Effect of exudate released from seeds and seedling roots of common bean (Phaseolus vulgaris L.) on proliferation of Rhizobium sp. (Phaseolus)

Effects of seed and root exudates obtained from common bean on the proliferation of Rhizobium sp. (Phaseolus) were examined in a combination of three plant cultivars with three Rhizobium strains. In the first experiment, seed or root exudate was mixed with an Andosol soil extract, and bacterial proliferation in the mixture was traced. Seed exudate was prepared from hydroponic solution used in seed imbibition for 24 h, and a series of root exudates was prepared from a hydroponic solution collected every 24 h from the initiation of rooting up to 96 h after rooting. Regardless of the common bean cultivars and Rhizobium strains used, Rhizobium population markedly increased of the 24 h of culture in the mixture containing seed exudates, whereas a negligible increase was detected in the mixture with root exudates. The mixture containing root exudates collected within a period of 72–96 h after initial rooting (96–120 h after seed imbibition) exerted an inhibitory effect on Rhizobium proliferation. The seed exudates contained large amounts of sugars, amino acids, nitrogen, phosphorus, potassium, and magnesium compared to any root exudates. In the second experiment, Rhizobium was inoculated directly to common bean seeds sowed in a vermiculite bed which was sterilized and moistened with a plant nutrient solution. Compared with the control (without seed), a remarkable increase in the number of bacterial cells was observed in all the combinations of plant cultivars and Rhizobium strains 24 h after sowing. These results reveal that seed exudates of common bean have a substantial potential to promote Rhizobium proliferation, and that root exudates in a particular period of culture contain some inhibitory factors.     

Rhizobium Proliferation-Supporting Substances in Seed Exudates of Common Bean (Phaseolus vulgaris L.)

Seed exudates collected from three cultivars (cv. Hokkaikintoki, Himetebou, and Kurodane-kinugasa) of common bean ( Phaseolus vulgaris L.) were fractionated based on several physicochemical properties, and the nutrient substances in the fractions effective for Rhizobium proliferation were determined. Regardless of the common bean cultivars, the low molecular weight and high polarity fraction showed the most beneficial effect on Rhizobium proliferation. After further separation of the low molecular weight and high polarity fraction, the promoting effect was detected in the non-ionic and the cationic plus ampho-teric subtractions. Although the amount of sugars or amino acids exuded from a seed was, respectively, similar in all the cultivars except for the sugars in Kurodanekinugasa, the content of these compounds per seed-weight was inversely proportional to the seed size. Ten sugars and twenty-one amino acids were, respectively, identified in the non-ionic and cat-ionic plus amphoteric subtractions, and there were some differences in the composition of these substances between common bean cultivars.     

Potential of seed and root exudates of the common bean Phaseolus vulgaris L. for immediate induction of rhizobial chemotaxis and nod genes

Abstract

Immediate induction of rhizobial chemotaxis and nod genes by seed and root exudates of the common bean Phaseolus vulgaris L. was investigated. One hour after the onset of Rhizobium incubation in a culture medium composed of common bean exudates and soil extract, a large number of Rhizobium cells were attracted by the seed exudates of all the cultivars (cvs Hokkaikintoki, Himetebou and Kurodanekinugasa), while the media containing root exudates was not statistically different from the control. After 1 h of incubation, the nod genes were induced significantly by the seed exudates of Himetebou and Kurodanekinugasa. In contrast, the seed exudate of Hokkaikintoki and the root exudates of all the cultivars failed to exert a beneficial effect on the immediate induction of the nod genes. These results suggested that the seed exudates displayed a higher potential for immediate induction of rhizobial chemotaxis and nod genes than the root exudates, except for nod gene induction by the seed exudate of Hokkaikintoki.     

