Biodeterioration of low-density polyethylene by mangrove-associated endolichenic fungi and their enzymatic regimes.

Fungal involvement in the biodeterioration of low-density polyethylene (LDPE) has received great attention in recent years. Among diverse groups of fungi, endolichenic fungi (ELF) are adapted to thrive in resource-limited conditions. The present study was designed to investigate the potential of mangrove-associated ELF, in the biodeterioration of LDPE and to quantify key-depolymerizing enzymes. A total of 31 ELF species, isolated from 22 lichens of mangrove ecosystems in Negombo lagoon, Sri Lanka were identified using DNA barcoding techniques. ELF were inoculated into a mineral salt medium, containing LDPE strips and incubated at 28 ± 2°C, for 21 days, under laboratory conditions. After incubation, biodeterioration was monitored based on percent reductions in weights and tensile properties, increments in the degree of water absorption, changes in peaks of infrared spectra and surface erosions using scanning electron microscopy. Out of 31 species, Chaetomium globosum, Daldinia eschscholtzii, Neofusicoccum occulatum, Phanerochaete chrysosporium, Schizophyllum commune and Xylaria feejeensis showed significant changes. Production of depolymerizing enzymes by these species was assayed qualitatively using plate-based methods and quantitatively by mass-level enzyme production. Among them, Phanerochaete chrysosporium showed the highest enzyme activities as (9·69 ± 0·04) × 10-3 , (1·96 ± 0·01) × 10-3 , (5·73 ± 0·03) × 10-3 , (0·88 ± 0·01), (0·64 ± 0·06), (1·43 ± 0·01) U ml-1 for laccase, lignin peroxidase, manganese peroxidase, amylase, lipase and esterase, respectively.

Bioactive constituents of wood rot extract of tea, Camellia sinensis L.O. Kuntze against alates of low country live wood termite Glyptotermes dilatatus Bugnion and Popoff (Isoptera: Kalotermitidae).

Low country live wood termite (LCLWT), Glyptotermes dilatatus is attractive to rotted stumps of tea plant, Camellia sinensis. Rotted stumps are formed due to the attack of wood rot fungi in pruned stems. The objective of the present study was to investigate the response of LCLWT to extracts of rotted and healthy stems of susceptible tea cultivars, TRI 2023 and TRI 4042 and tolerant cultivars, TRI 2027 and TRI 4049 and isolate the LCLWT attractive fractions of tea stem extract. Since pieces of rotted stem of both susceptible and tolerant tea cultivars were more attractive to the alates than that of healthy stems, effects of EtOAc extracts of rotted and healthy stems of four tea cultivars were compared on behavior of the alates. The results revealed that the alates positively responded to extracts of rotted tea stems of four tea cultivars than that of healthy tea stems. Therefore hexane, chloroform and aqueous methanol fractions of the extracts of rotted stems were tested against alates using orientation bioassays. Results revealed that the hexane fraction of rotted stem of each cultivar was more attractive than that of the chloroform and methanol fractions. The results of bioassay guided fractionation of the hexane fraction using column chromatography revealed the presence of two bioactive sub-fractions suggesting non-polar compounds in rotted tea wood are more attractive to G. dilatatus than other sub-fractions. These two fractions can be used to develop a trapping mechanism to strengthen present IPM program of LCLWT.

Control of stored grain pest, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using the essential oil isolated from Plectranthus zeylanicus.

The bruchid, Callosobruchus maculatus (F.) causes major losses during the storage of cowpea seeds [Vigna unguiculata (L.)Walp.] in Sri Lanka. Essential oil isolated from Plectranthus zeylanicus plant was tested for potential insecticidal activity against C. maculatus. The gas chromatography studies of the essential oil of P. zeylanicus showed that ρ-cymene (3.5%), ß-caryophyllene (0.2%), geranyl acetate (9.3%) and geraniol (7.2%) were the major constituents. The adults of C. maculatus were susceptible to both fumigant and contact toxicity of P. zeylanicus plant oil. LC(50) values of 0.927 and 0.010 g L(-1) were obtained for fumigant toxicity and contact toxicity assays, respectively. Oviposition and F(1) adult emergence were significantly inhibited by P. zeylanicus plant oil at a concentration higher than 0.001 g L(-1) in both fumigant and contact toxicities. The analysis of olfactometer and choice camber bioassays revealed the repellent effects of the oil of P. zeylanicus plant.

