Physiological Studies on Endophytic Fungi

Different fungi require different nutrients for its growth as all fungi are not able to utilize same substrate for their growth. This study revealed that Richard’s medium is best medium for growth of Daldinia eschscholtzii, Lasiodiplodia hormozganensis and Xylaria longipes. Same medium was earlier found to stimulate growth of Microsporum gypseum (Sharma and Sharma 2011), Colletotrichum gloeosporioides (Deshmukh et al. 2012), Aspergillus niger (Bitty and Nair 2014), Alternaria solani (Koley and Mahapatra 2015), Botriodiplodia theobromae (Mishra and Tripathi 2015) and Chrysosporium indicum (Jain and Sharma 2017).

A broad range of temperature tolerance for growth and sporulation fungi is an interesting feature. Daldinia eschscholtzii exhibited maximum growth at 28ºC which is similar to those reported by Kumara and Rawal 2008 in Colletotrichum gloeosporioides and Hoa and Wang 2015 in Pleurotus ostreatus and Pleurotus cystidiosus. The maximum growth was observed at 32ºC in Lasiodiplodia hormozganensis which is in accordance with Kalaw et al 2016 also reported the maximum growth of Ganoderma lucidum, Lentinus tigrinus and Coprinopsis cinerea strain incubated at 32 + 0.91oC. The literature revealed that Xylaria sp. are found to be mesophlic and maximum growth was observed at 25ºC (Osono et al. 2011) which is also proved during our experimentation where optimum growth of Xylaria longipes occurred at 24ºC.

The fungi can grow in wide pH range from 4-9 which make it adapt to the surroundings. The optimum growth of Daldinia eschscholtzii occurred at pH 5 as reported in Penicillium marneffei (Yamanaka 2003, Cao et al 2007). The highest dried mycelial weight of L. hormozganensis and X. longipes was obtained at pH 4.0 in Richard’s medium. These results are in accordance to data reporting maximum mycelia growth of Trichoderma spp. (Kredics et al. 2004), Aspergillus parasiticus (Abubakar et al. 2013) and Lentinula edodes (Quaicoe et al. 2014) at pH 4, whereas least mycelia weight was recorded at pH3 as obtained in Pleurotus ostreatus var. florida (Okwulehie and Okwujiako 2008).

Different fungi require varied growth periods to attain maximum growth in particular medium. It is essential to find optimum growth period to understand fungal physiology. D. eschscholtzii and L. hormozganensis attained maximum growth after 16 days of incubation whereas optimum biomass production in X. longipes occurred after 12 days, after which mycelia weight start decreasing. The decline in fungal dry weight may be due to autolysis of cells or depletion of nutrients in the medium.

Carbon is the most important constituent for the growth of mycelium. It constitutes about half of total dry weight of mycelium. Different fungi utilize different carbon sources for their growth and development. The highest growth of D. eschscholtzii was observed in pectin containing medium which is also reported by Prasher et al 2014 in Panellus stipticus whereas it is contradictory in Dictyoarthrinium synnematicum where least growth was found in pectin containing medium (Prasher and Chauhan 2015). The growth of mycelium is observed to be much more in all carbon sources as compared to control (without any carbon) whereas it is maximium in sucrose in L. hormozganensis. Sucrose was found to be best carbon source for growth of Alternaria zinniae followed by starch and maltose (Jash et al 2013). Similar results were also obtained by Zou (2005) in Oudemansiella radicata, Nagadesi and Arya (2013) in Lenzites sterioides, Mathan et al (2013) in endophytic Aspergillus terreus, Latha et al. (2013) in Lasiodiplodia theobromae Rajput et al. (2014) in Trichoderma harzianum and Wiriya et al. (2014) in Termitomyces sp. The maximum mycelial yield was obtained from the medium supplemented with Glucose as carbon source in case of X. longipes. Earlier reports also revealed that glucose supported maximum biomass production in Xylaria sp. Strain R006 (Ramesh et al 2014), Xylaria sp. 2508 (Xiaobo et al 2006), Lentinus edodes (Song and Cho 1987), Pseudonocardia sp. (Usha Kiranmayi et al 2011) and Pleurotus spp. (Sarria-Alfonso et al 2013).

Nitrogen comprises 6% of total dry weight of mycelium. The current study revealed that Potassium Nitrate is found best among different inorganic nitrogen sources for growth of D. eschscholtzii, L. hormozganensis and X. longipes. The fungi may have capacity to produces reductase or other associated enzymes which are essential for the metabolism of the nitrate (Walker and Nicholas 1962). Potassium nitrate was found to be best by various other researchers including Manjunath et al 2013 (Colletotrichum lindemuthianum), Lal et al 2014 (Curvularia lunata), Taware et al 2014 (Alternaria carthami) and Gawai and Shinde 2017 (Colletotrichum coccodes and Colletotrichum capsici).

The maximum biomass in terms of average mycelial dry weight production in D. eschscholtzii occurred in medium supplemented with DL-Aspartic acid whereas the medium supplemented with L- Cysteine HCl showed poor growth. Similar results were also reported in studies related to Pythium aphanidermatum (Grover and Sidher 1965) and Colletotrichum gloeosporioides (Kumara and Rawal 2008). L. hormozganensis was able to utilize all amino acids as sole nitrogen source. Out of various organic nitrogen sources, L- Proline was found to yield maximum mycelia weight followed by L-Tyrosine,L- Leucine and Lysine HCl. L-Proline have also been reported as best organic nitrogen source for Hirsutella rhossiliensis (Liu and Chen 2002), Trichoderma viride, Flagellospora penicilloides and Pestalotiopsis submerses (Bisht 2013), Arthrinium phaeospermum (Prasher et al. 2014), whereas these results are in contrary with literature data for Tetracladium marchalianum, Tetrachaetum elegans (Bisht 2013) and Alternaria alternata (Khandare 2014). In X. longipes, maximum mycelial production was observed in valine supplemented media. Our results are in accordance with those obtained by Kalaimani (1997), who investigated the nutrition of six isolates of Colletotrichum falcatum collected from sugarcane and found that valine induced maximal mycelia growth in all the six isolates.