Effects of arbuscular mycorrhizal fungi on fusarium wilt and disease resistance-related enzyme activity in cucumber seedling root

Fusarium.oxysporum f. sp. cucumerinum wilt disease severely limits cucumber production. There is a symbiotic relationship between arbuscular mycorrhizal fungus and over 80% of vascular plants including cucumber. This relationship is not only beneficial to growth, but also to tolerance of plant to pathogens. A pot experiment was conducted to investigate the bio-control effects of Glomus versiforme and Glomus intraradices against cucumber wilt. Meanwhile, the activities of three disease resistance enzymes in the root were examined. The results showed that the arbuscular mycorrhizal fungi improved cucumber seedling growth and reduced disease severity. G. versiforme presented more obviously growth-promoting and bio-controlling effects than G. intraradices. Compared with the control, G. versiforme significantly enhanced cucumber growth parameters such as seedling height, stem diameter, leaf area and dry weight while reducing disease index by 26.6%. Improved growth and early induction of defense enzymes of mycorrhizal seedlings increased plant disease resistance. Before F. oxysporum f. sp. cucumerinum infection, the main growth parameters (e.g., height, leaf area and dry weight) of G. versiforme or G. intraradices inoculated seedlings were significantly higher than those of the control. The index of seedling quality of G. versiforme inoculated seedlings was respectively 1.19 and 1.22 times of that of G. intraradices inoculated seedlings and the control seedlings. This implied that before F. oxysporum f. sp. Cucumerinum infection, G. versiforme inoculated seedlings were significantly stronger than both the G. intraradices inoculated seedlings and the control seedlings. The highest activities of chitinase, β-1,3-glucanase and PAL in G. versiforme pre-inoculated roots occurred 2, 7 and 7 days earlier than those in the control. The corresponding enzymes activities were 1.44, 2.16 and 92.00 times that of the control, respectively. The results provided efficient ways of protecting cucumber seedlings against Fusarium wilt by inducing arbuscular mycorrhizal fungi in cucumber seedlings.