Nitrogen fixation capacity and nodule occupancy by Bradyrhizobium japonicum and B. elkanii strains

 In a previous study soybean Bradyrhizobium strains, used in Brazilian studies and inoculants over the last 30 years, and strains adapted to the Brazilian Cerrados, a region frequently submitted to environmental and nutritional stresses, were analyzed for 32 morphological and physiological parameters in vivo and in vitro. A cluster analysis allowed the subdivision of these strains into species Bradyrhizobium japonicum, Bradyrhizobium elkanii and a mixed genotype. In this study, the bacteria were analyzed for nodulation, N₂ fixation capacity, nodule occupancy and the ability to increase yield. The goal was to find a relationship between the strain groups and the symbiotic performance. Two strains of Brazilian B. japonicum showed higher rates of N₂ fixation and nodule efficiency (mg of N mg^–1 of nodules) under axenic conditions. These strains also showed greater yield increases in field experiments when compared to B. elkanii strains. However, no differences were detected between B. japonicum and B. elkanii strains when comparing nodule occupancy capacity. The adapted strains belonging to the serogroup B. elkanii SEMIA 566, most clustered in a mixed genotype, were more competitive than the parental strain, and some showed a higher capacity of N₂ fixation. Some of the adapted strains, such as S-370 and S-372, have shown similar N₂ fixation rates and nodulation competitiveness to two Brazilian strains of B. japonicum. This similarity demonstrates the possibility of enhancing N₂ fixing ability, after local adaptation, even within B. elkanii species. Differences in the DNA profiles were also detected between the parental SEMIA 566 and the adapted strains by analyses with the ERIC and REP-PCR techniques. Consequently, genetic, morphological and physiological changes can be a result of adaptation of rhizobia to the soil. This variability can be used to select strains capable of increasing the contribution of N₂ fixation to soybean nutrition. Received: 28 May 1997     

Variability of nodulation and dinitrogen fixation capacity among soybean cultivars

 In order to identify soybean cultivars with higher biological N₂ fixation capacities, North American and Brazilian soybean [Glycine max (L.) Merrill] cultivars, belonging to maturity groups VI–VIII, were evaluated for nodulation parameters and N₂ fixation rates. The symbiotic performance of 152 cultivars was evaluated in pots containing 4 kg soil with an established population of the three Bradyrhizobium elkanii strains [29w (SEMIA 5019):SEMIA 566 : SEMIA 587, 22%:36%:34%] which are established in most Brazilian soils cultivated with soybean. Differences were verified among cultivars, with some accumulating up to twice as much nodule dry weight and N in tissues as others. The variability among cultivars was also confirmed when six of them were used in a field experiment, resulting in differences in nodulation, yield and total N accumulated in grains. The analysis of nodule occupancy in 12 cultivars grown either under sterile conditions and receiving a double inoculum and N-free nutrient solution, or in pots containing soil with an established population of bradyrhizobia, showed the preference of cultivars for specific strains. Received: 7 December 1998     

花生根系腐解物对根腐镰刀菌和固氮菌的化感作用研究

[目的]研究花生根系腐解物对花生根腐镰刀菌36194和固氮菌14046的化感作用。[方法]采用培养箱培养的方法得到了不同连作年限的花生根系腐解物,灭菌后添加到花生根腐镰刀菌和固氮菌的培养基中,测定花生根系腐解物对二者生长的影响。[结果]花生根系腐解物对根腐镰刀菌菌丝的生长均有一定的化感促进作用,对固氮菌的生长有一定的化感抑制作用,且化感作用随添加浓度和连作年限的增加而增强。[结论]连作条件下花生根系残茬在土壤中的累积及其腐解物对土壤微生物的化感作用很可能是导致花生连作障碍的原因之一。     

gusA基因检测慢生花生根瘤菌竞争性的研究

采用大肠杆菌和根瘤菌接合的方法,将gusA标记基因分别导入了2株慢生型花生根瘤菌Spr3-5和Spr4-5中。结果表明,gusA基因在2株慢生型花生根瘤菌Spr3-5和Spr4-5中可以有效表达;对出发菌株和标记菌株的代时测定结果表明,二者之间没有显著差异;在标记菌株与出发菌株等量接种的前提下,比较了二者的竞争结瘤能力,结果表明,标记菌株形成的根瘤(蓝瘤)的占瘤率与出发菌株差异不显著;为了研究标记菌株与出发菌株的固氮有效性,测定了标记菌株与出发菌株各自共生植株的干重、全氮和叶绿素含量,结果表明,标记菌株与出发菌株的这3项指标之间没有显著差异。这说明利用gusA基因研究慢生根瘤菌的竞争结瘤能力是可行的。     

Response of soybean cultivars toward inoculation with three arbuscular mycorrhizal fungi and Bradyrhizobium japonicum in the alluvial soil

