Ph.D

Mangosteen (Garcinia mangostana L.), known as the ‘Queen of Tropical Fruits’ is a parthenocarpic, evergreen fruit tree which is native to the Malay Archipelago. Fruits are valued for its exquisite luscious and delicious snow-white arils. It has numerous health benefits due to its rich content of glucose, vitamins (A, B, and B2), minerals (Ca, P, and Fe), fibre, tannins, xanthones, and antioxidants. The major cultivated countries are Indonesia, Thailand, Philippines, Malaysia, Cambodia, Vietnam, Myanmar, Sri Lanka, India and China. In India, commercial cultivation is restricted to southern states particularly Kerala with warm, humid climate, followed by Tamil Nadu and some parts of Karnataka. The fruits are highly priced domestically and globally. Farmers engaged in mangosteen cultivation are facing a lot of problems, mainly, low availability of seeds, poor seed viability, low germination percentage, and sluggish growth of seedlings. Additionally, they are also facing constraints such as lack of quality planting materials, protocol for microbial inoculation, proper nutrient management practices, usage of bio-stimulants and so on. To address these issues, this research project on “Production technology for augmenting yield and quality of mangosteen (Garcinia mangostana L.)” was undertaken with the objective of fostering seedling growth and enhancing the quality yield of mangosteen by adopting balanced nutrition practice. The study was conducted at Department of Fruit Science, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur, and at a farmer’s field in Pariyaram village near Chalakudy town in Thrissur district, Kerala, during September 2022 to August 2024. In the first experiment on ‘Microbial consortium seed treatment for improving germination attributes of mangosteen’ the results were found to be non-significant, however, the seeds treated with microbial consortium (100 g/kg of seeds) took only minimum number of days for germination with increase in germination percentage compared to the control. Microbial consortium seed treatments showed its effect at later stages of growth at 30 and 45 days, as compared to 15 days after germination. Among the treatments, the treatments T3 (PGPR Mix-1 + Piriformospora indica) and T4 {Arka Microbial Consortia (AMC)} were comparable. At 45 days after germination, treatments T3 and T4 recorded notable results regarding seedling height (6.34 & 5.80 cm), number of leaves (3.71 & 3.49), length of leaves (5.62 & 5.16 cm), breadth of leaves (2.79 & 2.56 cm), total leaf area (42.21 & 32.54 cm2), chlorophyll-a (0.749 & 0.715 mg/g), chlorophyll-b (0.712 & 0.706 mg/g), total chlorophyll (1.460 & 1.421 mg/g), in addition to length of roots (6.19 & 5.76 cm), girth of roots (1.90 & 1.81 mm), number of secondary roots (12.00 & 10.50), seedling fresh weight (3.33 & 2.74 g), and seedling dry weight (644.75 & 546.00 mg). This result might be due the better nutrient availability facilitated by the microbial consortium through atmospheric nitrogen fixation, mineral nutrient solubilization, mobilization, and presence of phytohormones, which in turn enhanced the efficiency of photosynthesis and seedling development and their characteristics. The study thus recommends the incorporation of PGPR Mix-1 + Piriformospora indica (T3) or Arka Microbial Consortia (AMC) (T4) into the seed treatment protocol to improve germination and to accelerate growth performance of mangosteen seedlings. The impact of microbial consortiums in combination with foliar application of NPK @ 3:1:1 ratio, on the growth and development of mangosteen seedlings were assessed over an eight-month period in the second experiment ‘Triggering seedling growth in mangosteen using microbial consortium and by foliar nutrition’ wherein the observations were recorded at two-months interval. After eighth month, two treatments, namely treatment T5 (PGPR MIX-1 (10 g/plant) + AMF-Glomus fasciculatum (5 g/plant) + foliar spray NPK (3:1:1) at 0.5 %) and T6 {Arka Microbial Consortia (20 g/plant)} recorded significant values regarding growth metrics such as stem diameter (3.60 & 3.34mm), number of leaves (13.13 & 12.03) and breadth of leaves (2.87 & 2.75 cm); biochemical traits including total chlorophyll (1.330 & 1.293 mg/g) and carotenoid (0.301 and 0.283 mg/g); biomass accumulation such as seedling fresh weight (11.02 & 9.43 g) and seedling dry weight (3.30 & 2.81 g); root characters including root length (20.70 & 19.70 cm) and number of secondary roots (19.33 & 17.33). The highest seedling survival rate and lowest mortality were also observed in T5 and T6. The enhanced overall growth of mangosteen seedlings in T5 and T6 can be attributed to the inoculation of microbial consortium, which assisted in biological nitrogen fixation, phosphate solubilization, micronutrient mobilization, production of growth promoters (IAA, Cytokinin, & Gibberellin). Additionally, they enhanced root surface area, thereby improving nutrient and moisture absorption and highest seedling survival rate by imparting physical blockage to entry by pathogens, inducing systemic resistance, and producing antimicrobial compounds (peptides and polypeptides), besides producing exopolysaccharides which improved soil aggregation, leading to better water retention and aeration. Furthermore, the foliar application of NPK (3:1:1) promoted vegetative growth by involving in the photosynthesis process. In the third experiment, ‘Impact of balanced nutrition on the development of mangosteen’, the application of balanced nutrition in the treatments T4 (460:180:600 g NPK + 50 kg FYM + 600 g calcium nitrate + 80 g borax/tree/year) and T5 (460:180:600 g NPK + 3 kg neem oil