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1.
Abstract

Caldwell and Vest (1968) planted soybeans (Glycine max L. Merr.) with various genotypes at Beltsville, USA, without inoculating them with Bradyrhizobium japonicum, and showed that soybeans preferred certain serotypes of rhizobial strains for nodulation. Recently, the authors have reported that soybeans carrying nodulation-conditioning genes preferred appropriate strains showing specific behavior for nodulation (Ishizuka et al. 1991). For instance, nodulation of soybean cv. Hardee which carries the nodulation-conditioning genes, Rj 2 and Rj 3, does not occur with B. japonicum USDA122, USDA33, Is-1, etc. Nodulation of cv. Hill which carries the Rj 4 gene, does not occur with B. japonicum USDA61, Is-21, etc. while A62-2 which carries a recessive gene rj 1, does not nodulate with almost any of the strains of B. japonicum. Therefore, the B. japonicum strains can be classified into three nodulation types based on the compatibility with these Rj-cultivars, that is, type A strains which effectively nodulated both Rj 2 Rj 3-cultivars and Rj 4-ones, type B strains which did not nodulate the Rj 2 Rj 3-cultivars and type C strains which did not nodulate the Rj 4-cultivars. When the nodulation types of the isolates from nodules of field-grown soybeans were examined, it was suggested that the Rj 2 Rj 3-cultivars and Rj 4-cultivars preferred the type C and type B strains, respectively (Ishizuka et al. 1991).  相似文献   

2.
For the increase of the occupation ratio of inoculum strain in the competition with indigenous rhizobia, the relationship between Rj-genotypes of soybean and the preference of Rj-cultivars for various types of rhizobia for nodulation was investigated by using the Rj 2 Rj 4-genotype of soybean isolated from the cross between the Rj 2 Rj 3-cultivar IAC-2 and Rj 4-one Hill (Ishizuka et al. 1993: Soil Sci. Plant Nutr., 39, 79-86). Firstly, these Rj 2 Rj 4-genotypes were found to harbor the Rj 3-gene. The Rj 2Rj3Rj4-genotypes of soybean were considered to exhibit a more narrow microsymbiont range for nodulation than the Rj 2 Rj 3-and Rj4-cultivars. Therefore, rhizobia were isolated from the nodules of various Rj-genotypes of soybeans grown in soils, and the preference of the Rj 2 Rj 3 Rj 4-genotype for indigenous rhizobia was examined. The nodule occupancy of serotype 110 was significantly higher in the bacteroids of the nodules from the Rj 2 Rj 3 Rj 4-rgenotypes than in those from the other genotypes, non Rj-, Rj 2 Rj 3-, and Rj 4-cultivars. These results demonstrated that the Rj 2 Rj 3 Rj 4-genotype prefers more actively serogroup USDA110 to the others of rhizobia. Thus, Rj 2 Rj 3 Rj 4-genotype is superior to non- Rj-, Rj 2 Rj 3-, and Rj 4-genotypes for the formation of efficient nodules for nitrogen fixation.  相似文献   

