Barley, Hordeum vulgares sp. vulgare, is cultivated worldwide in both high- and low-input agricultural systems, serving as a vital source of animal feed, human food, and drinks (Newton et al., 2011). Although high-income countries like France, Russia, and Germany are the largest producers, low- and middle-income economies such as Ethiopia, India, Iran, Iraq, Morocco, Syria, and Turkey are also significant producers (FAOSTAT, 2014). However, despite its considerable value on the global market, yields in several areas, especially Europe, have remained stagnant in recent decades (Fig. 1). These stagnant yields may be attributed to "inherent" limitations of the crop, coupled with increased emphasis on wheat breeding, resulting in a considerable gap between barley and wheat yields. Furthermore, Southern European wheat and barley yields have remained stable due to the effects of climate change (Brisson et al., 2010). This is concerning as several forecasts suggest that these problems will only escalate over time.

Human activity has contributed to climate change, which poses a significant threat to food security, according to the IPCC (2013). These hazards include variations in water supply, salinity, and temperature, as well as changes in disease and insect prevalence (Perez-Lopez et al., 2009; Hogy et al., 2013; Yau & Ryan, 2013). These hazards demand alternative international trade patterns, new economic growth models, and focused agriculture investments (Nelson et al., 2010). Therefore, it is crucial to understand how to integrate research and development agendas, as several results are possible in this regard (Olesen et al., 2011). Barley's broad climatic range, numerous end uses, and diverse consumers make it an exemplary model for studying and adapting to climate change (Newton et al., 2011). One potential solution is to cultivate spring-adapted barley varieties instead of autumn-adapted ones (known as "winter" types) to decrease climate-related stress factors. In addition, new tolerance or resistance characteristics may be essential to adapt to previously unseen abiotic and biotic stressors. Given the interrelations between climate change and other global challenges such as soil fertility reduction and expanding human populations (Rockstrom et al., 2009), tackling these problems simultaneously is imperative.

Barley production and genetic resource prediction through environmental modeling:

Compared to most other minor grains and wheat, barley yields are relatively less weather-sensitive (Cossani et al., 2011; Newton et al., 2011). Yield figures from FAOSTAT (2014) indicate that barley and wheat have similar degrees of responsiveness, implying that barley grain production may not be overestimated (Fig. 1). The yield gap between wheat and barley has increased to 10% since 2000, according to FAOSTAT. This gap widens to 34%, particularly in the UK's highly productive regions. Due to the high dimensionality of climate, estimating barley production precisely in the coming years is challenging. Still, several techniques have considered the effects of abiotic stressors such as temperature, water, and CO2 fertilization (although biotic stresses are not common), as demonstrated in European examples (Trnka et al., 2004; Rotter et al., 2013). Rotter et al. (2013) find that on favourable soils, CO2 fertilization and earlier planting, owing to a warmer spring, may boost barley yields in most climatic scenarios. However, in harsh climates or less-than-ideal soils, this is not the case. Given predicted uncertainties, producers are advised to cultivate different barley types.

Trnka et al. (2011) studied the effects of climate change on agriculture, covering western and central Europe. They used spring barley as the reference "crop surface" as it was grown in diverse environmental zones. By utilizing the AGRICLIM model (Trnka et al., 2010), agroclimatic indices, and daily climate data, they discovered that agroclimatic conditions deteriorated in several regions. This was caused by higher drought stress and a shorter growing season. Some European regions will be squeezed between a cold winter and a scorching summer, making climate less predictable. The authors advocate boosting resilience by increasing diversity.

The modelling of crop performance indicates that there is immense value in breeders of barley working alongside a diverse array of partners, to identify the characteristics that are essential to combat stressors induced by climate change in specific zones of production. Understanding how these traits interact, identifying important genes, and discovering additional management strategies like adjusting sowing dates or seasons must be implemented.

Examples of Genes and Traits Significant Under Climate Change

1. Impact of Abiotic Stresses and Climate Change:

Newton et al. (2011) conducted research on barley crop resilience that highlighted several genes that could respond to abiotic or biotic challenges. They identified landrace and wild barley and listed abiotic stress-related genes in Table 1. The response of plants to pressure from climate change depends on trait interactions, including the need for vernalization, photoperiod sensitivity (day-length), and flowering time.

2. Influence of Biotic Stresses and Climate Change:

Disease requires three elements: a vulnerable host, a virulent pathogen, and a favorable environment (known as the 'disease triangle,' Agrios, 2005). Climate change can alter disease distribution, incidence, or severity by impacting any of these factors. Disease resistance genes may be sensitive to temperature, as evidenced by the barley genes complex at the response to Pucciniagraminis (rpg) 4-Mediated Resistance Locus (RMRL) on chromosome 5H, which offers broad-spectrum resistance to wheat (P. graminis f. sp. tritici) and rye (P. graminis. f. secalis) stem rust pathogens (Steffenson et al., 2009). The RMRL complex is critical because it is the only source of resistance to the severe African stem rust pathotype TTKSK (isolate synonym Ug99), to which 97% of barley types are vulnerable (Steffenson et al., 2013).

Reduced rainfall could reduce the severity of leaf scald, Septoria speckled leaf blotch (produced by Septoria passerinii and Stagonospora avenae f. sp. triticaea), and bacterial leaf streak (caused by Xanthomonas translucens sensu latu). However, precipitation patterns may also affect fungal disease development since most require free moisture or high relative humidity (Steffenson, 2003). Drier conditions may increase root rot caused by Cochliobolus sativus, Fusarium culmorum, and Fusarium pseudograminearum (Paulitz & Steffensen, 2011).