Breeding for bean fly resistance in common bean (Phaseolus vulgaris L.): a review

The bean fly (Ophiomya spp) is the most important yield limiting insect pest of common bean in Africa. The insect pest can cause complete crop loss affecting bean production and productivity under epidemic conditions. Effective control of bean fly is essential for sustainable bean production Africa. The overall progress, opportunities and challenges of the bean fly control strategies. The biology and ecology of bean fly and the economic importance of the insect pest is presented as well as the existing controlling strategies, with an emphasis on the breeding on breeding strategies used, research progress achieved challenges and opportunities. In conclusion, significant research progress have been made in breeding for bean fly resistance evident by identification of breeding lines, understanding resistance mechanism and development of breeding strategies. However, there is a need for further research to validate the available information and also explore new breeding methods such molecular breeding which has not been explored at present. Such studies will accelerate breeding for bean fly resistance.     

Distribution and phenotypic characteristics of common bean (Phaseolus vulgaris L.) nodulating bacteria in diverse soils

ABSTRACT

Bacteria were isolated from the root nodules using common bean as a trap host. Growth and morphological characteristics of the bacterial isolates were described on yeast extract mannitol mineral salts agar and broth media. The results showed that over 67% of the isolates produced extracellular polysaccharide with an entire margin and convex elevation. The others differentiated into cream yellow, cream white and milky white colouration with colony area ranging from 0.8 to 26?mm². The population levels of bacteria nodulating common bean varied in soils and were not affected by the cropping system. However, selected soil parameters greatly influenced the occurrence and distribution of these bacteria. The isolation of indigenous bacteria in all the soils with different cropping systems is an indication that the soils are favourable for nitrogen fixation. Based on the differences in cultural characteristics of the isolates, our data demonstrate the presence of high diversity of bacteria associated with bean nodules.     

Proton toxicity interferes with the screening of common bean (Phaseolus vulgaris L.) genotypes for aluminium resistance in nutrient solution

Common bean (Phaseolus vulgaris L.) proved to be very sensitive of low pH (4.3), with large genotypic differences in proton sensitivity. Therefore, proton toxicity did not allow the screening of common bean genotypes for aluminium (Al) resistance using the established protocol for maize (0.5 mM CaCl₂, 8 μM H₃BO₃, pH 4.3). Increasing the pH to 4.5, the Ca²⁺ concentration to 5 mM, and addition of 0.5 mM KCl fully prevented proton toxicity in 28 tested genotypes and allowed to identify differences in Al resistance using the inhibition of root elongation by 20 μM Al supply for 36 h as parameter of Al injury. As in maize, Al treatment induced callose formation in root apices of common bean. Aluminium‐induced callose formation well reflected the effect of Ca supply on Al sensitivity as revealed by root‐growth inhibition. Aluminum‐induced callose formation in root apices of 28 bean genotypes differing in Al resistance after 36 h Al treatment was positively correlated to Al‐induced inhibition of root elongation and Al contents in the root apices. However, the relationship was less close than previously reported for maize. Also, after 12 h Al treatment, callose formation and Al contents in root apices did not reflect differences in Al resistance between two contrasting genotypes, indicating a different mode of the expression of Al toxicity and regulation of Al resistance in common bean than in maize.     

Genetic diversity of Rhizobium present in nodules of Phaseolus vulgaris L. cultivated in two soils of the central region in Chile

Although Phaseolus vulgaris L. is native from the Americas and is currently cultured in diverse areas, very little is known about the diversity of symbiotic nitrogen fixing Rhizobium (mycrosymbiont) in many of those cultures. Therefore, the aim of this study was to assess the genetic diversity of Rhizobium present in nodules of P. vulgaris in the central region of Chile. A method to extract DNA from surface-sterilized nodules was applied to two populations of the same seed variety grown in different fields. The 16S rRNA and nifH genes were amplified directly from the DNA extracted. DGGE analysis and clone libraries showed a restricted genetic diversity of the microsymbiotic populations that nodulate P. vulgaris. Both molecular markers revealed the presence of a microsymbiont closely related to Rhizobium etli in all the plants from the soils studied, indicating that the populations of Rhizobium sp. nodulating P. vulgaris in the central region of Chile displayed an extremely low genetic diversity. The level of genetic diversity in microsymbiont populations in plants grown in soils with different origin suggested that other factors rather than the indigenous soil rhizobial populations play a major role in the selection of the symbiotic partner in P. vulgaris.     

