Reassessing waterlogging: methods to compare the response of different sugarcane genotypes

Abstract

Many studies have been conducted to determine the effects of waterlogging on sugarcane using the depth of the water table from the soil surface as the measure of waterlogging. However, the range of depths reported to affect sugarcane has created confusion. The wide range of depths reported is likely to be due to the different cultivars and soils used, and the different environmental conditions experienced. A system using the level of dissolved oxygen as the measure of waterlogging has been developed. This has enabled comparisons of waterlogging tolerance to be made between sugarcane cultivars and related genotypes. Two ways of testing the response to levels of dissolved oxygen were developed. The first assayed germination at different levels of dissolved oxygen, the second, the ability to germinate after different lengths of exposure to 2 mg/L dissolved oxygen. Differences in response to levels of dissolved oxygen were found. For cultivars tested, there was only a 50% probability of a bud germinating and growing at a dissolved oxygen concentration of 5.3 mg/L. Measurements of the level of dissolved oxygen in waterlogged sugarcane fields showed levels below 2 mg/L. Consequently, the bud's ability to survive periods at these low oxygen concentrations is likely to be more important. Differences in the duration that buds can survive exposure to low dissolved oxygen have been shown for selected sugarcane cultivars and Saccharum spontaneum genotypes. The commercial cultivars tested had no probability of germination and growth after 7 days of exposure to low dissolved oxygen levels. However, one of the S. spontaneum genotypes had buds that were able to germinate and grow after 7 days of exposure. The genotype SES297A had 41% probability of germination and growth after 7 days of exposure and remarkably 11% probability of germination and growth after 11 days of exposure. The systems developed enable the differences found between genotypes to be investigated further. Identification of the differences and their basis could lead to strategies being developed to incorporate this trait of tolerating low oxygen conditions into parental material in breeding programs.