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in advance of the growing hyphae, and by facilitating nutrient uptake and further
growth of the fungus in plant tissue. The BZR-toxin produced by B. zeicola is
needed for the initial colonization of B. zeicola race 3 in both rice and maize tissues
(Xiao et al. 1992 ). Disease symptoms in wheat and barley which are affected by the
spot blotch disease are in the form of necrosis and chlorosis. Helminthosporal and
prehelminthosporol are suggested substances responsible for the disease symptoms
(Bach and Kimati 1999 ).
4.4 Wheat Stem Rust
Rust is a serious and widespread disease in wheat (Fetch et al. 2015 ). Rusts can also
attack other crops such as barley and oats (Avena sativa L.) (Hernandez et al. 2005 ;
Deadman et al. 2011 ). Fungi-causing rusts usually attack leaves and stems and pro-
duce rusty yellow–orange spots (Chen et al. 2009 ; Wanyera et al. 2009 ; Deadman
et al. 2011 ).
Puccinia spp. cause various rust diseases in wheat. They are biotrophic and can
complete their life cycle in one, two or more hosts. They are usually dispersed by
the wind, insects and rain splashing (Agrios 2005 ). Germination is stimulated by
exudates released from the plant surface and depends on several factors, including
water and temperature. Some species grow in different directions on the surface of
plants to increase the chance of finding stomata. Penetration into host tissues is usu-
ally attained through stomata. Hyphae move between plant cells and produce sev-
eral haustorium mother cells which produce a penetration peg and a haustorium
inside plant cells to absorb nutrients.
Stem rust affects growth, yield and the food value of wheat. Symptoms develop
on the stems, leaves, leaf sheath, and neck and glumes of the wheat spike (Szabo
et al. 2014 ). When infections are heavy, especially on stems, the plants may lodge.
Although some infections are mild, several studies have reported heavy losses due
to stem rust in different parts of the world. Stem rust is favored by hot days and wet
leaves. The optimum temperature for stem rust development is around 26 °C (Wiese
1987 ). There is also evidence for increased aggressiveness of some other rust spe-
cies at higher temperatures (Gautam et al. 2013 ).
The disease is caused by various races of the Puccinia graminis f.sp. tritici
(Szabo et al. 2014 ). The fungus overwinters as thick-walled teliospores that are
produced on wheat or other grass hosts. The rust fungi are separated into races by
their avirulence or virulence on the different host cultivars (Fetch et al. 2015 ).
5 Management of Fungal Diseases
The increase in disease incidence in dry environments and other parts of the world
has led to the adoption of management strategies including chemical, cultural and
biological methods. Many growers focus on applying chemical methods such as
A.M. Al-Sadi