Competition and persistence of Rhizobium tropici and Rhizobium etli in tropical soil during successive bean (Phaseolus vulgaris L.) cultures

Strains of Rhizobium tropici IIB, CIAT899 and F98.5, both showing good N₂ fixation, and a R. etli strain W16.3SB were introduced into a field which had no history of bean culture. Plant dilution estimates showed that in the presence of its host (Phaseolus vulgaris cv. Carioca) during the cropping seasons and the subsequent fallow summer periods, the bean rhizobial populations increased from less than 30 to 10³ g^–1 dry soil after 1 year and to 10⁴ g^–1 dry soil after 2 years. In the 1st year crop, the inoculated strains occupied most of the nodules, which resulted in a higher nodulation and C₂H₂ reduction activity. Without reinoculation for the second and third crops, however, little R. tropici IIB was recovered from the nodules and the bean population consisted mainly of R. etli, R. leguminosarum bv. phaseoli, and R. tropici IIA. Reinoculation with our superior R. tropici IIB strains before the second crop resulted in R. tropici IIB occupying the main part of the nodules and a positive effect on nodulation and C₂H₂ reduction activity, but reintroduction of the inoculant strain in the third season did not have any effect.     

The inorganic N requirement,nodulation and yield of common bean (Phaseolus vulgaris L.) as influenced by inherent soil fertility of eastern Ethiopia

Though mineral N application impaired nodulation initiation and function, it improves the productivity of common bean. The effect of inorganic application on common bean productivity, however, is dependent on the availability of plant nutrients including nitrogen (N) in the soils. Therefore, multilocation field experiments were conducted at Babillae, Fedis, Haramaya, and Hirna to evaluate the effect of inherent soil fertility status on responsiveness of common bean to different rates of N fertilizer application and its effect on nodulation, yield, and yield components of common bean. The treatments were six levels of N fertilizer (0, 20, 40, 60, 80, and 100 kg N ha^?1) laid out in randomized completed block design with three replications. The result revealed that 20 kg N ha^?1 application significantly improved the nodule number (NN) and nodule dry weight (NDW) except Hirna site, in which reduction of NN and NDW was observed. Although the remaining investigated yield and yield components were significantly improved due to N fertilizer in all study sites, 40 kg N ha^?1 application resulted in significantly increased GY of common bean at Fedis, Haramaya, and Hirna site, while 60 kg N ha^?1 at Babillae site. The highest total biomass yield (7011.6 kg ha^?1) and GY (2475.28 kg ha^?1) of common bean were recorded at Hirna and Haramaya sites, respectively, indicating the importance of better fertile soil for good common bean production. Hence, it can be concluded that the effect of inorganic N on common bean was irrespective of soil fertility rather the total amount of N in soil would affect the need of different rate of inorganic N.     

Arcelin in wild bean (Phaseolus vulgaris L.) seeds: sequence of arcelin 6 shows it is a member of the arcelins 1 and 2 subfamily

Arcelins are lectin-related proteins detected only in wild beans collected in Mexico and their presence has been related to resistance against the bean weevils. Six arcelin variants have been described and the gene sequence of four of them was determined. We have isolated and sequenced a cDNA clone encoding arcelin 6. Sequence data indicated that this protein is closely related to arcelin 1 and arcelin 2. The cluster dendrogram produced with the multiple alignment of the cDNA clones coding for arcelins showed that arcelins can be divided into three subgroups: i) arcelin 1, arcelin 2 and arcelin 6, ii) arcelin 4 and iii) arcelin 5a and arcelin 5b. Biochemical data indicate that arcelin 3 belongs to the same subgroup of arcelin 4. Southern blot analysis of genomic DNA yielded similar restriction patterns among members of each subgroup, confirming the results obtained with the multiple alignment. Furthermore, the hybridisation patterns were specific for each arcelin variant. On the basis of these evidences, we suggest that the lectin locus could be a useful tool for understanding evolutionary relationships in common bean and in the genus Phaseolus.     

