Rhizobial Populations Research Articles

Genomic diversity of chickpea-nodulating rhizobia in Ningxia (north central China) and gene flow within symbiotic Mesorhizobium muleiense populations

Diversity and taxonomic affiliation of chickpea rhizobia were investigated from Ningxia in north central China and their genomic relationships were compared with those from northwestern adjacent regions (Gansu and Xinjiang). Rhizobia were isolated from root-nodules after trapping by chickpea grown in soils from a single site of Ningxia and typed by IGS PCR-RFLP. Representative strains were phylogenetically analyzed on the basis of the 16S rRNA, housekeeping (atpD, recA and glnII) and symbiosis (nodC and nifH) genes. Genetic differentiation and gene flow were estimated among the chickpea microsymbionts from Ningxia, Gansu and Xinjiang. Fifty chickpea rhizobial isolates were obtained and identified as Mesorhizobium muleiense. Their symbiosis genes nodC and nifH were highly similar (98.4 to 100%) to those of other chickpea microsymbionts, except for one representative strain (NG24) that showed low nifH similarities with all the defined Mesorhizobium species. The rhizobial population from Ningxia was genetically similar to that from Gansu, but different from that in Xinjiang as shown by high chromosomal gene flow/low differentiation with the Gansu population but the reverse with the Xinjiang population. This reveals a biogeographic pattern with two main populations in M. muleiense, the Xinjiang population being chromosomally differentiated from Ningxia-Gansu one. M. muleiense was found as the sole main chickpea-nodulating rhizobial symbiont of Ningxia and it was also found in Gansu sharing alkaline-saline soils with Ningxia. Introduction of chickpea in recently cultivated areas in China seems to select from alkaline-saline soils of M. muleiense that acquired symbiotic genes from symbiovar ciceri.

Impact of palm oil mill effluent (POME) on the populations of rhizobium and meloidogyne species in Awka, Nigeria

The impact of palm oil mill effluent (POME) on the populations of Rhizobium and Meloidogyne species was tested at the Teaching and Research Farm of Nnamdi Azikiwe University Awka, Nigeria. Three cowpea cultivars ,Dan Kano, Borno local and Sokoto local were used as target crops on plots that received 0 l/ha(control),4000l/ha,6000l/ha and 8000l/ha levels of POME applications. The treatments combinations were randomized within each block and replicated three times. Generally, increasing level of POME application increased number of functional root nodules in all the cultivars, but decreased length of roots and number of non- functional nodules. Nematode populations drastically decreased with increase in POME quantities. Both Rhizobium and Meloidogyne species compete for establishment sites on cowpea roots and high POME rates decreased Nematode population which is why all the three cowpea cultivars had their highest yields at 8000l/ha POME application rate. So POME, an organic waste from oil palm processing can be used at up to 8000l/ha to effectively control obnoxious root knot nematode and enrich soil for crop cultivation especially Sokoto local cowpea cultivar.
 Keywords: POME (palm oil mill effluent), Rhizobium, Meloidogyne liters/hectare, cowpea cultivars

Identification of stress tolerant rhizobial strains inhabiting <em>Gliricidia sepium</em> in Polonnaruwa district, Sri Lanka

Rhizobia are well-reputed biological nitrogen fixing organisms due to their proficiency in symbiotic root nodule formation with leguminous plants. Gliricidia sepium is a widely distributed legume which hosts a wide range of rhizobia. Few studies have been carried out to identify the stress tolerant rhizobial populations inhabiting G. sepium in Sri Lanka. This study was focused on the characterization and identification of stress tolerant rhizobial strains residing in the root nodules of G. sepium growing in seven selected locations of Polonnaruwa district, Sri Lanka. Isolated rhizobial strains were separately subjected to stress conditions (pH, temperature, salinity, and drought) and to a combination of given stress conditions. Most of the strains were tolerant to 25 - 45oC temperature range, extreme drought conditions and 1.5 % and 2.0 % salinity levels. However all the strains were adversely affected by acidic pH. Among the fifteen strains that were selected from the statistical analysis, fourteen displayed higher survival capacity when the combinations of physiological conditions were applied. There was great genetic diversity within these isolates and they belonged to 10 clusters. Cross inoculation of these isolated stress tolerant strains into crop legumes can be used as an ideal alternative for chemical nitrogen fertilizers.

The Non-Legume Parasponia andersonii Mediates the Fitness of Nitrogen-Fixing Rhizobial Symbionts Under High Nitrogen Conditions.

