Organic-acid-producing,phytate-mineralizing rhizobacteria and their effect on growth of pigeon pea (Cajanus cajan)

Phytates represent a significant pool of organic phosphorus (Po) that is largely unavailable to plants. This study deals with phytate-mineralizing (PM), organic-acid-producing (OAP) rhizobacterial isolates, their characterization and their effect on plant growth. Their genetic diversity was assessed by 16S rRNA amplified ribosomal DNA restriction analysis (ARDRA) and selected isolates were identified by partial sequencing of 16S rRNA gene. Na-phytate and Po rich poultry farm manure (PFM) used as sources of phosphorus in semi-solid-agar (SSA) medium and soil respectively, for plant inoculation studies, where Cajanus cajan (pigeon pea) used as plant. Of thirty-nine rhizobacterial isolates, nineteen were proficient at releasing phosphate (Pi) (up to 85 μg/ml) from sparingly soluble calcium (Ca)-phytate and concomitantly decreasing the pH of minimal medium with 100 mM glucose from 8.0 to below 5. When the medium contained glycerol in place of glucose, Ca-phytate remained undissolved with no significant Pi released and no decline in pH. Genetic diversity of phytate-mineralizing (PM) rhizobacterial isolates suggests that the isolates mainly fall in two populations: acid-producing (AP) population (mainly represented by members of Enterobacteriaceae) and non-AP population. OAP-PM rhizobacterial isolates were identified as Citrobacter, Pantoea, Klebsiella and Enterobacter species. Organic acids (OAs) secreted by PM isolates were detected by HPLC, showed secretion of gluconic and acetic acids. Importance of OAs in Ca-phytate dephosphorylation was demonstrated in vitro using A. ficuum phytase. Gluconate and acetate additions enhanced phytase catalyzed dephosphorylation of Ca-phytate in vitro. Sonicated cell lysates of isolates showed significant Pi release from Ca-phytate compared to whole cells, indicating inaccessibility of Ca-phytate due to poor solubility. Selected isolates showed that they possess cell-associated acid phytase and modulators of phytase activity suggested that the enzymes are histidine acid phosphatase (HAP) type of phytase. OAP-PM isolates PP1 and DHRSS showed significant increase in dry shoot/root ratio and P content of shoot in Na-phytate containing semi-solid agar (SSA) medium, but isolate DHRSS did not increase dry shoot/root ratio in soil experiments containing poultry farm manure as source of P, although it significantly increased shoot P content of plants. The inoculation of isolates enhanced the shoot P content and dry shoot/root ratio, but did not increase the dry weight in SSA medium. It may be concluded that some OAP-PM rhizobacterial isolates that release P from Ca-phytate show increase in shoot P content in phytate containing SSA medium and in soils.     

Endophytic fungi from pigeon pea [Cajanus cajan (L.) Millsp.] produce antioxidant Cajaninstilbene acid

In this study, novel endophytic fungi producing cajaninstilbene acid (CSA) from pigeon pea [ Cajanus cajan (L.) Millsp.] were investigated and screened. CSA has prominent pharmacological activities. A total of 110 endophytic fungi isolates were grouped into 8 genera on the basis of morphological characteristics, and CSA-producing fungi were screened by liquid chromatography-tandem mass spectrometry (LC-MS/MS). According to ITS-rDNA sequences analysis, the CSA-producing fungi were identified as Fusarium solani (ERP-07), Fusarium oxysporum (ERP-10), and Fusarium proliferatum (ERP-13), respectively. The amount of CSA produced by the ERP-13 reached 504.8 ± 20.1 μg/L or 100.5 ± 9.4 μg/g dry weight of mycelium. In a DPPH radical-scavenging assay, when the concentration of fungal CSA was 500 μg/mL, inhibition percentage could reach 80%, which was almost the same as that of standard CSA. This study first reported the natural antioxidant CSA from endophytic fungi F. solani and F. proliferatum isolated from pigeon pea.     

