The Evaluation of Rice Varieties for Cold Water Tolerance 1

' I ^HE tolerance of rice varieties to cold water is impor•*• tant in areas with a cold water problem, either from cool early growing-season weather conditions or from cold reservoirs. Germination and growth of rice are slower in cold water and yields are reduced. Cold water conditions are of particular importance in California where rice seed is generally broadcast directly into 6 to 8 inches of standing water and this water is maintained through the growing season. Raney et al. have pointed out that cold water injury to rice occurs in a definite pattern relating to water flow from the intake boxes through the field. They also indicate that the use of new reservoirs in northern California has lowered the temperature of rice irrigation water as much as 15° F. in some areas. Other rice-growing areas of the United States are much less troubled with cold water problems but the situation in California may have its counterpart in other higher latitude rice-growing areas of the world. Tests were conducted in a refrigerated chamber with a glass front admitting sufficient sunlight for normal seedling growth. A temperature of 60 ± 2° F. was maintained in this chamber for 28 to 30 days from seeding. Ten varieties or selections in 4 replicates were tested at the same time. Fibreglass containers were used, one for each replication. A four-inch depth of fumigated pulverized Stockton clay soil was used in the test. Nitrogen, as (NH4)2SO4, at the rate of 45 pounds per acre was thoroughly mixed with the soil. The samples of seed were soaked in a 0.05% sodium hypochlorite solution for 24 hours and then drained for several hours before seeding to simulate the preplanting treatment commonly used in California. Rows were marked off and labeled at random in each container and separated from each other with plastic mesh. The seeds