193infection and invasion (Ravishankar et al. 2001 ; MacDonald et al. 2002 ), most of
these processes are facilitated by lytic enzyme secretions that help to disintegrate
the structural integrity of host cells and tissues (Campion et al. 1997 ) resulting in
tissue maceration and symptom induction. Colletotrichum develops a series of
infection structures that facilitate colonization of the host tissues. It attacks living
plant cells, and then switches to necrotrophic phase resulting in cell death (Kubo
et al. 2016 ).
Plants respond to fungal infection using a hypersensitive response, systemic
acquired resistance and other mechanisms. The hypersensitive response is one of
the most important plant defense mechanisms against fungi. It can prevent the
spread of fungal infection to healthy cells due to the activity of some chemicals such
as phenols, sterols and phytoalexins, and the oxidation of other chemicals in the
infected cells (Agrios 2005 ).
Systemic acquired resistance (SAR) is an example of induced resistance. It is
used to induce resistance on rust-infected plants using chemicals such as BTH (1, 2,
3-benzothiazole-7-thiocarboxylic acid-S-methyl-ester). This mechanism can also
be achieved by inoculating plants with weak strains. Other ways for defense
responses include lignification, production of callose papillae, cork layers and phe-
nolic compounds, and detoxification of pathogen toxins.
4 Case Studies of Plant Disease Epidemics in Dry
Environments
4.1 Black Point of Wheat
Wheat is subject to various biological stresses, including pathogen stresses (Table
1 ). The number of wheat diseases exceeds 200. Some of the major pathogens attack-
ing wheat are Bipolaris sorokiniana, Fusarium graminearum, Fusarium avena-
ceum, Alternaria alternata, Puccinia graminis, Ustilago tritici, Erysiphe graminis
and Rhizoctonia solani (Paulitz and Adams 2003 ; Smiley et al. 2005 ; Toklu et al.
2008 ; Vujanovic et al. 2012 ; Acharya et al. 2013 ; Zhu et al. 2015 ). The losses caused
by these pathogens and many others vary from no disease to very severe, depending
on the prevailing environmental conditions and the genetics of the host plant and the
pathogen.
B. sorokiniana is one of the most prevalent fungi in wheat and barley seeds and
is reportedly seed-borne in different temperate, tropical and arid countries (Clarke
et al. 2004 ; Toklu et al. 2008 ; Al-Sadi and Deadman 2010 ). Seed infection is favored
by warm and humid weather, and may simply discolor seeds or can cause black
point disease in barley (Hordeum vulgare L.) and wheat. Black point disease affects
the kernels of cereals, and exhibits a brown to black tip on the germ end; it can be
caused by different fungi, such as B. sorokiniana, Fusarium graminearum,
Alternaria alternata and Penicillium spp. (Toklu et al. 2008 ; Al-Sadi and Deadman
Epidemiology and Management of Fungal Diseases in Dry Environments