The role and impact of climate change on wheat domestication and epigenetic changes

The extinction, adjustment and/or adaptation of flora and fauna have been affected by climate changes through environmental elements alteration. The results from the previous studies showed that there was a relation between domestication of wheat, genetic variation and paleo-climatic conditions. Wheat has been adapted to colder and severe winds climatic conditions with formation of small cell and changing in size and shape of seeds together with shortening and thickening of stem approximately 12500 years ago. The studies showed that wheat crop was planted in the Fertile Crescent region for the first time and then spread out in other geographical areas. Structural and behavioral characters of wheat crop were made in different climatic periods so that it was disappeared in some geographical areas and adapted to others with the environment. As extent of plant communities were changed during different climatic periods, some crops dead and some of them were adapted to the new conditions. To understand that how much climate change have affected on domestication and evolution of wheat crop and the crop how much will be able for adaptation to future climate change, it needs to know about the domestication and evolution trend of wheat in different climatic periods. By identifying the relationship between climate and wheat morphology and genetic, It is possible to predict the future changes of the strategic plant under different scenarios of climate change. The highly adapted species can be selected on the basis of precipitation and temperature changes in the future. In addition, the suitable regions can be introduced for planting the crop.
In this study, about 80 national and international papers in the field of wheat genetic variations has been studied since its inception of Gramineae family. The effects of climate changes on different species of wheat were investigated in various periods as well. With regards to the growth and development together with the adaptation of the crop in different regions and climates in the past, the suitable climate as well as location were detected for planting in the future.
Gramineae family has been evolved during the Cretaceous period 55 million years ago. Although, phytolithes found in dinosaur fossils showed that the plants have existed 66 million years ago (Payprnv, 2005). Cretaceous is the third period of the Mesozoic era after Triassic and Jurassic in which occurred 145 to 65 million years ago and lasted seventy million years of the Cenozoic is the longest period. The area of broadleaf forest, grasses species and Gramineae family increased in North Africa and the Fertile Crescent in 110000 to 116000 years ago (Underhill et al., 2001). Wild Einkorn grains found in the Fertile Crescent has the precedence more than 12,500 years (Ren plentiful, 1979), but the grains of the domesticated type discovered in archaeological sites in Greece, Cyprus and Balkans of has the precedence of 9500 years old. Einkorn wheat was very important for early farmers in Central Europe (7000 years ago). The genetic studies on Einkorn wheat showed that it was grown in the basaltic foothills of the mountains of Karajadagh in southeastern Turkey as a volunteer plants, and settlements used the grains and later to cultivate it (WAN-friendly, 1981). Emmer wheat domestication was one of the most important stages of its domestication. Emmer wheat of Tetraploid and is the ancestor of T. dicoccoides. Wild emmer wheat is AABB with T.uratu gene Which causes relent and fragility of grains and the ear (Worrack and others, 1993). An accurate studies were not done about the domestication of wheat together with at what time epigenetic changes occurred in Einkorn and Emmer wild type in Iran. Research Results showed that the dominant food of Zagros residents was cereals (especially wheat) at 9000 years ago (Brvshky et al., 2016).
Man collected wild grains at least 20,000 years ago and knew that plants are grown better in a certain conditions. They were produced less yield or dead due to pests and disease at some years time. Recent finding related to results of survey of wild genes of agricultural products revealed that domestication of plant have been often took place in Asia more than 12,500 years ago (Salamís and others, 2002). Einkorn and emmer wheat, barley, peas, lentils, buffalo pea and flax were domesticated at the first time in the Fertile Crescent (Hillman, 1966). Einkorn wheat Was the first variety which successfully cultivated. It was a diploid species that was domesticated in the Fertile Crescent more than 12,500 years ago. Although, the cultivation the wheat was stopped in 5500 years ago. As polyploidy species had more adaptation with warm climate conditions, People began to cultivate it. In addition, it was harvested easier than einkorn type and had softer Glume as compared to einkorn one. Current wheat, hexaploid bread wheat (Triticum aestivum ssp. aestivum) are a conjunction between the emmer wheat tetraploid (emmer Triticum turgidum)and diploid species. It could be said that bread wheat in the nature does not wild ancestor of hexaploid and it is considered as a hybrid or transplant plant.
The Climatic conditions in the Younger Dryas period caused the most metagenesis changes in wheat that cultivated by inhabitants of the Fertile Crescent. This period was a period of cold climate in Europe whose an ice age happened and agricultural practices was only in the lower latitudes such as areas located in southwest Asia, southern parts of the Mediterranean and southern parts of India and China. Wheat crop can reduce the transpiration surface area by forming small cells against dry conditions. From the middle East, wheat migrated China throughout the Silk Road and other transportation routes, southern parts of central China was old and drier than the Middle East. The southern China districts had a warm humid climate in 7,000 years ago, but there was a relatively cool and dry conditions 6300 years ago and the size of grains of wheat and rice were smaller and similar to its current state at the same time. The size of wheat seed was reduced in the 2000-5000 years ago; It could be said that climate change during the Yangrdryas period has been effective on domestication and increasing the power adaptation of wheat in different geographical areas. However before that, wheat was cultivated for a long time but, it did not have the properties of domesticated wheat. Cold and dry climatic conditions in Yangrdryas (12,500 years ago) and dry climate in 5000-6000 years ago causes increasing the resistance of wheat and, created more morphological and metagenesis changes. According to the report (IPCC, 2007) warming of the Earth by 0.13 degrees Celsius per decade in the last 50 years is almost two times of the rate of recent past 100 years. Temperature increase has been estimated 0.74 degrees Celsius in the last century. Wheat is sensitive to high temperature, but the sensitivity depends on several factors such as variety, ambient temperature in which corn growth and its growth stages. The experiments showed that temperature increase affected wheat growth, and this reduces the crop growth period and the crop yield and quality will be decreased, consequently. Warmer climatic conditions is effective in reduction of fertility, changes in size, crop seed shape and quality, and achievement of consistency with current climatic conditions for cereals in low and middle latitudes. With the transferring of agricultural belts to high latitudes, although, there will be a desirable temperature conditions to grow wheat, factors including high humidity, poor soil organic matter, and low thickness of the soil are the most important issues that restrict the wheat cultivation. Moreover, the probability of the pests and fungus outbreak will be increased for cereals.