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CROP PHYSIOLOGY & METABOLISM

Genetic Variation for Carbon Isotope Discrimination in Sunflower

Association with Transpiration Efficiency and Evidence for Cytoplasmic Inheritance

^a School of Land and Food Sciences, Univ. of Queensland, St. Lucia 4072, Brisbane, Australia
^b Commonwealth Scientific and Industrial Research Organisation Plant Industry, 306 Carmody Rd., St. Lucia 4067, Brisbane, Australia
^c Commonwealth Scientific and Industrial Research Organisation Plant Industry, 306 Carmody Rd., St. Lucia 4067, Brisbane, Australia

^* Corresponding author (chris.lambrides{at}uq.edu.au).

Plants accumulate isotopes of carbon at different rates because of discrimination against ¹³C relative to ¹²C. In plants that fix carbon by the C₃ pathway, the amount of discrimination correlates negatively with transpiration efficiency (TE) where TE is the amount of dry matter accumulated per unit water transpired. Therefore, carbon isotope discrimination () has become a useful tool for selecting genotypes with improved TE and performance in dry environments. Surveys of 161 sunflower (Helianthus spp.) genotypes of diverse origin revealed a large and unprecedented range of genetic variation for (19.5–23.8). A strong negative genetic correlation (r_g) between TE and (r_g = –0.87, P < 0.001) was observed in glasshouse studies. Gas exchange measurements of field grown plants indicated that was strongly correlated with stomatal conductance to water vapor (g), (r_g = 0.64, P < 0.01), and the ratio of net assimilation rate (A) to g, (r_g = –0.86, P < 0.001), an instantaneous measure of TE. Genotype CMSHA89MAX1 had the lowest TE (and highest ) of all genotypes tested in these studies and low yields in hybrid combination. Backcrossing studies showed that the TE of this genotype was due to an adverse effect of the MAX1 cytoplasm, which was inherited from the diploid perennial H. maximiliani Schrader. Overall, these studies suggested that there is an excellent opportunity for breeders to develop sunflower germplasm with improved TE. This can be achieved, in part, by avoiding cytoplasms such as the MAX1 cytoplasm.

Abbreviations: , carbon isotope discrimination • A, net assimilation rate • CHLadj, chlorophyll content adjusted for leaf thickness • CMS, cytoplasmic male sterility • EMS, error mean square • g, stomatal conductance to water vapor • HGT, plant height • HI, harvest index • LA, leaf area • LDW, leaf dry weight • RDW, root dry weight • SDW, stem dry weight • SLW, specific leaf weight • TDW, total dry weight • TE, transpiration efficiency • VPD, vapor pressure deficit • WUE, water use efficiency • WUSE, total water use

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