Evaluation of Rice (Oryza sativa L.) Genotypes for Iron Toxicity Tolerance under Hydroponic Conditions

Abstract

Background: Iron toxicity is a major abiotic constraint limiting rice (Oryza sativa L.) productivity in lowland ecosystems, particularly under waterlogged acidic soil conditions. Identifying tolerant genotypes through efficient screening methods such as hydroponics is essential for developing sustainable, stress-resilient rice varieties. Aim: The study aims to evaluate rice germplasm for iron toxicity tolerance under controlled hydroponic conditions to identify potential donor lines for breeding programs. Study Design:  Completely randomized design (CRD) with three replications under hydroponic conditions. Place and Duration of Study: Farming Systems Research Station, Sadanandapuram, Kollam, on March 2022. Methodology: A total of 106 rice genotypes, including traditional cultivars and released varieties, were evaluated for iron toxicity tolerance using hydroponic culture. The study employed a Completely Randomized Design with three replications, assessing genotypes under four iron concentrations: 0 (control), 500, 750, and 1000 mg L⁻¹. Growth parameters, including shoot and root length, total and fresh root count, number of leaves and leaf bronzing scores, were recorded to evaluate tolerance levels. Results: Analysis of variance revealed highly significant differences among genotypes for all traits except number of leaves at 750 and 1000 mg L⁻¹ and leaf bronzing score under control conditions. Increasing iron concentrations led to a progressive decline in growth; mean shoot length decreased from 17.7 cm to 16.0 cm, and root length from 8.2 cm to 7.0 cm at 1000 mg L⁻¹. A drastic reduction was observed in the number of roots and fresh roots due to damages on root epidermis, while the mean leaf bronzing score rose to 6.1 under maximum stress. Based on the visual scoring, 30 tolerant and moderately tolerant genotypes were identified of which thirteen landraces and seventeen releases varieties with high growth maintenance and low leaf bronzing scores at highest iron concentration were identified as potential donors for developing iron toxicity tolerant rice varieties. Conclusion: Hydroponic screening proved to be an efficient and reliable method for rapid and early stage evaluation of iron toxicity tolerance in rice. Several tolerant and moderately tolerant genotypes identified can serve as valuable donor parents in breeding programmes focused on developing high yielding, iron toxicity tolerant rice varieties.