Culturable endophytic fungal diversity in the cadmium hyperaccumulator Solanum nigrum L. and their role in enhancing phytoremediation

In this study, the endophytic fungal community associated with Solanum nigrum was isolated and characterized for cadmium (Cd) tolerance and host plant growth modulation under Cd contamination for the first time. In total, 42 culturable endophytic fungal isolates representing various morphotypes were isolated, among which 14 different genera of the fungal phylum Ascomycota were identified based on the analysis of the internal transcribed spacer (ITS) region of the rRNA gene. Among the identified genera, Colletotrichum (18%) represented the dominant genus followed by Alternaria (14%), and Fusarium (14%). The majority of the endophytic isolates were sensitive to a lower concentration (0.5 mM) of Cd. However, Glomerella truncata PDL-1, and Phomopsis fukushii PDL-10 showed the highest tolerance to a concentration gradient of Cd (0.5⿿2 mM). Owing to the levels of Cd tolerance detected, in order to simulate a tripartite plant-microbe-metal interaction, S. nigrum plants were inoculated with PDL-1 and PDL-10 under Cd spiking of 0, 5, 15, and 25 mg kg^⿿1. The results indicated that PDL-10 inoculated plants had significantly higher Cd content in shoots as well as in roots than observed in the PDL-1 inoculated plants. Additionally, irrespective of Cd stress, PDL-1 and PDL-10 inoculation significantly improved plant growth attributes such as shoot and root length, chlorophyll content, and fresh and dry shoot/root weight as compared to those of non-inoculated control plants. The results of this study highlight the possible role of fungal endophytes harbored inside S. nigrum, which has the potential to improve the efficiency of phytoremediation or phytostabilization in the cleanup of Cd-contaminated soil.