Curcuma longa L. (Turmeric) is a rhizomatous herbaceous perennial plant of the ginger family, Zingiberaceae  . It is a naturally grown plant in the Indian subcontinent and Southeast Asia. Turmeric has been used in Asia for thousands of years and is a major part of Ayurveda, Siddha medicine, Unani, and traditional Chinese medicine  . A lot of scientific works on pharmacological properties of turmeric have been reported by many scientists and researchers such as anti-inflammatory   , antiallergic  , antiobesity  , lipid-lowering  , antiproliferative  , anti-microbial   , anti-oxidant   , anti-diabetic  , hypoglycemic  , immunomodulating  , insecticidal  , anti-fungal  , neuroprotective  , anti-mutagenic  , hypolipidemic  etc.
Endophyte, the most important integral part of plant tissues, is a progressively significant area of research in many fields because of their chemical miscellany and their ability to produce many unique secondary metabolites that can be utilized for fuel, medicine, restoration and agriculture. Endophytes are isolated from medicinal plants possess strong fungicidal, bactericidal and cytotoxic metabolites  . Previous studies indicate that there have been few investigations done on endophytic microbes of turmeric plant (Curcuma longa). Thus, exploring endophytic microbes from Curcuma longa increases the probability to discover novel compound which is extensive in resistance tissues. There is no review on the endophytic fungi from turmeric plants. Therefore, it is necessary to review the endophytic fungi from Curcuma longa. Hence, this review discusses the current research progresses on endophytic fungi from the turmeric plant, including types of endophytic fungi identified, described bioactive compounds, and biological activities of endophytes to discover the current scope of knowledge of endophytes.
2. Isolated Compounds from Curcuma longa
A total of 235 compounds with various activities were isolated and identified from the flowers, leaves, roots and rhizomes part of Curcuma longa which is the most phytochemically investigated plant in the world. These compounds are primarily phenolic and terpenoid compounds including diarylheptanoids (including commonly known as curcuminoids), diarylpentanoids, monoterpenes, sesquiterpenes, diterpenes, triterpenes, sterols, fatty acids and also some alkaloidal compounds. A list of isolated compounds from different groups of C. longa is presented in Table 1. Curcumin is the key phytochemical compound
Table 1. Isolated compounds from C. longa.
responsible for many of turmeric’s eccentric properties and bright yellow colouring. Curcumin has been shown to reveal antioxidant, anti-inflammatory, antiviral, antibacterial, antifungal, and anticancer activities and thus, has a potential against various malignant diseases, diabetes, allergies, arthritis, Alzheimer’s disease, and other chronic illnesses  . Ar-turmerone and curlone have antimutagenic activity   whereas sodium curcuminate has anti-inflammatory activity  . The structures of some bioactive compounds from C. longa are given in Table 2.
Table 2. Structures of some bioactive compounds from C. longa.
3. Isolated Endophytic Fungi from Curcuma longa
Endophytic fungi Fusarium nivale, Fusarium solani, Doratomyces stemonitis, Penicillium, Diaphorte sp. were isolated from Curcuma longa    . Various studies have been identified the prospective of endophytic fungi from this plant as antioxidant, antidiabetic, anti-microbial and antitumor      . Therefore, in this section, endophytic fungi from different parts of C. longa is reviewed and presented in Table 3.
3.1. Endophytic Fungi of Rhizome
From the rhizome of C. longa several endophytic fungi have been isolated  . Exactly 207 endophytic fungi were found to be isolated in one of the study that belongs to the seven genera namely, Acremonium, Aspergillus, Exophiala, Fusarium, Penicillium, Phoma, and Stachybotrys. Among the species F. solani, F. delphinoides, F. verticillioides and A. versicolor, A. venenatus bearing the genus of Fusarium sp. and Aspergillus sp. were recovered from rhizomes of C. longa. The rest of the genera were isolated as single species. From them, Exophiala lecanii the fungal endophyte was isolated for the first time from the rhizome of C. longa  . Another investigation reported 31 endophytic fungi from the rhizome of C. longa  . In most studies of endophytic fungi, the sterile mycelia fungi are reported as mycelia-sterile. Unlike those one mycelia-sterile was identified as Phaeosphaeria ammophilae from rhizome by Eris et al.,  . One of the genus Eurotium sp. was also noted from the healthy rhizomes of C. longa  .
