Isolation And Propogation Of Pasteuria Penetrans Ppqh-3and Its Control Effect On Root-knot Nematodes

Meloidogyne spp. is one kind of plant-parasitizing nematodes which is world-wide spread, damaging, difficult to control effectively, usually resulting massive losses to agriculture and horticulture. Currently, the methods of root-knot nematodes control dependent mainly on chemicals, but a series of problems caused by chemicals are on the rise, except insecticidal effect is not completely, a series of other side-effects are obviously, so it is limited gradually. So bio-control of root-knot nematodes become the preferred measures which according with the strategy of sustainable development in modern agriculture. Pasteuria penetran is an obligate parasite of Meloidogyne spp. with great potential as a biological control agent. The primary reasons are that it has lots of advantages such as obligatory parasitism, hardiness and so on, it has widespread application prospect in the root-knot nematodes control area because of it characteristics.Relevant strains to P. penetrans were obtained and identificated by isolating samples, high infection activity strain of P.penetrans to Meloidogyne spp. was selected by adsorption experiment. The system for propogation of Pasteuria penetran endospore was established based on the hyperparasitism relationship of Pasteuria penetran-Meloidogyne spp.-plant. The P. penetrans gotten by propogation was used to determine its control effect on root-knot nematodes and explore the mechanism of the control effect The results are as follows:(1)81root materials which were infected by root-knot nematodes were sampling from13cities and countries in Hainan.7strains relevant to Pasteuria penetrans were obtained by morphological identification. The16s rDNA gene of these strains has similar indentity with Pasteuria penetransT by comparison the sequence which has published in the GenBank database. The identity comparison and phylogenetic analysis results showed that3of these strains are99%similar indentity with Pasteuria penetransT and can be identified as Pasteuria penetrans; the other4are97%similar indentity with Pasteuria penetransT and may be new strains of Pasteuria species.(2)Strain Ppqh-3was obtained which has broad spectrum parasitic ability to Meloidogyne spp. and high activity by vivo adsorption experiment, the number of its endospores attached to the second-stage juveniles of Meloidogyne spp. is the highest, reached24.8/J2.(3) The results revealed that swamp cabbage and tomato were more suitable host plants for producing P. penetrans, with a mean yield of1.79×107and2.14×108mature endospores per plant, respectively. Results indicated that swamp cabbage seedlings with4-euphylla inoculated with7500nematodes by3times would produce the yield of mature endospores up to5.90×107per plant; tomato seedlings with6-euphylla inoculated with7500nematodes by3times would produce the yield of mature endospores up to7.77×108per plant.(4) The influence of physiological and biochemical indexes about P. penetrans to M. incognita were systemic analysed.①The content of total chlorophyll, chlorophyll a and chlorophyll b in tomato leaves reduces because of the infection of M. incognita. With the increase of inoculum dose in different treatments, the content of chlorophyll rises and coincides with inoculum dose. It reduces when the infection degree is serious.②The activity variation tendency of SOD, POD, CAT in leaves is similar, it increases firstly and then drops for the treatments of low inoculum and CK with root-knot nematode only and the decreasing amplitude is lot, the activity of kinds of enzymes increases slowly for the treatments with high inoculum and keeps a higher level later. The activity of SOD, POD in root drops gradually for the treatments of low inoculum and CK which only contain root-knot nematode, but it drops rapidly for CAT. the activity of kinds of enzymes increases slowly for the treatments with high inoculum and keeps a higher level later.③The content of VC in leaves and roots rises rapidly at initial infection stage; the increment is not high in every treatment which is inoculated P. penetrans. and it is higher in low inoculum quantity than high inoculum quantity treatment. With time extension, it decrease rapidly in low inoculum quantity treatment and increases slowly in high inoculum dose treatment, keeps a higher level. The content of MDA in tomato roots increases rapidly and decreases with infection time extension. The relative electrolytic leakage of leaves of every treatment increases and it is the highest in the treatment without inoculation after inoculation. It increases slowly in treatment3and4.④The content of H2O2、O2in tomato leaves and roots increases gradually with the infection time extension, P. penetrans incoluation has inhibitional effect on its rise. The content of total polyphenol and flavonoids compounds in leaves of every treatment is higher than the treatment without Meloidogyne spp.; it is the highest in low inoculum quantity treatment and the treatment without inoculation at initial, then decreases rapidly; it increases gradually in high inoculum quantity treatment and decreases to the level of the treatment without Meloidogyne spp.. (5) The results showed that with root-knot nematode infection, the plant height, fresh weight and crown weight dropped significantly, stem diameter became thin obviously, root weight and root shoot radio increased obviously, root weight and root activity increased firstly and then dropped, the dropping speed of root activity was rapidly for the control and low inoculation quantity treatment. With the increase of inoculation quantity, the plant height is6.55%higher than the treatment with root-knot nematode only, and the stem diameter increased16.99%, crown weight increased34.26%, the root weight decreased13.98%, the disease index decreased64%and the yield per plant increased61.56%and there is no significant difference with the treatment without root-knot nematode.The plant height and weight of tomato which is continuously in the diseases area is not only far below than other treatments but also is lower than the first experimental results value. The yield decreases significantly. The control effect of P. penetrans to M. incognita is obviously in the treatment with the highest inoculum dose. The root index and the number of female per plant are50%and47%lower in the treatment with the highest inoculum dose after planting tomato60days. The infection rate were52.9%and the yield increased83.64%..