3.
For examining the probability of increase in the occupation ratio of inoculated rhizobium in nodules, various Rj-soybean cultivars including the Rj 2 Rj 3 Rj 4-lines of soybean were grown in a field of the Kyushu University Farm. Bradyrhizobium japonicum USDA110 that carries uptake hydrogenase (Hup+) was used as an inoculum. The relative efficiency of nitrogen fixation generally increased by the inoculation. However, there were no significant differences in the effects among the genotypes of the host plants. The occupation ratio of serogroup USDA110 in the nodules on the taproot of the inoculated plants was in the range of 77–100%, suggesting that the B. japonicum strain USDA110 infected taproots immediately after inoculation. The occupation ratios in the nodules on the lateral roots were 53–67, 40–86, 63–83, and 62–77% in inoculated plants of the non-Rj-, Rj 2 Rj 3-, Rj 4-, and Rj 2 Rj 3 Rj 4-genotypes, respectively, and they decreased in all the genotypes with the progression of growth. At the time of the first sampling, the occupation ratios on the lateral roots of these Rj 2 Rj 3 Rj 4-genotypes showed values intermediate between those of IAC-2 (Rj 2 Rj 3) and Hill (Rj 4) , which were the parent cultivars of the Rj 2 Rj 3 Rj 4-lines, B340, B349, and C242. The reduction in the occupation ratio of the serogroup USDA110 for about 1 month after the first sampling was the lowest (0.13–0.16) in the Rj 2 Rj 3 Rj 4-genotypes, excluding B349, followed by the non-Rj- and Rj 2 Rj 3-genotypes and highest (0.52–0.69) in the Rj 4-genotypes, excluding Hill. Therefore, it was considered that the population of compatible rhizobia with host soybean plants increased in the rhizosphere with the progression of the development and growth. The results showed that with the expansion of the root area of host plants, the occupation ratio of type A rhizobia including the serogroup USDA110 was high. Therefore, the Rj 2 Rj 3 Rj 4-genotypes were superior to other Rj-genotypes in terms of the inoculation effects of nodulation type A rhizobium, B. japonicum USDA110. However, the preference of the Rj 2 Rj 3 Rj 4-genotype for serogroup USDA110 is not sufficient to rule out the competition with the other serogroups in this study. Therefore, the study should be centered on the isolation of more efficient (Hup+) and highly compatible rhizobial strains with the Rj 2 Rj 3 Rj 4- genotypes.  相似文献   

4.
Almost all of the soybean cultivars (Glycine max L. Merr.) form nodules on their roots by infection with Bradyrhizobium japonicum. However, it has been observed that the soybean cultivars harboring nodulation conditioning genes, for instance Rj 2, Rj 3, and Rj 4, do not form effective nodules with some strains of B. japonicum. Ishizuka et al. (1991b) classified the rhizobia isolated from field-grown soybeans into nodulation-types A, B, and C based on the compatibility with these Rj-soybean cultivars. Nodulation-type B is incompatible with Rj 2 Rj 3-cultivars and type C is incompatible with Rj 4-cultivars. Nodulation-type A rhizobia are compatible with both Rj 2 Rj 3 - and Rj 4-cultivars. Furthermore, the Rj-cultivars were found to prefer appropriate nodulation-type rhizobia for nodulation, that is, non-Rj-, Rj 2 Rj 3 -, and Rj 4-cultivars prefer nodulation-types A, C, and B rhizobia, respectively (Ishizuka et al. 1991a). In the present study, in order to examine the mechanisms of preference of Rj-cultivars for rhizobial strains for nodulation, root exudates from Rj-cultivars were examined for their effects on the growth rate and chemotaxis of various types of B. japonicum strains.  相似文献   

5.
The selection of effective rhizobia for higher efficiency nitrogen fixation is one of the most important steps for inoculant production. Therefore, this experiment was conducted to select the most effective type A and type B strains for specific Rj-gene harboring soybean varieties and to test the symbiotic effectiveness of selected strains on different Rj-gene harboring soybean varieties. Screening experiments using the specific soybean varieties were done with a completely randomized design and three replications in this study. Evaluation of the effective Myanmar Bradyrhizobium strains for plant growth, nodulation and N2 fixation were studied in pot experiments using sterilized vermiculite in the Phytotron (controlled-environmental condition). Then, a pot experiment was conducted using Futsukaichi soil in the screen house (natural environmental condition). The N2 fixation ability of soybean was evaluated by acetylene reduction activity (ARA) and the relative ureide index method. In the first screening experiment, type A and type B strains with higher nitrogen fixation and proper nodulation on their respective soybean cultivars were selected for the next screening. In the second screening, Bradyrhizobium elkanii AHY3-1 (type A), Bradyrhizobium japonicum SAY3-7 (type A), B. elkanii BLY3-8 (type B) and B. japonicum SAY3-10 (type B) isolates, which showed higher nitrogen fixation and nodulation in Yezin-3 (Rj4) and Yezin-6 (non-Rj), were selected for the next experiment. In the third screening experiment, SAY3-7 and BLY3-8, which had higher nitrogen fixing potential and proper nodulation, were selected as effective isolates. These two isolates were compatible with non-Rj and Rj4 soybean varieties for nodulation and nitrogen fixation. Based on the results of the screening experiment, these two strains were tested for their symbiotic efficacy in Futsukaichi soil. This study shows that inoculation treatment of SAY3-7 and BLY3-8 significantly increased plant growth, nodulation, and N2 fixation at the V6, R3.5 and R8 stages in Yezin-3 (Rj4) and/or Yezin-6 (non-Rj), and the seed yield at R8 stage, in Yezin-3 (Rj4) and Yezin-6 (non-Rj) soybean varieties compared with the control treatment. It can be concluded that SAY3-7 and BLY3-8 are suitable for inoculant production because of their higher nitrogen fixation ability, proper nodulation and better productivity of Myanmar soybean cultivars.  相似文献   

