Abstract
Plant-derived phenolic compounds contribute to the defense against various pathogens, including root-lesion nematodes (Pratylenchus spp.). However, there are no reports on the role of phenolic compounds in wheat (Triticum aestivum) against Pratylenchus thornei. In this study, wheat genotypes ranging from resistant to very susceptible to P. thornei 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 P. thornei 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 P. thornei inoculation. The activity of POD was induced in CPI133872 at 6 weeks after P. thornei inoculation. Different genetic sources of resistance to P. thornei showed diverse defense mechanisms and differences in timing responses. The combined effects of total phenols and oxidative enzymes could be important for defense against P. thornei in some resistant wheat genotypes.
Highlights
The root-lesion nematode Pratylenchus thornei is a plant-parasitic nematode that causes yield loss in wheat (Triticum aestivum) in many countries [1]
The concentration of totalofphenols in the roots of both resistant and susceptible genotypes increased over time of from weeks post-nematode inoculation (PNI), with non-inoculated
A similar trend was found in the moderately resistant genotypes GS50a and GS50a-derived lines QT8343 and QT8447, as well as moderately resistant landrace wheats Iraq43 and Morocco426, in which the phenol content was not significantly different from the susceptible genotypes. These results suggest that phenolic compounds may play a role in contributing to P. thornei resistance in the synthetic hexaploid lines but not in the other sources of P. thornei resistance evaluated in this study
Summary
The root-lesion nematode Pratylenchus thornei is a plant-parasitic nematode that causes yield loss in wheat (Triticum aestivum) in many countries [1]. It is one of the major threats to wheat production in the subtropical grain region of eastern Australia [2]. Pratylenchus spp. are migratory endoparasites that secrete cell wall degrading enzymes, such as cellulase, glucanase, and pectate lyase, and, together with stylet thrusting and body movement, they penetrate the epidermis of root cells to feed and migrate within the plant root cortex [3]. The feeding, migration, and multiplication of nematodes damages the root system, resulting in the poor uptake of water and nutrients by the plant, which in turn results in yield loss [4,5]. The life cycle (egg, J2, J3, J4, and adult) of Pratylenchus is completed within 45 to 60 days [3,6,7], resulting in exponential multiplication of the nematode population densities within the growing season of a susceptible wheat crop [8].
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