Vegetative malformation in Malabar Tamarind [Garcinia gummi-gutta (L.) N Robson]

Abstract

Malabar tamarind [Garcinia gummi-gutta (L.) N. Robson] is a multipurpose tree belonging to the Clusiaceae family and is native to the Western Ghats of India. The species has attained commercial importance due to the presence of Hydroxycitric Acid in its fruit rind, which exhibits anti-obesity properties and is also valued for its antioxidant activity attributed to polyphenols, anthocyanins, and garcinol. In Kerala, the fruit rind, locally referred to as kudampuli, is utilized as a condiment to impart a distinctive sour flavour to traditional cuisine. Previous studies on Malabar tamarind have primarily focused on its taxonomic diversity and phytochemical composition. However, limited research has addressed vegetative malformation, a disorder characterized by stunted leaves, loss of apical dominance, formation of scaly leaf shootlets, shortened internodes, and hypertrophied vegetative buds. These symptoms closely resemble those observed in mango malformation, a condition that substantially reduces flowering and fruit yield. Despite this similar resemblance, comprehensive information regarding the etiology of vegetative malformation in Malabar tamarind is lacking. The present study entitled “Vegetative malformation in Malabar tamarind [Garcinia gummi-gutta (L.) N. Robson]”, aims to elucidate the physiological, biochemical, and nutritional factors associated with this disorder. The research work was carriedout at the Department of Plantation, Spices, Medicinal and Aromatic Crops, College of Agriculture, Vellanikkara, during 2023-2025.The study utilized genetic resources of Malabar tamarind conserved at ICAR-National Bureau of Plant Genetic Resources (NBPGR), Regional Station, Vellanikkara, and Regional Agricultural Research Station, Kumarakom, Kerala Agricultural University, in addition to germplasm obtained through purposive sampling. A comprehensive survey of 352 genotypes across three locations in the first experiment revealed varying levels of malformation incidence. The genotypes conserved at the Regional Agricultural Research Station in Kumarakom exhibited the highest rate of malformation, followed by those conserved at the ICAR-NBPGR, Regional Station, Vellanikkara, whereas the Garcinia block, Department of Fruit Science, College of Agriculture, Vellanikkara showed a minimal incidence. Based on symptoms, trees were graded on a scale of 0-5. Eleven accessions, comprising ten malformed and one healthy genotype, were selected for detailed monthly observations from January to September 2025. Analysis of weather parameters revealed significant variations between environmental factors and malformation progression, as well as vegetative parameters. Total sunshine hours showed a significant and negative correlation with malformation incidence (r = -0.854), while relative humidity (r = 0.752) and rainfall (r = 0.703) also exhibited significant and positive correlations. Maximum temperature (r = -0.472) and minimum temperature (r = -0.514) were negatively correlated. Vegetative parameters, such as leaf length, leaf width, petiole length, internodal length, and leaf area, exhibited significant and positive correlations with relative humidity (r = 0.885 to 0.938) and rainfall (r = 0.681 to 0.909), and significant and negative correlations with total sunshine hours (r = -0.583 to -0.880). The nutrient analysis evaluated the concentrations of nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur in healthy and malformed tissues across four seasons. Significant interaction effects between season and tissue type were identified. Healthy tissues consist of higher levels of nitrogen (1.33%), calcium (1.10%), magnesium (0.30%), and sulphur (0.32%) compared to malformed tissues. In contrast, malformed tissues exhibited elevated potassium (0.51%), while phosphorus levels remained similar between tissue types. Nitrogen concentrations were highest during the post-monsoon and monsoon seasons (1.26%). Phosphorus (0.18%) and potassium (0.52%) peaked in winter. Calcium reached its maximum during the monsoon (1.56%), and magnesium was most abundant in summer (0.29%). Malformed tissues had significantly greater protein content (11.62%) than healthy tissues (6.36%), with the highest value observed in winter (17.62%). Ascorbic acid concentrations were significantly higher in healthy tissues (257.42 mg 100 g⁻¹) than in malformed tissues (224.42 mg 100 g⁻¹), with winter exhibiting the highest levels (264.89 mg 100 g⁻¹). Endogenous ethylene was substantially increased in malformed tissues (0.24 µL kg⁻¹ h⁻¹) compared to healthy tissues (0.18 µL kg⁻¹ h⁻¹), supporting the stress ethylene hypothesis. Auxin content was significantly reduced in malformed tissues (1790.24 µg g⁻¹ h⁻¹) relative to healthy tissues (2212.38 µg g⁻¹ h⁻¹), with the highest auxin levels recorded post-monsoon (3078.46 µg g⁻¹ h⁻¹) and the lowest during the monsoon (1285.58 µg g⁻¹ h⁻¹). Light microscopy of hand-microtome sections indicated normal cellular morphology in both healthy and malformed tissues. Vegetative malformation in Malabar tamarind appears to be a multifactorial disorder influenced by environmental stress, nutritional deficiencies, and hormonal imbalances. A significant and positive correlation with monsoon conditions, combined with deficiencies of nitrogen, calcium, and magnesium, as well as elevated stress ethylene and reduced auxin levels in malformed tissues, suggests that the disorder develops under physiological stress. These findings offer comprehensive insights into the etiology of vegetative malformation and provide a base for integrated management strategies. Further, research into pathological mechanisms, soil rhizosphere dynamics, and hormonal regulation may help identify the precise causes of these conditions. Additionally, screening and characterizing resistant genotypes will support breeding programmes aimed at developing malformation-tolerant cultivars and conserving genetic resources, thereby promoting the sustainable production of this economically important crop.