3.2. Endophytic Fungi of Leaf
A total of 6 endophytic fungi have been isolated from leaves of C. longa through a study  . Another study carried by Eris et al., have isolated one fungus Daldinia eschscholzii from leaf of C. longa  .
Table 3. Endophytic fungi from different parts of turmeric plant.
Rh = Rhizome, S = Stem, Fl = Flower, In = Inflorescence, L = Leaf, R = Root.
3.3. Endophytic Fungi of Stem
Several endophytic fungi from fresh stem of C. longa have been isolated  . The endophytic fungus Fusarium proliferatum was isolated from stems of healthy C. longa collected in Indonesia  .
3.4. Endophytic Fungi of Root
The endophytic fungus Arthrobotrys foliicola was isolated from the roots of C. longa  . Some endophytic fungi have also been isolated from roots of C. longa  .
3.5. Endophytic Fungi of other Parts
Some endophytic fungi from tubers and young tubers of C. longa have been isolated  . Eris et al., have isolated Fusarium verticillioides and Phanerochaete chrysosporium from the flowers of C. longa of which the later fungus is reported as mycelia-sterile. The group also isolated Cochliobolus kusanoi and Fusarium proliferatum from the inflorescence part of the plant. Cochliobolus kusanoi is the teleomorph stage of Drechslera kusanoi  .
4. Reported Bioactivity on Endophytic Fungi Isolated from Turmeric Plant
4.1. Antioxidant Activity
44 endophytic fungi from several parts of turmeric plant were investigated by a research group Bustanussalam et al., for their antioxidant bioactive compounds. They observed both filtrate and biomass ethylacetate extracts of endophytic fungi have antioxidant activity. On the basis of DPPH free radical scavenging method filtrate extracts gave higher antioxidant activity than biomass extracts. Due to presence of fatty acids, biomass extracts are less active as antioxidant. Filtrate extracts contain many secondary metabolites that may act as protection for the endophytic fungi of host plant  .
4.2. Anticancer Activity
A study carried out by Ratih et al., have shown inhibitory activity of 4 isolates of endophytic fungi towards human breast cancer MCF-7 cell line  . Endophytic fungus Eurotium sp. was isolated from rhizomes of C. longa by Ruby and Raghunath and it is utilized for the production of anticancer enzyme asparaginase for the first time  . The enzyme is considered to participate in major role in the asparaginase metabolism of the cells. It’s a likely therapeutic agent for acute lymphocytic leukemia, acute lymphoblastic leukemia and chronic myelogenous leukemia also reported to be an effective antilymphoma agent in humans.
4.3. Antifungal Activity
Suruchi et al., have separated endophytic fungi from C. longa for antifungal activity. The group reported the active constituent Gentisyl alcohol which is an anti-phytopathogenic molecule from fungal isolate P. herbarum. The purified compound showed antagonistic activity against C. gloeosporioides causing leaf spot of turmeric and could, therefore, be explored as a biocontrol agent for the host-specific phytopathogen  . Similarly, Vinayarani and Prakash have isolated T. harzianum from the rhizome of turmeric and they concluded that this can be exploited as a potential biocontrol agent for suppressing rhizome rot and leaf blight diseases in turmeric  .
4.4. Antibacterial Activity
Endophytic fungi could be a promising source for antibacterial bioactive agents. A study carried out by Sharmila et al., found that the endophytic fungus Chaetomium sp. isolated from C. longa exhibited protruding antibacterial activity against three different human pathogenic bacteria such as Proteus sp., Pseudomonas sp. and Staphylococcus aureus  .
Till today, the chemical composition of C. longa has thoroughly been investigated and a number of different active substances have been identified, which exhibit a wide range of medicinal value. But, very few structures of bioactive compounds are characterized and identified from endophytic fungi of C. longa. Most of the investigations are restricted to the level of fungal identification and bioactivity assay. But, endophytic fungi, producer of a wide array of secondary bioactive metabolites with their peculiar potential compounds, namely, antioxidant, antibacterial, antifungal, anticancer, etc., are the ideal targets for further drug discovery. These leads may play a major role in the recovery of infectious, inflammatory and also certain kinds of cancer diseases. So, extensive research is necessary in the area of endophytic fungi isolation and characterization of the compounds from C. longa.
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