Organisms rely on symbiotic associations for metabolism, protection, and energy. However, these intimate partnerships can be vulnerable to exploitation. What prevents microbial mutualists from parasitizing their hosts? In legumes, there is evidence that hosts have evolved sophisticated mechanisms to manage their symbiotic rhizobia, but the generality and evolutionary origins of these control mechanisms are under debate. Here, we focused on the symbiosis between Parasponia hosts and N2-fixing rhizobium bacteria. Parasponia is the only non-legume lineage to have evolved a rhizobial symbiosis and thus provides an evolutionary replicate to test how rhizobial exploitation is controlled. A key question is whether Parasponia hosts can prevent colonization of rhizobia under high nitrogen conditions, when the contribution of the symbiont becomes nonessential. We grew Parasponia andersonii inoculated with Bradyrhizobium elkanii under four ammonium nitrate concentrations in a controlled growth chamber. We measured shoot and root dry weight, nodule number, nodule fresh weight, nodule volume. To quantify viable rhizobial populations in planta, we crushed nodules and determined colony forming units (CFU), as a rhizobia fitness proxy. We show that, like legumes and actinorhizal plants, P. andersonii is able to control nodule symbiosis in response to exogenous nitrogen. While the relative host growth benefits of inoculation decreased with nitrogen fertilization, our highest ammonium nitrate concentration (3.75 mM) was sufficient to prevent nodule formation on inoculated roots. Rhizobial populations were highest in nitrogen free medium. While we do not yet know the mechanism, our results suggest that control mechanisms over rhizobia are not exclusive to the legume clade.

Medicago-Sinorhizobium-Ralstonia Co-infection Reveals Legume Nodules as Pathogen Confined Infection Sites Developing Weak Defenses.

Legumes have the capacity to develop root nodules hosting nitrogen-fixing bacteria, called rhizobia. For the plant, the benefit of the symbiosis is important in nitrogen-deprived conditions, but it requires hosting and feeding massive numbers of rhizobia. Recent studies suggest that innate immunity is reduced or suppressed within nodules [1-10]; this likely maintains viable rhizobial populations. To evaluate the potential consequences and risks associated with an altered immuni`ty in the symbiotic organ, we developed a tripartite system with the model legume Medicago truncatula [11, 12], its nodulating symbiont of the genus Sinorhizobium (syn. Ensifer) [13, 14], and the pathogenic soil-borne bacterium Ralstonia solanacearum [15-18]. We show that nodules are frequent infection sites where pathogen multiplication is comparable to that in the root tips and independent of nodule ability to fix nitrogen. Transcriptomic analyses indicate that, despite the presence of the hosted rhizobia, nodules are able to develop weak defense reactions against pathogenic R.solanacearum. Nodule defense response displays specificity compared to that activated in roots. In agreement with nodule innate immunity, optimal R.solanacearum growth requires pathogen virulence factors. Finally, our data indicate that the high susceptibility of nodules is counterbalanced by the existence of a diffusion barrier preventing pathogen spreading from nodules to the rest of the plant.

Evolutionary Geography of Root Nodule Bacteria: Speciation Directed by the Host Plants

Compared to free-living relatives, bacterial symbionts of plants exhibit higher rates of population diversification (microevolution), as well as of speciation and formation of super-species taxa (macroevolution). Analysis of rhizobia, the N2-fixing symbionts of leguminous plants, suggests that both evolutionary modes are determined by the hosts, which have mutagenic and recombinogenic effects on their microsymbionts, apart from activating the selective processes that determine the fate of newly emerged genotypes in their populations. Migration induced by leguminous plants plays a key role in the evolution of rhizobia, including: (1) joint movement of the symbionts and their hosts into new ecological zones and (2) local circulation of the symbionts in plant‒soil systems. In the first case, allopatric speciation occurs in rhizobia due to transfer of the symbiotically specialized (sym) genes from the introduced strains into local bacteria, which are transformed into novel symbionts. In the second case, a sympatric divergence of Rhizobium populations occurs, resulting in formation of intraspecies taxa (biovars and symbiovars) contrasting in their host ranges. In the evolutionarily advanced rhizobia, Rhizobium leguminosarum and Neorhizobium galegae interacting with galegoid legumes (tribes Fabeae, Galegae, and Trifolieae), these processes are associated with diversification of the sym genes representing the accessory genome parts due to the interaction between bacteria and the hosts differing in their symbiotic affinities. In parallel, formation of new cryptic (genomic) species was revealed in local rhizobia populations, which is associated with divergence of the core genome parts. It may be caused either by genetic drift or by selection for resistance against local edaphic stresses, which in combination with disruptive selection can sufficiently enhance the rhizobia diversity and change the structures of their pangenomes.

