Robert Aiken1, Zhanguo Xin2, Kenneth Kofoid3, M.B. Kirkham4, and Vara Prasad4. (1) NWREC, Kansas State University, 105 Experiment Farm Rd., Colby, KS 67701, (2) PSGDR, USDA-ARS, 3810 4th, Lubbock, TX 79415, (3) Kansas State University -, KSU Agric. Research Center, 1232 240th Ave., Hays, KS 67601-9228, (4) Agronomy, Kansas State University, Throckmorton Hall, Manhattan, KS 66506
Multiple traits could alter transpiration efficiency (TE) in sorghum, affecting primary productivity and yield potential (grain or biomass) with respect to water use. A greenhouse mini-lysimeter procedure for juvenile plants provided initial screening of TE among 400 PI accessions. Leaf gas exchange and fluorometry under standard conditions quantified the ratio of quantum yields of photosystem II and CO2 assimilation, ratio of assimilation to stomatal conductance (A/g), ratio of internal leaf CO2 to ambient CO2 (Ci/Ca) and TE normalized by vapor pressure deficit (nTE) under greenhouse and field conditions. Whole-plant TE from mini-lysimeters ranged from 6 to 9 g biomass/kg water. Steady state leaf measurements indicate A/g was highly correlated to nTE and to Ci/Ca. A similar range of values obtained from sorghum lines selected for pre- and post-flowering drought tolerance. Evidence for mechanisms altering TE include 1) reduced light use efficiency associated with bundle sheath leakage of CO2; 2) differential PEPC and RUBPC activity among lines; and 3) stomatal regulation of internal CO2. Identifying mechanisms accounting for differential TE could facilitate supplemental screening for enhanced TE in existing breeding programs as well as selecting for hybrids with transgressive TE traits.