Nature and bioactivities of endolichenic fungi in Pseudocyphellaria sp., Parmotrema sp. and Usnea sp. at Hakgala montane forest in Sri Lanka.

AIM: The aim of this study was to investigate the nature and bioactivities of endolichenic fungi in three abundant lichens, Pseudocyphellaria sp., Usnea sp. and Parmotrema sp. in the lower elevation of Hakgala montane forest in Sri Lanka. METHODS AND RESULTS: Endolichenic fungal strains, fungi that live asymptomatically in the lichen thallus, much the same way as endophytic fungi live within healthy plant tissues, were isolated from three abundant lichen species, Pseudocyphellaria sp., Usnea sp. and Parmotrema sp., at Hakgala montane forest in Sri Lanka, using the surface sterilization method. Nine endolichenic fungal strains were isolated from Parmotrema sp. and Usnea sp. separately, while 11 endolichenic fungi were recovered from the lichen Pseudocyphellaria sp. Isolation of endolichenic fungus Chrysosporium sp. 2 was common to all three lichen species. Substrate utilization patterns and antifungal activities of eight endolichenic fungal species were evaluated and the results revealed that all the test fungi were able to produce at least one enzyme to utilize the test substrates. Nigrospora sp., Chrysosporium sp. 1 and 2 and Cladosporium sp. showed antifungal activities on growth of some selected plant pathogenic fungi. CONCLUSIONS: Endolichenic fungal strains (29) were isolated from the lichens Parmotrema sp., Usnea sp. and Pseudocyphellaria sp. in Sri Lanka. Chrysosporium sp. 2 was common in all three lichens. Some of these endolichenic fungal strains showed antifungal activities against common plant pathogenic fungi and they are capable of utilizing the substrates by producing specific enzymes. SIGNIFICANCE AND IMPACT OF THE STUDY: The diversity and prevalence of the endolichenic fungi have not been studied extensively and this is the first report of isolation and identification of endolichenic fungi in lichens available in Sri Lanka.

Fungicidal and anti-aflatoxigenic effects of the essential oil of Cymbopogon citratus (DC.) Stapf. (lemongrass) against Aspergillus flavus Link. isolated from stored rice.

AIMS: To develop a natural fungicide against aflatoxigenic fungi, to protect stored rice, using the essential oil of lemongrass. METHODS AND RESULTS: Aspergillus flavus Link. was isolated from stored rice and identified as an aflatoxigenic strain. Lemongrass oil was tested against A. flavus and the test oil was fungistatic and fungicidal against the test pathogen at 0.6 and 1.0 mg ml(-1), respectively. Aflatoxin production was completely inhibited at 0.1 mg ml(-1). The results obtained from the thin layer chromatographic bioassay and gas chromatography indicated citral a and b as the fungicidal constituents in lemongrass oil. During the fumigant toxicity assay of lemongrass oil, the sporulation and the mycelial growth of the test pathogen were inhibited at the concentrations of 2.80 and 3.46 mg ml(-1), respectively. CONCLUSION: Lemongrass oil could be used to manage aflatoxin formation and fungal growth of A. flavus in stored rice. SIGNIFICANCE AND IMPACT OF THE STUDY: Currently, fungicides are not used to control fungal pests or mycotoxin production on stored rice. Rice treated with the essential oil of lemongrass could be used to manage fungal pests as well as the insect pests in stored rice. The essential oil is chemically safe and acceptable to consumers, as synthetic chemical fungicides can cause adverse health effects to consumers.