Promoting water deficit tolerance and anthocyanin fortification in pigmented rice cultivar (Oryza sativa L. subsp. indica) using arbuscular mycorrhizal fungi inoculation

Drought or water deficit is a major abiotic stress that can reduce growth and productivity in the rice crop especially in the rain-fed areas, which face long-term water shortage. The objective of this investigation was to promote the drought tolerant abilities in pigmented rice cv. Hom Nil' at booting stage using arbuscular mycorrhizal fungi (AMF)-inoculation, mixed spores of Glomus geosporum, G. etunicatum and G. mosseae in the soil before rice seedling transplantation. At booting stage, the AMF-inoculated (+AMF) and AMF-uninoculated plants (-AMF) were subjected to control (well-watering; 46.6% SWC) and water deficit condition (14 days water withholding; 13.8% SWC). Colonization percentage in the AMF-inoculated root tissues were evidently proved in both with and without water deficit conditions, leading to elevate total phosphorus in root and leaf tissues. Interestingly, sucrose and total soluble sugar concentration in the flag leaf were increased by 5.0 folds and 1.5 folds, respectively in the plants under water deficit (WD). Free proline was accumulated in flag leaf when exposure to water deficit, subsequently regulated by AMF-inoculation. Total soluble sugar and free proline enrichment in Hom Nil' was a major mode of osmotic adjustment to control osmotic potential in the cellular level when exposed to water deficit, leading to maintained photosynthetic abilities and growth performances. Concentration of chlorophyll b in AMF-inoculated plants under water deficit stress was retained, causing to improve chlorophyll fluorescence and net photosynthetic rate. Shoot height and number of tillers were significantly declined by 12.5% and 11.6%, respectively, when subjected to WD. At the harvest, grain yield, panicle dry weight and fertility percentage of AMF-inoculated rice from WD were greater than those without AMF by 1.5, 3.9 and 2.4 folds, respectively. Cyanidin-3-glucoside and peonidin-3-glucoside concentrations in pericarp were enriched in the grain derived from AMF-inoculation with water deficit stress. Overall growth characters and physiological adaptations in Hom Nil' grown under water deficit condition were retained by AMF inoculation, resulting in enhanced yield attributes and anthocyanin fortification in rice grain.