Thermotolerance of fungal endophytes isolated from plants adapted to the Thar Desert, India

A total of 507 endophytic fungal isolates belonging to 82 operational taxonomic units (OTUs) were isolated from fifteen plant species naturally occurring in the Thar Desert, Rajasthan, India. Aspergillus , Alternaria , Chaetomium , Penicillium and Nigrospora were among the dominant fungal genera. Thermotolerance of the isolates was evaluated by culturing the fungi at 40 °C and 45 °C in shake flasks. Growth of nine OTUs (ACJ-2, ACJ-5, ACL-2, ACT-2, ACT-3, LAS-4, LAS-6, SAP-3 and SAP-6) was unaffected at 40 °C. Of these, six endophytes, namely, ACJ-2, ACJ-5 ( Aspergillus flavus ), SAP-3 ( Aspergillus sp.), SAP-6, LAS-4 ( Aspergillus sp . ) and LAS-6 ( Chaetomium sp.), were tolerant to as high as 45 °C. Rest of the OTUs did not survive culture temperatures beyond 35 °C. We evaluated the ability of one thermotolerant endophyte, LAS-6 ( Chaetomium sp.) to confer high temperature tolerance and three OTUs, namely, LAS-4 ( Aspergillus sp . ), SAP-3 ( Aspergillus sp.) and SAP-6 to confer drought tolerance to a rice cultivar, IR-64, at early seedling stage. Seedlings treated with LAS-6 ( Chaetomium sp.) showed a higher survival percentage as well as maintained a significantly higher shoot and root growth under high temperature stress compared to seedlings not treated with the fungus. Under drought stress, endophyte treated seedlings maintained a significantly higher root growth compared to untreated seedlings. The identified thermotolerant fungal sources could be potentially useful in alleviating abiotic stress in agriculturally important crops.