Dinitrogen fixation and growth responses to phosphorus and aluminum application in pigeon. pea (Cajanus cajan L.)

Abstract

Responses to aluminum phosphate (Al-P) and superphosphate (Sup-P) application in terms of dry matter production by pigeon pea and soybean were compared under field conditions. The effect of aluminum on growth and symbiotic dinitrogen fixation was examined under hydroponic conditions. In a field experiment, Al-P application significantly increased whole plant dry weight and P amount in pigeon pea, whereas in soybean, Al-P application had no significant effect on the two parameters. The results indicate that P absorption ability from Al-P is higher in pigeon pea compared to soybean. With Al-P application, leaf and whole plant Al concentration in pigeon pea significantly increased unlike in soybean.

Under hydroponic conditions, 50 nig L^?1 Al application increased the plant weight of pigeon pea while it decreased that of soybean. This treatment decreased the total nodule activity of soybean more appreciably than that of pigeon pea. Under the Al treatment conditions, whole plant P amount increased in pigeon pea, whereas it decreased in soybean, and the amount of Al increased more appreciably in pigeon pea, most of which was deposited in roots.

These results suggest that compared to soybean, pigeon pea displays a higher ability to absorb P from P compounds with a low solubility i.e. Al-P and that it is more tolerant to Al toxicity.     

Rhizobium sp. exopolysaccharide production,nodulation, and acetylene reduction activity (N2-fixation) in pigeon pea (Cajanus cajan L.)

Summary There was no correlation between the quantity of exopolysaccharide produced and acetylene reduction activity by Rhizobium spp. or by Bradyrhizobium spp. (Cajanus). The exopolysaccharide-defective mutants of Rhizobium sp. strain P 116 either failed to nodulate or showed a decrease in effectiveness. The deficiency in exopolysaccharide production was corrected by the addition of purified exopolysaccharide from the parent strain, or from Bradyrhizobium sp. strain P 149 or S24 isolated from pigeonpea (Cajanus cajan) and mungbean (Vigna radiata), respectively. However, the nodules so formed were not fully effective compared to those formed by the parent strain.     

Insight to the genetic diversity of pigeon pea Cajanus cajan (L.) Millsp. and cowpea Vigna unguiculata (L.) Walp. germplasm cultivated in Nigeria based on rbcl gene region

Genetic Resources and Crop Evolution - Pigeon pea Cajanus cajan (L.) Millsp. and cowpea Vigna unguiculata (L.) Walp. are two of the important seed legumes of Africa and are relatively more...     

Survival and competitiveness of Bradyrhizobium sp. in the rhizosphere of pigeonpea (Cajanus cajan)

Summary The survival of Bradyrhizobium Cajanus strain CC1021 in the soil and rhizosphere of pigeonpea [Cajanus cajan (L.) Millsp] was determined by most probable number and fluorescent antibody techniques. The survival of strain CC1021 was poor under field compared with pot-culture conditions. Although the rhizosphere of pigeonpea promoted the growth of native pigeonpea rhizobia, although no increase in the number of rhizobia was observed with the inoculant strain. Under similar conditions of rhizosphere colonization the competitiveness of strain CC1021 with cv UPAS 120 and ICPL 312 was 10% and 66016 during the first year and 8.4% and 33.3%, respectively, during the second year.     

