1.1.History and Distribution of barley
Barley (Hordeum vulgare L.) has been cultivated mainly for food, since ancient times. It was domesticated from wild species Hordeum spontaneum about 10000 years ago(Badr et al., 2000;Kilian et al., 2009). It has been used both in ancient Hindus and Greeks as religious ritual and this provide great argument to the great antiquity of its cultivation 9. The first barley grains found at archeological sites in the Fertile Crescent of the Middle East indicated that the crop was domesticated from wild species Hordeum spontaneum about 10000 years ago (Badr et al., 2000;Kilian et al., 2009).The Fertile Crescent is considered the place of cultivated barley origin 9. However, there is strong evidence about the origin of barley, initiation from Iberian peninsula and extend to southwestern, eastern, southern Asia and North Africa 10.
In the last time, the Barley was used as a food source in several parts of the world including the Middle East, North Africa, and Europe in both eastern and northern and also in Asia like India and Tibet 14. Currently, it is cultivated globally in all tropical and non-tropical countries 13. Cultivated barley identified as Hordeum vulgare L. and belong to the order Poales, family Poaceae (Gramineae )-Grass family and genus Hordeum.
1.2.Description and Classification
Barley (Hordeum vulgare L.) is a self-pollinating diploid with 2n = 2x = 14 chromosomes, annual, short season crop, that stands 60-120 cm tall. It has two types of root systems, seminal and adventitious (Briggs, 1978; Reid, 1985). After seed germination, the seminal roots are develop and growing downward and outward, then forming fibrous, branched root system. leaves of barley are linear and each stem has leaves ranging from 5 to 10 that are 5-15 mm wide and leaf structure consist of glabrous ligule and auricles that envelop the stem (Gomez-Macpherson,2000). Mature barley comprises of central stem and in addition to 2-5 branch stems called tillers and each tiller has 5 to 7 internodes(Reid, 1985). Spikelets of barley are enclosed directly to rachis of the spike (Australian Government, 2008) . Because the rachis not terminate in spikelet, the inflorescence of barley is considered indeterminate (Reid, 1985). The barley seed is a dry indehiscent fruit that termed a caryopsis. The caryopsis has characteristic as oval, ridged and it is surrounded by the lemma and palea (Reid, 1985).
Barley is classified according to their growth habit as winter or spring cultivar. Most spring and winter cultivars require four to five days and temperature between 12 and 24?C to growth and development. Winter cultivars are planted in the fall season and mature in early summer and requires before flowering and complete their life cycle in the spring season to be exposed to the cold period (vernalization) (Stark 2003b). Spring cultivars are planted in the spring season and mature in mid-summer but these cultivars do not withstand frost temperature and require excess irrigation and less productivity than winter cultivars.
Barley is classified according to the spike morphology as two-row barley (Hordeum vulgare L. distichum) and six-row barley (Hordeum vulgare L. hexastichum) (Badr et al., 2000; Kilian et al., 2006).During the process of domestication, six –rowed barley was appeared from the two rowed wild barley as a result of mutation that cause differences in spikelets morphology (Komatsuda et al., 2007). The fertility of spikelets plays important role in determine row number of barley spike. Two-rowed genotype produces less grain(25-30) per spike than six-rowed genotype (25-60). Majority of the cultivated barley is six-rowed type whereas the wild barley is two-rowed type 3.Two-rowed barley have only the central spikelets are fertile but the lateral are sterile whereas six-rowed barley have all three spikelets (six spikelet in both sides) are fertile (Bonnett, 1966).
Barley also classified according to their hull adherence as hulless or naked (lemma and palea are separated or not attached to caryopsis ( and hulled or husked barley )at maturity, palea and lemma stay attached to caryopsis). Hulled barley has the hull that protects embryo during and after harvesting from destruction and has the characteristic of higher yielding and it is used to feed the animal. But, hulless (naked) barley used directly as a food for human. The great majority of the cultivated barley called hulled caryopses whereas the remaining genotypes called naked or hulless caryopses 34.
Barley is the fourth economically most important worldwide crops in crop production after wheat, maize, and rice and the average per year over 134 million tons(FAO 2014). It is produced for many uses, utilized almost 60-70% of the production is used for animal feed, around 30-40%
of the production is used in malting to make alcoholic beverage like whiskey and beer, and only 2-4% for human food (Newman and Newman 2008).
1.4.Uses and Chemical composition
The barley production is used for many purposes. The barley production is used primarily for feeding of animals, mainly pigs and cattle because the barley grains has higher content of crude protein and fiber in comparison with other cereals and are considered appropriate source of starch (Verstegen et al.,2014). Both barley grain and straw can be used for feeding in different forms of forages like silage (Heuzé, 2013).Because the barley silage has high nutrition value and digestibility so it is used as fed to beef cattle and dairy cows for the production of milk and meat (Walsh et al., 2008;Wallsten and Martinsson, 2009).Barley grains are most commonly used in feeding of poultry in majority of the European countries (Inborr et al., 1993).
