Roots Of Bean Plants Research Articles

Rhizoctonia species, anastomosis groups, and pathogenicity isolated from common bean in Lake Van Basin, Turkiye

Common bean (Phaseolus vulgaris L.) is an important vegetable crop grown in Lake Van Basin. Local genotypes are widely grown in the region. Rhizoctonia root rot induced by Rhizoctonia solani Kühn is an important soilborne plant disease that leads to global economic losses as well as in Turkey. The present study was conducted to determine anastomosis groups and pathogenicity of Rhizoctonia spp. obtained from bean plants in Lake Van Basin in 2013 and 2014. A total of 236 Rhizoctonia isolates in 5 anastomosis groups were obtained from bean plant roots. It was observed that AG- 4 (112) was the most isolated group in beans, followed by AG- 2 (41), AG- 3 (28), AG- 5 (33), and binucleate AG- K (22) isolates. Pathogenicity test conducted in thirty isolates in 5 anastomosis groups was analyzed for A64 (Bitlis/ Adilcevaz), TR68557 genotypes, and Gina (cv.) under growth chamber conditions. The study findings demonstrated that all tested isolates could infect the bean plant with different degrees of severity; however, the most virulent group was AG- 4. It was determined that the most virulent isolate was Isolate No. 19 in the A64 genotype, Isolate No. 2 in TR68557, and Isolate No. 18 in Gina cv. in in vivo tests. The identification and pathogenicity determination of Rhizoctonia isolates are the first steps towards an efficient control strategy for bean diseases caused by Rhizoctonia species. In order to obtain quality and productive products in the Van Lake Basin, where intensive bean production is carried out, precautions should be taken by considering the damage caused by Rhizoctonia spp. on plants.

Effect of Gamma-Irradiated Ceramic Wastewater Sludge on Photosynthetic Pigments of Phaseolus Vulgaris L. (Cv. Valentino and Cv. Nebraska) Plants

The common bean plant is a highly polymorphic species, annual herb, erect and bushy, 20–60 cm tall, or twining with stems 2–3 m long, with a taproot and nitrogen nodules which the bacteria could convert nitrogen gas and stores it in the common bean plant roots. Leaves are alternate, green, or purple, trifoliolate, stipulate, petiolate, markedly pulvinus at base; leaflets ovate, entire; acuminate, 6–15 cm long, 3–11 cm wide. Many soils have been contaminated with several pollutants, mostly arising from wastes of human activities such as the use of pesticides, sewer sludge, mining and smelting sources, radioactive substances, and industrial dischargers. These different contaminants can degrade the soil and cause a negative impact on the plant due to disturbing nutrient cycling within ecosystems and subsequently human health. This study aimed to elucidate the mechanism by which the plant may cope with heavy metals stress represented in this study in the form of industrial ceramic wastewater sludge. And, evaluating the role of gamma radiation on ceramic wastewater sludge, could reduce the percentage of the endogenous levels of heavy metals in ceramic sludge. This study investigates the influence of Photosynthetic pigments of the two common bean cultivars Valentino and Nebraska which are grown in light soil clay/sand (1:1) incorporated with ceramic-wastewater sludge (CWWS) non-irradiated (1% and 2%) and gamma-irradiated (2.5 kGy and 10 kGy) for 30 days. The application of non-irradiated CWWS induced an elevation in the contents of chlorophylls a, b, and carotenoids in the two cultivars while a reverse trend was observed in the leaves of both cultivars treated with gamma irradiated CWWS.

Evaluation of the incidence of endophytic fungi in leaves, stems and roots of bean plants in the State of Paraná

The present study aimed to isolate endophilic fungi from plant tissues (leaves, stems and roots) of beans, in addition to identifying them at the genus level. The experiment was conducted at IDR-Londrina. Bean samples were collected at the Londrina Research Station and at UENP-Bandeirantes. The leaves, stems and roots were separated, fragments of 5 mm diameter were cut and disinfested. They were later transferred to BDA culture medium. The plates were incubated at room temperature for seven days for growth of the microorganisms present. The presence and absence, colonization rate (TC) for each tissue and gender identification of fungi were evaluated. The experiment was conducted in a completely randomized design, with five replications. Forty-eight endophilic isolates were found, 13 in root, 17 in stem and 18 in leaf. CT ranged from 17-100% (leaf), 17-83% (stem) and 16-100% (root). The genus Alternaria sp. and Cladosporium sp. have greater specificity with the leaf and stem, Penicillium sp. root and stem. The genera Fusarium sp. and Aspergillus sp. are found in all organs, Curvularia sp., Nigrospora sp. and Thichoderma sp. demonstrated leaf specificity, Macrophomina sp. the root, and Colletotrichum sp. to the stem. Thus, the identified fungi present potential for future studies in their application in the biocontrol of various plant diseases.

