| Summary: | Carbon isotope ratio (δC) has been used as a proxy for water use efficiency (WUE) in several crops. We compared δC of soybean [ (L.) Merr.] tissues sampled at bloom with δC of mature seed (MS). Twenty Maturity Group IV accessions with contrasting δC values were evaluated in three environments. Genotype and environment effects on δC were significant for the uppermost mature trifoliolate leaf, center leaflets from main stems, whole shoot, and MS, but there were no significant genotype by environment interactions, indicating that genotype rankings were similar among environments. Repeatability of δC among tissues ranged from 0.79 to 0.94, and MS δC values were significantly correlated with δC from other tissues ( ≥ 0.69). For genotypes of similar maturity, MS δC may be used as a selection tool for WUE, simplifying the use of δC for high-throughput phenotyping.
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