bstract– Plant-parasitic nematodes are devastating pests of most crops, and their management still encounters challenges. Unraveling the plant-nematode interactions can shed light on the pathogenesis and resistance mechanisms, particularly in the case of the southern root-knot nematode Meloidogyne incognita interactions with monocots such as barley (Hordeum vulgare), to manage them properly. In this research, plant growth characteristics (length and fresh/dry weight of shoot and root), nematode gall index, resistance index, and reproduction factor were studied in barley genotypes namely ‘Bahman’, ‘Jolgeh’, ‘Khatam’, ‘Reyhan’,‘Yousef’, ‘Nik’, ‘Nimrouz’ and ‘Zarjow’ at 60 days post-inoculation (dpi). Afterwards, the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and phenylalanine ammonia-lyase (PAL) enzymes were measured at 0, 1, 2, 3, 4, and 10 dpi. The results showed that all plant growth characteristics except for the root weight decreased upon inoculation. While genotypes ‘Reyhan’, ‘Nik’ and ‘Yousef’ were proved to be resistant, moderately susceptible and susceptible, respectively, the remaining genotypes exhibited a moderate resistance response. In the ‘Reyhan’ genotype, the SOD, CAT, APX and GPX enzymes peaked at 1 dpi, whereas in other genotypes they increased over time. The genotype ‘Reyhan’ was completely different from the others in terms of peak time (except for PAL). The early enzymatic activity was likely related to the timely response of the resistant genotype ‘Reyhan’ to the nematode, while the late activity probably affected the tolerance to the nematode in the other genotypes. PAL exhibited an upward slope in the more resistant genotypes and probably had a positive correlation with resistance.

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