Peculiar Response in the Co-Culture Fermentation of Leuconostoc mesenteroides and Lactobacillus plantarum for the Production of ABE Solvents

Two bacterial strains (CL11A and CL11D) that are capable of ABE fermentation, identified as Leuconostoc mesenteroides and Weissella cibari, were isolated from the soil surrounding the roots of bean plants. Another strain (ZM 3A), identified as Lactobacillus plantarum, which is capable of purely ethanolic fermentation was isolated from sugarcane. Glucose was used as a standard substrate to investigate the performance of these strains in mono—and co-culture fermentation for ABE production. The performance parameters employed in this study were substrate degradation rates, product and metabolite yields, pH changes and microbial growth rates. Both ABE isolates were capable of producing the three solvents but Leuconostoc mesenteroides had a higher specificity for ethanol than Weissella cibari. The co-culturing of Leuconostoc mesenteroides and Lactobacillus plantarum enhanced ethanol production at the expense of both acetone and butanol, and also influenced the final substrate consumption rate and product yield. The experiments indicated the potential of these niche environments for the isolation of ABE-producing microorganisms. This study contributes to the formulation of ideal microbial co-culture and consortia fermentation, which seeks to maximize the yield and production rates of favored products.

Ionic responses of bean (Phaseolus vulgaris L.) plants under salinity stress and humic acid applications

This study aimed to investigate the effects of different humic acid application methods (control, soil, foliar and soil + foliar) on chlorophyll content, dry matter weight of shoots and roots, concentrations of potassium (K), calcium (Ca) and sodium (Na), and K/Na and Ca/Na ratios of bean plants exposed to increasing salinity levels (0, 50, 100 and 150 mM). The effects of salt damage on shoots and roots of bean plants were significantly differed in humic acid application methods. Chlorophyll content decreased with the increase in salt doses at control and soil application of humic acid, while the decrease in chlorophyll content was lower in foliar application of humic acid. Shoot dry weight was not affected by humic acid applications, while root dry weight increased in soil + foliar application method. Soil + foliar humic acid application caused the highest shoot and root Na concentrations. Shoot Ca (2.61%) concentration in soil + foliar application was significantly higher compared to the other treatments, while the highest Ca concentration in roots (1.55%) was recorded in soil humic acid application method. The highest K concentration in roots was obtained in the control treatment (2.50%) followed by soil + foliar humic acid application (2.48%). The ratios of K/Na and Ca/Na in shoots decreased with the increase in salt application rates. The highest shoot K/Na (1456.1%) and Ca/Na (1274.1%) ratio in humic acid x salt interactions was found in soil application of humic acid without salt treatment. The root and shoot dry matter yield and K and Ca concentrations of the plants indicated that soil+foliar application method has a preventive effect for the plants against the 50 mM salt damage. The results showed that soil+foliar humic acid application in addition to the mineral fertilization required for beans can contribute to the growth and mineral nutrition of the plants under moderate salt stress (50 mM NaCl).

Accumulation of Pb in Chinese cabbage (Brassica rapa) and bean (Phaseolus vulgaris) from the use of fertilizer and pesticide

A series of experiments in a plastic house were carried out to test the accumulation of Pb metal in Chinese cabbage and bean plants from the application of several Pb sources. The research method used was a split-plot design with the main plot was the application of Pb source consisting of A1 = pesticide (99 mg Pb/kg), A2 = fertilizer (21 mg Pb/kg), A3 = Pb(NO 3 ) 2 (50 mg Pb/kg) and A4 = control (without the application of Pb), and the subplot was the vegetable crops consisting of B1 = Chinese cabbage ( Brassica rapa ) and B2 = bean ( Phaseolus vulgaris ). The results of the experiment showed that the Pb content in the shoots of Chinese cabbage and bean plants that were previously sprayed with pesticide was significantly 231.02% (Chinese cabbage) and 257.18% (bean) higher than control plants. Meanwhile, the largest Pb concentrations in the roots of Chinese cabbage and bean plants were obtained in plants applied with Pb(NO 3 ) 2 . Compared to the control treatment, there was an increase in Pb concentration by 206.32% in the roots of Chinese cabbage plant and by 310.03% in the roots of bean plant which were applied with Pb(NO 3 ) 2 . Pb concentrations of Chinese cabbage which were given fertilizer increased by 14.86% in the shoot and 30.59% in the root, while those in bean increased by 10.74% in the shoot and 98.77% in the root. Pb concentrations in Chinese cabbage and beans that were given fertilizer were not significantly different from control plants. These results indicate that the application of pesticide and fertilizer containing Pb results in Pb accumulation in the plant shoots and roots as well as in the soil.

