79

Role of Endophytes, Plant Growth Promoting Rhizobacteria

plant (Diagne et al., 2020). AMF fungi is an important constituent of the soil

contributing 5–36% total biomass of the soil and 9–55% total microorgan­

isms that are living in the soil (Olson et al., 1999). In plant, there are mainly

two types of mycorrhizal association are found namely Arbuscular mycor­

rhizae (AM) and ectomycorrhizae, among which AM is the most abundant

fungi found in the soil biomass. AM fungi belong to the subkingdom

Mucoromyceta and phylum Glomeromycota which contains 11 families, 25

genera and about 250 species (Spatafora et al., 2016). AMF forms a hyphal

network in the root cells of the plant known as arbuscle which helps them

to draw foods from the host. These hyphal structures also penetrate the

soil and enables plant to uptake minerals and nutrients providing growth

(Nadeem et al., 2013). Aggregation of the mycelial structure increases both

the root surface and root length that helps plant to reach more nutrients pools

which are unavailable for the uncolonized root system. Moreover, some­

times AMF mycelia are function as nutrients absorbing organs in addition

to root. Extension of the hyphal network also facilitates soil aggregation

thus improves the physical properties of the soil. AMF also contribute to

the soil fertility by increasing the availability of different macro and micro-

nutrients like nitrogen, phosphorus, copper, and magnesium. It has been

reported that almost 80% phosphorus uptake is facilitated by the AM fungi

in plants (Allen, 2011). It was found that in legumes plant AM fungi in addi­

tion with Rhizobium sp. helped in better nutrients uptake and also increased

the efficacy of Rhizobium sp. to support plant under stress condition. The

fungal symbionts also positively regulate nodule formation in legumes (Guo

& Haung, 2010). Furthermore, these AM fungi can store several nutrients,

thereby giving protection to plants under nutrient deficit condition. AMF

fungi could promote nutrient cycling and increases nutrients in the soil by

creating soil environment favorable for other beneficial microorganisms

or by synergizing with other rhizobacteria and endophytes (Nadeem et al.,

2013). AM fungi produce a glycoprotein glomalin which is secreted from the

hyphae. Glomalin binds nitrogen and carbon with the soil particles, thereby

increasing soil carbon content and nutrients availability. Plant water relation

is directly associated with glomalin content present in soil, contributing to

approximately 20% total water uptake by plants (Gadkar & Rilling, 2006).

AMF is also used as broad spectrum biofertilizer in different agricultural

land providing high yields, better nutrients uptake, improved water status

and enhanced soil quality (Diagne et al., 2020).

In Cucurbita maxima inoculation with AM fungi significantly improved

metabolism including carbohydrate, crude protein and fiber content in the root