Correlation of inner gamboge disorder ratio and peel thickness as harvesting 4.2.1.2 Effect of gibberellic and naphthalene acetic acid as foliar spraying on the incidences of inner gamboge disorder at harvest Spraying GA3 at concentration of 50 and 100 ppm had higher inner gamboge disorder ratio from 2.42 – 2.47 folds than without spraying, respectively (Tab. 4.6) because it increased peel thickness (Tab. 4.7) and reduced pectin level in cell-wall of fruit-flesh (Tab. 4.9). Tab. 4.6 Effect of the concentration of gibberellic and naphthalene acetic acid as foliar spraying on inner gamboge disorder and translucent flesh disorder ratio (%) in mangosteen trees aged 20 – 25 in Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season. Treatments 0 ppm GA3 25 ppm GA3 50 ppm GA3 100 ppm NAA 25 ppm NAA 50 ppm NAA 100 ppm F CV (%) Inner gamboge disorder ratio (%) 14.6b 13.2b 35.4a 36.1a 15.3b 12.5b 13.9b ** 20.1 Translucent flesh disorder ratio (%) 18.3 16.0 18.2 15.8 16.2 15.5 17.5 ns 20.8 14 Tab. 4.7 Effect of the concentration of gibberellic and naphthalene acetic acid as foliar spraying on percentage of peel and edible weight (%), peel thickness (mm) in mangosteen trees aged 20 – 25 years in Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season. Treatments 0 ppm GA3 25 ppm GA3 50 ppm GA3 100 ppm NAA 25 ppm NAA 50 ppm NAA 100 ppm F CV (%) Percentage of edible weight (%) 29.4 26.7 26.9 29.7 28.7 29.9 30.8 ns 15.2 Percentage of peel weight (%) 68.6b 70.7b 72.2b 79.8a 71.3b 69.3b 68.1b ** 7.2 Peel thickness (mm) 7.4b 7.6b 7.7b 8.4a 7.7b 7.7b 7.6b * 5.7 Tab. 4.9 Effect of the concentration of gibberellic and naphthalene acetic acid as foliar spraying on the cell-wall composition of fruit-flesh in mangosteen trees aged 20 – 25 years in Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season. Treatments 0 ppm GA3 25 ppm GA3 50 ppm GA3 100 ppm NAA 25 ppm NAA 50 ppm NAA 100 ppm F CV (%) Pectin (mg.g-1) 2.23a 1.93bc 1.96bc 1.80c 2.06ab 2.04ab 1.98bc ** 7.9 Hemicellulose (mg.g-1) 2.21 2.15 2.16 2.18 2.15 2.12 2.19 ns 4.4 Cellulose (mg.g-1) 4.05 4.15 4.20 4.35 3.90 3.80 3.85 ns 13.6 Means within a column followed by the same letter are not significantly different by Duncan test; ns: no significant difference; *: significant difference 5%;**: significant difference 1%. 4.2.2 Survey on effect of soil moisture on the incidences of gamboge disorder in fruits 4.2.2.1 Relationship between changes of soil moisture before harvesting and the incidences of gamboge disorder Slight increase or decrease of soil moisture had no effect on sudden increase of inner gamboge disorder ratio, inner gamboge disorder ratio only increased sharply when changes of soil moisture had a tendency to increase quickly (Fig. 4.34). 15 Soil moisture 50 50 40 40 30 30 20 20 10 10 0 0 0 5 10 15 20 25 Soil moisture (%) 1 Inner gamboge disorder ratio (%) Inner gamboge disorder ratio 30 Period after the first harvest time (days) Fig. 4.34 Changes of inner gamboge disorder ratio and soil moisture in 0 – 20 cm depth upon harvest ( : ± SE) 4.2.2.2 Effect of timing of artificial water stress on the incidences of inner gamboge disorder Timing of artificial water stress in 2.5 months after completed flowering increased inner gamboge disorder ratio from 9.8 – 11.2% compared to other period at 1% significant difference (Tab. 4.11). Chutinunthakun (2001) considered that fruits had gamboge disorder after flowering 9 weeks earlier, Sdoodee and Chiarawipa (2005) also stated that timing of water stress only increased inner gamboge disorder ratio in the period of 9 weeks after flowering. Tab. 4.11 Effect of timing of artificial water stress on the inner gamboge disorder ratio and translucent flesh disorder ratio (%) in 23-year-old mangosteen trees in Long Thoi commune – Cho Lach district – Ben Tre province in 2011 crop season Timing of artificial water stress 0.5 month after HNHT 1.5 months after HNHT 2.5 months after HNHT When fruit had ”point” F CV (%) Inner gamboge disorder ratio (%) Translucent flesh disorder ratio (%) 15.2b 12.0 15.8b 11.5 26.4a 10.0 16.6b 8.75 ** ns 14.3 22.2 Means within a column followed by the same letter are not significantly different by LSD test; ns: no significant difference; **: significant difference 1%; HNHT: completed flowering; ”point”: reached level-0 color index according to MOA standard (2002). Timing of artificial water stress affected inner gamboge disorder ratio because it affected sudden changes of soil moisture and water absorption of latex, all period of water stress treament showed that sudden changes of soil moisture (Fig. 4.35) and reduced dry mater content in latex (Tab. 4.15). 