فیزیولوژی محیطی گیاهی (Sep 2021)
Biochemical defense response of the greenhouse cucumber (Cucumis sativus L.) to complex disease caused by a root-knot nematode and Fusarium wilt fungus
Abstract
Complex disease caused by the root-knot nematode, Meloidogyne javanica, and the fungus, Fusarium oxysporum f. sp. radicis-cucumerinum, has limited cucumber cultivation in Iran. Therefore, access to the nematode-resistant cultivars has a crucial role in disease control. The Assessment of plant defense compounds in the Complex disease helps understand the molecular mechanisms of resistance and the production of nematode-resistant cultivars. After inoculation of the plants in a greenhouse, the peroxidase enzyme and the phenolic compounds were measured using spectrophotometric method. The experiment was conducted based on a factorial completely randomized designed with 14 treatments, including control, fungi alone, nematode alone in four inoculations level viz. 1500, 3000, 4500, and 6000 J2s, fungus + nematode simultaneously, and fungus a week after nematode inoculation with 4 replications. Phenolic compounds increased by %54.74 and %92.34 and peroxidase enzyme activity increased by %50.64 and %63.31 in plants inoculated with fungus alone and nematode alone (6000 larvae) compared to the control, showing that these substances act as defensive compounds in cucumber. Results showed that increasing the nematode population in inoculated plants improved the defense compounds levels. Inoculation of nematode (6000 larvae) followed by fungus led to %80 and %54.48 increases in phenolic compounds and peroxidase activity, respectively as compared with the control which might be attributed to the synergistic effects of pathogens. The fungi had a more active role than nematodes in increasing the peroxidase compared to the phenolic compounds, which indicated the complex nature of nematode parasitism in the nematode-plant interaction. Decrease in the defense compounds in Negin cultivar (susceptible to Fusarium) and increase in the level of these compounds in Khasib (tolerant to Fusarium) and Dastjerdi (tolerant to nematode) cultivars showed that the production of the defensive compounds may be related to the cucumber resistance to pathogens.
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