| Abstract: | Abstract Studies examining iron (Fe) toxicity and zinc (Zn) deficiency in rice have shown that screening experiments in nutrient solutions are of limited use because the rankings of genotypes as tolerant or intolerant can be very different from the results obtained in field-screening experiments. A possible reason for such deviation is that crucial rhizosphere processes cannot be reproduced in nutrient solutions. The objective of the present study was to evaluate the suitability of low-concentration agar nutrient solutions (ANS) as an alternative screening tool. Agar was dissolved in boiling water and mixed with nutrient solution to achieve a final agar concentration of 0.1% (w/v). Zinc deficiency was induced by supplying Zn at a low concentration (0.1 × 10?3 µmol L?1), while Fe toxicity was induced by supplying excess Fe2+ (200 mg L?1). Three-week-old seedlings were transplanted into this medium. Symptoms of Zn deficiency and Fe toxicity developed more rapidly in ANS compared with conventional nutrient solutions (CNS). For Zn deficiency this was probably because of the development of Zn depletion zones as a result of the reduced convection in the viscous agar medium. In the case of Fe toxicity we observed far less Fe precipitation in ANS compared with CNS. Genotypic comparisons showed that the tolerance rankings obtained in ANS were very similar to the field tolerance rankings, whereas this was not the case in CNS. This was particularly evident with regard to the considerable root growth inhibition detected in intolerant genotypes when stress treatments were imposed in ANS. |