6.
Bradyrhizobium species are symbiotic partners of soybean plants. However, some Bradyrhizobium bacteria do not form functional nodules on the roots of Rj4 genotype soybean cultivars. Our objective was to identify the strains of Bradyrhizobium (i.e., type C strains) that are least competent to form nodules on the roots of this plant genotype. We checked (i) previously isolated type C strains of Myanmar Bradyrhizobium elkanii (MMY6-1, MMY6-2, and MMY6-5), (ii) previously isolated type C strains of Myanmarese Bradyrhizobium spp. (MMY3-5 and MMY3-7), and (iii) strain Is-34 of B. japonicum, for nodule formation when associated with Rj4 and other Rj genotype soybeans. Strains in groups (i), (ii), and (iii) are known to be incompatible with Rj4 soybean genotypes. MMY3-5 and MMY3-7 produced functional nodules when associated with Rj4 and other Rj genotype soybean cultivars, except Hill (Rj4) cultivar. The ratios of ineffective nodule numbers/total nodule numbers (I/T ratios) for MMY6-1, MMY6-2, MMY6-5, and Is-34 in association with Rj4 soybean cultivars were > 0.5, demonstrating incompatibility between these bacterial strains and the Rj4 genotype. Interestingly, the I/T ratios of MMY6-1 and MMY6-2 were higher than that of Is-34 in almost all Rj4 soybean cultivars. Thus, the nodule-forming abilities of the B. elkanii strains MMY6-1 and MMY6-2 were strongly suppressed in Rj4 soybean cultivars; these strains may therefore be useful to identify the Rj4 genotype in soybean cultivars.  相似文献   

7.
Abstract

Genetic diversity and distribution of indigenous soybean-nodulating bradyrhizobia in Japan were investigated based on restriction fragment length polymorphism analysis of PCR product (PCR-RFLP) analysis of the 16S?23S rDNA internal transcribed spacer (ITS) region using Bradyrhizobium USDA strains as reference strains. Soil samples were collected from five field sites in Hokkaido, Fukushima, Kyoto, Miyazaki and Okinawa in Japan. A total of 300 isolates were derived from three Rj-genotype soybean cultivars, Akishirome (non-Rj), CNS (Rj 2 Rj 3) and Fukuyutaka (Rj 4), and five field site combinations. The PCR products of the ITS region were digested with HaeIII, HhaI, MspI and XspI. Electrophoresed patterns were analyzed for phylogenetic relationship using Bradyrhizobium reference strains. Results revealed 22 RFLP patterns and 11 clusters. The RFLP patterns of the seven clusters were similar or identical to Bradyrhizobium japonicum USDA 6, 38, 110, 115, 123 and Bradyrhizobium elkanii USDA 76 and 94. Four minor clusters were independent from the clusters of the reference strains. The isolation ratio revealed the major clusters at each field site. These results suggested that major clusters of indigenous bradyrhizobia might be in the order Bj123, Bj38, Bj110, Bj6 and Be76 from the northern to southern regions in Japan.  相似文献   

