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Table 2 Current criteria for evaluation of cold tolerance in rice at different growth stages

From: Rice and cold stress: methods for its evaluation and summary of cold tolerance-related quantitative trait loci

Evaluation criteria Description Temperature and duration Reference
Treatment Recovery
Germination stage     
Vigor of germination Vigor of germination (%) = Number of germinated grains/Number of total grains × 100 14°C/7-17 d - (Han et al. [2006])
Seedling survival rate Seedling survival rate (%) = Surviving seedlings/Sprouting seeds × 100, determined when shoots are about 5 mm long. 2°C/3 d 20°C/7 d (Zhou et al. [2012])
Seedling stage     
Fresh weight (FW) Changes in FW of plants after cold treatment can be used as an indicator of cold damage. 10°C/1-48°h - (Bonnecarrère et al. [2011])
Survival rate Survival rate (%) after cold treatment is calculated as the Number of surviving plants/Total number plants treated × 100 4°C/6 d 26°C/6 d (Zhang et al. [2011b])
Leaf emergence New leaf emergence demonstrates maintained vigor and increased growth. 4°C/7 d 25°C/10 d (Xie et al. [2012])
Seedling growth 1 = dark green seedlings, 3 = light green seedlings, 5 = yellow seedlings, 7 = brown seedlings, 9 = seedlings dead. 9°C/8-14 d - (Kim and Tai [2011]; IRRI [2002]; Andaya and Tai [2006])
Leaf growth A score of 1-3 (tolerant, all leaves normal, no apparent visual injury), or 4-9 (susceptible, all leaves wilted, seedlings apparently dead). 10°C/7 d 25°C/7 d (Suh et al. [2012])
Metabolic assessments Metabolites include EL, proline, MDA, and AsA, and GSH. 9°C/1-14 d - (Tian et al. [2011]; Zhang et al. [2011a]; Kim and Tai [2011]; Yang et al. [2012])
Enzyme activities Enzymes include POD, SOD, and CAT, and APX. 4°C/0-4 d 25°C/7 d (Bonnecarrère et al. [2011]; Huang et al. [2009]; Sato et al. [2001])
Reproductive stage     
Spikelet fertility (CGC) Spikelet fertility is calculated as the ratio of filled grains to the total number of florets, basing on cold greenhouse cultivation. 12°C/6 d Until maturation (Sato et al. [2011])
Spikelet fertility (CDWI) Spikelet fertility is calculated as the same as spikelet fertility (CGC), but the cold treatment is based on cold deep-water irrigation. 18-19°C/~60 d - (Shirasawa et al. [2012])