Plant Protection, 06 (02) 2022. 143-149 DOI: 10.33804/pp.006.02.4261 143 Available Online at EScience Press Plant Protection ISSN: 2617-1287 (Online), 2617-1279 (Print) http://esciencepress.net/journals/PP SYNTHESIS OF 4-HYDROXYAZOBENZENE, A PROMISING AZO DYE FOR ANTIFUNGAL ACTIVITY AGAINST MACROPHOMINA PHASEOLINA a Aqsa Zafar, a Arshad Javaid, a Iqra Haider Khan, b Ejaz Ahmed, b Hamza Shehzad, c Aneela Anwar a Department of Plant Pathology, Faculty of Agricultural Sciences, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Pakistan. b Centre of Organic Chemistry, School of Chemistry, University of the Punjab, Quaid-i-Azam Campus, Lahore 54590, Lahore, Pakistan. c Department of Basic Sciences, University of Engineering and Technology, KSK Campus, Lahore, Pakistan. A R T I C L E I N F O A B S T R A C T Article history Received: 12 th July, 2022 Revised: 19 th August, 2022 Accepted: 20 th August, 2022 In the present study, an azo dye 4-hydroxyazobenzene was synthesized and its antifungal activity against a notorious soil-borne plant pathogen Macrophomina phaseolina was evaluated. The 4-hydroxyazobenzene was synthesized by azo coupling reaction between aniline diazonium salt and activated phenol. The azo coupling preferably occurred at para position of the phenol ring since the charge density get reinforced at this position and to minimize the steric hindrance between ortho positioned hydroxyl group. Azo coupling involved an electrophilic substitution reaction of phenyl diazonium cation with phenolate ion, the coupling partner. In vitro antifungal activity of the compound was assessed by dissolving the compound in dimethyl sulfoxide (DMSO) and preparing its different concentrations (ranging from 0.78 to 100 mg mL -1 ) in malt extract broth. All the concentrations of synthesized compound significantly (P≤0.05) reduced biomass of M. phaseolina by 31–49%. This study concludes that 4-hydroxyazobenzene can be used for control of M. phaseolina. Keywords Antifungal Azo dye 4-Hydroxyazobenzene Macrophomina phaseolina Corresponding Author: Arshad Javaid Email: arshad.iags@pu.edu.pk © 2022 EScience Press. All rights reserved. INTRODUCTION Macrophomina phaseolina occurs in the soil with a host range of more than 500 plant species (Iqbal and Mukhtar, 2014; Javed et al., 2021; Lodha and Mawar, 2020). It has a wide geographical distribution and occurs in subtropical and tropical countries with semi-arid to arid climates in Europe, Asia, Africa, and South and North America (Tancic et al., 2019). It is seed- as well as a soil-borne pathogen having varied distribution in different soils (Khan and Javaid, 2020; Marquez et al., 2021). It is responsible for seedling blight, stem canker, dry root rot, stem rot, charcoal rot, stem blight, leaf blight, wilt and damping off diseases in several economically important crops including vegetables and legumes (Banaras et al., 2021; Hyder et al., 2018; Javaid and Saddique, 2012; Lodha and Mawar, 2020). The production of sclerotial structures is responsible for its prolonged survival in the soil (Short et al., 1980). The pathogen becomes more severe under warm (28–35°C) and dry growing conditions (Ko et al., 2020). In recent decades, several management strategies such as agronomic practices, genetic resistance, chemical control, biological control, plant metabolites and elicitors of plant defense have been evaluated against M. phaseolina with varying degrees of success (Banaras et al., 2020; Iqbal and Mukhtar, 2020a; Iqbal et al., 2014;