Barley grains also used in a significant percentage for malting, a process that dries germinated cereal grains and which coming back in the Egypt and Middle East to at least 8000 years ago (Ullrich, 2011).For malt production, the grain features are important like hulled barley grains are favorites for malting and brewing because the effect on beer flavor (Baik and Ullrich, 2008). Hulled barley production has considered the most economical beneficial from the grains of barley. Malt is used to make alcoholic beverage like whiskey and beer through brewing and distilling. Malting barley compared with feed barley, it contains less amounts of protein (Verstegen et al., 2014).
A small proportion of the barley production is used for food consumption. The barley grains can be cooked for bread making and this use has been important in ancient times and has continued as a major source of food for some culture, mainly in North Africa and Asia (Newman and Newman, 2008). Barley grains are beneficial for human health because it is a good source of ?-glucans and high fiber content (Baik and Ullrich, 2008). Barley is used as medicinal uses such as lowering of blood sugar and pressure, lowering cholesterol, treating boils of skin and promoting weight loss 26.
There are several factors that affect on chemical constituents, bioavailable energy content and nutritive value, these include environmental factors, genetic factors, and interaction between two factors(Zhan et al., 1994; Valaja et al., 1997; Andersson et al., 1999).
The barley grain comprises of starch about 65-68% that forms the main components, and also protein 10-17%, ?-glucan 4-9%, lipids 2-3% and minerals 1.5-2.5% (Quinde et al., 2004). ?-glucan has the importance of maintaining human health through lowering the levels of blood cholesterol and glycemic index (Pins and Kaur, 2006). It also contains phenolic compounds, phytic acid, lignin that connected with good health 18, 19. Also, it rich in vitamin B-complex, vitamin E and a good source of trace elements like selenium, iron, magnesium, zinc, copper12.
Barley has a wide range of adaptation. In comparison with wheat, barley has commercial value that far less than that of wheat and it is highly tolerate to salt than wheat and has the ability to thrive in too cold conditions 9. Barley is sensitive to acidic soils but highly tolerant to alkaline soils compared with other cereals and soil PH ranging from 6.0 to 8.5 is agreeable for plant growth. If the calcium in the soil environment is active, the barley can resist the PH that ranging from 5.0 to 6.0 although barley is considered sensitive to acidic soils. In areas where salinity is a major problem, barley is considered a good rotation crop because it can resist to salinity very well and it can be planted in soils where salinity is 8-16 mili.mhos. Higher yielding of barley are obtained under coarse-textured with low nitrogen, well drained, and non-acidic soils (Young 1998).
At barley different stages from seed germination to maturity, drought (water deficit) has a negative effect on the final yield and these effect depends on the duration and severity of the stress 9.At the reproductive stag and under high temperature conditions, drought cause decreasing in the yield by decreasing in the number and size of the grain. At the flowering stage, water deficit cause significantly decrease in grain weight but at tillering stage it has no significant effect on the grain number per spike 9. At early growth stage, drought reduce the percentage of seed germination and it affect negatively on establishment of seedling 7. Drought condition at post-anthesis stage reduce the rate of grain filling and duration and this causes shriveled grains 9. At the pre-anthesis stage, drought causes greater yield reduction compared with post-anthesis stage of growth because it affect yield potential at the level of sink
through reducing the number of fertile spike per unit area at the phases of crop establishment and tillering, in addition to the grain number per spike 13.
Temperature is considered to be one of the most important factors that determine yield as it controls development. For barley growth, optimum temperature varies according the stage. For instance, at 22°C the rate of leaf emergence reach optimum while at 20°C the rate of leaf growth reach optimum Tamaki et al. (2002). During post-anthesis stage, high temperatures (>35°C) reduce the weight of grain significantly and causes changes in malting performance (Savin et al. 1996, Wallwork et al. 1998, Passarella et al. 2002). In comparison with drought, the reduction in grain weight was greater under the heat stress and this means, the short season varieties of barley under warmer areas have better yield Savin and Nicholas (1999).
Losses can occur at each stage of cereals grain storage, handling, and processing. These losses can be up to 100% in certain cases and considered highly variable and may be either qualitative or quantitative. The evaluation of quantitative losses is much easier than qualitative losses. Examples of qualitative losses, including contamination caused by mycotoxins development and mould, germination loss, insect infection, nutritional deterioration, physical emergence. Some of this qualitative losses are more difficult to visually detection(Navarro, 1997).
There are two important stages of losses in cereals like barley, rice, wheat and maize that can occur and these include pre-harvest and post-harvest losses. The pre-harvest losses may result from diseases, Insect pests, and weeds and are estimated at about 35% of total production of cereal crop(Schildbach, 1989).
Improper storage conditions like unbalanced temperature, O2 /CO2 ratio or levels, and humidity and improper operation during harvest and/or after harvest that allows insect pests, rodents, and microorganisms to be an infection of stored grains lead to post-harvest losses. In developing countries, FAO’s has estimated post-harvest losses of 10-15% during the 1980s (Navarro, 1997).