Genetic characteristics of water-use related traits in sugar beet

Improved water use efficiency (WUE, the ratio of dry matter produced to water used) can potentially result in yield improvement in water-limited environments. Genetic variation in WUE can be exploited by carbon isotope discrimination (Δ) in C₃ species. In order to improve WUE and its associated traits, it is necessary to understand the genetic systems controlling the expression of these traits. A full diallel analysis carried out on five inbred lines selected from a previous field experiment revealed that Δ, WUE and specific leaf weight (SLW, the ratio of leaf dry weight to leaf area) had high narrow-sense heritability (H_n, the ratio of additive variance to phenotypic variance) and were controlled largely by additive gene effects indicating that these traits can be improved by selection in early generations. In contrast, maternal effects had a large influence on phenotypic expressions of total dry matter yield, total water use, chlorophyll content and leaf area suggesting the important role of selection of female parent for improvement of these traits. The parental line R49 was found to be the best general combiner for all of the traits. Genetic variation in SLW was strongly associated with Δ (R ² =0.49, P < 0.01). This implies that SLW could be used as an inexpensive alternative measure for Δ to assess genotypes during the early phases of breeding programmes.