8.
Summary Previous laboratory and greenhouse studies have shown that phages significantly reduce soil populations of homologous rhizobia. Reductions in nodulation and N2 fixation have also been observed. The purpose of the current study was to examine the effect of a phage specific ofBradyrhizobium japonicum USDA 117 on nodulation, nodule occupancy, N2 fixation and soybean growth and yield under field conditions. The phage was inoculated in combination withB. japonicum USDA 117 and/orB. japonicum USDA 110 (resistant strain) into a rhizobia-free sandy loam soil and planted toGlycine max (L.) Merr. Williams. When the phage was applied to soil inoculated withB. japonicum USDA 117 alone, significant reductions in nodule weight and number, shoot weight, foliar N, nitrogenase activity, and seed index were observed. When, however, the soil also contained the non-homologous strain,B. japonicum USDA 110, no significant effects on any of these parameters were found. Nodule occupancy by competing strains ofB. japonicum USDA 110 and USDA 117 was also affected by the phage. In soil which did not contain the phage, 46% and 44% of the identified nodules were occupied by USDA 110 and 117, respectively. When the phage was present in the soil, nodule occupancy byB. japonicum USDA 117 was reduced to 23%, while occupancy byB. japonicum USDA 110 was increased to 71%. These results suggest that nodulation by selected strains of rhizobia can be restricted and nodulation by more effective, inoculated strains can be increased through the introduction of a homologous phage to soils.  相似文献   

9.
 The effect of six Bradyrhizobium sp. (lupin) strains (WPBS 3201D, WPBS 3211D, USDA 3040, USDA 3041, USDA 3042 and CB 2272) and Fe supply on nodulation, N2-fixation and growth of three lupin species (Lupinus termis, L. albus and L. triticale) grown under Fe deficiency in an alkaline soil, were examined in sterilized and non-sterilized pot experiments. When inoculated with USDA 3040, 3041, 3042 and CB2272 without Fe addition, the three lupin species had a very low nodule number and mass, low shoot and root dry matter accumulation and lower N yield. However, inoculation with WPBS 3201D and 3211D without Fe treatments increased all these parameters substantially. The ability of WPBS 3201D and 3211D to form nodules on the three lupin species under conditions of Fe stress could be attributed to their ability to scavenge Fe from Fe-deficient environments through their siderophore production. Addition of Fe to the other four strains significantly increased nodulation and N2-fixation of the three lupin species, indicating that the poorer nodulation and N2-fixation of these strains in the absence of Fe, resulted from a low ability to obtain Fe from alkaline soils. Bradyrhizobium strains WPBS 3201D and 3211D were superior to the other four strains in terms of promoting greater nodulation, N2-fixation, plant growth and N accumulation of L. termis and L. albus. However, the other four strains were more efficient in symbiotic association with L. triticale. The greater variations in nodule efficiencies (specific nitrogenase activity) under different levels of Fe supply could be attributed to the quantities of bacteroid protein and leghaemoglobin in the nodules. The results suggested that Bradyrhizobium (lupin) strains differ greatly in their ability to obtain Fe from alkaline soils, and that the selection of bradyrhizobial strains which are tolerant of Fe deficient soils could complement plant breeding for the selection of legume crops for Fe-deficient soils. Received: 5 January 1998  相似文献   

10.
Abstract

The diversities of communities of soybean-nodulating indigenous bradyrhizobia in Japan were estimated using mathematical ecology methods based on the results of polymerase chain reaction–restriction fragment length polymorphism analysis of the 16S–23S rDNA internal-transcribed spacer region. Polar ordination analysis indicated a significant correlation between the compositions of bradyrhizobial communities and northern latitudes in Japan. This result suggests that the composition and the geographical distribution of indigenous soybean-nodulating bradyrhizobia might be affected by soil temperature and the associated diversity of the host plants acclimatized to a particular climate. Furthermore, for estimation of the compositional difference in bacterial communities among three different Rj-genotype soybean cultivars, an analysis of the diversity indexes was conducted and this analysis indicated differences in the composition of the communities isolated from the Rj 2 Rj 3-genotype compared with those from the non-Rj- and Rj 4-genotype cultivars. This result suggests that Rj 2 Rj 3-genotype soybeans might affect not only compatibility with particular bradyrhizobia, but also preference to bradyrhizobia for nodulation.  相似文献   

