Augmented growth of Cd-stressed rice seedlings with the application of phytostimulating, root-colonizing, Cd-tolerant, leaf-endophytic fungi Colletotrichum spp. isolated from Eupatorium triplinerve

The potential of plant growth-promoting endophytic fungi (PGPEF) in mycoremediation has received notable attention in recent years. Unlike other root-colonizing microorganisms, PGPEF colonization under Cadmium (Cd) stress is a less-revealed phenomenon. Among eighteen fungal isolates from the leaves of Eupatorium triplinerve, twelve were found as the species of Colletotrichum and remaining six belong to Fusarium based on phenotypic characterization. However, only two PGPEF isolates (ALE15 and ALE18) were finally selected based on possession of ACCD activity (~0.84 and 0.47 nM/µg protein/h, respectively) and higher Cd tolerance (1000 and 750 µg/mL, respectively). Moreover, the said isolates showed IAA production (~248 and 289 µg/mL), GA production (~86 and 88 AUs), phosphate solubilization (~165 and 256 µg/mL, respectively) under Cd stress. ALE18 strain was found to produce siderophore too. Molecular identification through sequencing of ITS region of both isolates confirmed their identity as species of Colletotrichum. Furthermore, FESEM-EDAX and AAS analyses supported their Cd bioaccumulation ability in mycelial cells that directly impacted to assist rice seedlings' (IR-36 cultivar) growth under Cd stress. Successful root colonization was also observed through FESEM and fluorescence microscopic studies. Finally, the detached leaf experiment with six economically important crops assured their applicability on field-scale as non-pathogenic PGPEF candidates.