Arbuscular mycorrhizal fungi improve the growth and phosphorus uptake of mung bean plants fertilized with composted rock phosphate fed dung in alkaline soil environment

Inoculation effect of arbuscular mycorrhizal fungi (AMF) on phosphorus (P) transfer from composted dung of cattle with a diet supplemented with powdered rock phosphate (RP) and their successive uptake by mung bean plants was assessed in alkaline soil. The efficacy of composted RP fed dung alone or/and in combination with AMF inoculums containing six different species were compared with SSP in six replicates per treatment in pots. The results showed that the association of AMF with composted RP fed dung had a positive effect on mung bean shoot (3.04 g) and root (2.62 g) biomass, chlorophyll (a, b), carotenoid contents and N (58.38 mg plant−1) and P (4.61 mg plant−1) uptake. Similarly, the percent roots colonization (56%) and nodulation of mung bean plant roots and their post-harvest soil properties were also improved by the inoculation of AMF together with composted RP fed dung. It is concluded that the combined application of AMF with composted RP fed dung has almost the same effect as SSP for improving mung bean plants growth and their nutrients uptake. Moreover, AMF inoculants can be used as a suitable biofertilizer in combination with locally available organic sources of fertilizers for improving P status and growth of plants in alkaline soils.

Screening of bacteria of the genus Bacillus for the control of the plant-pathogenic fungus Macrophomina phaseolina

This study evaluated the efficiency of 19 Bacillus isolates, obtained from the rhizosphere and rhizoplane of wild and cultivated castor bean plants, to control the pathogenic fungus Macrophomina phaseolina. Using in vitro assays, we examined the antifungal effects of volatile and non-volatile compounds, the production of siderophores and the activity of chitinase in these isolates. In vivo experiments were conducted to determine the potential of the Bacillus isolates to colonise castor bean plant roots and to control the fungus. In general, results showed that isolates from wild castor bean, compared with isolates from cultivated castor bean, were more efficient producers of antifungal compounds, better colonisers of plant roots and more effective protectors of plant seedlings against infection with M. phaseolina. Altogether, isolate RP 5, originating from the rhizoplane of wild castor bean, was the most promising candidate for future evaluation as a biological control agent of M. phaseolina.

Assimilate distribution in bean plants (Phaseolus vulgaris L.) during phosphate limitation

The influence of phosphate deficiency on the increased "C-assimilate transport from shoot to root of bean plants (<em>Phaseolus vulgaris</em> L.) was studied. The roots of plants were cultured in split configurations (a half of the root system was exposed to a short-term or long-term culture in phosphate-deficient nutrient medium, while the other half - in complete nutrient medium) to establish the conditions of translocation enhancement. It was found that both short term Pi stress applied to a part of root and longer localized phosphate deficiency is not sufficient to increase assimilate transport from the shoot to the root. Low concentration of Pi in tissues of the whole plant as a signal for changes in assimilate distribution and sugar accumulation in the roots is discussed.

Changes in expression of soluble inorganic pyrophosphatases of Phaseolus vulgaris under phosphate starvation

Phosphorus is an essential element for all living cells, but its availability is often limiting in the soil. Plants have adapted to such limitation and respond to phosphorus deficiency. The soluble inorganic pyrophosphatases (PPase; EC 3.6.1.1) recycle the pyrophosphate produced by many biosynthetic reactions, and may play a role in the plant adaptation to phosphorus deficiency. In this work, three PPase mRNAs were identified from the Phaseolus vulgaris EST international database and their sequences were corroborated and completed using 3′RACE. After design and validation of the appropriate oligonucleotide primers, the PPase mRNA expression was measured by qRT-PCR in leaves, stems, and roots of bean plants grown with 1mM phosphate or under phosphate starvation. The plant tissues were classified according to their position on the plant, and some physiological signs of stress were recorded. qRT-PCR revealed changes in mRNA expression, but not for all isozymes under analysis, and not for all tissues. In addition, changes in the activity of some PPases were observed in zymograms. Our data are consistent with an important role for pyrophosphate in the adaptation of the plant to phosphate starvation.