11.
Soybean (Glycine max L. Merr.) cultivars Akisirome and Peking were inoculated with Bradyrhizobium japonicum Is-21 and Rhizobium fredii USDA 194, respectively, and were grown in cylindrical pots containing sterilized vermiculite which were aerated with CO2-free air or ambient air to study the effects of CO2 deficiency in the rhizosphere on plant growth, nodulation, and nitrogen fixation. The repressive effects of CO2-free air treatment were more conspicuous in Peking than Akisirome, and nodule number, nodule mass, amount of biologically fixed N and plant growth of Peking were reduced remarkably by the CO2-free air treatment.

Acetylene reduction activity (ARA) of Peking inoculated with USDA 194 and Akisirome inoculated Is-21 was assayed in the absence and presence of CO2, ARA of Akisirome was not affected by the absence of CO2, while that of Peking decreased drastically.

Based on these results, it was concluded that nitrogen fixation by Akisirome inoculated with B. japonicum Is-21 was not appreciably influenced by CO2 deficiency in the rhizosphere, while that of Peking inoculated with R. fredii USDA 194 was severely repressed, and the decrease was estimated to be due to both the reduction of the nodule mass and specific nitrogen-fixing activity.  相似文献   

12.
Summary Experiments to assess the ability of free-living cells of six strains of soybean rhizobia (Bradyrhizobium japonicum USDA 76, 94, 110, 122, 123, and 135) to denitrify nitrate in five soils showed that although some strains ofB. japonicum have the capacity to rapidly denitrify nitrate in soils under anaerobic conditions, it is unlikely that the numbers of soybean rhizobia commonly found under field conditions are sufficient to significantly influence either the extent or the products of denitrification in soil. It is our general conclusion that the advantages, if any, that the ability to denitrify conveys to rhizobia or to the rhizobia-legume symbiosis are not offset by increased losses of plant-available N when denitrifying strains of rhizobia are present as free-living cells in soil.  相似文献   

13.
Summary Differences between isogenic uptake hydrogenase (HUP) mutants of Bradyrhizobium japonicum in terms of nodule efficiency, N2 fixation and N incorporation into various plant parts were studied in a monoxenic greenhouse experiment in order to confirm previous results with soybeans and beans inoculated with various HUP+ and HUP– strains. The HUP+ revertant PJ17-1 of a HUP– mutant (PJ17) of strain USDA DES 122 showed a completely restored relative efficiency (100% versus 78±2% for the HUP– mutant), higher nodule efficiency (N2 fixed per g nodules), higher ureide-N transport rates, higher N contents in pods and higher N harvest indices. All these observations confirm previous experiments with HUP+ and HUP– strains.  相似文献   

14.
The genetic relationships among six strains of rhizobia, including three strains of Rhizobium fredii and three strains of Bradyrhizobium japonicum, was determined using random amplified polymorphic DNA (RAPD) technique. In this study, 46 arbitrary 10mer primers were employed for RAPD, generating a total of 251 informative fragments. A dendrogram of phylogenetic relationships among the six strains was constructed. The results indicated that geographical distribution may affect phylogeny, as there were closer relationships among the four Taiwanese strains, SB138, SB562, SB368 and SB651, than between these strains and USDA192, which originated from mainland China. The strain USDA110, obtained from the United States, was used in the parsimony analysis. The greatest similarity (55.6%), existed between two strains of B. japonicum, SB562 and SB138, which both, and the lowest R. fredii (44.4%) between two strains of R. fredii, SB368 and USDA192. We also found a RAPD marker specific to the four Taiwanese SB strains used in the study. The RAPD technique is a potential tool for the identification of the genetics and systematics of different populations. Received: 23 January 1997  相似文献   

