various cellular components including resistance mechanisms, thereby enhancing
growth attributes and reducing disease susceptibility of plants (Bari and Jones 2009;
Dohroo and Sharma 2012). This microbial activity has the potential to be used as an
eco-friendly and cost-effective alternative to chemical pesticides and fertilizers,
towards a sustainable approach for promoting plant growth, development, and
yield. This chapter is intended to describe microbe-activated resistance mechanisms
related to alleviation of biotic stresses in plants.
10.2 Impact of Biotic Stresses in Plants
The biotic stresses, primarily responsible for damages and diseases in plants, are
caused by pathogens (fungi—necrotrophs and biotrophs, bacteria, and viruses),
nematodes, and pests (insects and mites). The pathogens infect different parts of
plants to derive nutrients for their own growth and development and disturb hormonal balance, nutrient regulation, and physiology of the host plant; all such
changes once taken place in the host body are reflected through various diseases in
the form of vascular wilts, leaf spots, cankers, blight, nutritional imbalances, root rot,
scab, damping-off, blister, mildew, rust, smut, among other symptoms (Ramegowda
and Senthil-Kumar 2015).
Worldwide, pathogens are one of the foremost prolonged threats to food production and ecosystem stability as many crops are extremely prone to biotic stress in the
form of soil-borne and root diseases that cause huge losses in both quality and yield
(Sharma et al. 2004). For instance, the bacterial wilt disease of potato caused by
Ralstonia solanacearum causes a global loss of more than USD 950 million per
annum by affecting about 1.7 million hectares of crop in around 80 countries
(Champoiseau et al. 2009; Nion and Toyota 2015). Whereas, the epidemic bacterial
leaf blight disease of rice has caused severe crop losses of 50% in Asia (Ranjani et al.
2018). At least 350 different plant diseases caused by Xanthomonas spp. affect
agricultural crops (especially, rice, citrus, cassava, tomato, sugarcane, passion fruit,
and brassicas) of great importance in the world (Marin et al. 2019).
Fusarium spp. are amongst the most diverse and widely dispersed phytopathogenic fungi that cause economically important blights, rots, wilts, and cankers of
numerous field, forest, horticultural, and ornamental crops in agricultural
commodities and natural ecosystems. Amongst various species of Fusarium,
F. graminearum and F. verticillioides mainly infect cereals, and F. oxysporum
affects a wide host range of monocotyledonous and dicotyledonous plants (Sharma
et al. 2018). The fungus Hemileia vastatrix that causes a rust disease on coffee has
affected every coffee-producing region of the world (Melchor et al. 2018). Grapevine (Vitis vinifera) is a major fruit crop worldwide, which is susceptible to downy
mildew (caused by Plasmopara viticola), powdery mildew (caused by Erysiphe
necator), and gray mold (caused by Botrytis cinerea) diseases, all of which can cause
severe economic losses in both wine and table grape production (El-Sharkawy et al.
2018a).
10 Microbe-Mediated Biotic Stress Signaling and Resistance Mechanisms in Plants
299
growth attributes and reducing disease susceptibility of plants (Bari and Jones 2009;
Dohroo and Sharma 2012). This microbial activity has the potential to be used as an
eco-friendly and cost-effective alternative to chemical pesticides and fertilizers,
towards a sustainable approach for promoting plant growth, development, and
yield. This chapter is intended to describe microbe-activated resistance mechanisms
related to alleviation of biotic stresses in plants.
10.2 Impact of Biotic Stresses in Plants
The biotic stresses, primarily responsible for damages and diseases in plants, are
caused by pathogens (fungi—necrotrophs and biotrophs, bacteria, and viruses),
nematodes, and pests (insects and mites). The pathogens infect different parts of
plants to derive nutrients for their own growth and development and disturb hormonal balance, nutrient regulation, and physiology of the host plant; all such
changes once taken place in the host body are reflected through various diseases in
the form of vascular wilts, leaf spots, cankers, blight, nutritional imbalances, root rot,
scab, damping-off, blister, mildew, rust, smut, among other symptoms (Ramegowda
and Senthil-Kumar 2015).
Worldwide, pathogens are one of the foremost prolonged threats to food production and ecosystem stability as many crops are extremely prone to biotic stress in the
form of soil-borne and root diseases that cause huge losses in both quality and yield
(Sharma et al. 2004). For instance, the bacterial wilt disease of potato caused by
Ralstonia solanacearum causes a global loss of more than USD 950 million per
annum by affecting about 1.7 million hectares of crop in around 80 countries
(Champoiseau et al. 2009; Nion and Toyota 2015). Whereas, the epidemic bacterial
leaf blight disease of rice has caused severe crop losses of 50% in Asia (Ranjani et al.
2018). At least 350 different plant diseases caused by Xanthomonas spp. affect
agricultural crops (especially, rice, citrus, cassava, tomato, sugarcane, passion fruit,
and brassicas) of great importance in the world (Marin et al. 2019).
Fusarium spp. are amongst the most diverse and widely dispersed phytopathogenic fungi that cause economically important blights, rots, wilts, and cankers of
numerous field, forest, horticultural, and ornamental crops in agricultural
commodities and natural ecosystems. Amongst various species of Fusarium,
F. graminearum and F. verticillioides mainly infect cereals, and F. oxysporum
affects a wide host range of monocotyledonous and dicotyledonous plants (Sharma
et al. 2018). The fungus Hemileia vastatrix that causes a rust disease on coffee has
affected every coffee-producing region of the world (Melchor et al. 2018). Grapevine (Vitis vinifera) is a major fruit crop worldwide, which is susceptible to downy
mildew (caused by Plasmopara viticola), powdery mildew (caused by Erysiphe
necator), and gray mold (caused by Botrytis cinerea) diseases, all of which can cause
severe economic losses in both wine and table grape production (El-Sharkawy et al.
2018a).
10 Microbe-Mediated Biotic Stress Signaling and Resistance Mechanisms in Plants
299