Comparison of Agronomic and Physiological Traits of Rice Genotypes Differing in Cadmium-Tolerance

Abstract

Cadmium (Cd) is one of major contaminants in agricultural soil, threatening agricultural production and human health. To understand agronomic and physiological characteristics of rice ( Oryza sativa L.), genotypes differing in Cd-tolerance, 2 Cd-tolerant rice genotypes Shanyou 63 ( indica hybrid) and Yangjing 9538 ( japonica)and 2 Cd-susceptible genotypes Yangdao 6 ( indica) and Wuyunjing 7 ( japonica) were pot-grown in 2004 and 2005. In the Cd treatment, 150 mg kg −1 Cd was added into pot soil before seedling transplanting, and no Cd addition was taken as control. Under the Cd treatment, the grain yield was reduced by 6.2–8.9% for the Cd-tolerant genotypes and by 38.3–47.1% for the Cd-susceptible ones compared with their respective controls. The reduction in grain yield was mainly attributed to the reduction of panicles per pot and spikelets per panicle. The differences in seed-setting rate and 1000-grain weight were not significant between the Cd treatment and the control. The Cd treatment markedly inhibited the tillering of the Cd-susceptible genotypes, resulting in the reduction of dry matter accumulation during the whole growth period. Cd slightly affected the translocation of nonstructural carbohydrate from culms and sheaths, as well as harvest index. For Cd-susceptible genotypes from the tillering to the jointing stages, the Cd treatment significantly reduced root oxidation activity and photosynthetic rate, activities of superoxide dismutase, and the catalase in leaves, but obviously increased the content of the superoxidate radical, hydrogen peroxide, and ethylene evolution rate of leaves, as well as the concentration of 1-aminocylopropane-1-carboxylic acid in root bleedings. After the heading stage, the Cd treatment affected the above-mentioned physiological traits of the Cd-tolerant genotypes much less. The differences in the above-mentioned traits at heading and later, as also the abscisic acid content in leaves during the whole growth period were not significant between the Cd treatment and the control. The results indicated that the effects of Cd on rice growth and development were mainly during the early growth period (from tillering to jointing). More tillers, stronger root activity, and antioxidative defense system, and less ethylene synthesis in the plants during this period were considered as the agronomic and physiological traits of Cd-tolerant genotypes of rice.