Title: Diversity and Plant Growth-Promoting Effects of Fungal Endophytes Isolated from Salt-Tolerant Plants
Abstract: Unique microecosystems within the internal tissues of plants support diverse, symbiotic microbial communities that greatly influence plant adaptation and evolution [1,2].These microbial associations significantly influence the ability of plants to adapt and evolve in their environment.All plants in natural ecosystems appear to develop symbiotic associations with fungi [3,4].These symbioses provide a buffer against biotic and abiotic stresses and are important for the survival of plant hosts and their fungal symbionts in highstress habitats [3,4].Both plant and fungi obtain multiple benefits from symbiotic interactions in terms of fitness.Fungal symbionts may impart beneficial (mutualism, commensalism, and parasitism), harmful (competition), or neutral (amensalism and neutralism) activities on the plant host.Concurrently, host plants can also interact beneficially (mutualism), neutrally (commensalism and neutralism), or harmfully (parasitism, competition, and amensalism) during symbiosis with the fungi [5][6][7].Microbes living within plants are referred to as 'endophytes' and are host-specific fungi or bacteria, such as Actinomycetes spp.[8,9].Endophytes constitute a major portion of the fungal symbionts associated with the roots, stems, and leaves of plants, and generally do not impart adverse effects to the host [10,11].They comprise a diverse group and represent a wide taxonomical range of fungi belonging primarily to the phylum Ascomycota [12,13].Some fungal endophytes can synthesize plant growth hormones such as auxin, abscisic acid, and gibberellins (GAs) [14,15].Endophytic fungi increase the host's resistance to biotic stresses caused by insects, pests, and fungal pathogens and improve the host plant's fitness against harsh environmental factors [16].A large percentage of the world's biodiversity is concentrated within the coastal regions, although much of it is yet to be discovered.The coastal zone is the interface between the land and sea and is characterized by interconnections among neighboring ecosystems.Coastal salt marsh wetlands, located in this transition zone between land and salt or brackish water, are among the most important and biologically productive natural ecosystems on Fungal endophytes are symbiotic microorganisms that are often found in asymptomatic plants.This study describes the genetic diversity of the fungal endophytes isolated from the roots of plants sampled from the west coast of Korea.Five halophytic plant species, Limonium tetragonum, Suaeda australis, Suaeda maritima, Suaeda glauca Bunge, and Phragmites australis, were collected from a salt marsh in Gochang and used to isolate and identify culturable, root-associated endophytic fungi.The fungal internal transcribed spacer (ITS) region ITS1-5.8S-ITS2was used as the DNA barcode for the classification of these specimens.In total, 156 isolates of the fungal strains were identified and categorized into 23 genera and two phyla (Ascomycota and Basidiomycota), with Dothideomycetes and Sordariomycetes as the predominant classes.The genus Alternaria accounted for the largest number of strains, followed by Cladosporium and Fusarium.The highest diversity index was obtained from the endophytic fungal group associated with the plant P. australis.Waito-C rice seedlings were treated with the fungal culture filtrates to analyze their plant growth-promoting capacity.A bioassay of the Sm-3-7-5 fungal strain isolated from S. maritima confirmed that it had the highest plant growth-promoting capacity.Molecular identification of the Sm-3-7-5 strain revealed that it belongs to Alternaria alternata and is a producer of gibberellins.These findings provided a fundamental basis for understanding the symbiotic interactions between plants and fungi.