Rigidoporus microporus is the main causal of white root disease (WRD) in rubber trees (Hevea brasiliensis). The present study investigates the use of rhamnolipid, a biosurfactant produced by Pseudomonas aeruginosa USM-AR2 against R. microporus. In vitro dose-responses towards rhamnolipid were determined on different isolates of R. microporus using the poisoned food technique (PFT). Inhibition of mycelial growth was found to be dose-dependent, with the highest inhibition of 76.74% at 200 ppm (pH 6.29) on SEG isolate. On the contrary, the lowest concentration of rhamnolipid applied at 10 ppm (pH 5.97) had effectively inhibited the growth of RL 19 to 34.36%. AM isolate was assumed to be the most aggressive pathogen due to the lowest inhibition recorded on all rhamnolipid concentrations tested. At the same time, RL 19 was the least aggressive pathogen compared to the other R. microporus isolates. The rhamnolipid concentrations (ppm), which reduced mycelial growth at 50% (EC₅₀), were recorded at 17.82 ppm for AM isolate, 12.52 ppm for RL 26, and 11.80 ppm for RL 19 isolate. This result indicated that rhamnolipid concentrations to inhibit 50% of mycelial growth might vary based on the aggressiveness and the virulence levels of different R. microporus isolates. It was found that pH changes after incorporating rhamnolipid into the PDA were not the main factor affecting the inhibition of R. microporus isolates. It is obvious that rhamnolipid had an inhibitory effect on fungal growth in vitro. It is the first report on rhamnolipid that has been shown to control R. microporus potentially.

• AAT Bioquest Inc. (n.d.). Quest Graph™ EC50 calculator. https://www.aatbio.com/tools/ec50-calculator

• Andrew, B., Ahmad, K., Ismail, S. I., Ahmad, M. F., Ahmed, O. H., & Yun, W. M. (2021). Disease prevalence and molecular characterisation of Rigidoporus microporus associated with white root rot disease of rubber tree (Hevea brasiliensis) in Malaysia. Journal of Rubber Research, 24(1), 175–186. https://doi.org/10.1007/s42464-021-00083-x

• Arena, M., Auteri, D., Barmaz, S., Bellisai, G., Brancato, A., Brocca, D., Bura, L., Byers, H., Chiusolo, A., Court Marques, D., Crivellente, F., De Lentdecker, C., De Maglie, M., Egsmose, M., Erdos, Z., Fait, G., Ferreira, L., Goumenou, M., Greco, L., … Villamar-Bouza, L. (2017). Peer review of the pesticide risk assessment of the active substance propiconazole. EFSA Journal, 15(7), e04887. https://doi.org/10.2903/j.efsa.2017.4887

• Atan, S. (2015). Integrated pest and disease management (IPDM): Our story [Unpublished document]. Malaysian Rubber Board.

• Balamurugan, S. (2014). In vitro antifungal activity of Citrus aurantifolia linn plant extracts against phytopathogenic fungi Macrophomina phaseolina. International Letters of Natural Sciences, 13, 70–74. https://doi.org/10.18052/www.scipress.com/ILNS.13.70

• Bharali, P., Saikia, J. P., Ray, A., & Konwar, B. K. (2013). Rhamnolipid (RL) from Pseudomonas aeruginosa OBP1: A novel chemotaxis and antibacterial agent. Colloids and Surfaces B: Biointerfaces, 103, 502–509. https://doi.org/10.1016/j.colsurfb.2012.10.064

• Borah, S. N., Goswami, D., Sarma, H. K., Cameotra, S. S., & Deka, S. (2016). Rhamnolipid biosurfactant against Fusarium verticillioides to control stalk and ear rot disease of maize. Frontiers in Microbiology, 7, 1505. https://doi.org/10.3389/fmicb.2016.01505

• Charles Oluwaseun, A., Julius Kola, O., Mishra, P., Ravinder Singh, J., Kumar Singh, A., Singh Cameotra, S., & Oluwasesan Micheal, B. (2017). Characterization and optimization of a rhamnolipid from Pseudomonas aeruginosa C1501 with novel biosurfactant activities. Sustainable Chemistry and Pharmacy, 6, 26–36. https://doi.org/10.1016/j.scp.2017.07.001

