80
1. Introduction
Composting is defined as a biochemical
process managed under principally
thermophilic and aerobic conditions by active
microorganisms to produce a renewable
organic resource (Bohacz, 2018). This process
is a sustainable option for recycling various
agro-industrial wastes, on small or large scale,
to obtain a mature and stable organic matter
(Scotti et al., 2016). The final product, i.e.,
compost, can be used to improve soil
physicochemical and microbiological
properties and suppress various soilborne
diseases (Pane et al., 2019; Stavi et al., 2016).
These effects are partly attributed to their
associated beneficial microorganisms and
bioactive metabolites (Hadar & Papadopoulou,
2012). Thus, composts are becoming an
alternative tool for the extensive use of
synthetic inputs in cropping systems and are
deemed safer for the environment and human
health (Coventry et al., 2006). In the past
decades, the added value of composts
attributed to their disease-suppressive effects
have been extensively demonstrated against
various soilborne pathogens such as
Rhizoctonia solani, Verticillium dahliae,
Fusarium spp., Sclerotinia spp., Phytophthora
spp., Pythium spp., and Thielaviopsis sp.
causing plant wilting, damping-off and
decaying in many important crops (Tubeileh &
Stephenson, 2020; Pane et al., 2013; Alfano et
al., 2011; Bonanomi et al., 2007). The compost
disease-suppressive potential is mainly related
to the biological activity of its associated
microbiota, which interacts with the soil
organic matter and the host plant by regulating
the microbial communities in the rhizosphere
(Hadar & Papadopoulou, 2012; Manici et al.,
2004), and to its capacity to improve plant
nutrition and growth (Martin, 2015). Among
the widely documented compost-associated
microbial agents, bacteria, actinomycetes, and
fungi were the focal driving forces for plant
diseases suppression (Coelho et al., 2020; Joshi
et al., 2009). These microbial agents acted
against target pathogens through antibiosis,
hyperparasitism, and competition for space
and nutrients (Larkin & Tavantzis, 2013).
Actinomycetes, gram-positive bacteria, and
members of the Actinobacteria group are well
known as secondary metabolites producers and
are widely explored for various agricultural
features (Qin et al., 2011). Actinomycetes have
been recovered from diverse natural
environments such as rhizospheric soil,
composts, and healthy plant tissues.
Commercial bio-molecules are mostly
produced by Streptomyces, Saccharo-
polyspora, Micromonospora, Amycolatopsis,
and Actinoplanes (Palla et al., 2018). These
microbial agents can improve plant growth and
support its establishment even under stress
conditions (Srivastava et al., 2015; Hamdali et
al., 2008). Moreover, their antagonistic
potential against phyto-pathogenic organisms
was demonstrated (Nurkanto & Julistiono,
2014; Anouar et al., 2012). They can protect
roots by inhibiting the fungal pathogen
development mostly through the production of
antifungal compounds or cell wall degrading
enzymes (Bhatti et al., 2017). Sclerotium
rolfsii Sacc. is a soilborne pathogen that affects
a wide host range of over 500 dicotyledonous
and monocotyledonous plant species (Sun et
al., 2020; Punja, 1985; Aycock, 1966).
Infection by this pathogen may occur at all
growing stages and lower stems at or near the
soil surface by forming water-soaked lesions.
These lesions spread quickly to girdle stems
where white mycelial mats may be observed on
the infected plant tissues. Severely infected
plants may wilt thus leading to partial or total
yield loss (Sun et al., 2020; Kator et al., 2015;
Fery & Dukes, 2002). Stem rot diseases are
usually managed using chemical fungicides
such as carboxin, carbendazim, benomyl,
propiconazole, methyl thiophanate, and
oxycarboxin (Sridharan et al., 2020).
Nevertheless, the hazardous use of these
chemicals represents a severe threat to the
environment, food safety, and human health
(Sridharan et al., 2020). Biological control of
soilborne phytopathogens is of increased
interest where various microorganisms