Low temperature is the most important abiotic stress affecting rice (Oryza sativa L.) yield in Chile. Rice in Chile is usually planted when the minimum air temperatures are below 12 °C. This temperature is lower than the optimum needed for normal rice germination. Therefore, the aim of this study was to evaluate cold tolerance in 20 experimental lines from the Rice Breeding Program of the Instituto de Investigaciones Agropecuarias (INIA), Chile, at the germination stage. Coleoptile length reduction (CRED), coleoptile length after cold treatment (CLEN), coleoptile length recovery (CREC), and coleoptile regrowth (CREG) were evaluated at 13 °C for 4 d using 'Diamante-INIA' as the cold-tolerant control. To find genotypes with cold tolerance (low CRED value and high CLEN, CREC, and CREG values), genotypes were ranked, a biplot of principal components, and cluster analysis were performed. No differences were found among genotypes in the ranking based on CREC value so this trait was not considered. Analysis showed that only three experimental lines had cold tolerance similar to that of 'Diamante-INIA'; all other experimental lines exhibited intermediate to low cold tolerance. These results showed low cold tolerance of some Chilean genotypes at the germination stage, thus confirming the need to evaluate the rest of the germplasm from the Rice Breeding Program.

Low temperature is one of the main abiotic stresses affecting rice yield in Chile. Alterations in phenology and physiology of the crop are observed after a cold event. The objective of this work was to study the relative expression of genes related with cold stress in Chilean cultivars of rice. For this, we analyzed the expression of candidate genes using real-time polymerase chain reaction (rtPCR), after exposure to cold of the rice cultivars Diamante-INIA and Zafiro-INIA and one experimental line from INIA´s Rice Breeding Program in Chile, Quila 241701, with known high cold tolerance. For analysis, the Spanish cultivar, Susan, was used as check tolerance and Oryzica 1 as susceptible check. Oxidative stress was measured through lipid peroxidation. To find mechanisms of cold tolerance in Chilean cultivars, we determined the relative expression of genes related with oxidative stress, such as superoxide dismutase (SOD), glutathione reductase (GR), and catalase (CAT). Lipid peroxidation allowed the measurement of the physiological stress level of the genotypes under study. The results indicate that lipid peroxidation in Oryzica 1 was higher than in the other genotypes. No differences were observed in expression levels of gene-encoding SOD and GR between genotypes. Contrary to expected results, high level of the gene-encoding CAT enzyme in Oryzica 1 after cold stress was observed. Future experiment, related with enzymatic activity and non-enzymatic antioxidant mechanism, are necessary to elucidate the relationship between cold stress and expression levels of gene-encoding antioxidant enzyme in Chilean rice germplasm.