In vitro antioxidant properties, DNA damage protective activity, and xanthine oxidase inhibitory effect of cajaninstilbene acid, a stilbene compound derived from pigeon pea [Cajanus cajan (L.) Millsp.] leaves

The antioxidant properties, DNA damage protective activities, and xanthine oxidase (XOD) inhibitory effect of cajaninstilbene acid (CSA) derived from pigeon pea leaves were studied in the present work. Compared with resveratrol, CSA showed stronger antioxidant properties, DNA damage protective activity, and XOD inhibition activity. The IC(50) values of CSA for superoxide radical scavenging, hydroxyl radical scavenging, nitric oxide scavenging, reducing power, lipid peroxidation, and XOD inhibition were 19.03, 6.36, 39.65, 20.41, 20.58, and 3.62 μM, respectively. CSA possessed good protective activity from oxidative DNA damage. Furthermore, molecular docking indicated that CSA was more potent than resveratrol or allopurinol to interact with the active site of XOD (calculated free binding energy: -229.71 kcal mol(-1)). On the basis of the results, we conclude that CSA represents a valuable natural antioxidant source and may potentially be applicable in health food industry.     

Establishment and effectiveness of added pigeonpea (Cajanus cajan) rhizobia in different soils of narrow abiotic variability

Summary Pot and laboratory experiments were conducted to study the establishment and effectiveness of a streptomycin-sulphate-resistant (1 mg/ml of medium) pigeonpea rhizobia strain (RM₇) in sterile sand and non-sterile soils. Strain RM₇ increased the drymatter yield of pigeonpea plants (Cajanus cajan) by 106% over control plants under sterile conditions. However, when the rhizobia strain was introduced into 14 different non-sterile soils with a narrow abiotic variability, the comparable beneficial effect was observed only in one soil inoculated with log 6.70 cells/pot. At this inoculum rate, the percentage increase in yield over control plants varied from –1 to 140 in different soils. Rhizobium (RM₇), applied at log 3.70 cells/pot (3 kg soil), showed less than 5% establishment in four soils. However, establishment varied from 8% to 72% at a higher level of inoculation (log 6.70 cells/pot). Displacement of native rhizobia and creation of new sites for nodulation by the introduced rhizobia were also affected by soil properties. The increase in shoot dry-matter yield compared with control plants was positively correlated with the percent establishment of RM₇ (r = 0.60^*) in these soils. Experiments showed that some biotic stresses led to poor survival, proliferation and establishment of the added alien in the soil. Therefore, any culture that is efficient in one soil may not produce similar results under all situations.     

AFLP Fingerprinting in Pigeonpea (Cajanus cajan (L.) Millsp.) and its Wild Relatives

Detection of DNA polymorphism in cultivated pigeonpea (Cajanus cajan) and two of its wild relatives Cajanus volubilis and Rhynchosia bracteata is reported here for the first time using amplified fragment length polymorphism (AFLP) fingerprinting. For this purpose, two EcoRI (three selective nucleotides) and 14 MseI (three selective nucleotides) primers were used. The two wild species shared only 7.15% bands with the pigeonpea cultivars, whereas 86.71% common bands were seen among cultivars. Similarly, 62.08% bands were polymorphic between C. volubilis and pigeonpea cultivars in comparison to 63.33% polymorphic bands between R. bracteata and pigeonpea cultivars, and 13.28% polymorphic bands among pigeonpea cultivars. The cluster analysis revealed low polymorphism among pigeonpea cultivars and very high polymorphism between cultivated pigeonpea and its wild relatives. The AFLP analysis also indicated that only one primer combination (EcoRI + ACT and MseI + CTG), at the most any four primer pair combinations, are sufficient for obtaining reliable estimation of genetic diversity in closely related cultivars like pigeonpea material analyzed herein. AFLP analysis may prove to be a useful tool for molecular characterization of pigeonpea cultivars and its wild relatives and for possible use in genome mapping.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of temperature on flavonoid production in pigeonpea [Cajanus cajan (L) Millsp] in relation to nodulation

To ascertain the reasons for poor nodulation of pigeonpea, we studied the effect of high temperature on the production of flavonoids by the pigeonpea host. A high temperature affected flavonoid production by pigeonpea and mungbean. At 37°C pigeonpea root exudates contained four flavonoids and the root extract contained five. The proportion of the second flavonoid in the pigeonpea and the mungbean was higher and the proportion of the third flavonoid was lower at 37°C compared to 30°C. At the higher temperature the flavonoids exuded from pigeonpea roots were same those in the root homogenate.     

