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An optimized index for cold tolerance assessment in rice during germination and early seedling stage
Monzón Daisy Leticia Ramirez,Cantero Jorge,Danielowski Rodrigo,da Luz Viviane Kopp,Venske Eduardo,Mota Monalize Salete,da Silva Raissa Martins,de Oliveira Victoria Freitas,de Oliveira Antonio Costa,de 한국작물학회 2023 Journal of crop science and biotechnology Vol.26 No.2
Cold tolerance at germination and seedling stage is one of the most seeked traits in Southern Brazilian rice (Oryza sativa L.) cultivars, thus, the availability of improved methods for germplasm assessment is of high importance for breeding programs. The aim of this study was to validate an optimized Average Tolerance Index (ATI) for rice germplasm assessment under cold at germination and early seedling stage. A diverse panel composed by 124 rice accessions was assayed. Four genotypes with known performance under cold were used as controls (two tolerant and two sensitive). The genotypes were sown in roll papers, and evaluated at 13 °C for 28 days (cold stress) and 25 °C for seven days (control). Four traits were measured, germination percentage, coleoptile length, root length and shoot length, which were converted in terms of relative perfor‑ mance (cold/control). A PCA analysis was carried out. The ATI was calculated as a linear combination of all trait’s relative performance, weighted by the importance of each trait in explaining the genetic variability in the set, through including the PC1 vectors as trait coefcients. K means was applied for genotype classifcation. The panel showed expressive genetic variability for performance under low temperature. The ATI successfully distinguished the controls regarding their cold tolerance and allowed the formation of four classes of genotypes, sensitive, moderately sensitive, moderately tolerant and tolerant. The assessment of rice germplasm for cold tolerance at germination and seedling stage through ATI is a viable alternative for the identifcation of tolerant genotypes.