Development of a simple testing method for cool weather tolerance at the flowering stage of rice using an air conditioned room

We report a simple method devised for testing the cool weather tolerance at the flowering stage in rice. In small square pots, 15 cm in length, 5 cm in width and 10 cm in height, eight plants having only the main culms were cultivated. The temperature was constantly kept at 17.5 degreesC for 15 days in an air conditioned room with 50% shading. The tolerance to cool weather damage was estimated from the fertility percentage of panicles which headed at the day when the low temperature treatment was started. At least 10 panicles (3 similar to4 pots) were needed to classify the varieties into 7 ranks, from extremely high tolerance to extremely vulnerable, with statistical errors of +/-0.8 rank. In this method, the treatment starting at the heading day caused the lowest fertility percentage in almost all varieties. Therefore, fertility percentage could be determined using fewer panicles compared with the 8-day treatment at 15 degreesC. There was a significant positive correlation (r=0.808**, n=14) between the results obtained by this method in different years. The results obtained by this method showed significant positive correlations with those obtained by the 8-day treatment method at 15 degreesC and 6-day treatment method at 12 degreesC (r=0.750** and 0.802**, respectively, n=14). Although the plants examined by this method were very small, there was a significant positive correlation (r=0.922**, n=8) between the results obtained using these small plants and the plants cultivated in a 1/5000a pot, which were similar in size to those in the paddy field.