Genotypic variation for water use efficiency, carbon isotope discrimination, and potential surrogate measures in sugar beet

Crop water use efficiency (WUE) is increasingly of interest to plant breeders of major crops, including sugar beet (Beta vulgaris L.), but it is difficult and time-consuming to measure directly. Carbon isotope discrimination (Delta), which can be an indirect, time-integrated measure of WUE in C-3 species, could be used to select for improved WUE in sugar beet if it were shown to be a stable character with high heritability. This study investigated the magnitude of genotype by environment (G x E) interactions with Delta, and tested the strength of association between WUE, Delta and other traits as potential surrogate measures of WUE. Using sugar beet breeding lines and hybrids with diverse genetic backgrounds, the genotypic variation in WUE, seasonal water use, and total dry matter (TDM) yield were measured under droughted and irrigated conditions in the field in 2004 and 2005. Samples for Delta analysis were taken from mature leaves and from roots at harvest. Results showed that genotypes differed in WUE and sensitivity to water deficit. There was significant genotypic variation for Delta, which was inversely related to WUE. The genotype x treatment x year interaction for TDM was significant but was non-significant for Delta and leaf mass per area (LMA), and some genotypes showed better stability for Delta than others. Leaf ash and chlorophyll content were not related to WUE. In 2005, LMA showed strong negative association with Delta. The results suggest that Delta can be used as an effective selection criterion for improving WUE in sugar beet breeding programmes. (C) 2009 Elsevier B.V. All rights reserved.