Low root zone temperature effects on bean (Phaseolus vulgaris L.) plants inoculated with Rhizobium leguminosarum bv. phaseoli pre-incubated with methyl jasmonate and/or genistein

Abstract

Methyl jasmonate (MeJA) has recently been shown to act as a plant-to-bacteria signal. We tested the hypothesis that pre-induction of Rhizobium leguminosarum bv. phaseoli cells with genistein and/or MeJA would at least partially overcome the negative effects of low root zone temperature (RZT) on bean nodulation, nitrogen fixation and plant growth. Otebo bean plants were grown at constant air temperature (25^oC) and two RZT regimes (25 and 17^oC) and inoculated with R. leguminosarum bv. phaseoli pre-induced with MeJA and/or genistein. Our results indicate that low RZT inhibited nodulation, nitrogen fixation and plant growth. The plants growing at low RZT began fixing nitrogen seven days later compared to those at higher RZT. The low RZT plants had fewer nodules, lower nodule weight, less N fixation, slower plant growth, fewer leaves, smaller leaf area, and less dry matter accumulation comared to plants at a higher RZT. Rhzobium leguminosarum bv. phaseoli cells induced with genistein and/or MeJA enhanced bean nodulation, nitrogen fixation and growth at both optimum and suboptimum RZTs. The results of this study indicate that MeJA improves bean nitrogen fixation and growth at both optimum and suboptimum RZTs, and can be used alone or in combination with genistein to partially overcome the low RZT induced inhibitory effects on nodulation and nitrogen fixation.     

Genotypic diversity and symbiotic effectiveness of rhizobia isolated from root nodules of Phaseolus vulgaris L. grown in Tunisian soils

 One hundred and sixty isolates of rhizobia were sampled from the root nodules of common bean (Phaseolus vulgaris L.) cultivated in Tunisian soil samples originating from three geographically distinct fields. Plasmid profiling was used as a primary method to rapidly screen the isolates, and then 38 plasmid types were recorded among the 160 isolates. A sample representing the majority of plasmid types was chosen for further characterization by restriction fragment length polymorphism (RFLP) analysis of genomic DNA using chromosomal and symbiotic gene probes, and by their ability to nodulate a potential alternative host, Leucaena leucocephala. One third of the isolates showed a high similarity to Rhizobium gallicum isolated from common bean in France, another third showed the same characteristics as the R. etli-R. leguminosarum group, while the remaining isolates could not be related to any of the five species nodulating bean. When reexamined for nodulation, some of these isolates, showing similarities to R. tropici and Agrobacterium with respect to colony morphology and growth in different media, failed to nodulate their original host. The R. gallicum-like isolates, R. etli-like isolates, and R. leguminosarum-like isolates were recovered from regions where bean is frequently grown, while in fields which had not been cultivated with beans for at least the 10 previous years, solely unrecognized taxa of ineffective isolates were recovered. We detected variations in the symbiotic regions, but certain pSym RFLP patterns for nifH were conserved between Tunisian, French, and Austrian populations of bean rhizobia. Evaluation of symbiotic effectiveness showed that R. gallicum-like isolates and R. etli-like isolates were effective, whereas some R. leguminosarum-like isolates were ineffective. Furthermore, effective isolates were also found among the unrecognized taxa. Received: 10 March 1998     

Response of field-grown bean (Phaseolus vulgaris L.) to Rhizobium inoculation and nitrogen fertilization in two Cerrados soils

 Most soils sown with field beans (Phaseolus vulgaris L.) contain indigenous rhizobia which might interfere with the establishment of inoculated strains. As a consequence, the benefits of bean inoculation are usually questioned, and the use of N fertilizer is gradually becoming a common practice. The present study had the objective of evaluating the effectiveness of inoculation and N fertilization in field soil with (site 1) and without (site 2) a previous bean-cropping history. At site 1, which had a rhizobial population of 7×10² cells g^–1 soil, inoculation had no effect on nodulation or yield, whereas at site 2 (<10 cells g^–1 soil) inoculation increased nodulation, nodule occupancy by the inoculated strain and grain yield. N fertilizer decreased nodulation at both sites, but increased grain yield at site 1 but not at site 2, indicating that the response to inoculation and N fertilization depends on the cropping history. When bean was cultivated for the first time, indigenous populations of rhizobia were low and high yields were accomplished solely with seed inoculation, with no further response to N fertilizer. In contrast, previous cultivation of bean increases soil rhizobia, preventing nodule formation by inoculated strains, and N fertilizer may be necessary for maximum yields. A significant interaction effect between N fertilizer and inoculation was detected for serogroup distribution only at site 2, with N fertilizer decreasing nodule occupancy by the inoculated strain and increasing the occurrence of indigenous strains. Consequently, although no benefits were obtained by the combination of inoculation and N fertilizer, this practice may be feasible with the selection of appropriate N-tolerant strains from the indigenous rhizobial population. Received: 26 May 1999     

