CerealsA total of 128 species under 17 genera belong to the five cultivated cereals. Wheat is having high number of species (62) followed by rice (19), barley (18), oats holding (11), Adaly (Coix) (9) and Maize (7) and two Secale species respectively (Table 2). Narrow genetic base of cultivars coupled with low utilization of genetic resources are the major factors limiting cereals production and productivity globally.
Barley is one of the oldest of cultivated cereals and is extensively used as food and cattle feed and for malting, brewing and pearling (Kling and Hayes, 2004). Eighteen Hordeum species are present in India. The isolation barriers are very strict among the species of domesticated barley (Badr et al. 2000). H. spontaneum is resistant to Helminthosporium, powdery mildew, mildew, leaf rust, cold and drought tolerance (Hawkes, 1977; Yun et al. 2005; Hodgkin and Hajjar, 2008; Nevo and Chen 2010). H. bulbosum is a perennial species considered secondary genepool and it is used for haploid barley productiona and it is resistant to leaf rust, powdery mildew and septoria (Khoury et al 2013). H. murinum subsp. gussoneaanum and subsp. leporinum is tolerance to water logging, salinity and leaf-scaald (Colmer et al. 2006; Ullrich 2011).
Manglesclorf (1974) suggested that teosinte is derived from wild maize as is cultivated Maize. Zea diploperennis, the diploid perennial form of teosinte (Iltis et al, 1979; Doebley 2004; Matsuiko 2002). Manglesdorf (1986) modified his view and hypothysized that the perennial teosinte was the more ancient wild plants and that annual teosinte may have originated through the hybridization of maize and perennial teosinte. Maize arose from its wild ancestor teosinte (Zea mays ssp. parviglumis) (Matsuoko, 2002; Dahlberg, 2004). Tripsacum a distant relative of maize helped in improve yield to popular varieties (Reeves and Bockholt, 1964).
The evolution and geographical distribution of oat species over the continents and localization of the areas of their origin and diversity was proposed by many researchers (Baum et al. 1972; 1975; Baum 1977; Coffman 1977; Loskutov 2008). Domestication of different oat species and some of their forms, as derivatives of wild species, took place simultaneously and independently in some regions (Trabut 1914). Eleven Avena species are occurring in India. Avena barbata Pott is an autotetraploid of one of the diploid species have been engendered by duplication of chromosomes in one of the diploids, because this genome consists of two identical or very similar (AA’) genomes (Ladizinsky and Johnson 1972; Fabijanski et al. 1990).
The progenitor of the diversity of hexaploid forms was A. sterilis L. originated in the Asiatic continent. This species most likely brought the cultivated species A. byzantina C. Koch into existence, followed by a harmful weedy A. fatua L. that inflicts cultivated crops (Coffman 1977; Loskutov 2008). A. fatua resistant to fungal diseases, Barly Yellow Dwarf virus (BYDV), drought tolerance (Mol 1990). A. sterilis having tallness genes, resistant to pests, crown rust, BYDV, cereal-cyst nematodes, powdery mildew, crown-rust (Roy and Choubey 2005; Holden 1976; Loskutov and Rines 2011). Frey and Brown (1971) improved yield of cultivated Oats Avena sativa by crossing with wild species A. sterilis and the yield improvement was between 4.6 – 6.7. Lawrence and Frey (1974) also reported yield improvement in the cross A. sativa x A. starilis. The transgressive segregants showed yield increase of more than 20 per cent over the recurrent parent.
Rice is the staple food of half of the world’s population. Rice domestication is thought to have begun ̴ 9000 years ago within a broad geographic range spanning eastern India, Indochina and portions of southern China (Kush, 1997). The genus Oryza consist 21 wild and two cultivated species. Roschevicz (1931) proposed a polyphyletic origin for rice, and that rice might have arisen in the region of India, China and Indo-China. He proposed that majority of sativa varieties to have arisen from f. spontanea (O. rufipogon annual) some of the seeded varieties from minuta and and some of the West African cultivated forms grouped under glaberrima arising from breviligulata. To the best of scientific knowledge, Oryza rufipogon is considered the ancestor of O. sativa and served as a rich genetic resource providing favorable alleles/genes to improve cultivated rice yield and quality (Oka, 1974, 1988; Xiao et al, 1996; Tanksley and McCouch, 1997; Kush et al. 1997).
O. rufipogon and O. nivara may represent the most recent ancestor of O. sativa (Kush et al. 1997; Yamanaka 2003). These both wild species considered as part of the same ancestral genepool and do not differentiate between these names when referring the wild rice (Londo, 2006). Through the process of domestication, cultivated rice has lost many of the traits associated with other wild grass species; in addition to a shift from perennial to annual populations, cultivated rice differs from O. rufipogon in its non-shattering seeds, lack of awns, erect habit, and high grain yield (Hoshikawa 1989). Oryza nivara, the only source of resistance to one of the strains of grassy stunt Virus (GSV1) and Oryza sativa F. spontanea only source of cytoplasmic male sterility is based on the Wild Abortive (WA) (Lu et al., 1997).