Author
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Jaradat, Abdullah |
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Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/26/2018 Publication Date: 1/1/2019 Publication URL: http://handle.nal.usda.gov/10113/6299364 Citation: Jaradat, A.A. 2019. Comparative assessment of einkorn and emmer wheat phenomes: I. Plant architecture. Genetic Resources and Crop Evolution. 66:491-512. https://doi.org/10.1007/s10722-018-0729-z. DOI: https://doi.org/10.1007/s10722-018-0729-z Interpretive Summary: Ancient hulled wheat species (e.g., einkorn and emmer) fed the Old World for thousands of years before they were largely displaced by bread wheat around 4,000 years ago. However, they persisted in several isolated mountainous regions and under subsistence, low-input farming systems in parts of West Asia, North Africa, Ethiopia, India and Southeast Europe. Growing consumer demand for organic, traditional and healthier wheat products from hulled wheats revived the interest in collecting and evaluating their remaining genetic resources and selecting and developing varieties with improved agronomic and nutritional traits. Plant shape comparison using several traits in einkorn and emmer wheat varieties provided in-depth information on which traits, and to what extent, have been influenced by several factors and contributed to larger plant size and grain yield of emmer compared to einkorn wheat. Plant size and shape were modified to produce a less compact emmer compared to einkorn plants and resulted in larger biomass per plant in emmer, despite the inherently larger number of tillers per plant in einkorn. Natural selection and early domestication has modified wheat plant size and shape from the einkorn to emmer type. Selected varieties and the species-specific traits identified in this research are under in-depth evaluation. The current varieties are a valuable source to identify parents for planned hybridization and to combine and select appropriate trait combinations for better adaptation to local environmental conditions and production systems. The overall objective was to produce new hulled wheat types for large-scale production. Technical Abstract: The domestication syndrome of wheat was based on genetically-mediated mutation(s) in reproductive traits, with no due consideration to traits that comprise the plant “phenome” as an abstract expression of phenotypic architecture and a central component of the plant phenotype. Genetically and phenotypically variable germplasm source of diploid einkorn (Triticum monococcum L. subsp. Monococcum) and tetraploid emmer wheat (Triticum turgidum subsp. dicoccum Schrank ex Schübl) was phenotyped for architectural (plant, tillers, leaves) and reproductive (spike, spikelet, and kernel) components of its phenome to quantify, describe, and contrast plant architecture of both species, and estimate the level of genetic divergence of emmer from einkorn due to polyploidy. Inter-specific variation for all architectural and reproductive components exhibited significant differences; while, intra-specific phenotypic variation estimates in both species decreased as follows: kernels>spikelets>spikes; and smaller values were estimated for leaves>plants>tillers. Diploid and tetraploid architectural modules, expressed as loadings on principal components, were significantly different; einkorn and emmer were 97.1 and 89.8 correctly classified, respectively, and were significantly separated (Mahalanobis D2 = 127.5; p<0.001). More traits exhibited larger magnitude and expressed larger genotypic variation due to polyploidy; however, heritability of these traits displayed different patterns, with large species differences for leaf area index and tillers per plant. Reduced major axis analysis of inter-specific functional relationships suggested that phenotypic traits were divided almost equally between allometric and isometric; the same trend was observed for reproductive traits. Paired comparisons suggested close relationships (r = 0.54 to 0.97; p<0.05) between spikelet and kernel traits in each species. However, the magnitude of trait estimates in pairwise comparisons between ploidy levels were not in unison; the magnitude of emmer exceeding einkorn in almost all spikelet traits was larger than those for kernel traits. Polyploidy caused phenotypic increases in traits that can support larger grain yield, including stems, peduncles, leaves and spikes, but not tillers. In addition to phenome differences due to polyploidy, and even under the high production potential of the Upper Midwest, USA, einkorn may be source-limited due to its lower spike fertility index, while emmer may be sink-limited due to its limited tillering capacity and larger spikes. Nevertheless, the larger level of phenotypic integration in emmer due to genetic linkage or pleiotropy can be deduced from the functional relationships between traits within species (due to selection) or among species (due to polyploidy and selection). Results of phenome analysis are expected to complement classical germplasm characterization and evaluation, and to provide a holistic approach to whole-plant development in the quest of new, adapted and more productive hulled wheat "ideotypes." |
