Improved mass screening of tolerance to iron toxicity in rice by lowering temperature of culture solution

Breeding for tolerance to iron (Fe) toxicity in rice (Oryza sativa L.) is hindered by lack of a suitable screening technique. In the culture solution methods used to date, a major difficulty has been maintaining an excess level of iron concentration in order to reveal toxicity symptoms. Experimental results showed that this problem was solved by lowering the solution temperature to around 20 degrees C, at which leaf discoloration in susceptible cultivars became more pronounced. At 20 degrees C Fe uptake was increased from a threshhold content of 300 mg/kg of dry weight of shoot for toxic symptom to more than 1000 mg/kg in susceptible and in tolerant cultivars. Concentrations of other related minerals in the plant tissue, i.e., potassium (K) and phosphorus (P), were not affected by the low solution temperature itself but by Fe content, which can be inferred on the basis of their response curves to the excess Fe treatment. Using the proposed screening method makes it possible to obtain reproducible results in screening a large number of plants or breeding lines.