Endophytic microorganisms of tropical tuber crops: Potential and perspectives

Endophytic microorganisms which include both bacteria and fungi colonise almost every plant species. In order to colonize the plant and compete with other microorganisms, they produce a plethora of secondary metabolites, including toxins, enzymes, antibiotics, anti-cancer, anti-inflammatory and antifungal compounds. Endophytic fungi can have profound impacts on plant communities which include abiotic and biotic stress tolerance, increase of biomass, decrease of water consumption and alteration of resource allocation, nitrogen fixation, increased drought resistance, thermal protection, survival under osmotic stress and degradation of pollutants. Though tuber crops are the second most important group of crop plants providing food energy to humans after cereals, less attention has been paid to the these traditional crops in general. Investigations regarding the association of endophytes with the tuber crops have been sparsely studied though in some tuber crops like cassava, sweet potato and yams, presence of endophytes have been reported. Hence from the scarcely available literature, in the current review an attempt was made to put light on the various beneficial activities of endophytes on tuber crops. These reports glorified many symbiotically associated endophytes to have antagonistic properties against many plant pathogens like Rhizoctoniasolani, Pythiumaphanidermatumand Sclerotiumrolfsii. Species like Rahnellawas resilient to cold shock, UV irradiation and antibiotics. Many diazotropihic and non-diazotropihicendophytic bacteria were involved in nitrogen fixation. Actinomycetesendophytes were novel sources of industrially important thermostableamylolytic enzymes. However, inspite of all these profound beneficial effects endophytic associations are still to be studied in many tuber crops like taro, elephant foot yam, greater yam etc. So this review put forward the urge to carry out comprehensive research on these important microbes on such important crops.