15.
The use of phosphate-solubilising bacteria as inoculants increases plant phosphorus (P) uptake and thus crop yield. Strains from the genus Mesorhizobium are among the most powerful phosphate solubilizing microorganisms. In order to study efficiency in P uptake and N2 fixation in chickpea (Cicer aritenium), forty-two rhizobia strains natively from Tunisian soils were studied in symbiosis with the chickpea variety “Béja1” which is frequently cultivated in Tunisia. Plants were inoculated separately with these strains under controlled conditions in perlite under two sources of P i.e. soluble (KH2PO4) and insoluble P (Ca2HPO4). At flowering stage, growth, nodulation, P uptake and N2 fixation were assessed in all symbiotic combinations. The results showed that the S27 strain efficiently mobilized P into plants, observed as a significant increase of plant P content when insoluble P (Ca2HPO4) was supplied to the soil. This was associated with a significant increase in plant biomass, nodule number and N content under insoluble P conditions. Additionally, inoculation with the Mesorhizobium strain S27 significantly increased the root acid phosphatase activity under insoluble P. This study also shows significant correlations found between plant P content and acid phosphatase activity under low P conditions which may highlight the contribution of acid phosphatases in increasing P use efficiency. A field experiment also showed that most of the chickpea analyzed parameters were improved when plants inoculated with two selected rhizobia strains (S26 and S27) and supplied with P2O5. Overall, these findings postulate that rhizobial inoculation should not only be based on the effectiveness of strains regarding N fixation, but also to other traits such as P solubilisation potential.  相似文献   

16.
Soybean plant is characterized by a systemic autoregulatory control system of nodulation (autoregulation) by initial infection with rhizobia, and plants commonly display a systemic acquired resistance (SAR) to pathogenic microbe infection related to salicylic acid (SA) signal transmission. We investigated the effect of exogenous SA supply on soybean nodulation to determine whether SA affects the autoregulation of nodulation. Seedlings of the hypernodulating mutants NOD1-3, NOD2-4 and their parent cv. Williams were treated or not treated (control) with a 100 μmS-SA solution at 5 d before the inoculation of Bradyrhizobium japonicum strain USDA110. The nodule dry weight and the number of nodules of the wild type soybean Williams exhibiting autoregulation drastically decreased by the addition of 100 μm SA. The decrease in the nodule number was not caused by the reduction of the rhizobium number in the medium. Salicylic acid inhibited only early nodule formation and did not affect the growth of formed nodules. The inhibitory effect of SA on the nodulation of NOD1-3 and NOD2-4 was significantly less pronounced than that in Williams. These results indicate that SA is directly involved in signal transmission in the autoregulation, and that SA or the SAR induced by SA stimulates the autoregulation of nodulation in soybean.  相似文献   

17.
Summary Bacteria isolated from the root zones of field-grown soybean plants [Glycine max (L.) Merr.] were examined in a series of glasshouse experiments for an ability to affect nodulation competition among three strains of Bradyrhizobium japonicum (USDA 31, USDA 110, and USDA 123). Inocula applied at planting contained competing strains of B. japonicum with or without one of eleven isolates of rhizosphere bacteria. Tap-root nodules were harvested 28 days after planting, and nodule occupancies were determined for the bradyrhizobia strains originally applied. Under conditions of low iron availability, five isolates (four Pseudomonas spp. plus one Serratia sp.) caused significant changes in nodule occupancy relative to the corresponding control which was not inoculated with rhizosphere bacteria. During subsequent glasshouse experiments designed to verify and further characterize these effects, three fluorescent Pseudomonas spp. consistently altered nodulation competition among certain combinations of bradyrhizobia strains when the rooting medium did not contain added iron. This alteration typically reflected enhanced nodulation by USDA 110. Two of these isolates produced similar, although less pronounced, effects when ferric hydroxide was added to the rooting medium. The results suggest that certain rhizosphere bacteria, particularly fluorescent Pseudomonas spp., can affect nodulation competition among strains of R. japonicum. An additional implication is that iron availability may be an important factor modifying interactions involving the soybean plant, B. japonicum, and associated microorganisms in the host rhizosphere.Paper No. 10648 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601, USA  相似文献   