BIOCONTROL OF PHASEOLUS VULGARIS ROOT ROT USING ARBUSCULAR MYCORRHIZAE

The arbuscular mycorrhizal fungi (AM fungi) as mixture of Glomus spp. was used to induce resistance in Phaseolus vulgaris against root rot disease caused by Rhizoctonia solani. Results showed that % disease incidence was significantly reduced in AM-inoculated plants as compared with infected and AM-free control. Production of hydrogen peroxide (H2O2) and level of lipid peroxidation increased in both roots and shoots bean plants with increasing the time of infection. AM fungi markedly alleviated oxidative stress in infected bean plants, thus, levels of H2O2 and lipid peroxidation was markedly reduced. Also, activity of antioxidant enzymes (catalase, ascorbate peroxidase and superoxide dismutase) significantly increased in bean tissues in response to both R.solani and/or AM fungus. The highest enzyme activity was recorded in shoots of 14 days old plants inoculated with AM fungi. Total phenolic compounds and various phenolic acids especially cinnamic and ferulic acids greatly increased in roots of bean plants infected with R.solani and/or inoculated with AM fungi. However, coumarin was found only in AM-treated plants. But quercetin markedly increased in bean roots infected by R.solani and decreased in AM-treated plants, as compared with non-infected control. Finally, activity of lignification enzymes (polyphenol oxidase, peroxidase and phenylalanine-ammonia lyase) increased in all infected plants. Our results indicate that AM fungi increased resistance in infected bean plants by inducing both antioxidant system and phenolic compounds pathway.

Role of dissimilatory fermentative iron-reducing bacteria in Fe uptake by common bean (Phaseolus vulgaris L.) plants grown in alkaline soil

Iron (Fe) is an essential element for plant growth and development. Some plant growth-promoting rhizobacteria can increase Fe uptake by plants through reduction of Fe(III) to Fe(II) at the root surface. The aim of this work was to identify novel bacterial strains with high Fe(III) reduction ability and to evaluate their role in plant Fe uptake. Four bacterial strains (UMCV1 to UMCV4) showing dissimilatory Fe-reducing activity were isolated from the rhizosphere of bean and maize plants and further identified by 16S rDNA amplification and sequence analysis. From these analyses, UMCV1 and UMCV2 isolates were identified as Bacillus megaterium and Arthrobacter spp., respectively, whereas UMCV3 and UMCV4 were identified as Stenotrophomonas maltophilia. All four isolates showed Fe reduction in a nonflooded soil and when associated with roots of bean plants grown in alkaline soil or in mineral medium. In addition, the bacterial isolates were able to stimulate plant growth in vitro and on a broad level, plants grown in inoculated soil were generally bigger and with higher Fe content than those grown in sterilized soil. These results indicate that bacterial species isolated from the rhizosphere of bean and maize plants contribute significantly to Fe uptake by plants likely through increased Fe(III) reduction in the rhizosphere.

Identification of novel drought-related mRNAs in common bean roots by differential display RT-PCR

Drought is a major constraint for the production of common bean (Phaseolus vulgaris L.). To identify molecular responses to water deficit, we performed a differential display RT-PCR (DDRT) analysis using roots of bean plants grown aeroponically and submitted to dehydration. This allowed us to visualise 1200 DDRT bands, 8.7% of which showed a clear regulation by dehydration, and to clone 42 cDNAs, called PvD1 to PvD42. Among them, 20 early-dehydration-responsive cDNAs were selected by reverse northern that were induced or repressed before detectable water status changes and induction of ABA-regulated genes. Northern analysis for 16 PvD clones confirmed these early regulations and allowed us to identify four late dehydration-responsive genes. Their putative involvement in signalling, protein turn-over and translocation, chaperones as well as root growth modulations in response to water stress is discussed.

Water gradient profiles at bean plant roots determined by neutron beam analysis

We present profiles of the water gradient near the roots of bean plants measured by neutron beam analysis. Three kinds of bean plants were grown in cylindrical aluminum containers and were irradiated by thermal neutrons from a research reactor, JRR-3M, installed at Japan Atomic Energy Research Institute. After penetrating the sample, neutrons were converted to light by a fluorescent converter and the resulting photons were counted by a cooled CCD camera. Taking the projection images at different angles of the samples, CT images as well as simple projection images were constructed. It is seen here, for the first time, that water is significantly concentrated within the first 1 mm from the root surface in all three kinds of the plants. Soybean root grown under stress from added aluminum was studied by calculating root volumes and total root surface area from the spatial images. The suppression in root development as calculated from this nondestructive in-situ method correlates well with destructive techniques.

