Selection of Wheat Varieties Part 2

The Australian Grains Genebank houses an extensive range of ancient and modern germplasm. Material is made available through a Standard Material Transfer Agreement as governed by the International Treaty on Plant Genetic Resources for Food and Agriculture. This is a Multilateral System which facilitates fair and equitable access to genetic resources for purposes of research, conservation and sustainable use.

I selected varieties that I felt best represented each of the main groups shown in the Table of Wheat Species (see my previous blog post).

Some ancient precursors to wheat, such as Aegilops tauschii (photo below), were important in the development of domesticated wheat. However seed of these species is not available due to Quarantine restrictions.

Photo: Aegilops tauschii (syn. A. squarrosa, Triticum tauschii). 

Copyright: International Maize and Wheat Improvement Center (CIMMYT), 2007.

Source: Flickr @ https://www.flickr.com/photos/cimmyt/6681448641

License Attribution-NonCommercial-ShareAlike 2.0 Generic (CC BY-NC-SA 2.0).

A species of Wild Goatgrass, Aegilops tauschii, is one of the ancestors of common bread wheat (Triticum aestivum). Modern hexaploid wheat Triticum aestivum (2n = 6x = 42; AABBDD) owes its existence to one or more rare, natural hybridization events between the diploid Aegilops species (2n = 14; DD) and Triticum turgidum (2n = 4x = 28; AABB), a domesticated, tetraploid wheat, in the Fertile Crescent around 8,000 years ago. (Source: Jia, 2013)

I was also unable to source any of the truly wild counterparts of some other species, such as Wild Einkorn (T. monococcum L. subsp. aegilopoides Thell. and Triticum urartu Tumanian ex Gandilyan) and Wild Emmer (Triticum turgidum L. subsp. dicoccoides (Korn. ex Asch. & Graebn.) Thell.).

The domesticated forms of these species were however available and these possess the same genomes as the wild forms. Some ancient landrace varieties may be considered close to being "wild", due to their cultivation in relatively isolated, rural provenances over many years. In such situations the selection/breeding processes have been minimal or left mostly to natural processes.

Many of the truly wild forms of wheat frequently lack vigour and disease resistance, due to their long separation from the influences of human domestication. The widespread distribution, cultivation and selection of varieties in different climate zones over many thousands of years has significantly altered the biochemistry and physiology of domesticated wheat. Modern wheat is genetically predisposed to an agrarian life cycle.

Natural hybridization occurs only rarely (as most domesticated wheat and barley varieties are self-pollinating). Sporadic hybrids have been selected out and perpetuated if they have shown favourable traits. Moreover, most domesticated cereal varieties do not easily naturalize, and even when they do volunteer on disturbed ground, such as along roadsides or rail lines, they and their progeny generally do not persist for more than a year or two. Once the soil becomes hard and dry and natural grasses reclaim the space, the less adapted wheat and barley can no longer compete.

For my trial plots I selected examples of The A, B, and D genomes to show the progression from Diploid wheat to modern Hexaploid cultivars. I will discuss the different species, varieties and cultivars in more detail in future blogs.

References:

Jia J, et. al., Aegilops tauschii draft genome sequence reveals a gene repertoire for wheat adaptation. In Nature. 2013 Apr 4;496(7443):91-5. doi: 10.1038/nature12028. Epub 2013 Mar 24.