Evaluation of the translocation of fungicides and their efficacy for control of brown root rot disease of trees

Abstract

Brown root rot (BRR), caused by Phellinus noxius, is a devastating disease of over 200 species of woody plants in tropical/subtropical areas. To achieve maximum chemical control of BRR and deter the emergence of fungicide resistance, this study conducted efficacy screening for systemic fungicides with different modes of action. Fourteen fungicides were tested for inhibitory effects in vitro on thirty-nine P. noxius isolates from Taiwan, Hong Kong, Malaysia, Australia, and the Pacific Islands, using potato dextrose agar containing 0.1, 1.0, and 10 ppm (mg L–1) of each fungicide. Results showed cyproconazole, epoxiconazole, and tebuconazole (FRAC G1) inhibited colony growth of P. noxius by 97.8–99.8% at 1 ppm. Other effective fungicide treatments were cyprodinil (FRAC D1) + fludioxonil (FRAC E2) and mepronil (FRAC C2), which showed growth inhibition of 76.7–100% and 79.1–100% at 10 ppm, respectively. P. noxius isolates from American Samoa, which exhibited high resistance to mepronil, carry point mutations in the SdhC gene. Upward translocation of six selected fungicides was evaluated in bishop wood (Bischofia javanica) seedlings by treating the root tips with 100 ppm of the fungicides, followed by liquid or gas chromatography tandem-mass spectrometry analyses of consecutive segments of root, stem, and leaf tissues at 7- and 21-days post-treatment. Cyproconazole was evenly distributed throughout the plant at the highest concentrations. Further research is needed to determine the optimal dose and application method to achieve effective control of BRR in planta.