Effects Of Rootstocks And Arbuscular Mycorrhizal Fungi On Root-knot Nematodes Of Watermelon Seedlings

Root-knot nematode Meloidogyne incognita disease is one of important soil-borne diseases in growing watermelon plants,which often aggravates long-term continuous cropping.This disease can be effectively reduced by grafting using disease-resistant rootstocks,while arbuscular mycorrhizal fungi(AMF)could also antagonize the nematodes,inducing host plant resistance to diseases.The aim of the present study is to evaluate the effects of grafting and AMF inoculation on the growth of melon plants and their resistance to nematode disease.The main results are as follows:1.The growth indexes and disease indexes of 16 watermelon rootstocks which were planted in pots and inoculated with M.incognita were measured in the experiment,and the clustering analysis and subordinate function analysis were conducted.The results showed that 'Qingnong 2'(Cucurbita maxima × C.moschata)with the subordinate function value 6.26 had the strongest resistance capacity,while 'Qingnong 3'(Cucurbita maxima × C.moschata)with the subordinate function value 1.48 had the lowest resistance capacity.2.The growth indexes and disease indexes of 'Qingnong 2' watermelon grafted seedlings,'Qingnong 3'grafted watermelon seedlings and 'Jingxin 2'(Citrullus lanatus)own root watermelon seedlings which were planted in pots and inoculated with M.incognita were measured in the experiment.The plant height,stem diameter,shoot fresh weight and root fresh weight of 2 species of grafted seedlings were higher than 'Jingxin 2' own root seedlings significantly;except disease index outside,the gall index,egg index and reproduction index of 'Qingnong 2' grafted seedlings were lower than 'Qingnong 3' grafted seedlings and 'Jingxin 2' own root seedlings significantly,except reproduction index outside,the disease index,gall index and egg index of'Qingnong 3' grafted seedlings were lower than 'Jingxin 2'own root seedlings.It is considered that grafting is an effective way to reduce root-knot nematodes.3.'Qingnong 2' and 'Qingnong 3' grafted with 'Jingxin 2' watermelon plants were inoculated with or without Funneliformis mosseae,Glomus versiforme and Rhizophagus intraradices,while the control grafted plants were not inoculated with any of AMF.The growth status and photosynthetic index of the plants in treatments were determined.Results showed that'Qingnong2' G.versiforme combination was the best treatment to enhance plant growth and photosynthesis.4.Two pumpkin varieties 'Qingnong 2' and 'Qingnong 3' each grafted with watermelon cv.'Jingxin 2' were inoculated with F.mosseae,G.versiforme and R.intraradices separately prior to inoculation of root-knot nematode M.incognita.The disease index,gall index,plant growth status,and defense enzyme activities etc.were determined.Results showed that AMF inoculation reduced disease severity caused by the nematode,and significantly enhanced plant growth.G.versiforme showed superior effects on increasing plant growth of 'Qingnong 2' and disease resistance.It is indicated that 'Qingnong 2' + G.versiforme combination could increase root activity,soluble sugar content,and activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT),and decrease the content of malondialdehyde in plants.5.G.versiforme could antagonize the nematodes.The combination of 'Qingnong 2' and G.versiforme could achieve the purpose of using AMF against the root-knot nematodes.