Next generation bioformulation prepared by amalgamating Bradyrhizobium, cell free culture supernatant, and exopolysaccharides enhances the indigenous rhizospheric rhizobial population, nodulation, and productivity of pigeon pea

Addition of living cells for plant growth promotion has several constraints including erratic and inconsistent field performance, poor shelf life, and reduced population due to tough competition with resident microbes. Due to the focus on employing cell-based formulation, bacterial cell free culture supernatant (CFCS), and metabolites produced by them, have been largely ignored. Hence, present study aimed to enhance productivity and nodulation of Cajanus cajan (pigeon pea) by using diverse formulations developed from Bradyrhizobium strain IC-4059 (cell based formulation), its CFCS (supernatant based), and exopolysaccharides (EPS) (metabolite based), blended formulation (cells with CFCS; cells with metabolite; metabolite with CFCS), and combinational formulation (IC-4059+EPS + CFCS). Efficacy of developed formulations was monitored initially in tube assay, followed by field experiment with Pusa 991 pigeon pea cultivar in randomized block design. Growth promoting metabolites present in CFCS and EPS were analyzed by metabolomic approach using UPLC–MS and HPLC, respectively. In both tube assay and field experiment, seeds receiving treatment with combination of IC-4059 cells plus CFCS and EPS performed best, followed by blend IC-4059 CFCS + EPS, and IC-4059 cells + EPS, in terms of plant parameters. During field experiment seeds treated with combination showed significant enhancement in shoot length, root length, dry weight, protein content, and nodule number by 1.2, 1.3, 1.2, 1.1 and 2.0-fold, respectively, in comparison with rhizobia-based formulation. The prominent compounds identified by UPLC–MS were phosphatidylserine, phosphatidylcholine, FMC-5, pantoic acid, ascorbic acid, benzoic acid, 4-pentyl-4-formylphenyl ester, benzimidazole, and phosphatidylethanolamine. The study disseminates the use of combinational formulation developed from Bradyrhizobium sp. IC-4059, its CFCS, and its EPS for augmenting nodulation and growth of pigeon pea crop in field in comparison with application of rhizobial cell alone, as next generation of bioformulations.

Increasing biological nitrogen fixation by white clover-rhizobia symbiosis

Biological nitrogen fixation (BNF) is the process of converting atmospheric nitrogen to ammonia through legume–rhizobia symbiosis. The nitrogen fixed by rhizobia in root nodules is available for plant use. This process can be harnessed to improve N fertility on farm. Field surveys across New Zealand (NZ), within a farm and within paddocks, have revealed large spatial variability of rhizobial population size and symbiotic effectiveness with white clover. These results indicate that naturalised rhizobia may not be supporting optimal BNF. Over 500 strains of clover-nodulating rhizobia were isolated from NZ pasture soils, with more than 90 demonstrating greater N-fixation capacity with white clover than the commercial inoculant strain TA1. Seven NZ isolates were tested for nodule occupancy and all seven had significantly higher occupancy rates than TA1 in an in vitro assay, indicating increased competitiveness of those strains. In addition, novel seed-coating technology improved the survival of TA1 and isolate S10N9 from 1 month to more than 4 months compared with a standard coating formulation. There is potential to increase the symbiotic capacity of white clover in pastures through use of more effective and competitive rhizobial strains, along with their improved survival on seed provided by a new coating technology.

