| Root-knot nematode(RKN)is the most seriously damaging plant-parasitic nematode and is also an important pathogen in agricultural production owing to its worldwide distribution and numerous hosts.At present,with the implement of national dual reduction project,the long term use of chemical nematicide leads to drug resistance and resistance loss of resistant varieties,more and more researchers are turning their attention on biological control.The metabolites of 890 fungi strains were screened and identified to kill the second stage juveniles(J2)of Meloidogyne incognita,and carried out pot and plot experiments in greenhouse to verify control efficacy of efficient isolates.Finally,the bioactive substance of fungal fermentation was preliminary studied.The main results are as follows:1.The nematode bioactivity test of the fungi fermentation broth: In secondary toxicity screening test of J2,the eight strains of fungi were screened by corrected mortality of over 85%.The eight strains of fermentation broth not only showed high lethal effect but also significantly inhibited egg hatching.2.Identification of efficient isolates: The eight screened biocontrol strains were identified in morphological and sequences analysis of the rDNA-ITS region molecular characterization.The results showed that one strain of fungi belong to Aspergillus sp.,and the strain Snef354 was identified as A.niger.Four strains of fungi belong to Trichoderma sp.,and Snef622,Snef1883,Snef1910,and Snef2382 were identified as T.atroviridis,T.harzianum,T.citrinovirid,and T.koningiopsis,respectively.Three strains of fungi belong to Penicillium sp.,and Snef1851,Snef2367,and Snef2281 were identified as P.commune,P.chrysogenum,and P.crustosum,respectively.3.Somatotrophic and antimorbific pot and plot experiments in greenhouse of fungi fermentation broth: Pot and plot experiments in greenhouse showed that the fermentation broth of Snef1910 and Snef2367 significantly decreased gall index and J2 density in soil and significantly promoted the growth of tomato plants,respectively.Root fresh weight and root dry weight significantly decrease compared to control owing to serious RNK in greenhouse experiments.Meanwhile,pot experiment showed the decrease rate of RKN by Snef1910 and Snef2367 were as high as 61.02% and 56.67%,respectively.The biocontrol efficacy of Snef1910 and Snef2367 under greenhouse were 71.43% and 64.29% in 30 days after the treaments,respectively.In summary,the fermentation broth of T.citrinoviride Snef1910 and P.chrysogenum Snef2367 showed excellent effects of promoting growth and preventing disease,and could be considered to be two promising biocontrol agent against M.incognita with a high efficacy in the future.4.Preliminary study on the bioactive substance of fungal metabolites: The nematicidal active substances were not found in the mycelium of strain Snef1910,but in the fermentation broth of strain Snef1910.Gliotoxin has a good nematicidal activity and has a stable effect.The metabolites of T.citrinoviride have not gliotoxin,or the gliotoxin content is less,not enough to reflect in the chromatogram by the mycelium pretreatment and HPLC analysis. |
