Studies On Polymorphism Of Fusarium Oxysporum And Its Nonpathogenic Strain As Plant Vaccin Against Fusarium Wilt

Fusarium oxysporum includes pathogenic strains and nonpathogenic strains. The pathogenic strains are important soil-bome pathogens of plant wilt. Nonpathogenic strains, which can colonize inside the plant without causing plant diseases, are promising biological control agents against Fusarium wilt. The present study aimed to analyze the genetic polymorphisms of pathogenic F.oxysporum strains by examining the characteristics of ISSR and fatty acid biomarkers. Nonpathogenic F. oxysporum strain FJAT-9290, used here as a plant vaccin strain, was studied on its biological characteristics and controled efficiency against Fusarium wilt. The results may provide molecular basis and technical methods for further research on phylogeny and differentiation of F. oxysporum pathogenic strains. Moreover, the study will lay the foundation for developing a plant vaccine to control Fusarium wilt.Forma specials of F. oxysporum from different geographical origins were analyzed using ISSR molecular marker technique. The results showed that 147 fragments were amplified with 15 screened primers, among them the number of polymorphic loci was 144 accounting for 98% in the total amplified fragments. The analysis of dendrograms and genetic similarity coefficient showed that genetic similarity coefficient of 16 F. oxysporum strains from Cucurbitaceous crops was 0.621～0.966. At the level of 0.84, the 16 strains could be obviously divided into six ISSR groups:3 groups with F. oxysporum f. sp. melons were from Minhou, Putian and Yongtai in Fujian Province, respectively; 1 group with F. oxysporum f. sp. momodicae from Minhou in Fujian Province; 2 groups with F. oxysporum f. sp.niveum from Yongtai and Fuqing in Fujian Province, respectively. Genetic similarity coefficient of the 16 F. oxysporum strains from Solanaceae was 0.521～0.940. At the level of 0.77,16 strains were divided into six ISSR groups:2 groups with F. oxysporum f. sp. lycopersici were from Fuzhou in Fujian Province and Zhejiang Province, respectively; 3 ISSR groups with F. oxysporum f. sp. capsicum from Zhangzhou, Putian and Fuqing in Fujian Province, respectively; 1 ISSR group with F. oxysporum f. sp. melongenae from Xiamen in Fujian Province.The characteristics of PLFA biomarkers in different forma specials of F. oxysporum were analyzed using Gas chromatography (GC). The results indicated that the fatty acids such as 17:1 G (w 11),15:0 ANTE ISO and 15:0 iso were occasionally presented and closely related to host species. Cluster analysis revealed that forma specials of F. oxysporum showed much closer relation to forma specials than to their geographical origins. Based on characteristics of the fatty acids, the F. oxysporum strains from Cucurbitaceous crops were clustered into 3 groups with A=13.5. Group I was composed of the strains from F. oxysporum f. sp. melonis, the strains in group II were mainly F. oxysporum f. sp. momodicae and groupIII from F. oxysporum f. sp. niveum. The F. oxysporum strains from Solanaceae were clustered into 3 groups with λ=12.54. Group i was composed of strains mainly from F. oxysporum f. sp. lycopersici, group ii were mainly F. oxysporum f. sp. melongenae and groupiii from F. oxysporum f. sp. capsicum.The plant vaccin strain (nonpathogenic F. oxysporum strain FJAT-9290) was experimented on its biological characteristics incubation time, pH, temperature, and effects of nutritional conditions on its growth with a pathogenic strain as control. The experiments showed that no significant difference in fermentation pH and the mycelium dry weight between the plant vaccine strain and the pathogenic strain during growing time. The most sporulation of strain FJAT-9290 was 1.47×106 cfu·mL-1 on the 6th day. With the extending of incubation time, the concentration of reducing sugar in FJAT-9290 fermentation reduced faster than that of FJAT-282. The pH 7-8 and temperature 25℃-30℃ were most suitable for strain growth.The growth rate of strain FJAT-9290 was sensitive to carbon source, but sporulation was less sensitive. Carbon source caused little effects on colony morphology. Sodium nitrate was conducive to strain growth.Nitrogen sources had a greater influence on colony morphology.The plant vaccine strain (nonpathogenic F. oxysporum strain FJAT-9290) was determined for its biocontrol efficiency against Fusarium wilt of watermelon and banana. In the determination, the nonpathogenic F. oxysporum was inoculated to the test host plant 7 d prior to the inoculation of pathogenic strain s originated from corresponding host plants. The results showed that the control efficiency was 62.96% for watermelon and 75.00% for banana.