| The thesis was about the changes of fungi communities at different growth stages of potato in rhizosphere soil under four various rotation systems in arid-irrigated area of Gansu province by plate counting. The results showed as following:the total amount of colony forming units of fungi in rhizosphere soil of rotation cropping was different from continuous cropping (1-3 years), which indecating that the total amount of colony forming units of rhizosphere soil fungi was affected by continuous cropping; under four various rotation systems, the total amount of colony forming units of fungi in rhizosphere soil at before seeding stage was highest in the different growth stages; the total amount of colony forming units of fungi in rhizosphere soil under rotation cropping was more significant difference than that of the continuous cropping third year at squaring stage; though the total amount of colony forming units of fungi in rhizosphere soil was changed, it was no significant difference at other growth stages in different stubbles. Fungi genera in rhizosphere soil were not consistent completely at every growth stages in different stubbles and 50 fungi genera were abtained in this research. Characters of these 50 genera were illustrated in this thesis. Among these fungi genera the main isolated genera were Acremonium, Aspergillus, Penicillium, Phthium, Stysanus, Trichoderma, Verticillum, Xemopus and the less isolated genera were Fusarium, Geotrichum, Gliocladium, Phtophthora, Rhizopus. The variation of different dominating fungi genera were different, some fungi genera decreased and some others increased because of continuous cropping. The Richness index and the Even degree index of rotation cropping were highest at maturity stage in different stubbles, and the Richness index of continuous cropping 1-3 years were higher than that of rotation cropping, however, the Even degree index was no significant difference between them at before seeding stage. But for the squaring stage and harvest stage, the Richness index and the Even degree index were no significant difference under four various rotation systems. The changes of Fusarium in rhizosphere soil of potato growth stages were studied in detail. Fusarium species were isalated by the ways of Root Debris Separation on each plate and identified based on the shape of macroconidea, presence or absence of microconidia, shape and mode of formation of macroconidia, nature of the conidiogenous cell bearing microconidia and presence or absence of chlamydospores, colony diameters on PDA after incubation for 3 days at 25℃and 30℃, colony morphology on PDA after incubation for 10-14 days at alternating day and night temperatures of 25℃day/20℃night and a 12 hour photoperiod. The results showed:compared with the rotation cropping, the amount of Fusarium was all increased at the growth stages of potato with increasing year of cropping within 3 years, such as before seeding, squaring stage, maturity stage, harvest stage.13 Fusarium species were obtained in this research, they are F. acuminatum, F. avenaceum, F. camptoceras, F. compactum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum, F. oxyspoum, F. proliferatum, F. semitectum, F. solani, Characters of these 12 species were illustrated in this thesis, among these Fusarium species the main isolated species were F. culmorum, F. equiseti, F. oxyspoum and F. solani. On the large, with the years of potato continuous cropping lasted, the changes of these main species were different:the amount of F. culmorum was decreased and the amount of F. equesiti changed warmly, on the contrary, the amounts of F. solani and F. oxysorum showed an increased trend.
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