Varietal variations in rate of ripening and respiration of mango (Mangifera indica L.) fruits: anatomical substantiation

Anatomical features of mango (Mangifera indica L.) fruits were examined at three different maturity stages in four varieties namely; Langra (L), Amrapali (A), Dushehari (D) and Ramkela (R) which differ in their rate of ripening. Gross anatomical variations were observed among the varieties in terms of cuticle thickness, number of cellular layers in hypodermis, compactness of hypodermal region and pattern of staining of exocarp region representing lignin and suberin depositions on cell walls. At cellular level, significant differences were observed in cell density which was primarily due to variations in cell size rather than the extent of intercellular spaces. The varietal differences in cell density was more prominent in the mesocarp region compared to the peel region of the mango fruits. The rate of ripening of fruits was in order of L > A > D > R and was found to be directly related to the cell density. While the respiration rate was in order of L > D ≈ A > R and this was inversely related with the cell size (L ≈ D < A < R). Fruits of variety Langra with smallest cell size and highest rate of respiration showed fastest rate of ripening. In contrast to this, fruits of variety Ramkela having the largest cell size and lowest rate of respiration showed slowest rate of ripening. The results indicated that the cell size is inversely linked to the rate of ripening due to its influence on the rate of respiration. This association between the cell size and the rate of respiration is explained on the basis of positive relationship between surface to volume ratio of cells and the respiration rate or basal metabolic rate in tissues/organs. The study pointed out the role of fruit anatomy in varietal differences which is having implications on respiration rate and on ripening.