CHARACTERISTICS OF THE PROPERTIES OF CHICKPEA NODULE BACTERIA EXTENDED IN THE FOREST-STEPPE AND STEPPE ZONES UKRAINE

Objective. To compare morphological, cultural, physiological, biochemical, and symbiotic properties of strains of nodule chickpea bacteria isolated from different soil and climatic zones of Ukraine. Methods. Microbiological, microscopic, gas-chromatographic, statistical. Results. From the nodules of chickpea plant of varieties Skarb, Admiral, Odissei, Budzhak, Triumf and Pamiat, grown in the steppe zone of Ukraine (Region of Odessa), where an active rhizobia population was formed due to the continuous cultivation of this crop, 58 isolates of bacteria were isolated; 11 iso-lates were isolated from the nodules of plants of Triumf and Pamiat varieties selected in the forest-steppe zone (Region of Lviv), in the fields where chickpea was grown for the first time. It has been established that the strains of Mesorhizobium sp. 1 and Mesorhizobium sp. 2, which were isolated from the nodules of chickpea plants grown in the fields with an active rhizobia population of this culture, form colonies of 2–4 mm in size at day 3–4 on the mannitol yeast agar and, according to cultural and morphological properties correspond to the characteristics of the species Mesorhizo-bium ciceri. Their use for pre-sowing chickpea inoculation increases the mass of nodules (2– 3 times) and nitrogenase activity (1.4–2 times) compared with the results obtained using the pro-duction strain of Mesorhizobium ciceri H-12. Inoculation with Mesorhizobium sp. 11, isolated from the forest-steppe zone, which on a mannitol yeast agar forms a colony of 1–2 mm in size at day 5–6, contributed to a significant increase in the number of nodules on the roots of plants (by 40.5 %), their mass (by 31 %), but the increase in nitrogenase activity was negligible. Conclusion. Strains of Mesorhizobium sp. isolated from chickpea nodules grown in different soil-climatic zones of Ukraine, have similar cell morphology, but differ in growth rate, cultural, physiological, biochemi-cal, and symbiotic properties.

Determination of Rhizobial Population of Soils from North Western Nigeria for Biological Nitrogen Fixation on Soybeans

Determination of Rhizobial Population of Soils from North Western Nigeria for Biological Nitrogen Fixation on Soybeans

Rhizobia population was favoured during in situ phytoremediation of vanadium-titanium magnetite mine tailings dam using Pongamia pinnata

Mine tailings contain toxic metals and can lead to serious pollution of soil environment. Phytoremediation using legumes has been regarded as an eco-friendly way for the rehabilitation of tailings-laden lands but little is known about the changes of microbial structure during the process. In the present study, we monitored the dynamic change of microbiota in the rhizosphere of Pongamia pinnata during a 2-year on-site remediation of vanadium-titanium magnetite tailings. After remediation, overall soil health conditions were significantly improved as increased available N and P contents and enzyme activities were discovered. There was also an increase of microbial carbon and nitrogen contents. The Illumina sequencing technique revealed that the abundance of taxa under Proteobacteria was increased and rhizobia-related OTUs were preferentially enriched. A significant difference was discovered for sample groups before and after remediation. Rhizobium and Nordella were identified as the keystone taxa at genus rank. The functional prediction indicated that nitrogen fixation was enhanced, corresponding well with qPCR results which showed a significant increase of nifH gene copy numbers by the 2nd year. Our findings for the first time elucidated that legume phytoremediation can effectively cause microbial communities to shift in favour of rhizobia in heavy metal contaminated soil.

Peran Eksopolisakarida Azotobacter dan Bahan Organik untuk Meningkatkan Nodulasi dan Biomassa Kedelai pada Dua Ordo Tanah

Exopolysaccharide (EPS) produced by nitrogen-fixing bacteria Azotobacter protect nitrogenase from oxygen. In legume,EPS plays a role in the immobilization of rhizobia to the roots. The objective of this experiment was to study the effect of EPSAzotobacter and organic matter on increasing number of nodules and biomass of soybeans grown in Inceptisols and Ultisols;as well as nitrogen-fixing bacteria population in soybean rhizosphere. The experiment was set up in a completely randomizedblock design with five replications to test combined treatments of two doses of crude EPS and organic matter. Nodule number,shoot dry weight and nitrogen uptake, as well as Azotobacter and Rhizobium population in soybean grown in Inceptisolsfollowing crude EPS and compost application, were higher than those grown in Ultisols. The application of EPS and compostIn Ultisols did not affect the number of nodule and other traits, but in Inceptisols, adding 6.25 g of compost and 20 mL of EPSto each plant increased the number of nodules and shoot weight at 42 days after planting. However, the highest N uptake wasdemonstrated by soybean received 10 mL and 20 mL EPS along with 12.5 g compost.

