Germination Potential of Aspergillus niger and Fusarium solani Spores on Live Gyrinops walla Stem Tissues

Abstract

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Gyrinops walla (Walla patta) is the only member of the family Thymelaeaceae naturally growing in Sri Lanka which produces agarwood, a fragrant resinous tissue which is highly demanded in the world market. Since natural formation is rare, fungal inoculations are commonly practiced to induce agarwood formation in Aquilaria species. However, the response of live wood tissues of G. walla for the growth of fungi has not been investigated, the present study was conducted to identify the behavior of the fungal spores on the G. walla stem tissues after the inoculation. Non-resinous, non-wounded, fresh G. walla stem samples were collected minimising contaminations and water loss from three different mature trees with the age of 10-15 years in three different locations. Samples were cut into 3.0×3.0×3.0 cm and cutting surfaces were sterilised and 5 ml of spore suspension of 107 spores ml -1 and 105 spores ml-1 of Aspergillus niger and Fusarium solani respectively were applied to four vertical surfaces of the wood cube until those were saturated and placed in a sterile moist chamber. Three replicates were used for each tree for both fungal species and spore germination in sterile distilled water was used as the control. Percentage of spore germination on live tissues was determined at every 3 hour intervals for 36 hours and data were analysed by Kruskal-Wallis test using MINITAB software. Results revealed that the percentage of germination was higher in F. solani spores than A. niger after 3 hours of incubation on fresh G. walla tissues. Further at the 15th hour, germination was almost equal in both A. niger and F. solani. Though A. niger germination was lower until the 15th hour, it was gradually increased with time and obtained the maximum germination percentage at about nearly 70% at the stationary phase. However, F. solani germination was lower after the 15th hour and reached its maximum level of about 66%. However, the germination of A. niger and F. solani spores on live G. walla wood were not significantly different (p=0.817). The findings of the present study showed that percentage of spore germination of A. niger on live wood (70%) was higher than in water (60%). Similarly F. solani also showed an increment of germination on live wood (66%) than in water (53%). Results revealed that the germination on live wood tissues of A. niger and F. solani was not inhibited by biochemical/ phytochemical compounds in wood of G. walla on the cutting surface. The findings demonstrated the compatible interactions between two tested fungal species and G. walla stem tissues.