Oats are a cereal grain of the family (Poaceae) with unknown origin, but most likely lies in the western part of the Mediterranean region. The origin of the cultivated oats (A. sativa) is within the Asia Minor of the crop (Murphy and Hoffman, 1992 and descended from wild oats (A. sterilis L). A. sativa was spread as a weed of wheat and barley from the Fertile Crescent (a region spreading from Israel to western Iran) to Europe (Ladizinsky, 2012b; Leggett and Thomas, 1995). A sativa L was domesticated about 3,000 years ago.
A. abyssinica and A. vaviloviana are endemic to the Eastern Africa region, namely Ethiopia (Ladizinsky, 1975). Once present in man’s ?eld they were subjected to the sowing-harvest cycles of the cereal crops. They were, in?ltrated, eventually giving rise to establishment of the domesticated oats. In several publications for example the global strategy for the ex-situ conservation of oats (Avena spp.) (Millet and Relatives, 2012), the Ethiopian oat (A. abyssinica Hochst) is also referred to as a domesticated form. Ladizinsky (1975), elucidated A. abyssinica is very wide spread as a weed in Ethiopia. Although it contains the domesticated condition it is never grown purposely as a crop plant (Millet and Relatives, 2012). A. abyssinica occurs only as a tolerated weed in Ethiopia. In rainy years the farmers weed it out but in dry years it is harvested, threshed, consumed together with barley (Ladizinsky, 1975). As A. abyssinica originated from A. barbata by adaptation to the practice of barley growing by the Ethiopian farmers. Similarly, A. sativa in Europe originated from the weedy forms of A. sterilis. It is a wild hexaploid oat species which is native in the Mediterranean regions (Harlan, 1977).
The domestication of oats occurred much later than wheat and barley and likely outside its area of diversity (Murphy and Hoffman 1992). In northern Europe none shattering grain was probably selected from the weedy oats present as a contaminant in wheat and barley; as these species were introduced and grown as cereal crops. Some of the earliest records of cereal grown as a grain crop date to the period of the Roman occupation of Europe. The primary spring-habit A. sativa was brought to the United States and southern Canada; as an important grain crop by northern European colonists and immigrants, and also to Australia and New Zealand, where they became substantial winter season crop.
A. sativa is considered as a crop with comparatively short cultivation history. Its cultivation began several 1,000 years later than wheat or barley. A. sativa is considered as a secondary crop because for many centuries it was mostly present as a weed in the field together emmer wheat (Vavilov 1992). In contrast to wheat and barley, archaeological research did not show that oats were known in ancient Egypt, Greece or Rome. The beginning of oats cultivation dates back to the start of Christianity (Warburton 1910). Along with wheat and barley, oats migrated from Asia Minor to the North (Loskutov 2008). Because of more enormous cold resistance and adaptation to barren soil, it gradually transformed into a separate crop. In Europe hexaploid oats were domesticated at the turn of the Bronze and Iron Age (Ladizinski 1988; Leggett and Thomas 1995). However, for an extensive time it was grown as livestock feed and was used as food only in times of famine. Oats entered the human diet along with the development of milling machines (Boczkowska et al., 2014b).
2.2 Taxonomy, Ecology and Biology of Oats
The genus Avena belongs to the family Poaceae (Gramineae) that composed of approximately 30 species (Baum, 1977; Ladizinsky, 1998). The genus are foremost in importance in the order Poales (Bremer, 2002). It consisted of three ploidy levels: diploid, tetraploid and hexaploid species, with a basic chromosome number of seven. This study comprises the two ploidy levels, these are; the tetraploid (A. abyssinica, and A. vaviloviana) and hexaploid (A. sativa, A. sterilis, and A. fatua). From hexaploid, A. sativa is cultivated oats the remaining are wild oats.

Ladizinsky and Zohary (1971) and Baum (1977) suggested that all hexaploid oats considered as one biological species because they share the same genome, and they are inter-fertile. But now they have been allocated to a number of taxonomic species.

