Arbuscular mycorrhizal fungi (AM fungi), and rhizobia, is agronomically important symbiont, which can make easy absorption of soil P, and atmospheric N₂, respectively, in the leguminous host plants. Hirsch and Kapulink (1998) published a review suggesting the existence of the common symbiotic system to both of AM fungi and rhizobia, which they called “common pathway”, to support the symbiotic relations between these microorganisms and the host plant.
The purpose of the present paper is to elucidate the impacts of the nodulation density on infection rate and on community structure of AM fungi in the root system of the host soybean plants. In the experiment, three soybean genotypes; Enrei, a normal nodulation variety, Sakukei 4, a super-nodulation variety derived from Enrei, and En1282, non-nodulation variety also derived from Enrei, were used for the experimental materials. The plants were grown in the research field of Nihon university in Fujisawa, Japan. The amplification of a portion of the large subunit region of rDNA was conducted with the nested PCR method. The species of AM fungi colonizing in the roots were identified from the sequence homologies with those recorded in the DDBJ.
The infection rate of AM fungi of Sakukei 4 was significantly higher than the other two genotypes. Community structure of AM fungi varied with the genotype used in the present experiment. The dominant strain of AM fungi infecting in Enrei and En1282 was Glomus. And Gigaspora&Scutellospora, Glomus sp. and a undetermined clade were definitely identified as the dominant strain for Sakukei 4. It was clarified by the present study that the extent of nodulation alters the community structure of AM fungi in the root system of the soybean plant.