Genetic diversity of Bradyrhizobium strains isolated from Arachis hypogaea

Rhizobia are used exclusively in agricultural systems for enhancing the ability of legumes to fix atmospheric nitrogen. Knowledge about the indigenous population is necessary for the selection and application of inoculant strains. In this study, we have assessed the genetic diversity of Bradyrhizobium strains isolated from the host plant, Arachis hypogaea along the coastline of Tamil Nadu. Different populations collected from varying environmental conditions were analysed for salt and pH tolerance. Genetic diversity among the strains was studied using RAPD markers and PCR-RFLP of 16S rDNA and nifD genes. The approaches used in this study yielded consistent results, which revealed a high degree of heterogeneity among strains and detection of two distinct genetic groups.     

Three new species of Aspergillus section Flavi isolated from almonds and maize in Portugal

Three new aflatoxin-producing species belonging to Aspergillus section Flavi are described. They are Aspergillus mottae, A. sergii and A. transmontanensis. These species were isolated from Portuguese almonds and maize. An investigation examined morphology, extrolite production and DNA sequence data to characterize these isolates and describe the new species. Phylogenetic analysis showed that A. transmontanensis and A. sergii form a clade with A. parasiticus whereas A. mottae shares a most recent common ancestor with the combined A. flavus and A. parasiticus clade.     

Competition between effective and ineffective bradyrhizobia nodulating peanuts (Arachis hypogaea)1

The competitive ability of effective and ineffective isolates of Bradyrhizobium to form nodules on four peanut (Arachis hypogaea) genotypes from which they were originally isolated was investigated in a greenhouse study. Pregerminated seeds of each genotype were inoculated with five ratios of ineffective effective bradyrhizobia: 10⁴:0, 10⁴:10² 10⁴:10⁴ 10²:10⁴ and 0:10⁴. Plants were harvested 35 days after planting and nitrogenase activity, total nodule number per plant, plant shoot dry weight and the proportion of nodules formed by each Bradyrhizobium isolate were determined. Nodulation suppression occurred on plants inoculated with the mixed cultures, especially on those inoculated with the 10⁴:10² ineffective effective inoculum ratio. More than 85% of the nodules on plants inoculated with the 10⁴:10⁴ and 10²:10⁴ ineffective effective Bradyrhizobium mixtures were formed by the effective isolates. The number of effective nodules per plant, nitrogenase activity and plant shoot dry matter production all increased with the proportion of the effective bradyrhizobia in the inocula.     

外源多胺对盆栽花生盐胁迫的缓解作用

为探讨外源多胺对花生(Arachis hypogaea)抗盐性的影响, 以盆栽花生‘花育22’为试验材料, 通过叶面喷施1 mmol·L^-1腐胺(Put)、1 mmol·L^-1亚精胺(Spd)、1 mmol·L^-1精胺(Spm)的方法, 研究多胺对150 mmol·L^-1 NaCl胁迫下盆栽花生的缓解作用。结果表明, 与对照(CK)相比, 盐胁迫显著抑制了花生植株的生长与荚果产量, 降低了叶绿素含量和抗氧化酶活性, 丙二醛(MDA)含量、叶片相对电导率增加; 在盐胁迫下, 叶面喷施Put、Spd、Spm处理均可有效促进花生植株的生长, 提高了超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)的活性, 增强植株抗氧化能力, 显著降低了花生叶片相对电导率和MDA的积累量, 从而缓解盐胁迫对质膜的过氧化伤害; 提高了叶绿素含量, 促进了植株高度的生长与分支数增多, 增加了干物质积累量, 从而提高了花生荚果产量; 其中, Spm处理引起的变化幅度大于Spd和Put处理。研究结果说明, 多胺有利于花生幼苗在盐胁迫下活性氧代谢和光合色素含量的提高, 促进花生植株的生长, 降低盐胁迫对花生植株的抑制作用, 且Spm处理的效果最好。     

Exogenous polyamines alleviating salt stress on peanuts (Arachis hypogaea) grown in pots