• Chen, C., Sun, N., Li, D., Long, S., Tang, X., Xiao, G., & Wang, L. (2018). Optimization and characterization of biosurfactant production from kitchen waste oil using Pseudomonas aeruginosa. Environmental Science and Pollution Research, 25(15), 14934–14943. https://doi.org/10.1007/s11356-018-1691-1

• de Freitas Ferreira, J., Vieira, E. A., & Nitschke, M. (2019). The antibacterial activity of rhamnolipid biosurfactant is pH dependent. Food Research International, 116, 737–744. https://doi.org/10.1016/j.foodres.2018.09.005

• Deepika, K. V., Ramu Sridhar, P., & Bramhachari, P. V. (2015). Characterization and antifungal properties of rhamnolipids produced by mangrove sediment bacterium Pseudomonas aeruginosa strain KVD-HM52. Biocatalysis and Agricultural Biotechnology, 4(4), 608–615. https://doi.org/10.1016/j.bcab.2015.09.009

• Durgeshlal, C., Sahroj Khan, M., Prabhat, S. A., & Aaditya Prasad, Y. (2019). Antifungal activity of three different ethanolic extract against isolates from diseased rice plant. Journal of Analytical Techniques and Research, 1(1), 47–63. https://doi.org/10.26502/jatri.007

• Farhana, A. H. K. F., Bahri, A. R. S., Thanh, T. A. V., & Zakaria, L. (2017). Morphological features of Rigidoporus microporus isolated from infected Malaysian rubber clones. Malaysian Journal of Microscopy, 13(1), 17–23.

• Go, W. Z., Wong, M. Y., Tan, G. H., Chuah, A. L., Salmiah, U., Soni, O., Wong, W. Z., Chin, K. L., & Chai, E. W. (2013). Occurence and characterisation of mycoflora in soil of different health conditions associated with white root rot disease in Malaysian rubber plantation. Journal of Rubber Research, 18(3), 159–170.

• Goswami, D., Borah, S. N., Lahkar, J., Handique, P. J., & Deka, S. (2015). Antifungal properties of rhamnolipid produced by Pseudomonas aeruginosa DS9 against Colletotrichum falcatum. Journal of Basic Microbiology, 55(11), 1265–1274. https://doi.org/10.1002/jobm.201500220

• Hadi, S. M. H. S. A., Zakaria, L., Sidique, S. N. M., Mahyudin, M. M., & Mohd, N. (2021). The potential of soluble silicon for managing white root disease in rubber (Hevea brasiliensis). Australian Journal of Crop Science, 15(10), 1346–1354. https://doi.org/10.21475/ajcs.21.15.10.p3343

• Hashim, I., & Chew, B. H. (1997). Effects of integrating Trichoderma and fungicide on control of white root disease of Hevea rubber. Journal of Natural Rubber Research, 12(1), 43–57.

• Ismail, H., & Azaldin, M. Y. (1985). Interaction of sulphur with soil pH and root diseases of rubber. Journal Rubber Research Institute Malaysia, 33(2), 59–69.

• Jayasuriya, K. E., & Thennakoon, B. I. (2007). Biological control of Rigidoporus microporus, the cause of white root disease in rubber. Chiang Mai Journal of Science, 46(5), 850-866.

• Jishma, P., Shad, K. S., Athulya, E., Sachidanandan, P., & Radhakrishnan, E. (2021). Rhizospheric Pseudomonas spp. with plant growth promotion and antifungal properties against Sclerotium rolfsii mediated pathogenesis in Vigna unguiculata. Plant Biotechnology Reports, 15(4), 483–491. https://doi.org/10.1007/s11816-021-00687-0

• Kaiser, C., Merwe, R. Van Der, Bekker, T. F., & Labuschagne, N. (2005). In-vitro inhibition of mycelial growth of several phytopathogenic fungi, including Phytophthora cinnamomi by soluble silicon. South African Avocado Growers’ Association Yearbook, 28(1), 70–74.