Sustainable production of pigeon pea and sarpagandha (Rauvolfia serpentina) by intercropping

Sarpagandha (Rauvolfia serpentinaBenth. Ex Kurz.), a natural source of the alkaloid reserpine, is generally found growing under partial shade of deciduous forests in the tropics and subtropics. To promote its commercial cultivation under subtropical environment of the north Indian plains, a field trial was conducted during 2006–2009 to optimize the plant populations (row ratios) of pigeon pea and sarpagandha for higher productivity, land utilization efficiency and economic return in an intercropping system. Intercropping of two rows of sarpagandha with pigeon pea sown at a row distance of 90 cm proved highly beneficial in terms of total production (5.15 t ha^?1 grain and 10.27 t ha^?1 straw + stalk of pigeon pea and an additional dry root yield of 2.56 t ha^?1 of sarpagandha) from a unit area and time. The highest land equivalent ratio, LER (2.21), area time equivalent ratio, ATER (1.76), monetary equivalent ratio, MER (2.0), land-use efficiency, LUE (198%) and net return (Rs. 273,810 ha^?1) were obtained for the combination of pigeon pea and sarpagandha in 1:2 row ratio. Integration of two rows of sarpagandha as an intercrop with pigeon pea sown at 90 cm row distance is recommended for sustainable crop production.     

Comparative salinity tolerance of symbiotically dependent and nitrogen-fed pigeonpea (Cajanus cajan) and its wild relative Atylosia platycarpa

Summary Once symbiosis between the pigeonpea cultivar ICPL 227 and the Rhizobium sp. strain IC 3024 is established, it is efficient in fixing N₂ under saline conditions and can support growth comparable to N-fed plants in growth media with up to 6 dS m^-1 salinity. However, the early stages of establishment of the pigeonpea-IC 3024 symbiotic system have proved sensitive to salinity. The present study showed that the number of nodules was markedly reduced at 8 dS m^-1 salinity; however, nodule development and functioning were not affected by salinity in the pigeonpea-IC 3024 symbiosis. The symbiotic system of Atylosia platycarpa and Rhizobium sp. strain IC 3087 was established successfully even at 12 dS m^-1 and supported growth comparable to that of N-fed plants. P levels in leaves were increased under saline conditions in N-fed and N₂-fixing pigeonpea and A. platycarpa. There were no consistent differences in the leaf Na and chloride levels between N-fed and N₂-fixing plants of pigeonpea and A. platycarpa. The present study suggests that the rhizobial symbiosis may not be a necessary factor for initial screening of pigeonpea and related wild species for salinity tolerance.Submitted as JA No. 964 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Synergistic effects of plant-growth promoting rhizobacteria and Rhizobium on nodulation and nitrogen fixation by pigeonpea (Cajanus cajan)

Plant‐growth promoting rhizobacteria (PGPR), in conjuction with efficient Rhizobium, can affect the growth and nitrogen fixation in pigeonpea by inducing the occupancy of introduced Rhizobium in the nodules of the legume. This study assessed the effect of different plant‐growth promoting rhizobacteria (Azotobacter chroococcum , Azospirillum brasilense, Pseudomonas fluorescens, Pseudomonas putida and Bacillus cereus) on pigeonpea (Cajanus cajan (L) Milsp.) cv. P‐921 inoculated with Rhizobium sp. (AR‐2–2 k). A glasshouse experiment was carried out with a sandy‐loam soil in which the seeds were treated with Rhizobium alone or in combination with several PGPR isolates. It was monitored on the basis of nodulation, N₂ fixation, shoot biomass, total N content in shoot and legume grain yield. The competitive ability of the introduced Rhizobium strain was assessed by calculating nodule occupancy. The PGPR isolates used did not antagonize the introduced Rhizobium strain and the dual inoculation with either Pseudomonas putida, P. fluorescens or Bacillus cereus resulted in a significant increase in plant growth, nodulation and enzyme activity over Rhizobium‐inoculated and uninoculated control plants. The nodule occupancy of the introduced Rhizobium strain increased from 50% (with Rhizobium alone) to 85% in the presence of Pseudomonas putida. This study enabled us to select an ideal combination of efficient Rhizobium strain and PGPR for pigeonpea grown in the semiarid tropics.     

