Antiphytopathogenic activity of the bioluminescent mushroom Neonothopanus nambi against root-rot disease

Abstract Aurisin A (1) and the culture medium of the luminescent mushroom Neonothopanus nambi showed antifungal activity against Phytophthora palmivora, which causes the root-rot disease of Monthong durian, in a preliminary greenhouse experiment. Moreover, a new natural product, neonambiquinone B (2), was isolated. Their structures were elucidated by mass, IR and extensive analysis of their 1D and 2D NMR spectroscopic data. The results demonstrated that the culture medium of N. nambi is a promising potential for their agricultural applications. Graphical Abstract


Introduction
Pest is one of the major causes of damage and yield loss in both quality and quantity of crop production.Phytophthora is a genus of plant-pathogenic oomycetes responsible for economically important losses in crops worldwide.Phytophthora palmivora, a tropical relative of the potato late blight pathogen, causes rotting diseases in many tropical crops including papaya, cocoa, oil palm and durian (Evangelisti et al. 2017).Fungal bioluminescence mushrooms were used to biologically control plant diseases, especially to control root-knot nematode (Meloidogyne incognita Chitwood), which caused damage to the economic crops over 3000 species in temperate and tropical areas (Bua-Art et al. 2010;Buchel et al. 1998;Engler et al. 1998).
Neonothopanus nambi belongs to the family Omphalotaceae.It is called 'Hed Ruang Sang Sirin-ratsami' or 'Sirin-ratsami mushroom' , in Thai.It can be found on logs or dead wood in broad-leaved forests in the northeast of Thailand (Sangsopha et al. 2020).Its secondary metabolites are less investigated and have revealed the presence of sesquiterpenes, p-terphenyls and benzoquinones (Kanokmedhakul et al. 2012;Sangsopha et al. 2020;Tsarkova et al. 2016).Secondary metabolites from N. nambi were discovered greatly vary in nature based on the conditions of its culture, which have useful biological effects such as cytotoxicity, antibacterial, and antimalarial activities (Wisetsai et al. 2021).
Consequently, the objective of this research was to extract the bioactive compound from different growing conditions of luminescent mushroom N. nambi and to examine the effect of bioactive compound against root-rot disease.We report herein the isolation and structural characterization of a major constituent aurisin A (1) and one new natural occurring, named neonambiquinone B (2) from the culture N. nambi.Their structures are depicted in Figure 1.Potency of aurisin A and the culture medium toward the root-rot disease of Monthong durian was assessed by monitoring the inhibition of P. palmivora, which causes the root-rot disease.

Results and discussion
In this letter, we describe the isolation and structural explanation of a new natural compound and a known aurisin A (1) from culture liquid of N. nambi.The purified compounds were identified by physical and spectroscopic methods (IR, 1D and 2D NMR) and the data of aurisin A was compared to values from existing literature (Kanokmedhakul et al. 2012).
The study of an efficiency of bioactive extracted compound and its culture from N. nambi against root-rot disease was evaluated by monitoring the inhibition of P. palmivora as showed in Figure S12.Root rot symptoms in durian tree showed in 2 days after mycelia P. palmivora transferred to the durian wound until 60 days during experiment was finished.Aurisin A, a major compound from mushroom N. nambi strongly reduced the inoculum potential of P. palmivora, shown by a significant reduction in pea root rot symptoms compared to that of control with inflection of P. palmivora.However, aurisin A 500 ppm with red lime coat applied to the wound or injected directly into the bark were not significantly different results after 60 days, measuring every 7 days.Moreover, culture filtrate of N. nambi was used.Culture filtrate 50% and 100% with red lime coat applied to the wound, injected directly into the bark, the results were not significantly different as aurinse A. All experiments were compared to that of positive control metalaxyl 25% WP with red lime coat applied to the wound.Aurisin A and its culture shown by a significant reduction in pea root rot symptoms as positive control metalaxyl (Figure S12).

Experimental section
Please see the supplementary material.

Conclusions
The extracts of culture liquid of N. nambi was investigated and led to the isolation of one known, aurisin A (1) and one new natural product (2).The current study shows the preliminary results that aurisin A and its culture showed the potential of reduction in pea root and stem rot symptoms of durian that good as a commercial standard metalaxyl.Importantly, it might not be necessary to purify aurisin A to use such an active compound against root and stem rot disease of durian because the inhibition of aurisin A and its culture were similar.However, the findings from this study need further verification under more population and field conditions.