| Cucumber,Cucumis sativus L, is a worldwide cultivated vegetable crop. However, its production is seriously threatened by root knot nematodes. Nematicides application is the main control strategy used in practice to enhance the yield, but the high cost, toxicity as well as the environment problem caused by nematicides have urged extensive researches on alternative control methods. In the recent years, using endophytic fungi for biological control of plant parasitic namatodes have been proved to be successful. Because root knot nematodes are soil borne pathogens, seed treatment is considered to be a suitable application method for controlling the nematodes since the early plant growth stage. However, up to date little research has been conducted on this aspect. In this thesis the possibility of using endophytic fungi from cucumber seedlings as seed treatment for the biocontrol of M.incognita was studied, the main results are as followed:1.Five hundred and fourteen endophytic fungi originated from tropical, subtropical and temperate area were isolated from cucumber seedlings, they were distributed in Acremonium spp., Actinomucor spp., Aspergillus spp., Aureobasidium spp., Cercospora spp., Chaetomium spp., Cla-adosporium spp.,Colletotrichum spp.,Curvularia spp., Fusarium spp.,Humicola spp.,Paecilomyces spp.,Penicillium spp., Phyllosticta spp.,Stagonospora spp., Trichoderma spp. and other unknown genera. Among them Fusarium was most frequently isolated. Two hundred and ninety four strains which grew and sporulated well on PDA were screened for their control efficacy against M.incognita in glasshouse when applied as seed treatment. Among them 23 significantly reduced galls formed by M.incognita, the 10 fungi with the highest reduction were Fusarium strains Fu7, Fu9, Fu546, Fu234,Fu654, Phyllosticta strain Ph511, Chaetomium strain Ch1001, Trichoderma strain Tr882, Pacelomycies Pa972, Acremonium Ac985 with galls formation reduction ranged from 24.0% to 58.4% in the first time test and 15.6%-44.3%in the repeat test.In the two times test Fu234, Ch1001 and Pa972 showed the highest inhibition to galls formation.2.None of the ten fungi strains negatively affected the growth of the seedlings, indicating that they are non-pathogenic, strain Ac985 and Fu546 showed the promotion effect to seedlings growth. All of the five Fusarium strains preferred to colonize in roots with root colonization ratio ranged from 20.1% to 44.0%. Tr882, Pa972 and Ac985 colonized poorly both on roots and aboveground part of the plants. Ch1001 and Ph511 colonized well both on roots and aboveground parts, Ch1001 showed the highest colonization, which was 70.5% in roots and 73.5% in aboveground part respectively.3. The culture filtrates of Ch1001, Pa972 and Ac985 demonstrated nematicidal activity, while that of Ph511 showed nemastatic activity against J2 of M.incognita. The repellent activity to J2 was showed with the culture filtrate of Tr882, Pa972, Ac985, Ph511 and Ch1001. Eggs hatching and viability were reduced in the culture filtrate of Fu234, Ch1001, Fu654, Fu9 and Ac985. Penetration of J2 was seen by the mycelim of Fu234, Fu653, Pa972, Ph511 and Ch1001, parasitism on eggs was seen with the mycelim of Pa972, Ch1001, Fu234, Fu654 and Fu9.4. Split root system was designed to test the induced systemic resistance by the 10 fungi to M.incognita. Fu234, Fu654, Ch1001 and Ph511 challenge inoculation reduced the nematodes penetration 42.4%,35.7%,38.4% and 23.6% respectively in the responding roots;None of the strains treatment delayed the development of M.incognita in the responding roots;Ch1001, Fu234 and Pa972 treatment reduced the average eggs production per female in the responding roots, indicating that the reproduction of M.incognita was negatively affected.5. Based on the control efficacy, impact on cucumber growth, colonization ability, in vitro activity as well as the induced systemic resistance Ch1001 was considered to be a potential seed treatment agent for root knot nematodes control. According to its morphological and rDNA-ITS characteristics it was identified as C.globosum Kunze.6. A pure compound suspected as chaetomin was extracted with ethyl acetate from the culture filtrate, but the bioassay showed that it was not responsible for the nematicidal activity of Ch1001. The compound responsible was probably a volatile organic acid. Chitinase activity was detected from the culture filtrate of Ch1001, colloidal chitin increased the yield of chitinase activity, which was correlated with the inhibition effect of the culture filtrate to egg hatching.7. Root vitality was not negatively changed when the inoculum dose was less than 1×107 spores per seed, indicating that 1×107 spores per seed treatment was safe. PAL and chitinase activity of the seedlings were not influenced by Ch1001 colonisation. POD and CAT activity significantly increased when Ch1001 were treated between 1×105 to 1×107 spores per seed. 1×103 to 1×104 spores per seed treatment did not increase POD and CAT activity. Nematodes penetration was significantly reduced when the inoculum dose was between 1×104 to 1×107 spores per seed, the penetration reduction reached highest when the inoculum were 1×106 and 1×107 spores per seed, which were 45.3% and 57.0% respectively.8. Root exudates of cucumber attracted J2 and stimulated the eggs hatching of M.incognita, the attraction index and eggs hatching in the root exudates was not influenced by Ch1001 treatment; border cells from cucumber root tip had little attraction to J2 and did not stimulate egg hatching. Nematode stylet secretions accumulated in the root exudates of the plants both with and without Ch1001 treatment, but in the suspension of border cell of the root tips treated with Ch1001 the amount of secrections was seen to be decreased, indicating that Ch1001 affected nemaotodes plants interaction.
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