Date of Defense
9-4-2025 9:00 AM
Location
F3-110
Document Type
Dissertation Defense
Degree Name
Doctor of Philosophy in Horticulture Science
College
CAVM
Department
Integrative Agriculture
First Advisor
Dr. Shyam Kurup
Keywords
Drought stress, Grafted grapevines, Phytohormones, Amino acids, MDA, Antioxidants, DGE, Polyamines, Osmo protectants, Epicuticular wax, Pigments.
Abstract
Grapevines, among the most commercially significant fruit crops, are valued for their use in table grapes, raisins, and winemaking but are highly vulnerable to abiotic stresses such as drought, heat, and salinity. This study investigated the morphological, physiological, biochemical, and transcriptomic responses of grafted grapevines to drought stress, emphasizing rootstock-scion interactions. Grafting experiments were conducted with three rootstocks (Ramsey, RU140, and Paulsen) and table grape varieties (Thomson Seedless, Crimson Seedless, and Flame Seedless), with five combinations as Flame seedless × Ramsey (V1), Thompson seedless × Ramsey (V2), Crimson seedless × R110 (V3), Crimson seedless × Ramsey (V4) and Thompson seedless × P1103 (V5) under irrigation regimes of 100%, 75%, and 50% field capacity to simulate moisture stress. Results demonstrated the pivotal role of amino acids, including proline, cysteine, and arginine, in drought stress tolerance. Although several amino acids contribute to stress tolerance, cysteine and arginine play crucial roles with an increase in V2, V3, and V5 grafts, the former concomitant with downregulation of the chlorophyllase gene restricting chlorophyll pigment degradation, corresponds with increased nitrogen uptake while the latter as precursor amino acid involved in direct pathway for polyamine biosynthesis found in grafts are involved in various metabolic processes with anti-senescence and anti-stress effects by maintaining the integrity of the plasma membrane system. Phenylalanine was associated with enhanced photosynthetic activity through increased nitrogen and magnesium uptake, while glutamate, derived from nitrogen metabolism, supported stress tolerance in specific graft combinations. The antioxidant defense system, particularly the activities of CAT, SOD, and APX enzymes, effectively scavenged reactive oxygen species, maintaining redox balance and cellular water status. Hormonal dynamics, especially the interaction between ABA and GA3, revealed distinct antagonistic behavior, with cytokinin levels modulated by rootstock performance under soil moisture stress. Elevated glucose, glycine betaine, and macro and micronutrient accumulation further supported the physiological adjustments to deficit irrigation. Physiological traits such as net photosynthetic rate, stomatal conductance, and transpiration efficiency indicated enhanced water-use efficiency in specific grafts, particularly under 50% field capacity, correlating with increased biomass production. Scanning electron microscopy revealed the role of mineral elements, including calcium, in extracellular matrix formation, stomatal behavior, and trichome development under drought stress. Proline, arginine metabolism, and H₂O₂ detoxification are the main topics of this study's transcriptome and metabolic analyses of Thompson Seedless * Ramsey grafted grapevines under drought stress. AREB1, AREB2, and NAC transcription factors were significantly upregulated, according to RNA sequencing, which encouraged proline buildup. Nitrogen recycling was supported by increased expression of ornithine aminotransferase (OAT), which connected proline production to arginine metabolism. Increased H₂O₂ levels improved ROS detoxification by activating antioxidant defences (SOD, POD, and CAT). Clear metabolic and transcriptomic changes were shown by the differential grouping of the stress and control samples, which was confirmed by Principal Component Analysis (PCA). This comprehensive study validates the significant role of rootstock-scion interactions in modulating drought-responsive mechanisms in grapevines. The findings provide valuable insights into the development of stress-resilient grafting strategies, enabling sustainable viticulture in arid and water-scarce regions.
EVALUATION OF FIELD GROWN GRAPEVINE GRAFTS FOR DROUGHT TOLERANCE UNDER WATER DEFICIT IRRIGATION IN THE ARID REGIONS OF UAE
F3-110
Grapevines, among the most commercially significant fruit crops, are valued for their use in table grapes, raisins, and winemaking but are highly vulnerable to abiotic stresses such as drought, heat, and salinity. This study investigated the morphological, physiological, biochemical, and transcriptomic responses of grafted grapevines to drought stress, emphasizing rootstock-scion interactions. Grafting experiments were conducted with three rootstocks (Ramsey, RU140, and Paulsen) and table grape varieties (Thomson Seedless, Crimson Seedless, and Flame Seedless), with five combinations as Flame seedless × Ramsey (V1), Thompson seedless × Ramsey (V2), Crimson seedless × R110 (V3), Crimson seedless × Ramsey (V4) and Thompson seedless × P1103 (V5) under irrigation regimes of 100%, 75%, and 50% field capacity to simulate moisture stress. Results demonstrated the pivotal role of amino acids, including proline, cysteine, and arginine, in drought stress tolerance. Although several amino acids contribute to stress tolerance, cysteine and arginine play crucial roles with an increase in V2, V3, and V5 grafts, the former concomitant with downregulation of the chlorophyllase gene restricting chlorophyll pigment degradation, corresponds with increased nitrogen uptake while the latter as precursor amino acid involved in direct pathway for polyamine biosynthesis found in grafts are involved in various metabolic processes with anti-senescence and anti-stress effects by maintaining the integrity of the plasma membrane system. Phenylalanine was associated with enhanced photosynthetic activity through increased nitrogen and magnesium uptake, while glutamate, derived from nitrogen metabolism, supported stress tolerance in specific graft combinations. The antioxidant defense system, particularly the activities of CAT, SOD, and APX enzymes, effectively scavenged reactive oxygen species, maintaining redox balance and cellular water status. Hormonal dynamics, especially the interaction between ABA and GA3, revealed distinct antagonistic behavior, with cytokinin levels modulated by rootstock performance under soil moisture stress. Elevated glucose, glycine betaine, and macro and micronutrient accumulation further supported the physiological adjustments to deficit irrigation. Physiological traits such as net photosynthetic rate, stomatal conductance, and transpiration efficiency indicated enhanced water-use efficiency in specific grafts, particularly under 50% field capacity, correlating with increased biomass production. Scanning electron microscopy revealed the role of mineral elements, including calcium, in extracellular matrix formation, stomatal behavior, and trichome development under drought stress. Proline, arginine metabolism, and H₂O₂ detoxification are the main topics of this study's transcriptome and metabolic analyses of Thompson Seedless * Ramsey grafted grapevines under drought stress. AREB1, AREB2, and NAC transcription factors were significantly upregulated, according to RNA sequencing, which encouraged proline buildup. Nitrogen recycling was supported by increased expression of ornithine aminotransferase (OAT), which connected proline production to arginine metabolism. Increased H₂O₂ levels improved ROS detoxification by activating antioxidant defences (SOD, POD, and CAT). Clear metabolic and transcriptomic changes were shown by the differential grouping of the stress and control samples, which was confirmed by Principal Component Analysis (PCA). This comprehensive study validates the significant role of rootstock-scion interactions in modulating drought-responsive mechanisms in grapevines. The findings provide valuable insights into the development of stress-resilient grafting strategies, enabling sustainable viticulture in arid and water-scarce regions.
