Rice Seedling Vigor at Sub‐optimal Temperatures1

A laboratory method was devised for evaluating seedling vigor of rice ( Oryza sativa L.) cultivars, hybrids, and segregating populations at sub‐optimal temperatures. Seeds of 20 cultivars of diverse origin were soaked in distilled water for 24 hours at 30 C and then germinated in the dark on moist blotters at 15, 18, 20, 25, and 30 C. Seedling height was used as the primary criterion for evaluation. Growth differences among cultivars, temperatures, and their interaction were highly significant. The same cultivars were evaluated in a field trial where mean days to emergence ranged from 9.4 to 17.7 with a mean of 12.9, and percentage emergence ranged from 22.0 to 87.5 with a mean of 57.4. The above two traits were components of an emergence index which ranged from 12.9 to 76.0 with a mean of 44.4. Correlation coefficients of laboratory seedling heights at five temperatures with days to emergence in the field ranged from ‐0.74 to ‐0.89, at the 1% level, with percentage emergence — from 0.56 to 0.69, at the 5% level, and with emergence index — from 0.75 to 0.81, at the 1% level. Results indicated that performance hi laboratory tests was a satisfactory indicator of field performance.