Abstract
Understanding the mechanisms involved in iron toxicity tolerance of rice would help develop technologies to close yield gaps. A study was conducted aiming to understand the role of rhizosphere microorganisms in tolerance of iron toxicity in rice plants. Three varieties with different iron toxicity tolerance capacities were selected [BW 267-3 (tolerant), BW 363 (moderately tolerant) and BW 272-6b (susceptible)]. A pot experiment was conducted in a three factor factorial design including soil treatment with microorganisms (presence and absence), three iron levels in growth medium (2, 75 and 300 mg/L) and three rice varieties as grouping factors. At 42 days after germination dry matter yield and total Fe, K and P in shoots were determined. Rhizosphere oxidizing potential of each variety was determined by visualizing oxidizing power of rice roots embedded in a semisolid agar medium containing iron sulfide. Results indicated that presence of soil microorganisms significantly (p<0.05) reduced dry matter yield but increased Fe uptake of all three varieties. However, in presence of microorganisms, Fe uptake remained more consistent irrespective of the Fe concentration in growth medium. Root oxidizing power had a positive relationship with iron toxicity tolerance. The highest oxidizing potential was observed in BW 267-3. Plant-microbial interactions on growth and uptake of Fe, K and P were more prominent in BW 363 and BW 272-6b compared to BW 267-3. We conclude that microorganisms mobilize Fe to rice plants. Further, remarkable differences exist between rice varieties in root oxidizing power and plant-microbial interactions depending on their iron toxicity tolerance.
Highlights
Rice growers are in a continuing struggle to reach the potential yield to cater to the food demands of the continuously increasing population (Papademetriou et al, 2000)
In BW 272-6b and BW 363 varieties, dry matter yield was significantly high in the absence of microorganisms; whereas, the dry matter production of the Fe toxicity tolerant variety BW 267-3 was not significantly affected by the presence of microorganisms
Plant-microbial interaction in dry matter yield and uptake of Fe, K and P were more prominent in BW 363 and BW 272-6b rice varieties which are moderately tolerant and susceptible, respectively, to Fe toxicity in comparison to BW 267-3, which is an Fe toxicity tolerant variety
Summary
Rice growers are in a continuing struggle to reach the potential yield to cater to the food demands of the continuously increasing population (Papademetriou et al, 2000). Iron toxicity has been reported in several countries in Asia, South America, West and Central Africa (Audebert & Fofana, 2009; Bandara & Gunatilaka, 1994; Papademetriou et al, 2000; Sahrawat, 2004) It has been observed in a wide range of soil types inherently rich in Fe such as acid sulphate soils, peat soils and acidic clay soils in valley bottoms that receive interflow water from nearby upper slopes, and generally under lowland rice production with permanent flooding during growth (Becker & Asch, 2005; Sahrawat, 2004). In addition to Fe concentration of soil solution, crop growth stage, physiological status of plant, genotypic characters, and plant-microbial interactions may contribute to the severity of Fe toxicity related stress experience by a crop
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