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. 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. 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.

SUMMARY: Heterosis, also known as hybrid vigor, is the phenomenon wherein a progeny exhibits superior traits relative to one or both parents. In terms of crop breeding, this usually refers to the yield advantage of F₁ hybrids over both inbred parents. The development of high‐yielding hybrid cultivars across a wider range of crops is key to meeting future food demands. However, conventional hybrid breeding strategies are proving to be exceptionally challenging to apply commercially in many self‐pollinating crops, particularly wheat and barley. Currently in these crops, the relative performance advantage of hybrids over inbred line cultivars does not outweigh the cost of hybrid seed production. Here, we review the genetic basis of heterosis, discuss the challenges in hybrid breeding, and propose a strategy to recruit multiple heterosis‐associated genes to develop lines with improved agronomic characteristics. This strategy leverages modern genetic engineering tools to synthesize supergenes by fusing multiple heterotic alleles across multiple heterosis‐associated loci. We outline a plan to assess the feasibility of this approach to improve line performance using barley (Hordeum vulgare) as the model self‐pollinating crop species, and a few heterosis‐associated genes. The proposed method can be applied to all crops for which heterotic gene combinations can be identified.

Summary: Global agriculture faces increasing pressure to produce more food with fewer resources. Drought, exacerbated by climate change, is a major agricultural constraint costing the industry an estimated US$80 billion per year in lost production. Wild relatives of domesticated crops, including wheat (Triticum spp.) and barley (Hordeum vulgare L.), are an underutilized source of drought tolerance genes. However, managing their undesirable characteristics, assessing drought responses, and selecting lines with heritable traits remains a significant challenge. Here, we propose a novel strategy of using multi‐trait selection criteria based on high‐throughput spectral images to facilitate the assessment and selection challenge. The importance of measuring plant capacity for sustained carbon fixation under drought stress is explored, and an image‐based transpiration efficiency (iTE) index obtained via a combination of hyperspectral and thermal imaging, is proposed. Incorporating iTE along with other drought‐related variables in selection criteria will allow the identification of accessions with diverse tolerance mechanisms. A comprehensive approach that merges high‐throughput phenotyping and de novo domestication is proposed for developing drought‐tolerant prebreeding material and providing breeders with access to gene pools containing unexplored drought tolerance mechanisms.

Leaf rust, caused by Puccinia hordei, is an economically significant disease of barley, but only a few major resistance genes to P. hordei (Rph) have been cloned. In this study, gene Rph3 was isolated by positional cloning and confirmed by mutational analysis and transgenic complementation. The Rph3 gene, which originated from wild barley and was first introgressed into cultivated Egyptian germplasm, encodes a unique predicted transmembrane resistance protein that differs from all known plant disease resistance proteins at the amino acid sequence level. Genetic profiles of diverse accessions indicated limited genetic diversity in Rph3 in domesticated germplasm, and higher diversity in wild barley from the Eastern Mediterranean region. The Rph3 gene was expressed only in interactions with Rph3-avirulent P. hordei isolates, a phenomenon also observed for transcription activator-like effector-dependent genes known as executors conferring resistance to Xanthomonas spp. Like known transmembrane executors such as Bs3 and Xa7, heterologous expression of Rph3 in N. benthamiana induced a cell death response. The isolation of Rph3 highlights convergent evolutionary processes in diverse plant-pathogen interaction systems, where similar defence mechanisms evolved independently in monocots and dicots.