| Root-knot nematodes (Meloidogyne spp.) have a worldwide distribution and are important endoparasitic pathogens of many plant species. In China, they are becoming one of the most serious diseases with the increase of greenhouse vegetable production. Most studies have found yield reductions in the range of 10% to 15% due to the disease. Maximum infection results in 30% to 40% up to complete yield loss. Root-knot nematode disease could inhibit growth and development, and decrease yield and quality of vegetables. The major species of root-knot nematode include M. incognita, M.hapla, M. arenaria and M. javanica. M. incognita is widely spread in Shandong province and causes a serious damage to vegetable production. Although physical and chemical approaches have been used to control the disease, they are not always effective and add the cost to tomato production. In addition, the use of chemicals causes severe environmental pollution and the residue in vegetable products may be harmful to human health. Recently, grafting cultivation using resistant rootstock could effectively prevent tomato from this disease. As a result, the purpose of this study is to evaluate tomato rootstock for resistance to Meloidogyne incognita, examine growth and resistant indexes of grafed tomato seedlings inoculated with the Meloidogyne incognita, which were planted in pots.1. The effect of five resistant rootstocks on root-knot nematode disease and change of growth were investigated in grafted tomato seedlings, using 401, Dahong FA-2160, Guozhen No.1,Telusi and Bulusite as rootstocks, Oumeiyuan as scion. The tomato seedlings were planted in pots and inoculated with 4500 of 2nd instars of larval M. incognita. The results showed that tomato seedlings grafted with rootstocks were highly resistant and self-rooted grafted seedlings were sensitive to M. incognita. At the early stage of first infection, growth indexes of rootstocks grafted seedlings were markedly lower than self-rooted grafted seedlings. With the increase of inoculation time, plant height and fresh weight of overground part of rootstocks grafted seedlings were higher than self-rooted grafted seedlings. The growth of overground part of self-rooted grafted seedlings was inhibited significantly by southern root-knot nematode, whereas rootstocks grafed seedlings maintained the strong growth.2. Changes of antioxidant enzyme activities and level of reactive oxygen species (ROS) in grafed tomato seedlings were studied after inoculating M. incognita. The activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) in leaves of scion grafted with different rootstocks were significantly increased, and the production rate of superoxide anion radical (O2-), the contents of malonaldehyde (MDA) and hydrogen peroxide (H2O2) were reduced comparison with own-rooted grafted seedling, which suggested that the infection aggravated the extent of membrane lipid peroxidation in leaves, especially in the leaves of susceptible variety. Rootstock grafting significantly enhanced resistance of tomato seedlings to M. incognita, while the seedlings of own-rooted grafted were easily infected and formed more large nodules. Rootstock grafting increased the activities of antioxidant enzymes, decreased the level of ROS in the leaves of scion. The level of ROS and the activities of antioxidant enzymes are closely related to their ability of resistance to root-knot nematode. Low level of ROS and high activities of antioxidant enzymes were helpful for reducing the damage of root-knot nematode to membrane system and increasing resistance to root-knot nematode. It was concluded that rootstock grafting can improve resistance to M. incognita, reduce the damage of root-knot nematode infection in tomato.3. The effect of infecting M. incognita on the activities of phenylalanine ammonia-lyse (PAL), tyrosine ammonia-lyse(TAL) and polyphenoloxidase(PPO) and the contents of total phenolic compounds and lignin of grafted tomato seedlings were investigated. The results showed that the activities of PAL, TAL and PPO and the contents of total phenolic compounds and lignin of grafted tomato seedlings have occured significant change after infecting southern root-knot nematode. The activities of PAL, TAL and PPO and the contents of total phenolic compounds and lignin of rootstock grafted tomato seedlings were significantly higher than that of the own-root grafted seedlings. So in the process of infecting, rootstock grafted tomato seedlings showed a strong resistance response to M. incognita, while own-root grafted seedlings showed weak. The activities of key enzymes and contents of secondary metabolic products in phenylpropanoid metabolites of grafted tomato seedlings are closely related to the level of resistance to southern root-knot nematode.4. The response of ascorbate-glutathione circulation system of rootstocks grafted and own-root grafted tomato seedlings to southern root-knot nematode were studied. The results showed that tomato seedlings grafted with different rootstocks were highly resistant and own-root grafted seedlings were sensitive to M. incognita. After infecting M. incognita, activities of antioxidant enzymes, such as APX, dehydro-ascorbate reductase (DHAR), monodehy droascorbate reductase (MDHAR) and glutathione reductase (GR), regenerating rates of ascorbate (AsA), dehydroascorbic acid (DHA), oxidized glutathione (GSSG) and glutathione (GSH) and redox statuses (ratios of AsA/DHA and GSH/GSSG) were significantly higher and H2O2 content in leaves of rootstochs grafted seedings was significantly lower than those of own-root grafted seedings. It was concluded that tomato seedings grafted with resistant rootstocks had efficient metabolism of ascorbate-glutathione cycle, which rapidly scavenged the H2O2 to alleviate the oxidative damage of root-knot nematode, therefore, rootstocks grafted tomato seedlings had a stronger tolerance to southern root-knot nematode. |
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