Compatibility of crosses between gene pools and evolutionary classes in the common bean (Phaseolus vulgaris L.)

The extent of genetic divergence between the Mesoamerican and Andean gene pools and between evolutionary classes (wild, landrace and bred) in Phaseolus vulgaris was explored. The compatibility of crosses was assessed by the frequency with which pollination was successful and the number of seeds in the resulting pod. Mesoamerican genotypes were more effective as pollinators than Andean genotypes, regardless of the gene pool of the female parent. Though certain individual genotypes were more easily pollinated by genotypes of one or other of the gene pools, there was no consistent tendency for pollinations between genotypes within a gene pool to be more successful than those between gene pools. In crosses among wild and landrace genotypes, the landrace genotypes were more easily pollinated. In those among wild and bred genotypes, the bred genotypes were more effective as pollinators, and the number of seeds per pod was greater in crosses between the evolutionary classes than in those within classes. In crosses among landrace and bred genotypes, those within evolutionary classes had higher success rates than those between classes (47.2% vs. 38.9%), and produced more seeds per pod. However, these results do not represent a major barrier between the evolutionary classes. The hypothesis that dwarf-lethal incompatibility in inter-gene pool crosses is controlled by two complementary dominant genes (the DL-gene hypothesis) was tested by comparing the numbers of normal and abnormal plants in the progeny of three-way crosses, and the ratios obtained were consistent with the hypothesis. It is concluded that there is no biological barrier between the two gene pools and that they are distinct because, by accident of ancestry, they are located in geographically isolated and ecologically distinct areas, with different cultural practices and preferences. Research programmes aimed at transferring desirable traits between the gene pools should therefore be encouraged.     

Effectiveness of native Rhizobium on nodulation and yield of faba bean (Vicia faba L.) in Eastern Ethiopia

This study was initiated to evaluate the effect of locally isolated Rhizobium on nodulation and yield of faba bean at Haramaya, Ethiopia for three consecutive years. Ten treatments comprising of eight effective isolates of rhizobia, uninoculated, and N-fertilized (20 kg N ha^?1) were laid out in a randomized complete block design with three replications. The result of the experiment indicated that all inoculation treatments increased nodule number and dry weight over the control check in all cropping seasons. The result, however, showed the non-significant effect of Rhizobium inoculation on shoot length, number of tiller per plant and 100 seed weight in all cropping season. Inoculating Haramaya University Faba Bean Rhizobium (HUFBR)-15 in 2011 and National Soil Faba Bean Rhizobium (NSFBR)-30 in 2012 and 2013 gave the highest grain yields (4330, 5267 and 4608 kg ha^?1), respectively. These records were 75%, 48%, and 5% over the uninoculated treatment of respective years. Over the season, NSCBR-30 inoculation resulted in the highest nodulation and grain yield production as compared to the other treatments. In general, isolates from central Ethiopia were better than those isolated from eastern Ethiopia and Tropical Agricultural Legume (TAL)-1035 in enhancing faba bean production at Haramaya site. Therefore, NSFBR-30 is recommended as a candidate isolate for faba bean biofertilizer production in eastern Ethiopia soils.     

Competitive interaction among strains of Rhizobium leguminosarum bv. phaseoli in the nodulation of kidney beans (Phaseolus vulgaris L.)

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.     