• Knebel, C., Neeb, J., Zahn, E., Schmidt, F., Carazo, A., Holas, O., Pavek, P., Püschel, G. P., Zanger, U. M., Süssmuth, R., Lampen, A., Marx-Stoelting, P., & Braeuning, A. (2018). Unexpected effects of propiconazole, tebuconazole, and their mixture on the receptors CAR and PXR in human liver cells. Toxicological Sciences, 163(1), 170–181. https://doi.org/10.1093/toxsci/kfy026

• Md Noh, N. A., Mohd Salleh, S., & Yahya, A. R. M. (2014). Enhanced rhamnolipid production by Pseudomonas aeruginosa USM-AR2 via fed-batch cultivation based on maximum substrate uptake rate. Letters in Applied Microbiology, 58(6), 617–623. https://doi.org/10.1111/lam.12236

• Monnier, N., Cordier, M., Dahi, A., Santoni, V., Guénin, S., Clément, C., Sarazin, C., Penaud, A., Dorey, S., Cordelier, S., & Rippa, S. (2020). Semipurified rhamnolipid mixes protect Brassica napus against Leptosphaeria maculans early infections. Phytopathology, 110(4), 834–842. https://doi.org/10.1094/PHYTO-07-19-0275-R

• Monnier, N., Furlan, A., Buchoux, S., Deleu, M., Dauchez, M., Rippa, S., & Sarazin, C. (2019). Exploring the dual interaction of natural rhamnolipids with plant and fungal biomimetic plasma membranes through biophysical studies. International Journal of Molecular Sciences, 20(5), 1009. https://doi.org/10.3390/ijms20051009

• Nalini, S., & Parthasarathi, R. (2018). Optimization of rhamnolipid biosurfactant production from Serratia rubidaea SNAU02 under solid-state fermentation and its biocontrol efficacy against Fusarium wilt of eggplant. Annals of Agrarian Science, 16(2), 108–115. https://doi.org/10.1016/j.aasci.2017.11.002

• Ndlovu, T., Rautenbach, M., Khan, S., & Khan, W. (2017). Variants of lipopeptides and glycolipids produced by Bacillus amyloliquefaciens and Pseudomonas aeruginosa cultured in different carbon substrates. AMB Express, 7, 109. https://doi.org/10.1186/s13568-017-0367-4

• Nicole, M. R., & Benhamou, N. (1991). Ultrastructural localization of chitin in cell walls of Rigidoporus lignosus, the white-rot fungus of rubber tree roots. Physiological and Molecular Plant Pathology, 39(6), 415–431. https://doi.org/10.1016/0885-5765(91)90008-6

• Noh, N. A., Salleh, S. M., Abdullah, A. A., & Mohd, A. R. (2012). Fed-batch cultivation of Pseudomonas aeruginosa USM-AR2 producing rhamnolipid in bioreactor through pulse feeding strategy. International Proceedings of Chemical, Biological and Environmental Engineering, 40(34), 168-174.

• Ogbebor, O. N., Adekunle, T. A., Eghafona, O. N., & Ogboghodo, A. I. (2015). In vitro and in vivo botanical control of Rigidoporus microporus (sw.) overeem of para rubber in Nigeria. European Journal of Academic Essays, 2(3), 60–68.

• Oghenekaro, A. O., Raffaello, T., Kovalchuk, A., & Asiegbu, F. O. (2016). De novo transcriptomic assembly and profiling of Rigidoporus microporus during saprotrophic growth on rubber wood. BMC Genomics, 17(1), 234. https://doi.org/10.1186/s12864-016-2574-9

• Prasetyo, J., Aeny, T. N., & Suharjo, R. (2009). The corelations between white rot (Rigidoporus lignosus L.) incidence and soil characters of rubber ecosystem in Penumangan Baru, Lampung. Jurnal Hama dan Penyakit Tumbuhan Tropika, 9(2), 149–157.