Influence of fly ash seed pelleting on root rhizosphere populations of black gram and green gram

Investigations were carried out to study the influence of flyash seed pelleting on microbial populations of bacteria, fungi, actinomycetes, and rhizobium in black gram and green gram. The experimental results revealed that seed pelleting with fly ash seed pelleting @ 250 g with rice gruel as adhesive increased rhizobium population in black gram and fungi and actinomyctes population in green gram by 10 to 15 %. Increased microbial activity will enrich soil microflora and in turn will be helpful in increasing the crop yield.

Legacy of prior host and soil selection on rhizobial fitness in planta.

Measuring selection acting on microbial populations in natural or even seminatural environments is challenging because many microbial populations experience variable selection. The majority of rhizobial bacteria are found in the soil. However, they also live symbiotically inside nodules of legume hosts and each nodule can release thousands of daughter cells back into the soil. We tested how past selection (i.e., legacies) by two plant genotypes and by the soil alone affected selection and genetic diversity within a population of 101 strains of Ensifer meliloti. We also identified allelic variants most strongly associated with soil- and host-dependent fitness. In addition to imposing direct selection on rhizobia populations, soil and host environments had lasting effects across host generations. Host presence and genotype during the legacy period explained 22% and 12% of the variance in the strain composition of nodule communities in the second cohort, respectively. Although strains with high host fitness in the legacy cohort tended to be enriched in the second cohort, the diversity of the strain community was greater when the second cohort was preceded by host rather than soil legacies. Our results indicate the potential importance of soil selection driving the evolution of these plant-associated microbes.

Diversity and nodulation effectiveness of rhizobia and mycorrhizal presence in climbing dry beans grown in Prespa lakes plain, Greece.

The Prespa lakes plain is an isolated area where about 1000ha are seeded to Phaseolus vulgaris L. and Phaseolus coccineus L. Nodulation, arbuscular mycorrhizal fungal (AMF) presence and the genetic diversity of rhizobia were evaluated by 16S-ITS-23S-RFLP patterns and by sequencing. The bean rhizobial population in the region was diverse, despite its geographic isolation. No biogeographic relationships were detected, apart from a Rhizobium tropici-related strain that originated from an acidic soil. No clear pattern was detected in clustering with bean species and all isolates formed nodules with both bean species. Most strains were related to Rhizobium leguminosarum and a number of isolates were falling outside the already characterized species of genus Rhizobium. Application of heavy fertilization has resulted in high soil N and P levels, which most likely reduced nodulation and AMF spore presence. However, considerable AMF root length colonization was found in most of the fields.

Insights into the Phylogeny, Nodule Function, and Biogeographic Distribution of Microsymbionts Nodulating the Orphan Kersting's Groundnut [Macrotyloma geocarpum (Harms) Marechal & Baudet] in African Soils.

Kersting's groundnut [Macrotyloma geocarpum (Harms) Marechal & Baudet] is a neglected indigenous African legume adapted to growth in N-deficient soils due to its ability to fix atmospheric N2 via symbiosis with rhizobia. Despite its nutritional and medicinal uses, to date there is little information on the phylogeny and functional traits of its microsymbionts, aspects that are much needed for its conservation and improvement. This study explored the morphogenetic diversity, phylogenetic relationships, and N2-fixing efficiency of Kersting's groundnut rhizobial isolates from contrasting environments in Ghana, South Africa, and Mozambique. BOX-PCR fingerprinting revealed high diversity among the rhizobial populations, which was influenced by geographic origin. Of the 164 isolates evaluated, 130 BOX-PCR types were identified at a 70% similarity coefficient, indicating that they were not clones. Soil pH and mineral concentrations were found to influence the distribution of bradyrhizobial populations in African soils. Phylogenetic analysis of 16S rRNA genes and multilocus sequence analysis of protein-coding genes (atpD, glnII, gyrB, and rpoB) and symbiotic genes (nifH and nodC) showed that Kersting's groundnut is primarily nodulated by members of the genus Bradyrhizobium, which are closely related to Bradyrhizobium vignae 7-2T, Bradyrhizobium kavangense 14-3T, Bradyrhizobium subterraneum 58-2-1T, Bradyrhizobium pachyrhizi PAC48T, the type strain of Bradyrhizobium elkanii, and novel groups of Bradyrhizobium species. The bradyrhizobial populations identified exhibited high N2 fixation and induced greater nodulation, leaf chlorophyll concentration, and photosynthetic rates in their homologous host than did the 5 mM KNO3-fed plants and/or the commercial Bradyrhizobium sp. strain CB756, suggesting that they could be good candidates for inoculant formulations upon field testing.IMPORTANCE Rhizobia play important roles in agroecosystems, where they contribute to improving overall soil health through their symbiotic relationship with legumes. This study explored the microsymbionts nodulating Kersting's groundnut, a neglected orphan legume. The results revealed the presence of different bradyrhizobial populations with high N2-fixing efficiencies as the dominant symbionts of this legume across diverse agroecologies in Africa. Our findings represent a useful contribution to the literature in terms of the community of microsymbionts nodulating a neglected cultivated legume and its potential for elevation as a major food crop. The presence of potentially novel bradyrhizobial symbionts of Kersting's groundnut found in this study offers an opportunity for future studies to properly describe, characterize, and delineate these isolates functionally and phylogenetically for use in inoculant production to enhance food/nutritional security.