Host-finding ability of three entomopathogenic nematode isolates in the presence of plant roots

Abstract The effect of plant roots on the host-finding ability of three isolates of entomopathogenic nematodes (EPN), Heterorhabditis bacteriophora D-H-Da1, Steinernema sp. Dongrae and Steinernema sp. BJ was studied. In Petri dish experiments the overall response of the infective juveniles (IJ) of these isolates differed from one another, but all were attracted to a Galleria mellonella larva and to a tomato seedling when either of these targets was presented with a blank control. The BJ and D-H-Da1 IJ aggregated more around a tomato root than a G. mellonella larva when these targets were presented separately, but showed no preference for a G. mellonella-tomato seedling combination over a blank control. Dongrae IJ showed no preference for a G. mellonella larva or tomato seedling when each was presented simultaneously in the same Petri dish. In experiments in pots of soil, plant roots did not affect the host-finding ability of Dongrae IJ. In contrast, compared to control pots with no roots, roots of bean plants hindered the ability of BJ IJ to infect a G. mellonella larva, but tomato roots increased host-finding by D-H-Da1 IJ. Roots of certain plant species modify the host-finding ability of EPN, but the extent and direction of the response varied with the EPN applied.

Regulation of alternative oxidase activity during phosphate deficiency in bean roots (Phaseolus vulgaris).

Cyanide-resistant respiration was studied in mitochondria isolated from the roots of bean plants (Phaseolus vulgaris L. cv. Złota Saxa) grown hydroponically up to 16 days on a phosphate-sufficient (+P, control) or phosphate-deficient (-P) medium. Western blotting indicated that the alternative oxidase (AOX) was present only in its reduced (active) form, both in phosphate-sufficient and phosphate-deficient roots, but in the latter, the amount of AOX protein was greater. Addition of pyruvate to the isolation, washing and reaction media made mitochondria from +P roots cyanide-insensitive, similar to mitochondria from -P roots. The doubled activity of NAD-malic enzyme (NAD-ME) in -P compared with +P root mitochondria may suggest increased pyruvate production in -P mitochondria. Lower cytochrome c oxidase (COX) activity and no uncoupler effect on respiration indicated limited cytochrome chain activity in -P mitochondria. In -P mitochondria, the oxygen uptake decreased and the level of Q reduction increased from 60 to 80%. With no pyruvate present (AOX not fully activated), inhibition of the cytochrome pathway resulted in an increased level of the ratio of reduced ubiquinone (Qr) to total ubiquinone (Qt) (Qr/Qt) in +P mitochondria, but did not change Qr/Qt in -P mitochondria. When pyruvate was present, the kinetics for AOX were similar in mitochondria from -P and +P roots. It is suggested that AOX participation in -P respiration may provide an acclimation to phosphate deficiency. Stabilization of the ubiquinone reduction level by AOX might prevent the harmful effect of an increased formation of reactive oxygen species.

Growth of Pseudomonas aureofaciens PGS12 and the Dynamics of HHL and Phenazine Production in Liquid Culture, on Nutrient Agar, and on Plant Roots.

The growth of Pseudomonas aureofaciens PGS12 was followed in nutrient broth (NB), on nutrient agar (NA), and on plant roots by monitoring cell numbers, the production of the autoinducer hexanoyl-homoserine lactone (HHL), and the antibiotic phenazine-1-carboxylic acid (PCA). In NB, as the growth rate declined in transition phase, HHL synthesis increased rapidly, shortly followed by PCA production. During stationary phase, HHL concentration declined rapidly while PCA concentration continued to increase slowly. The luxAB reporter genes were inserted in the phzB gene of the phenazine operon and phenazine transcriptional activity was monitored using measurement of luminescence. Levels and pattern of light output were similar to HHL accumulation and indicated that gene expression was maximal in transition phase and silenced in stationary phase. PCA production continued in stationary phase, suggesting that the protein products of the phenazine operon were maintained in the cell after down regulation. HHL accumulation was 60 times higher on NA than in NB per equivalent volume because of a 60-fold increase in cell density on NA. Higher levels of PCA per cell (6.8 times) and per equivalent volume (360-fold) accumulated in a colony compared to that found in broth. HHL remained at a high concentration in a colony for a longer period compared to a short burst in NB, and this may explain the increased PCA production. In contrast, on wheat seedlings and bean plant roots, bacterial growth was observed, but neither HHL nor PCA was detected; however, transcriptional activity of the phzB::luxAB reporter occurred on the bean plant roots.

