Studies on the testing methods of cold resistance in rice.

Abstract

Cold resistance in rice plants shows high correlation with cold water tolerance, so the cold water irrigation method has been used for the testing method of cold resistance. This cold water irrigation method takes a long irrigating period from transplanting to maturing, and requires too large a plot size for accurate evaluation for testing a number of lines at the same, time. So this investigation was conducted to establish some efficient method for accurate testing on the cold resistance of a number of bred lines. The newly devised methods are as follows. For keeping the effect of cold water in the paddy field as homogeneous as possible, the cold water irrigation was practised only at night time, from the premordia stage of the early varieties to the starting time of the heading of the late varieties, and the inlets and outlets of the water were interchanged in every seven or eight days. Owing to this testing method, the distribution of water temperature was highly hornogenized in the field (Fig. 2), and so the uniformity of the sterility occurrence could be kept at a high level.