Phylogenetic relationships among introduced and autochthonous rhizobia nodulating Trifolium spp. in Uruguayan soils

Trifolium pratense (red clover) and T. repens (white clover) inoculated with Rhizobium leguminosarum sv. trifolii strain U204 are used to improve pastures in Uruguay. Although inoculation is a common practice in the country, there has been a progressive abandonment by farmers because they do not always see the benefits. The presence of efficient rhizobial populations may be one of the reasons why a response to inoculation is not always observed. We studied the identities and phylogenetic relationships among the clover rhizobia populating Uruguayan soils by analysis of 16S rRNA genes, ITS sequences and housekeeping (atpD, glnII, recA, rpoB) and symbiotic (nodA, nodC, nifH) genes. Strains like P3 and P33, isolated from the endemic Trifolium polymorphum, are inefficient in red and white clover. These strains clustered separately from the symbionts of these clovers. Bacteria which are efficient in red and white clovers clustered in either of two groups: one, represented by isolate 249, are likely naturalized rhizobia derived from the inoculant U204; and other included strains like U317 and N2, which share symbiotic genes with the inoculant. We hypothesize that these strains may be derived from native strains that acquired symbiotic gene from inoculant strains. These types of rhizobia are strong candidates for a second generation of clover inoculants for Uruguay.

Physiological Characterization and Genetic Diversity Assessment of the Rhizobial Populations Inhabiting <em>Gliricidia sepium</em> in selected Locations of Ampara District, Sri Lanka

Purpose: Gliricidia sepium is a wide spread multipurpose legume plant which is effective in nitrogen fixation and host to many Rhizobial strains. However, few studies have been carried out to identify and characterize the Rhizobial populations inhabiting G. sepium in Sri Lanka. The main objective of this study was to isolate and identify the stress tolerant Rhizobial strains in G. sepium. Research Method: Root nodules of G. sepium were collected from seven locations in Ampara district, which belongs to dry zone in Sri Lanka. Total of 35 isolates were screened for the tolerance for different pH, salinity, drought conditions and temperatures separately as well as in combinations. Genetic diversity of stress tolerant isolates was assessed using ERIC fingerprinting.Findings: All isolates were grown under wide range of stress conditions. The Rhizobial strains isolated from the site closer to the coast showed a high tolerance for all salinity levels as they are adapted to the high salt stress experienced in their natural habitat. The growth response to drought conditions and temperature was variable. Moreover, 14 isolates showed a high tolerance for more than two extreme stress conditions. When extreme conditions were combined, 12 isolates among 14 were survived. These 14 isolates grouped in to ten clusters at 69% similarity coefficient that make them genetically diverse. Research Limitation: The stress tolerance was observed under laboratory conditions and it does not provide enough evidence for the effectiveness of selected isolates in field.Original Value: The 14 stress tolerant Rhizobial isolates can be used to cross inoculate crop legumes to identify possible cross inoculation groups in order to reduce nitrogen fertilizer usage.

Strengthening soil health under rice (Oryza sativa) fallows in Eastern Plateau of India with dwarf rice and moisture conservation practices

