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Evaluating leaf wax and bulk leaf carbon isotope surrogates for water use efficiency and grain yield in winter wheat

Bulk leaf carbon isotopic composition (dCbulk) has been widely used to investigate leaf level water use efficiency (WUEl) in efforts to boost grain yield relative to crop water use. Although widely used for isotopic analyses, the bulk leaf represents a complex mixture of compounds. Single-compound isotopic analyses carry diagnostic advantages over bulk analyses in a range of applications and may also serve as surrogates for WUEl and grain yield in crops. This study tests whether compound-specific carbon and hydrogen isotopes of leaf wax n-alkanes (dCalk and dDalk) and n-alcohols (d Calc) could be used as surrogates for WUEl and grain yield using conventional dCbulk as a reference. Ten winter wheat (Triticum aestivum L.) cultivars were planted under two irrigation treatments (full and deficit irrigation) at Uvalde (wet location) and Amarillo (dry location), TX, during two growing seasons. There were significant relationships between dCalk or dDalk and d Cbulk, indicating they can all serve as surrogates for WUEl in most cases. Compared with d Cbulk, we found stronger relationships between dCalk at Uvalde or dDalk under deficit irrigation at Amarillo and grain yield. The dCalk also had higher broad-sense heritability than dCbulk, indicating larger cultivar effects in dCalk than in d Cbulk. In contrast, the dCalc was not consistently related with dCbulk or grain yield. Our study introduces the idea that dCalk and dDalk may supplement conventional dCbulk with potential to assist in the breeding process when selecting for high-WUE and high-yielding cultivars. X. Liu, X. Dong, and D.I. Leskovar, Texas A&M AgriLife Research and Extension Center at Uvalde, 1619 Garner Field Rd., Uvalde, TX 78801; X. Liu, Key Lab. of Agricultural Water Resources, The Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, The Chinese Academy of Sciences, 286 Huaizhong Road, Shijiazhuang, Hebei, 050021, China; S.J. Feakins, Dep. of Earth Sciences, Univ. of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089; Q. Xue and T. Marek, Texas A&M AgriLife Research and Extension Center at Amarillo, 6500 Amarillo Blvd. W., Amarillo, TX 79106; J. Han, Independent Researcher, 1606 Knox Rd., Ardmore, OK 73401; C.B. Neely and A.M.H. Ibrahim, Dep. of Soil and Crop Sciences, Texas A&M Univ., 370 Olsen Blvd, 2474 TAMU, College Station TX 77843. Received 20 July 2018. Accepted 5 Dec. 2018. *Corresponding authors (feakins@usc.edu; xuejun.dong@ ag.tamu.edu). Assigned to Associate Editor Michael Grusak. Abbreviations: BSTFA, bis(trimethylsilyl) trifluoroacetamide; CID, carbon isotope discrimination; dCalc, leaf n-alcohol carbon isotopic composition; dCalk, leaf n-alkane carbon isotopic composition; dCbulk, bulk leaf carbon isotopic composition; dDalk, leaf n-alkane hydrogen isotopic composition; ETc, crop evapotranspiration; ET0, reference evapotranspiration; FID, flame ionization detection; TMS, trimethylsilyl; VPD, vapor pressure deficit; WUE, water use efficiency; WUEg, water use efficiency in grain production; WUEl, leaf level water use efficiency. Published in Crop Sci. 59:718–732 (2019). doi: 10.2135/cropsci2018.07.0452 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. Published February 14, 2019