Change of microflora in the rhizoplane and rhizosphere of different disease resistance soybean cultivarsⅡ.Change of microflora in the rhizoplane and rhizosphere of soybean under continuous cropping condition

The mechanisms of soybean continuous cropping obstacle were complicated.Previous research found many factors might cause the obstacle,such as the change of physical and chemical properties in the soil,plant allelopathy and soil-borne disease,among which soil-borne disease was the dominant reason for replanting obstacle.The microflora in the rhizoplane and rhizosphere were affected by the root activity of the soybean in the pervious year,a case in point was that the root exudates changed the soybean rhizosphere microorgnism communities,as a result of which the biological environment in rhizosphere was changed.So root exudates was a significant factor leading to soil-borne disease of the soybean in the next year.Many studies had indicated that the soybean root rot(SRR) was one of the most serious replanting diseases.Our previous experiment showed that the microflora is different in the rhizoplane and rhizosphere between resistant(Suinong 10,S10) cultivar and susceptible cultivars(Hefeng 25,H25).A more pathogenic microbe(Fusarium) was observed in the rhizoplane and rhizosphere soil of susceptible cultivar at the mature stage.The aim of the experiment was to investigate how the root of resistant cultivars and susceptible cultivars resisting SRR further influence the microflora in the rhizoplane and rhizosphere soil.Seeds were sowed in the soil and leaves and roots was removed out after the harvest of soybean planted the last year.With pot experiment,two cultivars were sowed,no planting as the control(bulk).The experiment was conducted in a greenhouse.Sampling was taken at the trifoliate stage,beginning of flowering stage,early filling stage and harvest maturity stage,respectively.The microflora in the rhizoplane,rhizosphere of the two cultivars and bulk soil were investigated during the growth stage with plate culture method. The results showed the numbers of colony forming units(CFU) of bacteria in the rhizoplane of the two cultivars decreased gradually with the growth of soybean indicating no significant difference in the rhizoplane and rhizosphere soil between the two cultivars.The numbers of CFU of bacteria in the rhizosphere of H25 decreased gradually with the growth of soybean,while that of S10 increased during the trifoliate stage to early filling stage,and then decreased dramatically at the mature stage.The root nodule weight of resistant cultivar S10 was significantly higher than that of the susceptible cultivar H25.It was observed that the number of CFU of fungi and fusarium in rhizoplane of H25 was much more than that of S10 at both trifoliate stage and mature stage.The seedling stage was the stage that soybean was easily infected of the root rot disease.In a word,the decrease in the number of rhizoplane and rhizosphere soil bacteria of both the resistant cultivar and susceptible soybean cultivars and the increase of fungi and fusarium at the mature stage indicated that soybean root exudates had certain selective acceleration or inhibition on the microflora in rhizoplane and rhizosphere soil.