Relationship between taproot morphological traits, carbon isotope composition and grain yield in safflower

Abstract

The purpose of this study was to determine to what extent root characteristics, other than the taproot length, contribute to high grain yield and/or high water use efficiency (WUE) in safflower. A greenhouse trial was conducted using four safflower accessions (USDA6, USDA23, USDA29 and VARTOUG) with contrasting yield and WUE. A randomised complete block design was chosen, which included a typical (control) and a drought stress (withholding watering at the pre-flowering stage) treatments. The carbon isotope composition (δ13C) as an estimate of WUE, taproot diameter (DTR), diameter and number of secondary roots (DSR and NSR, respectively), biomass of the upper section of the taproot (BMTR-up) as well as grain yield (GY) and its components were measured. Our results revealed that NSR could be involved in drought adaptation of USDA23, with NSR increasing significantly (p = 0.045) by 27% under drought stress in this accession. BMTR-up was the only taproot trait correlated to GY and/or WUE, however the nature of the correlation was different for control and stressed plants. BMTR-up was significantly (p = 0.01) and negatively correlated with δ13C (r = –0.63) but had no correlation with GY (r = 0.23) in control plants. In contrast, BMTR-up was significantly (p = 0.03) and positively correlated with GY (r = 0.56) but not with δ13C (r = 0.23) under drought stress conditions. This finding suggests that, in the absence of drought conditions selecting safflower for a lower biomass in the upper section of the taproot may lead to high WUE, without affecting the yield.