Variation Of Competitive Nodulation Ability Of Rhizobium Meliloti From Different Ecological Region

Seven alfalfa varieties in the study were collected from three kind of different ecological region, in which 3 varieties from Xinjing, respectively Xinmu No. 1 (MI), Xinmu No.2 (MII) and Xinjiang wild variety (MX) , 3 from Chongqing, Xinong No. 1 (MC) , a variety of resistant humid (MH) and a variety of resistant acid (MA), and one local variety (MB) from Beijing. Seven rhizobium meliloti strains were separated and purified from the plant of these varieties. These wild type strains were marked as I , II, X, C, H, A and B strains. And after the antibiotic resistance were examined, four antibiotic mutant strains from corresponding ones, H+Str, A+Neo, II +Spe and X+Kan, were obtained by the way of experiment of strains labeled with 4 kinds of antibiotics. The mutant strains were employed to carry out all of experiments because they and their corresponding wild strains had the same capacity of nodulation and fixation nitrogen representing their wilding strains. Two experiments in the study were carried out. The first was the research of nodulation competition of rhizobium meliloti strains. The strains solutions, mixed equally with amount of the four mutant strains, were inoculated in seven alfalfa varieties. The plants were cultured in four different culture conditions. After 40d, five nodules from per plant were extracted to identify the kind of rhizobia and their occupancy in the same nodule, while the nodule occupancy frequency and double infection or excessive infection frequency of each strain were calculated. Another one was studied for the nitrogen fixation capability of different combination of host plant varieties × rhizobium strain. Seven alfalfa varieties were separately inoculated four rhizobium strains. The nitrogen fixation capability was measured by the dry weight of per plant after 40d. The results were as follows.Rhizobium's genotype is the key factor of competitive nodulation under experimental condition of general culture, high humid culture and acid culture, while both alfalfa's genotype and alfalfa-rhizobium reciprocity had hardly any influences on competitive nodulation ability of rhizobium. Every experimental rhizobium strains had the same trend of competitive nodulation ability in the three culture conditions. But the competitive nodulation ability of the four strains was different significantly, in which the ability of X+Kan was feebler than other three strains. Both high humid culture condition and acid culture condition didn't alter affecting factors of competitive nodulation ability, but the rhizobium's genotype and the alfalfa varieties × rhizobium strains reciprocity could influence competitive nodulation ability, while the alfalfa's genotype doesn't affect the competitive nodulation ability under drought condition. That is to say, the drought resistance could alter affecting factors of competitive nodulation ability. And the stress could enhancesignificantly the competitive nodulation ability of I +Spe strain compared with other strains. Culture conditions didn't influence competitive nodulation ability.From the first experiment, the result also showed that the alfalfa plant infected by rhizobium meliloti appeared the characteristic of double infection or more infection. The conditions of adversity could enhance double infection or more infection frequency. Alfalfa genotype and R. meliloti 's genotype were the main factor of affecting the frequency of double infection or more infection under the general culture and high humid culture condition, but it had not any relation with the alfalfa varieties × rhizobium strains reciprocity. Alfalfa genotypic was the unique factor influenced the frequency of double infection or more infection under drought stress condition. Yet under the acid condition, both Rhizobium's genotype and alfalfa varieties x rhizobium strains reciprocity didn't influence the frequency, and the culture condition might be the affected factor. Culture conditions altered double or more infection frequency according to the different varieties. Culture con...