Comparative assessment of einkorn and emmer wheat phenomes: II. Phenotypic integration

Authors: Jaradat, Abdullah

Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2019
Publication Date: 2/13/2020
Citation: Jaradat, A.A. 2020. Comparative assessment of einkorn and emmer wheat phenomes: II. Phenotypic integration. Genetic Resources and Crop Evolution. 67(3):655-684. https://doi.org/10.1007/s10722-019-00840-3.
DOI: https://doi.org/10.1007/s10722-019-00840-3

Interpretive Summary: Einkorn and emmer hulled wheat species underwent major changes and accumulated differences in their characteristics during their long history of cultivation under domestication. These changes affected their adaptation to and yield potential in different environment around the world. Naturally, most changes under domestication contributed to securing stable yield. However, maximum yield was not an objective under changing environments and subsistence farming. During centuries of evolution under domestication, different intensities of selection pressure may have acted differentially upon single or multiple traits. Therefore, it produced einkorn and emmer varieties with divergent levels of trait integration. Also, it resulted in the development of strategies linked to resource conservation. A collection of einkorn and emmer, representing different origins and improvement status of both species, was evaluated for the strength of trait relationships using several analysis methods. These trait relationships were assumed as indicators of the of plant's ability to respond to changing environmental conditions and management practices. Generally, emmer exhibited larger levels of closely linked traits than einkorn making it more challenging for the species to withstand future stresses and to adapt to changing environmental conditions. The study indicated that there are many opportunities and benefits in influencing future agroecosystems. This can be possible if agronomists and plant breeders compile databases on the strength of multiple traits in einkorn and emmer and use the data to develop more resilient and productive cultivars of both species.

Technical Abstract: Phenotypic integration, as the outcome of the number and strength of (co)variation among phenotypic traits in the evolutionary-related diploid einkorn (Triticum monococcum L. subsp. monococcum) and tetraploid emmer wheat [Triticum turgidum subsp. dicoccon (Schrank) Thell.], was estimated for seven modules (i.e., area, density, dimensions, dry weight, ecophysiology, structure, and yield components) based on 110 traits measured or estimated on plant, tiller, leaf, spike, spikelet and kernel samples at three growth stages during four growing seasons. Classical methods of phenotypic integration assessment using algorithms for dimensionality reduction, matrix correlation, ordination, discrimination, multidimensional scaling and functional relationships, generated insightful but inconsistent estimates of phenotypic integration; thus, making it challenging to compare the strength of integration across species and modules. Divergence between einkorn and emmer due to polyploidy, although evident at the mean phenotypic index at whole plant phenotypic level (0.37±0.08 and 0.59±0.09, respectively), was manifested more at the reproductive than at the vegetative level; while emmer exhibited larger correct classification (86.0%) than einkorn (69.5%) at a multidimensional scale. A standardized z-score, which was based on partial least squares analysis of trait variation, when adjusted for plant size, provided unbiased estimates of phenotypic integration indices comparable across modules and species (minimum z-score of 16.9±1.1 for density module in einkorn to 32.1±2.0, for yield components module in emmer). These differences could be attributed to the different numbers of significant common principal components shared between the species with a range from three (area module) to nine (dimensions module) components. Future research needs to explore how inter- and intraspecific phenotypic variation affect population dynamics and performance under field conditions. Therefore, considerable opportunities and benefits, in influencing the structure and function of agroecosystems, are expected if intraspecific trait databases are developed for einkorn and emmer wheats, two of the earliest domesticates, as potential alternative crops.