Wheat total current world cultivating what production. common wheat

Wheat (Triticum spp.) originated
in the south-western part of Asia approximately 10,000 years ago (Kingfisher,
2004). In Ethiopia, durum wheat was introduced in to the northern highlands of Ethiopia around
3,000 BC and the country is second world centre of diversity (Vavilov, 1951) while the bread wheat is relatively a recent introduction by the Portuguese or Italians although the exact period is unknown
(Hailu, 1991). Based on ploidy level, wheat can be
divided into three: diploid wheat (2n=14); tetraploid wheat (2n=28) and
hexaploid wheat (2n=42) (Feldman 2001). Though there are many species are found
under genus Triticum, only common
wheat (T. aestivum, 2n=6x=42, BBAADD) and durum wheat (T. turgidum)
are contributing approximately a total current world cultivating
what production. common wheat (T. aestivum) is a result of two
polyplodizations in which the first cross is between two wild grass species, T.
Urartu (AA, 2n=2x=14) with an unknown species of which the closest
relative is Aegilops speltoides (BB, 2n=2x=14), to form wild emmer, T.
Dicoccoides (AABB, 2n=4x=28) (Daud and Gustafson, 1996) followed by
mutation of emmer wheat to form durum wheat (AABB) in 9000 years ago (Landi,
1995). The second cross is between durum wheat (AABB) with the wild grass Ae.
Tauschii (DD, 2n=2x=14) to form hexaploid wheat  known as T. aestivum (AABBDD,
2n=6x=42) (Feldman 2001).

 

1.1.1.     
Importance
of Wheat

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Wheat
is the most important staple crop that provides on average 21% of the total
caloric and 20% protein requirement of world population. It is also a leading
crop in economic value and area of production worldwide. In 2016, production of
753.2 million tons of grain makes the crop third most important cereal in the
world next to maize and rice (FAO, 2017). In the same year, the world wheat
imported to purchase worth US$36.8 billion in which 77% is imported by
developing countries (World Factbook, 2017).  
All Africa countries import wheat to
fulfill the demand, though the crop grow on around 10 million ha of land in the
region every year. The consumption in this continent, especially in regions of
Sub-Saharan Africa (SSA), is dramatically increasing during the past 20 years
as a result of growing population, changing food preferences and socioeconomic
change associated with urbanization. Currently, the import share of SSA reaches 50%
of total wheat consumption which accounts 10% of world wheat import.  From the total wheat production of this
region, Ethiopia accounts for more than 50% production, with South Africa,
Kenya, and Sudan accounting for most of the remainder (USDA, 2017). 

 

1.2.  Stem
Rust and Stripe Rust of Wheat

Puccinia
graminis, the causal agent of stem rust (black) and Puccinia striiformis?, the causal agent
of stripe (yellow)  rust disease,  are belong to kingdom Fungi, phylum
Basidiomycota, class Urediniomycetes, order Uredinales, family Pucciniaceae/ uredinaceae and the
genus Puccinia. The genus be able to
attacks around 365 species of cereals and grasses in 54 genera (Leonard and
Szabo, 2005; Groth et al., 1995). The stem rust of wheat is
characterized by production of black telia towards the end of growing season
and production of uredinia on the plant on leaf sheaths, but is also found on
stems, leaves, glumes and awns. Stripe rust of wheat is
characterized by appearance of yellow-colored stripes (urediniospores) parallel
to the venations of each leaf blade (Chen et
al., 2014). The pathogens are obligate parasites with primary hosts are wheat, triticale, barley and rye. They
dispersed from plant to plant through wind, rain splash, and by infected plant
material (Singh
et al., 2008).

 

The
diseases are the most important treats for wheat, thus for world food security.
Their importance is dramatically increased through the emergency of new
virulent strain due to mutation and selection pressure. The stem rust of wheat
is becoming highly significance since the outbreak new strain known as Ug99 in
1999. This race has continued spreading over vast areas causing to epidemic and
high yield losses in countries such as; Kenya and Ethiopia (2002), Sudan, Iran
and Yemen (2007), and in Europe (2016). In Ethiopia, a new virulent race other
than Ug99 linage known as (TKTTF) was also recorded in 2014.  In the future, new pathogenic races are
expected to be emerged due to mutations and selection pressure of virulence
races (Singh et al., 2008; Olivera et
al., 2015).   New races of stripe
rust were also emerging in different part of the world from divergent genetic
lineages. Major reported epidemics are: in East Africa (1986),  in North Africa (2000) (Ezzahiri et al., 2009), in East Africa (2010-2016)(Singh
et al., 2016), in Central Asia (2010 and 2012)
(Rahmatov et al., 2012) in Syria and Lebanon(2010) (El
Amil, 2015) in Europe(2010-2016) (Rahmatov et al., 2016). Outbreaks of the diseases in
different years were also reported in North America, Australia and North Africa
(Bahiri et al., 2009; Ali et al., 2014).

 

1.3. 
 Stem
Rust and Stripe Rust Resistant
of Wheat

To mange rust of wheat, use of resistant
variety is the most amicable solutions in respect to cost, environmental
safety, and effectiveness for the fight against the most virulent race than
using crop rotation and application of fungicides (Akello et al., 2016). To date, about 59 stem rust resistant genes and 80 stripe rust resistant genes from common wheat and it’s relatives
have been  officially recorded (Mclnlosh et
al., 2017). Thus, wheat resistance rust genes can be categorized as
race-specific resistance seedling resistance (R genes) and adult plant
resistance (APR) genes based molecular genetics and extensively used class in
breeding programs(Ellis et al.,
2014).

1.3.1.     
Race-specific
Resistance

The race specific resistances (R genes) are those genes which are
effective throughout all wheat growth stages from seedling to adult plant
stages. It is also known as major gene resistance, seedling or all-stage resistance. It is mainly qualitative in
nature and follows a simple Mendelian inheritance.

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