Oxidative stress during phosphate deficiency in roots of bean plants ( Phaseolus vulgaris L.)

Summary The oxidative stress symptoms were studied during phosphate deficiency. Prolonged phosphate starvation of bean plants (Phaseolus vulgaris L.) and severe decrease of inorganic phosphate concentration resulted in increased lipid peroxidation and hydrogen peroxide concentration in root tissues. The ratio of reduced to total ubiquinone was also higher in whole roots and isolated mitochondria from the roots of phosphate-deficient plants. No effect of phosphate deficiency on ascorbate peroxidase and superoxide dismutase activities was detected. However, the activities of catalase and total peroxidase were higher in extracts of phosphate-deficient roots compared to control roots. These results indicate that phosphate starvation is an abiotic stress that imposes an oxidative stress in bean root cells. The role of alternative oxidase in stabilizing the reduction level of ubiquinone, and thus preventing active oxygen species formation, is discussed.

The effect of slash/mulch and alleycropping bean production systems on soil microbiota in the tropics

Mulch applied to tropical soil may increase soil health both through stimulation of microbiota beneficial to plant nutrient uptake and the suppression of plant disease. To test this hypothesis, we compared beans in three cropping systems: (1) mulched with secondary vegetation (slash/mulch), (2) mulched with foliage from alleycropped nitrogen-fixing trees, Calliandra calothyrsus, Gliricidia sepium and Inga edulis (alleycrop/mulch), and (3) unmulched, for their effect on positive microbial interactions (nodulation with Rhizobium and arbuscular mycorrhiza (AM)), and pathogenic associations (foliar and root diseases) in long-term field experiments in Costa Rica. In some dry years slash/mulched beans nodulated significantly more than the unmulched, though in wet years the nodule biomass was not significantly different between treatments. Beans grown in alleycropping systems mulched with foliage from Calliandra and Inga had lower nodule biomass than beans in slash/mulched and Gliricidia mulched plots at 3 and 5 weeks, probably due to high nitrogen levels from the decomposing vegetation of the tree mulch. Roots of bean plants were 95–98% colonized by AM fungi and there were no differences between the slash/mulched beans and the unmulched treatments. Slash/mulch had no effect on the foliar diseases angular leaf spot and web blight, due to their naturally low incidence in that year; slash/mulched decreased the severity of anthracnose (caused by Colletotrichum lindemuthianum). Slash/mulch decreased severity of a Fusarium-type root rot, but increased a Rhizoctonia-type. In the laboratory, microbial activity as determined by measurements of CO 2 respiration was greater in the slash/mulched than the unmulched system due to the high respiration of the mulch material. Our hypothesis that the use of mulch would favor mutualistic symbionts was not supported, which may be due to weather and nutrient interference. However, the hypothesis that mulch would reduce disease incidence was supported for certain diseases. A comparison of the microbial community with those of nearby natural systems can help provide a standard for the assessment of microbial health in agroecosystems and allow us to avoid the circularity of defining microbial communities as ‘healthy’ because they are found in cropping systems whose plants appear without disease.

Seeds of Phaseolus vulgaris bean carry Rhizobium etli

The presence of soil bacteria on seeds could provide an explanation for bacterial geographical spread. We report that Phaseolus vulgaris bean seeds naturally carry rhizobia on their testa. One hundred eighteen Rhizobium isolates from L-3-1-1-1 seeds were characterized by multilocus enzyme electrophoresis and compared to Rhizobium species which form nitrogen fixing nodules on the roots of bean plants. As a result of this and other analyses, seed isolates were classified as R. etli. Seed borne rhizobia are probably moisture limited and are acquired from contaminating soil during the harvesting process as seeds from non-opened pods do not carry them. Rhizobia on seeds are in a presumably desiccated or dormant state as they require a rehydration process during which they are antibiotic sensitive. With an improved procedure to detect rhizobia on seeds, we found that 5 out of 13 Phaseolus vulgaris bean cultivars tested harbor rhizobia on the seeds.