11.1 Introduction
The term endophyte wasfirst coined by De Bary in 1884 for microorganisms
including bacterial, yeast, archaeal, fungal, and protistic taxa colonizing internal
plant tissues (De Bary 1884 ). Hallmann et al. ( 1997 )defined endophytes as, con-
sidering any microorganism as an endophyte if it can be isolated or extracted from
inside surface disinfected plant tissue and it does not seemingly harm the plant. This
definition has been widely accepted for cultivable species in most laboratories in the
world over the last 20 years. However, due to the suspected lack of adequate
elimination of nucleic acids after sterilization of plant surfaces, this definition
seemed to be less suited for non-cultured species upon the interpolation of
molecular detection techniques in endophyte research. Coombs and Franco ( 2003 )
defined microbial endophytes as ubiquitous colonizers of the interior tissues of host
plants and can constitute a range of different relationships such as symbiotic,
mutualistic, and commensalistic where they do not usually have any substantial
morphological changes and disease symptoms.
11.2 Microbial Volatile Organic Compound (MVOC)
Several prokaryotic and eukaryotic microorganisms generate a plethora of complex
and dynamic array of gaseous secondary metabolites, usually known as volatile
organic compound (VOCs) of low molecular weight lipophilic (<300 Da) com-
pounds, high vapor pressure (0.01 kPa or higher at 20 °C), low boiling point,
belonging to different chemical classes that vaporize and diffuse easily through air
and water-filled pores and thus play essential biological/ecological roles in
aboveground as well as belowground habitats (Penuelas et al. 2014 ; Tyc et al. 2014 ;
Wenke and Piechulla 2013 ). Recent studies showed that soil microbiotas can use
these volatile compounds as ideal info-chemical as growth stimulants, growth
inhibitors, and inhibitors of quorum-sensing, i.e., quorum quenching (Effmert et al.
2012 ; Kim et al. 2013 ). In living organism, these compound are formed as part of
normal metabolism and derived from different biosynthetic pathways and act as
signal molecules for inter- and intra-organismic communication between plants,
antagonists, and mutualistic symbionts both below (soil) and above ground (at-
mosphere) (Kanchiswamy et al. 2015 ). At the plant–microbe community level,
substantial progress has been made in studying the multifaceted role of MVOCs
produced by bacteria, fungi, and phytopathogens in agroecosystems. Researcher
considers MVOCs as potential semiochemicals that function as attractants and
repellents to insects and other invertebrates, as biocontrol agents to control various
phytopathogens, as biofertilizers for plant growth promotion, as a potential source
of biofuel, and are also used to prevent postharvest plant diseases.
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