Effects of Fusarium oxysporum on rhizosphere microbial communities of two cucumber genotypes with contrasting Fusarium wilt resistance under hydroponic condition

Two cucumber genotypes were chosen that differ in Fusarium wilt resistance and inoculated with Fusarium oxysporum (Schlechtend, Fr) f. sp. cucumerinum (Owen) Snyder & Hansen (FO) in a hydroponic nutrient solution system to determine whether differences in plant genotype affected rhizosphere microbial community and its involvement in resistance to root-borne pathogens. Response of the FO population and microbial communities were compared in the nutrient solution and on root surfaces. Results demonstrated that FO inoculation resulted in a higher FO population on root surfaces and a lower population in the nutrient solution for the susceptible genotype JinYan NO. 4 (JYan); however, an inverse pattern was observed in the resistant JinYou NO. 1 (JYou). Similarly, promotive effects on FO spore germination and germ-tube elongation were only observed in root exudates from FO-inoculated susceptible JYan. FO inoculation resulted in overall increases in cultivable fungi and oomycetes, and actinomycete populations on root surfaces of the resistant JYou compared to the JYan counterpart. PCR-DGGE analysis of 16S rDNA fragments indicated that following FO inoculation, significant changes in the bacterial structure isolated from the root surfaces of susceptible plants were observed, such as an increased diversity index, a decreased evenness index, and the occurrence of several types of bacteria that decomposed organic substances. These results suggest that a complex interaction between plant genotypes and pathogen affected the rhizosphere microbial community.