18.
This study tested the competitive ability of three locally isolated Cyclopia rhizobia and strain PPRICI3, the strain currently recommended for the cultivation of Cyclopia, a tea-producing legume. Under sterile glasshouse conditions, the three locally isolated strains were equally competitive with strain PPRICI3. In field soils, the inoculant strains were largely outcompeted by native rhizobia present in the soil, although nodule occupancy was higher in nodules growing close to the root crown (the original inoculation area). In glasshouse experiments using field soil, the test strains again performed poorly, gaining less than 6% nodule occupancy in the one soil type. The presence of Cyclopia-compatible rhizobia in field soils, together with the poor competitive ability of inoculant strains, resulted in inoculation having no effect on Cyclopia yield, nodule number or nodule mass. The native rhizobial population did not only effectively nodulate uninoculated control plants, they also out-competed introduced strains for nodule occupancy in inoculated plants. Nonetheless, the Cyclopia produced high crop yields, possibly due to an adequate supply of soil N.  相似文献   

19.
We examined the competitiveness of five effective Rhizobium leguminosarum biovar phaseoli strains in the nodulation of kidney beans (Phaseolus vulgaris L.), either alone or in pairwise combination, against the indigenous strains. The results showed that the introduced Rhizobium sp. strains (B2, B17, B36, T2, or CIAT 652) occupying 64–79% of the total nodules (as single inocula) were more competitive in nodulation than the native rhizobia. However, the competitiveness of the individual Rhizobium sp. strain either increased or decreased when used in a pairwise combination of double-strain inocula. For example, strain B17, although quite competitive against the indigenous population (68% nodule occupancy), became poorly competitive in the presence of strain B2 (reduced from 68 to 2.5%). A similar reduction in nodule occupancy by strain B17 was observed in the presence of B36 or CIAT 652, indicating that two competitive strains may not always be compatible. These results suggest that it is important to co-select competitive as well as compatible rhizobia for multistrain inoculant formulation.  相似文献   

20.
The inability to utilize a fungal siderophore as source of iron nutrition by most of the rhizobial cultures isolated from pigeon pea, could be considered a negative fitness factor since hydroxamate siderophores are found in significant amounts in natural soils. Thus these cultures were engineered to use ferrichrome a prototype of hydroxamate type siderophore. Pigeon pea Rhizobium spp. IC3123 and ST1 harboring Escherichia coli fhuA gene, responsible for uptake of Fe3+-ferrichrome, were obtained by transformation with pGR1, a broad host range plasmid carrying the fhuA gene under the control of the lac promoter of E. coli. Expression of fhuA in transformed rhizobial strains IC3123::pGR1 and ST1::pGR1 was confirmed by the ability of the plasmid-bearing strains to utilize iron bound to ferrichrome. Inoculation of pigeon pea plants with fhuA expressing rhizobial strains in pot experiments showed a significant increase in plant growth as well as nodule density as compared to those inoculated with the parent as well as the empty vector-bearing strain. Inoculation of pigeon pea seedlings with IC3123::pGR1 and ST1::pGR1 led to marked increase in shoot fresh weight, nodule number per plant, chlorophyll content of leaves and effective nodule symbiosis when compared with plants inoculated with the parent strains IC3123 and ST1. The positive effect of IC3123::pGR1 and ST1::pGR1 treatment on plant growth was more significantly observed when ferrichrome producing Ustilago maydis, known to secrete ferrichrome, was co-inoculated along with the transformed rhizobia. The presence of fhuA gene in rhizobial strains also led to an increased survival and root colonization.  相似文献   

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