Evaluation of Leaf Morpho-anatomical and Gas Exchange Parameters in Relation to Fruit Yield in Indian Subtropical Grapefruit (Citrus paradisi Macf.) Varieties

The present study aimed to investigate the leaf morpho-anatomical and gas exchange parameters in relation to fruit yield in Indian subtropical grapefruit varieties (Citrus paradisi Macf.) during 2022–2023. Scanning electron microscopy (SEM) of leaf tissues revealed the highest stomatal density in ‘Flame’ (2920.26 mm²) and ‘Rio Red’ (2485.67 mm²), while the open to closed stomata index was highest in ‘Ray Ruby’ (23.44) followed by ‘Flame’ (11.31), ‘Oroblanco’ (9.74), ‘Rio Red’ (7.24), and ‘Ruby Red’ (6.93). The leaf greenness referring to the chlorophyll content varied from 34.50 (‘Marsh Seedless’) to 52.33 (‘Oroblanco’) SPAD units. The gas exchange parameter showed significant variations among the grapefruit varieties. The highest stomatal conductance was recorded in ‘Ray Ruby’ (0.23 mol H₂O m²/s) along with maximum photosynthetic rate (13.79 µmole CO₂ m²/s) and relatively higher transpiration rate (4.76 moles H₂O m²/s). The fruit yield also varied among the genotypes, with ‘Rio Red’ exhibiting the highest fruit yield (80.65 kg/tree) followed by ‘Ray Ruby’ (69.71 kg/tree). A correlation study utilizing Pearson’s correlation analysis indicated that the most significant factors affecting fruit yield in grapefruit are stomatal conductance (0.63**, p < 0.01), photosynthetic rate (0.63**, p < 0.01), intercellular CO₂ concentration (0.41*, p < 0.05), and stomatal cavity width (0.41*, p < 0.05). The study indicated a clear relationship among the leaf morpho-anatomical and gas exchange parameters and fruit yield in grapefruit varieties. The number of stomata, stomatal conductance, stomatal opening length, dimensions of leaf lamina, and palisade parenchyma were shown to be valuable markers for early selection in crop improvement programme.