Efficiency of adaptation mechanisms of rice to diverse conditions of iron toxicity

Tolerant lowland rice cultivars are considered the most effective approach to cope with iron toxicity, however, the currently available cultivars often fail when exposed to varying environmental and Fe(II) stress conditions. Iron toxicity appears to differentially affect rice cultivars as a function of plant development stage, stress intensity and duration , and climatic conditions. There is a need to match genotypic resistance mechanisms with prevailing site conditions. Ten contrasting rice genotypes were evaluated in hydroponic culture regarding their iron tolerance and the involved mechanisms. Fe(II) stress was applied at the seedling, vegetative, and early reproductive growth stages with varying concentrations and durations and under conditions of high and low vapor pressure deficit. Leaf symptoms were scored and the amount of root plaque and the uptake and partitioning of Fe species (Fe(III) by AAS; Fe(II) by 2,2- dipyridyl method) were determined. Both the mechanisms (exclusion, deposition, tissue tolerance) and their effectiveness to counteract elevated Fe(II) levels differed between cultivars and varied with plant age and environmental conditions. There is a need for a site- and environment- specific selection of genotypes and of tolerance mechanisms to effectively counteract conditions of iron toxicity