16 Sdoodee and Limpun-Udom (2002) considered that main causes of gamboge disorder were sudden changes of water potential in soil and tree. Soil moisture (%) 0,5 month 2,5 month 1,5 month Fruit had “point” 35 31 27 23 19 15 NKHN 0.5 1.5 2.5 NKTH Time after full flowering (month) Fig. 4.35 Changes of soil moisture in 0 – 20 cm depth after completed flowering ( : ± SE, NKHN: beginning at flowering, NKTH: beginning at harvesting) Tab. 4.15 Effect of timing of artificial water stress on dry mater content in latex (%) according to the time in 23-year-old mangosteen trees in Long Thoi commune – Cho Lach district – Ben Tre province in 2011 crop season Period of water stress treatment 0.5 month after HNHT 1.5 month after HNHT 2.5 months after HNHT When fruit had ”point” F CV (%) NKHN 33.2 34.0 33.9 31.9 ns 5.6 Solids content in latex (%) 0.5 month 1.5 month 2.5 month 29.0b 47.6a 70.9a 35.7a 40.8b 71.0a 35.3a 47.2a 56.9b 35.8a 46.5a 68.5a ** ** ** 6.0 3.9 3.2 NKTH 92.2 92.2 92.3 92.0 ns 2.4 Means within a column followed by the same letter are not significantly different by LSD test; ns: no significant difference; **: significant difference 1%; HNHT: completed flowering; NKHN: when flower fully opened; NKTH: beginning after harvesting; ”point”: reached level-0 color index according to MOA standard (2002). 4.2.2.3 Effect of the number of artificial water stress times on the incidences of inner gamboge disorder in fruit Water stress once and twice had inner gamboge disorder ratio of 21.3 and 26.8%, increased 7.8 – 13.3% and water stress three times and four times also increased when compared to the control of 20.8 – 24.8% (Tab. 4.17). Aartificial water stress affected inner gamboge disorder ratio because it affected sudden changes of soil moisture; the more water stress were conducted, the higher changes of soil moisture increased (Fig. 4.37). 17 Tab. 4.17 Effect of the number of water stress treatment on inner gamboge disorder and translucent flesh disorder ratio (%) in 24-year-old mangosteen trees in Long Thoi commune – Cho Lach district – Ben Tre province in 2012 crop season The number of artificial water stress times (time) 0 1 2 3 4 F CV (%) Inner gamboge disorder ratio (%) 13.5c 21.3b 26.8b 34.3a 38.3a ** 14.2 Translucent flesh disorder ratio (%) 9.3c 11.5c 13.0c 17.5b 24.0a ** 16.5 Means within a column followed by the same letter are not significantly different by Duncan test; **: significant difference 1%. Control Water stress once Water stress 3 times Water stress 4 times Water stress twice Soil moisture (%) 60 48 36 24 12 0 0 1 2 3 4 Period after artificial water stress (week) Fig. 4.37 Changes of soil moisture in 0 – 20 cm depth after artificial water stress ( : ± SE) 4.2.3 Relationship between calcium content in soil and fruit and inner gamboge disorder ratio There was a negative correlation between inner gamboge disorder ratio and exchangeable Ca2+ and total Ca2+ content in flesh at 1% significance level (r = - 0.44** và - 0.52**) (Fig. 4.41 and 4.42). The analysis results showed that total Ca2+ content in normal fruits was 1.29 folds higher than inner gamboge disorder ones (Hình 4.43); Pechkeo et al. (2007a) found that Ca2+ content in peel of normal fruits was higher than that of gamboge disorder ones. Inner gamboge disorder ratio1 (%)1 18 50 40 30 20 y = -2.9168x + 49.191 r = - 0.44** 10 0 3 4 5 6 7 8 Echangeable calcium content in flesh (meq.100g-1) Inner gamboge disorder ratio1 (%)1 Fig.4.41 Correlation of the inner gamboge disorder ratio with exchangeable calcium in soil 50 40 30 20 y = -0.3676x + 49.081 r = - 0.52** 10 0 20 30 40 50 60 70 -1 Total calcium content in flesh (mg.100g ) 50 45 (mg.100g-1) Total calcium content in flesh1 Fig. 4.42 Correlation between inner gamboge disorder ratio and total calcium content in flesh 40 35 30 25 Normal Inner gamboge disorder Fig. 4.43 Total calcium content in flesh of normal fruit and inner gamboge disorder fruit after harvesting ( : ± SE) 4.3 Study on preventing the incidences of inner gamboge disorder in fruits and improving yield 4.3.1 Study on early flowering inducement Flowering inducement after PBZ or KClO3 drenching for 1 and 2 months had lower inner gamboge disorder ratio from 5.3 and 4.4 folds when inducing flowering in 3-month period lower 1.8 folds compared to the control
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