Screening And Application Of Biocontrol Bacteria Against Meloidogyne Incognita And Pythium Aphanidermatum

Root-knot nematodes(Meloidogyne spp)and Pythium aphanidermatum are important soil-borne pathogens that harm crops and vegetables,and their hosts are extensive,causing serious economic losses to agricultural production.Root-knot nematodes are hidden in the soil,which is not only difficult to control,but also easy to form a compound infection with other plant diseases,thereby speeding up the incidence of disease,which leads to difficult plant disease prevention and control and exacerbates the severity of soil-borne diseases.In the fields where nematodes are seriously harmful,we collected the root soil of healthy plants and used the root soil as experimental materials to isolate and screen the biocontrol strains with antagonistic effects on southern root-knot nematodes.A total of 457 strains of bacteria were isolated by dilution separation.Through the antagonistic experiment of root-knot nematodes in vitro,16 strains with better effect of antagonizing nematodes were finally obtained.Two strains of bacteria RL3 and RL11 with higher lethal nematode resistance were selected for greenhouse pot experiment.The experimental results show that:compared with the control treatment,the RL3 and RL11 fermentation broth treatment of tomato plants can reduce the number of tomato root knots by 60.61%and 64.08%,respectively.At the same time,RL11 has a certain inhibitory effect on the reproductive capacity of southern root-knot nematodes.After RL11 treatment,the number of egg pieces in tomato roots was reduced by 49.83%compared with the control treatment.The results of field control showed that the disease index of tomato plants treated with bacteria RL11 was lower than that of clean water control,RL3 treatment,and 10%thiazoline treatment.The disease index of tomato treated with strain RL11 was the lowest,with disease index of 19.88 and relative control effect of 49.85%;RL11 had better biocontrol effect.Through the physiological and biochemical analysis of the strain RL11 and the sequencing and sequence comparison of the gyrB and 16S rRNA genes,it was identified as Pseudomonas sp.In order to preliminary study the control effect of biocontrol bacteria RL11 on southern root-knot nematodes,different concentrations of biocontrol bacteria fermentation broth was used to treat tomato young roots for nematode attraction experiment.The results showed that 100 times of biocontrol bacteria significantly inhibited nematodes in tomato Gathering of roots.Compared with the control,the tomato roots treated with fermentation broth at 12h had the best inhibition effect on nematodes,and the number of nematode infections was reduced by 68%.The young tomato roots treated with fermentation broth at other time points significantly reduced the nematode infection compared with the control number.In order to obtain biocontrol strains with high efficiency of antagonizing southern root-knot nematodes and Pythium aphanidermatum,16 isolated strains of bacteria with good effect of antagonizing root-knot nematodes in vitro and plate-antagonism experiments with various Pythium were carried out Two strains RL3 and RL11 with obvious antibacterial effect were obtained.On this basis,the antibacterial spectrum of the biocontrol strains was determined.The results showed that the strains RL3 and RL11 were resistant to pathogenic fungi and oomycetes.The bacterium also has obvious plate antagonistic effect,which initially shows that it has a certain broad spectrum.In addition,the antibacterial effect of two biocontrol bacteria against some Pythium was measured.The results showed that the strain had an efficient and broad-spectrum antibacterial effect and the concentration of the fermentation broth of the strain was proportional to the antibacterial rate.The potted greenhouse results showed that the disease index of the two biological control bacteria treatments was lower than that of the control group,especially the cucumber and tomato plants treated with the strain RL11 had the lowest disease index,the disease index was 29.20 and 28.73 respectively;the relative control effects reached 42.90%,47.41%.It shows the broad potential development and application prospect of biocontrol strain RL11.