Phylogenetic relationships of Cajanus cajan (L.) Millsp. (pigeonpea) and its wild relatives based on seed protein profiles

Total seed storage protein of 9 accessions of cultivated C. cajan and 10 wild Cajanus species was reported and compared by sodium dodecyl sulphate polyacrylamide gel electrophoresis. A considerable variation was detected among the protein profiles of different accessions of C. cajan while those of wild species were very specific and distinctly different from each other. Relative similarities between various taxa were estimated by Jaccard's similarity index and cluster analysis was performed to produce a UPGMA dendrogram. The clustering of 10 wild species and C. cajan more or less agrees with their sectional classification and available data based on morphological characteristics, crossability, genome pairing in hybrids and nuclear RFLPs. The species closest to C. cajan is C. cajanifolia although the accessions of C. cajan also share some bands present in the profiles of C. scarabaeoides, C. goensis, C. lineatus, C. acutifolius and C. volubilis. This points towards polyphyletic origin of the cultigen which has been discussed in this paper.     

Alkylresorcinol content and homologue composition in durum wheat (Triticum durum) kernels and pasta products

The total alkylresorcinol (AR) content and relative homologue composition of 21 durum wheat (Triticum durum) kernel samples, as well as 5 pasta products and the corresponding flour mixtures, were determined. Durum wheat contained on average 455 microg/g ARs, and the average relative homologue composition was C17:0 (0.4%), C19:0 (14%), C21:0 (58%), C23:0 (21%), and C25:0 (6.5%). The homologue composition was found to be relatively consistent among samples, with durum wheat being different from common wheat by having a higher proportion of the longer homologues. No differences in content or homologue composition were observed in pasta products compared to flour ingredients, showing that alkylresorcinols are stable during pasta processing. The ratio of the homologues C17:0 to C21:0 was < or =0.02 for whole grain durum wheat products, which is different from those of common wheat (0.1) and rye (0.9).     

Differences between Cajanus cajan (L.) Millspaugh and C. cajanifolius (Haines) van der Maesen, the progenitor species of pigeonpea

A study was undertaken to know the difference/diversity between pigeonpea and its closely related wild species C. cajanifolius by studying their morphology, crossability, cytology of the hybrid between the two, and molecular studies. Studies revealed that there are at least 5–6 traits that separate the two species such as flower morphology, pod color and morphology, pod constriction, seed color and strophiole, 100 seed weight that separate C. cajan from C. cajanifolius. Molecular studies revealed that a genetic dissimilarity index value ranging from 0.81 to 0.94 exists between the two species.     

Iron dependent ureides and allantionase synthesis in pigeon pea

The effect of iron (Fe) on ureide metabolism was examined in 45‐day‐old pigeon pea (Cajanus cajan L.) (ureide plant) and alfalfa (Medicago sativa) (amide plant). Plants were either inoculated with Rhizobium or fertilized with ammonium nitrate (NH₄NO₃). The ureides, allantoin and allantoate, and allanotinase activity were increased in pigeon pea with Fe supplementation. Specific effect of Fe on ureide metabolism of pigeon pea was indicated by the lack of same effect in alfalfa under similar conditions. Nitrogenase activity was elevated with increasing concentrations of Fe in pigeon pea (ureide) as well as alfalfa (amide) symbiosis. Nitrogen (N₂) fixation, ureides, and allantoinase activity were reduced at 10 ppm and above concentration of Fe.