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1) A. sativa L.
It has 2–3 ?orets per spikelets, none disarticulates at maturity. In addition, usually has a yellow lemma and awns may be present but reduced in size or absent. A. sativa is inter-fertile with other hexaploid oats and share dentate lemma tips. It is a domesticated form, extremely variable as result of human selection and breeding. This gives a chance for high distribution as compared to other oat species.
2) A. sterilis L.
It is annual. It has to erect to prostrate growth habit at Juvenile; erect flowering stems; plant height of 30–145 cm; equilateral panicle; large, sized V shaped spikelets containing 3-5 ?orets, and bidentate lemma tips (Loskutov and Rines, 2011). In addition, this species has only the lowest disarticulates florets at maturity; awn inserted at lower 1/2 of the slightly moderate pubescent lemma (Loskutov and Rines, 2011). This subspecies has been divided into a number of species by various taxonomists despite being inter-fertile.

It is extensively spread in most area of Eurasia and all countries of northern Africa. A. sterilis, is rare in Ethiopia. Small dislocation populations of A. sterilis are found along road sides and edges of cultivations in the provinces Shewa, Tigray and Eritrea. The most astonishing degree of genetic polymorphism observed in the areas of wide range of rainfall, at altitudes above 600m on almost all types lands that have different edaphic conditions apparently failed to adapt to the conditions prevailing in the Ethiopian plateau (Ladizinsky, 1975). It is also not unlikely that the present A. sterilis populations were introduced into Ethiopia not very many years ago. Several forms of A. sterilis can be found at present in Japan and South Korea (Ladizinsky, 1975; Loskutov, 2007).

3) A. fatua L.
It is annual. It has erect to prostrate growth habit at Juvenile stage ; erect flowering stems; plant height 40–150 cm long; equilateral panicle; 20-25mm equal glume sized; hairy or glabrous lemma and bidentate lemma tips (Loskutov and Rines, 2011). It differs from ssp. sterilis mainly by the mode of spikelet disarticulation, which occurs at each ?oret. It also differs by its geographic distribution which is mainly Europe and North America. This subspecies has also been divided into a number of species by various taxonomists but these are all inter-fertile.

This is mainly a weed form in cultivation and other man-made habitats. Occurs only rarely in primary habitats and usually for a short period. It is the most widely distributed oat species that occurs everywhere in mainly Europe, Asia, North America, and on other continents. A. fatua grows on different soils under different climatic conditions ranging from the Tropics right up to the Polar Circle; it climbs great into the mountains up to the upper limit of crop cultivation (till 3,000 m) and indicates the highest degree of genetic polymorphism. Wild oats have penetrated almost all agricultural areas around the globe from the Atlantic Ocean across Eurasian into Mongolia, Japan and South Korea; spread throughout southern and northern Africa and got into North and South Americas, Australia and New Zealand (Malzev 1930; Vavilov and Bukinich 1959; Baum et al. 1972).

4) A. vaviloviana (Malz.) Mordv
It is an annual. Has the following features, these are: prostrate to erect growth habit at juvenile stage: erect flowering stems; plant height of 80–110 cm; unilateral panicle; medium sized awned spikelet and containing 2–3 A. In addition, A. vaviloviana has equal glume longer than florets; 20–25 mm long with 8 veins: Lemma tips biaristulate 1 mm long with 2 denticula. All florets disarticulate at maturity. Awn inserted at 1/2 of the lemma. Callus short, oval, about 3–5 mm long.

A. vaviloviana is an endemic species in Ethiopia, Eritrea and Yemen. In these countries, it occurs everywhere and is very common on the Ethiopian Plateau at altitudes between 2,200 and 2,800 m, mostly on cultivated fertile lands (Ladizinsky, 1975; Loskutov et al., 2017).

5) A. abyssinica H.
It is an erect, annual grass growing up to 1.5 meters tall. Glumes equal or almost equal in size, Lemma tips biaristulate, Callus blunt, glumes shorter, Lemmas glabrous, Florets 2–4 not disarticulate, and all have awned inserted at or just below the middle of the valve. Grain tightly embraced, long, hairy all over (Ladizinsky, 2012a).

It grows in Ethiopia. This species also con?ned to Ethiopia where it grows as tolerated weed in barley ?elds. It does not shatter its seeds at maturity and in that sense can be regarded a domesticated form, but it is never purposely planted. It endures because the Ethiopian farmers cannot select them out by their threshing-winnowing methods (Harlan, 1977). Therefore, this oats are planted, harvested, and consumed together with barley (Harlan, 1977) .

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