Germanium (Ge) is a metalloid with chemical properties similar to silicon (Si). In Si accumulators like rice (Oryza sativa L.), micromolar concentrations of Ge can result in necrotic lesions and chlorosis. Ge phytotoxicity has been employed to great effect to identify rice mutants defective in silicon (Si) uptake, leading to the cloning of the first Si transporters in plants. A population of M₄ mutants derived from chemical mutagenesis of the temperate japonica Kitaake underwent Ge screening to identify mutants with more rapid development of Ge-induced lesions than the wild type. From 30 mutant lines identified in the preliminary screening, the line designated KDS-557B emerged as hypersensitive, exhibiting a more rapid development of necrotic lesions even at 5 μM GeO₂, a 10-fold lower concentration than the normal used for screening. An analysis of mapping populations from crosses of KDS-557B with Kitaake (χ2 = 2.63, df = 1, P = 0.105, not significant at P ≤ 0.01) and a tropical japonica variety, Sabine (χ2 = 0.04, df = 1, P = 0.841, not significant at P ≤ 0.01) supported a single gene recessive mutation model. Further characterization of KDS-557B will contribute to understanding the interaction of metalloid elements and plants.

Keywords: Rice (O. sativa L.), induced mutations, germanium, toxicity, hypersensitivity

Key findings: Identification of a rice (O. sativa L.) mutant exhibiting hypersensitivity to the phytotoxic metalloid germanium was successful. This mutant, which exhibits a single gene recessive mode of inheritance, and its further characterization will contribute to advancing our understanding of the interaction of crop plants with metalloid elements in the environment.