Genetic diversity analysis of common bean (Phaseolus vulgaris L.) genotypes for resistance to Mexican bean weevil (Zabrotes subfasciatus), using single nucleotide polymorphism and phenotypic markers

ABSTRACT

The objective of this study was to examine the genetic diversity present among 297 common bean genotypes using 2554 SNPs and 12 insects and seed-related traits. The phenotyping was done under laboratory condition while the genotyping was conducted by using the Illumina SNP BeadChip. High phenotypic diversity among traits were recorded, ranging from 0.87 to 0.96, with a mean of 0.92. Principal component and discriminant analyses identi?ed four PCs and three discriminant functions, which explained 82% and 100% of the total phenotypic variations among genotypes, respectively. Polymorphic Information Content ranged from 0.21 to 0.38, with a mean of 0.34. The mean gene diversity among genotypes ranged from 0.24 to 0.50, with a mean of 0.44. Genetic distance ranged from 0.19 to 0.82, with a mean of 0.62, while the phenotypic distance ranged from 0.00 to 1.00, with a mean of 0.64 were observed aamong genotypes. The analysis of molecular variance revealed highly signi?cant differences (p<0.001) among and within individuals and among populations. Both the SNP and the phenotypic markers grouped the 297 genotypes into two major distinct clusters and three sub-clusters. This information is useful for identi?cation and development of common bean germplasm with economically valuable traits and the conservation and utilization of genotypes.     

Rhizobial inoculation improves drought tolerance,biomass and grain yields of common bean (Phaseolus vulgaris L.) and soybean (Glycine max L.) at Halaba and Boricha in Southern Ethiopia

ABSTRACT

While pulses are staple food-legumes in Ethiopia, their productivity is low due to low soil fertility. Elite rhizobial strains that significantly increased shoot dry weight and nitrogen (N) contents of common beans and soybeans in greenhouse were selected for two-year field trials to evaluate their effect on yields of the pulses in the field. Each pulse had six treatments, namely four rhizobial inoculants, uninoculated control, and synthetic N fertilizer. In the drought-affected year 2015, inoculated pulses tolerated moisture stress better than non-inoculated controls. Inoculation was conducive to higher or equivalent yields compared to synthetic N fertilizer. At Halaba, bean inoculated with strain HAMBI3562 gave the highest grain yield (1500 ± 81 kg ha^?1; mean±SE) while the control yielded only 653 ± 22 kg ha^?1. At Boricha, HAMBI3570 gave a grain yield (640 ± 35 kg ha^?1) comparable to synthetic N. When rainfall was optimal in 2016, inoculation with HAMBI3562 and HAMBI3570 gave grain yields (around 4300 kg ha^?1) equivalent to synthetic N. With soybean, strain HAMBI3513 produced consistently higher or comparable biomass and grain yields compared to synthetic N. In conclusion, HAMBI3562 and HAMBI3570 for beans and HAMBI3513 for soybeans can serve as inoculants for areas having similar conditions as the test areas.     

Effect of nitrogen levels and Rhizobium strains on symbiotic N2 fixation and grain yield of Phaseolus vulgaris L. genotypes in normal and saline-sodic soils

Summary Following screening, selection, characterization, and symbiotic N₂ fixation with 12,5, 25.0, and 40.0 mg N kg^–1 in normal and saline-sodic soils, only two Phaseolus vulgaris genotypes (HUR 137 and VL 63) and two Rhizobium spp. strains (ND 1 and ND 2) produced maximum nodulation, nitrogenase activity, plant N contents, and grain yields in saline-sodic soil, with 12.5 mg N kg^–1, compared with the other strains. However, interactions between strains (USDA 2689, USDA 2674, and ND 5) and genotypes (PDR 14, HUR 15, and HUR 138) were significant and resulted in more nodulation, and greater plant N contents, nitrogenase activity, and grain yields in normal soils with 12.5 mg N kg^–1 compared with salt-tolerant strains. Higher levels of N inhibited nodulation and nitrogenase activity without affecting grain yields. To achieve high crop yields from saline-sodic and normal soils in the plains area, simultaneous selection of favourably interacting symbionts is necessary for N economy, so that bean yields can be increased by the application of an active symbiotic system.