cake + 2 kg bone meal + 600 g calcium nitrate + 80 g borax/tree/year) remarkably improved vegetative growth characters {mean canopy diameter (6.72 & 6.58 m), new flush leaf breadth (11.33 & 10.63 cm)}, biochemical contents {total chlorophyll (1.707 and 1.667 mg/g) and carotenoids (0.268 and 0.259 mg/g)}, yield attributes {yield per tree (15.68 & 13.60 kg) and yield per hectare (2.445 & 2.122 t)}, fruit quality traits {vitamin-C (18.67 & 17.34 mg/100mg) and overall acceptability (7.80 & 7.70)}. Besides, it also improved the availability of key nutrients {N (389.19 & 352.56 kg/ha) and B (0.70 & 0.68 ppm)} in soil and in plant {N (2.68 & 2.57%) and B (15.50 & 14.75 mg/kg)}. Additionally, from the economic point of view, the highest gross (6,12,500 & 5,30,000 Rs/ha) and net returns (5,08,237 & 4,13,881 Rs/ha) along with excellent benefit-cost (B:C) ratio (4.87 & 3.56 respectively) were documented in the treatments T4 and T5. The superior results obtained could be due to the availability of all essential nutrients in sufficient quantities in the leaves, achieved through the integrated application of organic and inorganic nutrient sources. This nutrient availability might have supported the synthesis of chlorophyll and carotenoids, subsequently, favouring the overall growth of trees, indicating the use of balanced nutrition for profitable commercial mangosteen cultivation. Both in T4 and T5, the whole quantity of P, FYM, neem oil cake, bone meal and 25% of N and K were applied as basal dose (October). The remaining N and K were applied in 3 splits (December, flowering, and fruit development stage). Additionally, calcium nitrate and borax were applied in the soil one week later after the 3rd (flowering stage) and 4th (fruit development stage) split application of N and K. In the fourth experiment ‘Role of bio-stimulants on the performance of mangosteen’, foliar application of biostimulants in treatments T6 (seaweed extract spray at 2%), T5 (seaweed extract spray at 1.5%), and T8 (humic acid spray at 1% + seaweed extract spray at 1%) were found to significantly enhance majority of the growth metrics {mean canopy diameter (6.28, 6.08 & 5.83 m) and new flush leaf breadth (11.70, 11.20 & 10.90 cm)}, biochemical contents {total chlorophyll (1.794, 1.742 & 1.706 mg/g) and carotenoids (0.282, 0.272 & 0.267)}, yield attributes {yield per tree (21.72, 18.76 & 18.24 kg) and yield per hectare (3.39, 2.93 & 2.85 t)} and fruit quality traits {total sugar (15.44, 14.68 & 14.75 %)} respectively. In addition, it also enhanced nutrient status in plant tissues {N (3.08, 2.94 & 2.80%), P (0.22, 0.20 & 0.19%), K (3.37, 3.12 & 2.85%), and Ca (0.89, 072 & 0.68%)}. Further, from the economic point of view, the highest gross (8,47,500, 7,32,500 & 7,12,500 Rs/ha) and net returns (6,12,091, 5,06,447 & 6,00,359 Rs/ha) along with high benefit-cost (B:C) ratio (5.90, 5.08 & 5.35) were also observed in treatments T6, T5, and T8 respectively. The superior outcome could be attributed to foliar spray with seaweed extract, which contained proteins, carbohydrates, macro- and micronutrients, phytohormones, amino acids and polysaccharides in addition to the presence of antioxidants (which protects oxidative stress), and vitamins (further support overall plant health). The role of humic acid was also significant, as it aided in nutrient chelation, improved nutrient availability and cation exchange capacity, and provided amino acids, peptides, and essential trace elements. These components collectively contributed to numerous biochemical processes, primarily enhancing photosynthesis and overall plant growth which substantiates the economic advantage of using biostimulants for enhancing the productivity and profitability of mangosteen cultivation. To conclude the results, seed treatment with microbial consortium (100 g/kg of seeds){PGPR Mix-1 + Piriformospora indica or Arka Microbial Consortia (AMC)} led to better germination and superior initial growth characteristics of seedling. When three-month-old seedlings were inoculated using microbial consortium sprayed with NPK {PGPR MIX-1 (10 g/plant) + AMF-Glomus fasciculatum (5 g/plant) + foliar spray NPK (3:1:1) at 0.5 %) or Arka Microbial Consortia (20 g/plant)} resulted in significant seedling growth and development. Further, higher yield, good quality of fruits, and high B:C ratio could be achieved through the application of 460:180:600 g NPK + 50 kg FYM + 600 g calcium nitrate + 80 g borax/tree/year or 460:180:600 g NPK + 3 kg neem oil cake + 2 kg bone meal + 600 g calcium nitrate + 80 g borax/tree/year in the soil. Additionally, foliar spray of bio-stimulants {seaweed extract spray (2% or 1.5%) or combined spray of humic acid (1%) + seaweed extract (1%)} gave excellent B:C ratio with superior quality fruits and higher yield in mangosteen. Based on the study conducted, research is needed to standardize a comprehensive nutrient package of practice of nutrients from seed to commercial yielding stage. Growth and development of mangosteen seedlings to a greater extent rely on environmental factors, such as optimum shade level, relative humidity, and temperature. As seed propagation is associated with long gestation period, alternative and more efficient methods for propagation has to be explored. Furthermore, fruits are with short shelf life and to address this challenge, development of improved storage, packaging, and handling techniques for extending the fruits shelf life is essential. It is also needed to focus on formulating effective integrated pest management (IPM) strategies for controlling the emerging insect pests such as mangosteen caterpillars, thrips and so on, through a detailed study.