The importance of barley genetics and domestication in a global perspective

Abstract

Background: Archaeological evidence has revealed that barley (Hordeum vulgare) is one of the oldest crops used by ancient farmers. Studies of the time and place of barley domestication may help in understanding ancient human civilization.

Scope: The studies of domesticated genes in crops have uncovered the mechanisms which converted wild and unpromising wild species to the most important food for humans. In addition to archaeological studies, molecular studies are finding new insights into the process of domestication. Throughout the process of barley domestication human selection on wild species resulted in plants with more harvestable seeds. One of the remarkable changes during barley domestications was the appearance of six-rowed barley. The gene associated with this trait results in three times more seed per spike compared with ancestral wild barley. This increase in number of seed resulted in a major dichotomy in the evolution of barley. The identification of the six-rowed spike gene provided a framework for understanding how this character was evolved. Some important barley domestication genes have been discovered and many are currently being investigated.

Conclusions: Identification of domestication genes in crops revealed that most of the drastic changes during domestication are the result of functional impairments in transcription factor genes, and creation of new functions is rare. Isolation of the six-rowed spike gene revealed that this trait was domesticated more than once in the domestication history of barley. Six-rowed barley is derived from two-rowed ancestral forms. Isolation of photoperiod-response genes in barley and rice revealed that different genes belonging to similar genetic networks partially control this trait.

Fig. 1.

A schematic diagram of the domestication process in barley regarding brittle rachis and row-type.

Fig. 2.

Consensus map of barley domestication-related genes. RFLP markers from the cross Azumamugi × Kanto Nakate Gold (Mano et al., 2001) were considered. Distances between markers are given in centimorgans. Genes were imposed on the genetic map by comparative mapping approach.

Fig. 3.

Barley spikelets in one rachis node. (A) Ethiopian landrace var. deficiens; rudimentary lateral spikelets (Vrs1.t). (B) Wild barley var. spontaneum; sterile lateral spikelets (Vrs1.b). (C) Two-rowed cultivar var. distichon; sterile lateral spikelets (Vrs1.b). (D) Wild barley var. proskowetzii; short-awned or tip-pointed lateral spikelets (Vrs1.p). (E) Six-rowed cultivar convar. vulgare; fully fertile and awned lateral spikelets (vrs1.a).