Effects of Root Restriction and Water Stress on Growth Performance, and Physiological and Biochemical Responses of Mango (Mangifera Indica Cv. Chokanan)

Abstract

The effects of restricted root volume (10, 30 and 50-litre of soil) on growth,stomatal conductance and photosynthesis rate of mango (Mangifera indica) cv.Chokanan trees were investigated under a rain shelter condition.Root restriction (10-litre of soil) significantly (P􀂔0.05) reduced all growth parameters and leaf gas exchange of plants. However, stem and root dry weight, root:shoot ratio, number of branches and stem diameter were not significantly (P>0.05) different between the 10 and 30-litre of soil.There were a linear relationships between root and total leaf dry weight; diameter of stem and plant height; and between photosynthesis rate and stomatal conductance.Similarly, growth of mango plants was significantly affected by root restriction in a 24-litre volume of soil compared to control roots (unrestricted) under field condition.Root restriction reduced the number of fruits by 56.3% in the first season,but it increased the total number of fruits and total fruit weight in the second season compared to the control.Average fruit weight per plant was not affected by the root restriction treatment in the second season.Root restriction in combination with water stress was also studied.Root restriction inhibited the growth of mango trees as reflected in the reduction of leaf expansion with greater reduction under water stress conditions.Under well-watered condition, restricted root resulted in a considerable reduction in stomatal conductance and leaf water potential compared to the control root growth.Decreases in stomatal conductance and leaf water potential were rapid under restricted root and water stress condition compared to the control.On the other hand, leaf proline and abscisic acid (ABA) accumulation increased as a result of root restriction and water stress. Re-watering of mango trees increased stomatal conductance, leaf water potential and peroxidase accumulation in plants with both restricted and control root growth.However, proline and ABA accumulation decreased with re-watering.Anatomical studies of cross section of secondary branch of mango also showed that root restriction and water stress brought about various changes,such as smaller and compacted cell size (as estimated by epidermis thickness and area,as well as by cortex thickness),but increased the size of some of the cells (as measured by schelerenchyma, phloem and xylem thickness,schelenchyma and pith area and pith diameter).These results suggest that reduction of soil volume and water stress could effectively control tree size by physiological and morphological changes and trigger reproductive development of fruit trees like mango