|SZYMANSKI, RYAN - Washington State University|
Submitted to: Vegetation History and Archaeobotany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2014
Publication Date: 6/8/2015
Publication URL: http://handle.nal.usda.gov/10113/60959
Citation: Szymanski, R.M., Morris, C.F. 2015. Internal structure of carbonized wheat (Triticum spp.) grains-relationships to kernel texture and ploidy. Vegetation History and Archaeobotany. 24:503-515.
Interpretive Summary: In the present experimental study, the carbonized endosperm of three representative wheat species, einkorn, emmer and spelt, bearing very soft, very hard, and soft kernel texture phenotypes, respectively, were analyzed using field emission scanning electron microscopy (FESEM). The internal endosperm structure and fracture pattern of each textural type was characterized in an effort to identify observable patterns diagnostic in the identification of carbonized wheat grains at the species level. Grains were heat treated at 250'C, 270'C and 400'C, and the effects of carbonization were examined when grains were broken before or after heating. A unique and defining trait related to wheat phylogeny and ploidy is kernel texture (grain hardness). Einkorn is very soft, emmer/durum is very hard, and bread wheat/spelt is soft. This trait manifests itself when the kernel is broken, and if broken prior to charring/carbonization up to 270 'C, diagnostic morphological features are, to varying degrees, maintained. As such, a consideration of kernel texture in the archaeobotanical record may assist in better defining wheat evolution and some features of early agriculture.
Technical Abstract: The identification of wheat grains to the genus level is problematic in many archaeobotanical samples, yet this is key to better understanding wheat phylogeny and agricultural trajectories. This study was conducted to see if the pronounced differences in kernel texture (grain hardness) which exist among einkorn (very soft), emmer/durum (very hard), and bread wheat/spelt would manifest themselves after charring (carbonization). Grains of these three species were either broken and then charred, or charred and then broken (charring at 250'C, 270'C, and 400'C). All specimens were then examined using Field Emission Scanning Electron Microscopy (FESEM). At 250'C, grains broken before charring showed distension across the broken exposed endosperm surface. In the two soft wheats (einkorn and spelt), starch granules were still evident, whereas in emmer, the fracture surface was nearly smooth. When charring occurred before breaking, a flat fracture face resulted. At 270'C, distension increased for grains broken before charring whereas in those broken after charring, the fracture plane was again perpendicular to the longitudinal axis and was present as an open sponge-like topography. At 400'C, distension was pronounced and represented Apuffing@ in grains that were broken before charring. Those that were charred and then broken produced a markedly open porous structure. In conclusion, several morphological features related to grain hardness, and therefore ploidy and genus were present at the lower charring temperatures. These differences largely disappeared at 400'C. Consequently, the results also indicate that FESEM can provide information as to wheat species, charring temperature and grain processing in archaeobotanical contexts.