The aim of this study was to assess the comparative efficacy of three arbuscular mycorrhizal fungi (AMF) combined with cultivar specific Bradyrhizobium japonicum (CSBJ) in soybean under greenhouse conditions. Soybean seeds of four cultivars namely JS 335, JS 71-05, NRC 2 and NRC 7 were inoculated with three AM fungi (Glomus intraradices, Acaulospora tuberculata and Gigaspora gigantea) and CSBJ isolates, individually or in combination, and were grown in pots using autoclaved alluvial soil of a non-legume cultivated field of Ajmer (Rajasthan). Assessment of the data on nodulation, plant growth and seed yield revealed that amongst the single inoculations of three AMF, G. intraradices produced the largest increases in the parameters studied followed by A. tuberculata and G. gigantea indicating that plant acted selectively on AMF symbiosis. The dual inoculation with AMF + CSBJ further improved these parameters demonstrating synergism between the two microsymbionts. Among all the dual treatments, G. intraradices + B. japonicum brought about the largest increases in the studied characteristics particularly in seed weight per plant that increased up to 115.19%, which suggested that a strong selective synergistic relationship existed between AMF and B. japonicum. The cv. JS 335 exhibited maximum positive response towards inoculation. The variations in efficacy of different treatments with different soybean cultivars indicate the specificity of the inoculation response. These results provide a basis for selection of an appropriate combination of specific AMF and Bradyrhizobium which could further be utilized for verifying the symbiotic effectiveness and competitive ability of microsymbionts under field conditions of Ajmer region.     

The Effect of Cyst Nematode Race 3 and Bradyrhizobium japonicum Interactions on Nodulation and Other Agronomic Characters of Three Soybean Genotypes

The effect of soybean cyst nematode (SCN) race 3 and strains of Bradyrhizobium japonkum interactions on nodulation and other agronomic characters of several soybean genotypes was investigated. Nodule weight was reduced in soybean cultivar Ogden treated with SCN plus Bradyrhizobia strains USDA 110 and 6 and on soybean cultivar Essex treated with SCN plus strain USDA 6. The result was reversed on soybean cultivar Essex treated with SCN plus strain USDA 110. The nodule number also decreased on soybean cultivars Ogden and Essex treated with SCN plus strains USDA 110 and 6. The fresh root weights of soybean cultivars Ogden and Essex treated with SCN plus strain USDA 110 were heavier than the fresh root weight of Essex treated with SCN plus strain USDA 6. Lower nitrogen content of stems and leaves was noted only in cultivar Essex treated with SCN plus strains USDA 110 and 6. Bradyrhizobia strain USDA 110 was more efficient in the initiation of nodules in cultivars Ogden and Essex than strain USDA 6. The nitrogen-fixing capacity of strain USDA 6 in Ogden was better than strain USDA 110. The differences in the agronomic performances of the various soybean genotypes were due to their degree of susceptibility to SCN and Bradyrhizobia strains and also to their genetic make-up.     

Bradyrhizobium japonicum基因工程菌株HN32中外源片段的来源检验

采用Southern转移,放射性同位素分子杂交等研究手段,对本课题组构建的一株高效固氮大豆根瘤菌HN32中的外源片段的来源进行了分析。研究结果证实:该外源片段确系来源于Sinorhizobium fredii B52菌株,并且在受体Bradyrhizobium japonicum 22—10菌株中本不存在。     

诱发油菜结瘤固氮的研究

用果胶细菌处理油菜幼根,使花生根瘤菌侵入油菜根部并结瘤。试验结果表明:根瘤菌侵入油菜根细胞,形成含根瘤菌的根瘤,结瘤率为31.25％。从这些根瘤中分离出的菌株能回接到原寄主。血清学方法测定,油菜根瘤分离物与原接种的根瘤菌起凝集反应。根瘤石蜡包埋切片观察,根瘤细胞内充满了细菌。根瘤固氮酶活性为0.17—3.43nMC_2H_4/株小时,酰脲丰度为0.10％—3.58％。     

Effect of Bradyrhizobium Strain on Combining Ability for Nitrogen Fixation in Peanut (Arachis hypogaea L.)*

Improving the host genotype is one method of increasing biological nitrogen fixation by Bradyrhizobium in symbiosis with peanut (Arachis hypogaea L.), but host-strain interactions also must be considered. The objective of this study was to estimate the effect of Bradyrhizobium strains on the inheritance of traits related to nitrogen fixation. Eight parents and the F₁ generation of a diallel cross were evaluated in symbiosis with two bacterial strains for combining ability in a factorial arrangement in the greenhouse. The parents represented three taxa of cultivated peanuts. The two Bradyrhizobium strains NC 92 and NC 123 produced different general and specific combining ability, maternal (reciprocal general) effects, and reciprocal specific effects for the host genotypes. With strain NC 92, the peanut cultivars NC 7 and NC Ac 2821 had the best general combining ability for all traits evaluated; while, with strain NC 123, Robut 33-1 exhibited a high general combining ability (GCA) for nitrogenase activity and specific activity. Genotype NC Ac 2821, when inoculated with strain NC 123, had a negative GCA effect for nodule number, while with strain NC 92 this cultivar had the highest GCA effect. The importance of strain selection in evaluating lines in a breeding program is discussed.