• Radzuan, M. N., Banat, I. M., & Winterburn, J. (2017). Production and characterization of rhamnolipid using palm oil agricultural refinery waste. Bioresource Technology, 225, 99–105. https://doi.org/10.1016/j.biortech.2016.11.052

• Rodesuchit, A., Suchatgul, S., Klaewklong, B., & Damnoi, S. (2012). Efficacy of fertilizers to control white root disease of rubber caused by Rigidoporus microporus at the early planting stages. Rubber Thai Journal, 72(3), 62–72.

• Satapute, P. P., & Kaliwal, B. B. (2015). In vitro toxicity screening of triazole fungicide propiconazole. International Journal of Recent Scientific Research, 6(9), 6525–6528.

• Satchuthananthavale, V., & Halangoda, L. (1971). Sulphur in the control of white root disease. Journal Rubber Research Institute Ceylon, 48, 82–91.

• Sha, R., & Meng, Q. (2016). Antifungal activity of rhamnolipids against dimorphic fungi. The Journal of General and Applied Microbiology, 62(5), 233–239. https://doi.org/10.2323/jgam.2016.04.004

• Shi, J., Chen, Y., Liu, X., & Li, D. (2021). Rhamnolipid production from waste cooking oil using newly isolated halotolerant Pseudomonas aeruginosa M4. Journal of Cleaner Production, 278, 44–54. https://doi.org/10.1016/j.jclepro.2020.123879

• Siddiqui, N., Middleton, C., Ribeiro, C., Atan, S., & Di Cola, A. (2017). Gel-based proteomic study for differential expression of Hevea brasiliensis root proteins in response to infection by soil fungus Rigidoporus microporus. Acta Horticulturae, 1152(31), 229–234. https://doi.org/10.17660/ActaHortic.2017.1152.31

• Skidmore, A. M., & Dickinson, C. H. (1976). Colony interactions and hyphal interference between Septoria nodorum and phylloplane fungi. Transactions of the British Mycological Society, 66(1), 57–64. https://doi.org/10.1016/s0007-1536(76)80092-7

• Sotirova, A., Avramova, T., Stoitsova, S., Lazarkevich, I., Lubenets, V., Karpenko, E., & Galabova, D. (2012). The importance of rhamnolipid-biosurfactant-induced changes in bacterial membrane lipids of Bacillus subtilis for the antimicrobial activity of thiosulfonates. Current Microbiology, 65(5), 534–541. https://doi.org/10.1007/s00284-012-0191-7

• Soytong, K., & Kaewchai, S. (2014). Biological control of white root of rubber trees using Chaetomium cupreum. International Journal of Agricultural Technology, 10(1), 93–103.

• Vanavil, B., & Seshagiri Rao, A. (2018). Dual substrate fermentation using palm oil and glucose for production of eco-friendly biosurfactants using P. aeruginosa NITT 6L. Indian Journal of Chemical Technology, 25(1), 101–105.

• Wattanasilakorn, S., Sdoodee, S., Nualsri, C., Chuenchit, S., Meesawat, U., & Sopharat, J. (2017). Assessment of rubber clonal rootstocks for the tolerance of white root disease (Rigidoporus microporus) in Southern Thailand. Walailak Journal of Science and Technology, 14(7), 549–561.

• Yan, F., Xu, S., Chen, Y., & Zheng, X. (2014). Effect of rhamnolipids on Rhodotorula glutinis biocontrol of Alternaria alternata infection in cherry tomato fruit. Postharvest Biology and Technology, 97, 32–35. https://doi.org/10.1016/j.postharvbio.2014.05.017

• Yan, F., Xu, S., Guo, J., Chen, Q., Meng, Q., & Zheng, X. (2015). Biocontrol of post-harvest Alternaria alternata decay of cherry tomatoes with rhamnolipids and possible mechanisms of action. Journal of the Science of Food and Agriculture, 95(7), 1469–1474. https://doi.org/10.1002/jsfa.6845