Objectives The geological background of cadium (Cd) in paddy fields of Guangxi is high, and rice plants may absorb and accumulate Cd during growth, posing a threat to human health. We studied the uptake, translocation, and accumulation patterns of Cd in different indica-type rice cultivars, as well as the possible influence factors, and prelimarily screened for low-Cd-accumulating rice cultivars for the safe production of rice in Guangxi.

Methods Field experiments were conducted in high-cadmium farmland in Guilin City, Guangxi (with a total Cd content of 1.30±0.21 mg/kg). The tested rice varieties included 142 widely cultivated indica rice varieties (including indica three-line hybrid rice (three-line), indica two-line hybrid rice (two-line), and conventional indica rice (conventional). At maturity, rice plants were harvested to analyze the contents and accumulations of Cd, As, Cu, and Pb in roots, stems, leaves, and grains. Meanwhile, soil samples were collected to determine the contents of DTPA-Cd, As, Cu, and Pb.

Results 1) There were no significant differences in grain Cd content among the three types of indica rice. The Cd accumulation in various organs of indica rice showed a common pattern: roots>stems>leaves>grains. The average Cd content in each organ of indica hybrid rice was higher than that of conventional indica rice. 2) The Cd translocation factors (TF) between tissues in the three types of indica rice all exhibited the pattern TF_root-stem>TF_root-leaf>TF_root-grain. The Cd translocation factors between grains and other tissues all showed TF_leaf-grain>TF_stem-grain>TF_root-grain. The mean Cd enrichment coefficient in roots of indica hybrid rice was significantly higher than that of conventional indica rice. There was a significant correlation between grain Cd content and Cd absorption and translocation coefficients in various organs among different indica rice varieties. 3) There was a significant positive correlation between the contents of Cd, Cu, and Pb in roots of three-line and conventional indica rice, while a significant positive correlation existed between Cd and As in roots and between Cd content in stems and Cu content in grains of two-line rice. Additionally, there was a significant positive correlation between Cd and Cu contents in grains of two-line rice, and between grain Cd content and Pb content in roots of conventional indica rice. 4) The rate of grain Cd exceeding the standard reached 97.2%. The highest grain Cd content among different rice varieties was 1.94 mg/kg, and the lowest was 0.08 mg/kg, with a 24.25-fold difference between high- and low-accumulating varieties. 5) Through systematic clustering, five low-Cd-accumulating rice varieties were preliminarily screened: ZLY30, KY7463, ZLY819, XLY838, and BY429.

Conclusions Hybrid rice in high Cd geological background areas has a stronger ability to absorb and transport Cd than conventional rice. There are significant differences in cadmium enrichment and transport coefficients among different organs of indica rice varieties. Meanwhile, the correlation between these coefficients and cadmium content in rice varies greatly depending on the variety. In addition, there is a significant correlation between the contents of Cu, As, and Pb in the grains and roots of indica rice and the Cd content in various organs, indicating the possibility of combined toxicity from multiple heavy metals. Therefore, the variety characteristics largely determine the safety of indica rice. Through cluster analysis screening, the rice varieties with low Cd enrichment are ZLY30, KY7463, ZLY819, XLY838, and BY429.