Effect Of Arbuscular Mycorrhizal Fungi On Resistance Of Catalpa Bungei To Root-knot Nematode Disease

Catalpa bungei is a unique valuable timber and ornamental tree species in China,and has a long cultivation history.In recent years,the government has planned to plant this species on a large scale in suitable areas.With the expansion of C.bungei nurseries and artificial forests,the occurrence and harm of root-knot nematode disease are gradually intensified.Arbuscular mycorrhizal fungi(AMF)can improve plant disease resistance and form a good symbiotic relationship with C.bungei.However,the effect of AMF on root-knot nematode disease of C.bungei has not been reported.In order to find an effective way to control the root-knot nematode disease of C.bungei,this paper analyzed the disease resistance levels of 8 C.bungei clones according to the growth and resistance indexes,screened out the best clone with strong resistance to root-knot nematode disease.Furthermore,the effect of AMF on the resistance to root-knot nematode disease of 3 C.bungei clones with different resistance were studied,and the related physiological and biochemical mechanisms were elucidated.The main results were listed as follows:(1)The resistance of 8 clones to root-knot nematode disease was in order of 2 > 1-1 >008-1 > 2-8 > 19-01 > 1-3 > 8402 > 0.Among them,clones 2,19-01 and 0 were used as resistant,medium resistant and susceptible clones for subsequent studies.(2)AMF established a good symbiotic relationship with three different resistant clones,but its colonization rates in resistant clones 2 and 19-01 were significantly higher than that of susceptible clone 0,and the difference in arbuscular colonization rate reached a significant level(P<0.05).After the infection of root-knot nematode,the colonization rate of AMF decreased.(3)AMF could significantly promote the growth of three clones with different resistance,and improve their resistance to root-knot nematode.The growth promoting effects of AMF on infected clones were significantly higher than those on healthy clones.After inoculation,the increase rates of plant height,root and leaf fresh weight of infected clones were significantly higher than those of healthy clones(P<0.05).However,the effects of AMF on the three clones were different.AMF significantly increased the plant height and leaf number of resistant clone2,the ground diameter of medium resistant clone 19-01,and the ground diameter and root fresh weight of susceptible clone 0.In general,the effects of AMF on growth promotion and disease resistance of clones 2 were better than those of clones 19-01 and 0.(3)AMF may improve the resistance of C.bungei clones to root-knot nematode disease through the following mechanisms:a.Inhibited the infection and propagation of root-knot nematode.After AMF inoculation,the egg number of root-knot nematode in clone 2 decreased by 87.9%,and the larval number in clones 19-01 and 0 decreased by 40.6% and 41.3%,respectively.In general,the inhibition effect of AMF on the infection and propagation of root-knot nematode in resistant clone 2 with was significantly lower than those in susceptible clones 19-01 and 0.b.Promoted photosynthetic pigment content and photosynthesis,with the largest variation in clone 0.c.Increased the contents of proline,soluble protein and peroxidase activity in the roots,while decreased the content of soluble sugar.Therefore,the capacity of osmotic regulation and antioxidant in infected clones were improved.The changes of these indexes in resistant clones reached significant levels.d.Increased nutrient absorption and improved nutrient distribution.After AMF inoculation,the contents of total phosphorus content increased significantly,while the contents of total nitrogen and potassium decreased significantly.The content of nitrogen and phosphorus in roots decreased,and the content of potassium in stems and leaves decreased.e.Adjusted the content and ratio of endogenous hormones,leading to the improvement of root structure.After AMF inoculation,the contents of cytokinin in the roots of infected clones were significantly increased,while the contents of auxin and aurolactone,and the ratio of auxin and cytokinin were significantly decreased.The root structure parameters of susceptible clone 0 increased significantly.In conclusion,clone 2 had the strongest resistance to root-knot nematode,while clone 0had the weakest resistance;AMF could improve the resistance and growth of clones by various ways,and the action mechanisms on different clones were different.This study will lay a foundation for resistance breeding of C.bungei,and provide a theoretical basis for the control of root-knot nematode disease by using AMF.