There is great scope in converting rice (Oryza sativa L.) fallows into productive agro-ecosystems through appropriate crop based interventions involving suitable varieties and appropriate resource conservation technologies (RCTs). Pulses such as chickpea, lentil, lathyrus and blackgram -through rotation or relay with rice - are the candidate crops for efficient utilization of conserved and scarce resources including soil moisture. Therefore, studying bio-physical aspects of popular rice - chickpea rotation so as to conserve resources and deriving maximum benefits is important and is the crux of the current investigation. A study was carried out in a vertisols at Indira Gandhi Krishi Vishwavidyalaya, Raipur (India) during 2011-14 under the existing conditions guarded by a tropical sub-humid climate receiving an annual precipitation of 1582 mm. Two transplanted rice habit groups (a tall local rice Masuri, maturing at 130-140 days and a dwarf HYV of rice Swarna, with 110-120 days duration grown during rainy season) were combined with three residue management practices, viz. residue removal, stubble (30 cm) and mulch for growing two contrasting varieties of chickpea (early high biomass JG 130 and medium high biomass JG 226) grown during winter season. Chickpea was planted with a zero till drill after rice. The study showed that soil moisture depletion (SMD) pattern was decreased over the crop season in case of mulched or 30 cm stubble retained plots in comparison to absence of mulch due to its possible role as a soil cover. On the contrary, SMD was higher in case of tall rice (Masuri) habit due to its relatively longer duration as compared to dwarf rice (Swarna) habit. Similar although to a lower degree in SMD was apparent in case of early biomass accumulating variety (BAV) chickpea JG 130 over medium BAV JG 226. Soil health parameters in terms of its physical and microbiological parameters (like, bulk density, soil strength, dehydrogenase activity etc), crop physiological parameters (such as relative leaf water content (LWC) and specific leaf weight (SLW), plant population), nodulation activities (Rhizobium population, nodule number and its dry weights) and crop growth/yield parameters (pods/plant, root characteristics etc) were positively influenced by mulch or stubble retention (due to its beneficial role as a soil cover) and dwarf rice habit (Swarna). Small yet consistently superior values of soil fertility indicators, viz. soil organic carbon (SOC) and nutrients (NPKZn, Fe, Mn and Cu) availability status were also evident following mulch or retention of stubble on the soil surface, whereas the values were abysmally small when comparison was made between chickpea cultivars (early BAV JG 130 and medium BAV JG 226). Besides these, weed dynamics, grain yield attributes and the resultant grain yield were especially favoured following soil moisture conservation strategies involving dwarf rice habit and mulch/stubble retention since availability of soil moisture was fairly extended over a period of time following these measures. Thus, it is inferred from the study on rice-chickpea system that efficient agronomic management of soil and land resources is crucial for augmenting soil health and enhancing output in prevalent rice fallow of Eastern Indian Plateau.

Distribution and correlation between phylogeny and functional traits of cowpea (Vigna unguiculata L. Walp.)-nodulating microsymbionts from Ghana and South Africa

Cowpea (Vigna unguiculata L. Walp.) is indigenous to Africa, and highly valued for its N2-fixing trait and the nutritional attributes of its grain and leaves. The species’ ability to establish effective symbiosis with diverse rhizobial populations gives it survival and growth advantage in N-limited environments. To explore the functional diversity and phylogenetic positions of rhizobia nodulating cowpea in Africa, nodules were collected from various cowpea varieties grown in soils from the Guinea savanna and Sudano-sahelian agroecologies of Northern Ghana, and from the lowveld and middleveld areas of Mpumalanga Province in South Africa. Box-PCR profiling and multilocus sequence analysis revealed the presence of diverse microsymbionts responsible for cowpea nodulation across the study sites. BOX-PCR amplifications yielded variable band sizes, ranging from 618 bp to 5354 bp, which placed the isolates in six major clusters (Cluster A–F). Phylogenetic analysis based on 16S rRNA, atpD, glnII, gyrB, rpoB, nifH and nodC genes revealed the presence of diverse Bradyrhizobium sp. closely related to Bradyrhizobium daqingense, Bradyrhizobium subterraneum, Bradyrhizobium yuanmingense, Bradyrhizobium embrapense, Bradyrhizobium pachyrhizi, Bradyrhizobium elkanii and novel Bradyrhizobium species in the soils studied, a finding that could be attributed to the unique edapho-climatic conditions of the contrasting environments. The test isolates exhibited distinct symbiotic efficiencies, and also induced variable (p ≤ 0.001) photosynthetic rates, leaf transpiration, total chlorophyll and shoot biomass accumulation on cowpea (their homologous host). Canonical correspondence analysis showed that the distribution of these microsymbionts was influenced by the concentrations of macro- and micronutrients in soils. The pairwise genetic distances derived from phylogenies and nodule functioning showed significant (p < 0.05) correlation, which suggests that local environmental factors played a major role in the cowpea-Bradyrhizobium symbiosis.