| Summary: | Plant-derived phenolic compounds contribute to the defense against various pathogens, including root-lesion nematodes (<i>Pratylenchus</i> spp.). However, there are no reports on the role of phenolic compounds in wheat (<i>Triticum aestivum</i>) against <i>Pratylenchus thornei</i>. In this study, wheat genotypes ranging from resistant to very susceptible to <i>P. thornei </i>were used to investigate the level of total phenols and phenol oxidases, polyphenol oxidase (PPO), and peroxidase (POD) expressed in root tissues when grown in the presence and absence of <i>P. thornei</i> over time (2–8 weeks). Higher constitutive levels of total phenols were found in resistant synthetic hexaploid wheats CPI133872 (576 µg gallic acid equivalent (GAE)/g root) and CPI133859 (518 µg GAE/g root) at 8 weeks after sowing, compared with moderately resistant and susceptible genotypes (192 to 390 µg GAE/g root). The activity of PPO was induced in resistant (CPI133872) and moderately resistant (GS50a and its derivate QT8343) genotypes, becoming maximal at 4 weeks after <i>P. thornei</i> inoculation. The activity of POD was induced in CPI133872 at 6 weeks after <i>P. thornei</i> inoculation. Different genetic sources of resistance to <i>P. thornei</i> showed diverse defense mechanisms and differences in timing responses. The combined effects of total phenols and oxidative enzymes could be important for defense against <i>P. thornei</i> in some resistant wheat genotypes.
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