Aims Soil salinity is a major limiting factor for plant establishment, development and productivity. In recent years, the contradiction between oil crops and food crops for land is increasingly prominent. In order not to take up the land for food, peanut planting on saline-alkali land could be a promising option. However, peanuts have been rarely grown in saline-alkali land, which may be due to the reduction of peanut yield caused by salt stress. Therefore, research of peanut salt resistance has important practical significance.Methods In order to investigate the effects of exogenous polyamines on peanut (Arachis hypogaea) grown in pots under salt stress, ‘Huayu 22’, one of the peanut cultivars, was used as materials by being foliar-sprayed with 1 mmol·L^-1 putrescine (Put), 1 mmol·L^-1 spermidine (Spd) and 1 mmol·L^-1 spermine (Spm) to elucidate the role of exogenous polyamines on peanuts under 150 mmol·L^-1NaCl. Important findingsResults showed that growth, yield, chlorophyll contents and antioxidant enzyme activities of peanut seedling decreased, however, malondialdehyde (MDA) content and relative electrolytic leakage increased under salt stress. Meanwhile, exogenous polyamines significantly improved the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and reduced the relative electrolytic leakage and MDA content in peanut leaves under salt stress and thus alleviating the oxidative damage of salt stress on plasma membrane. It is obvious that exogenous polyamines could improve chlorophyll contents, plant height, number of branch and the amount of dry matter accumulation, even pod yield under salt stress. Among these three polyamines, the effects of exogenous Spm on alleviating salt stress were most effective These results showed that exogenous polyamines, especially Spm, were favorable for the seedlings to increase reactive oxygen metabolism and photosynthesis, which improved peanut growth and reduced the inhibitory effects of salt stress on peanuts.     

DNA fingerprinting analysis of Petromyces alliaceus (Aspergillus section Flavi)

The objective of this study was to evaluate the ability of the Aspergillus flavus pAF28 DNA probe to produce DNA fingerprints for distinguishing among genotypes of Petromyces alliaceus (Aspergillus section Flavi), a fungus considered responsible for the ochratoxin A contamination that is occasionally observed in California fig orchards. P. alliaceus (14 isolates), Petromyces albertensis (one isolate), and seven species of Aspergillus section Circumdati (14 isolates) were analyzed by DNA fingerprinting using a repetitive sequence DNA probe pAF28 derived from A. flavus. The presence of hybridization bands with the DNA probe and with the P. alliaceus or P. albertensis genomic DNA indicates a close relationship between A. flavus and P. alliaceus. Twelve distinct DNA fingerprint groups or genotypes were identified among the 15 isolates of Petromyces. Conspecificity of P. alliaceus and P. albertensis is suggested based on DNA fingerprints. Species belonging to Aspergillus section Circumdati hybridized only slightly at the 7.0-kb region with the repetitive DNA probe, unlike the highly polymorphic hybridization patterns obtained from P. alliaceus and A. flavus, suggesting very little homology of the probe to Aspergillus section Circum dati genomic DNA. The pAF28 DNA probe offers a tool for typing and monitoring specific P. alliaceus clonal populations and for estimating the genotypic diversity of P. alliaceus in orchards, vineyards, or crop fields.     

Aspergillus section Flavi populations from field maize in Argentina

AIMS: Populations of Aspergillus section Flavi were studied from a commercial field of maize in Río Cuarto, Córdoba, Argentina. METHODS AND RESULTS: The Aspergillus species were isolated from soil, debris and insects during three periods: pre-planting, growing maize and post-harvest. The colony count from non-rhizospheric soil in the pre-planting period was higher than in growing maize and the post-harvest period. Debris samples analysed during all periods showed similar infection percentages for Aspergillus section Flavi. The samples of insects collected during the maize-growing period showed a lower percentage of Aspergillus isolates than the samples from soil and debris. Aflatoxigenic strains were present in lower levels in each component of the agroecosystem studied. All the strains that produced sclerotia were L strains. CONCLUSIONS: In this field agroecosystem, the only strains with a high probability for transfer to the storage agroecosystem were L strains with low toxigenic potential. SIGNIFICANCE AND IMPACT OF THE STUDY: Maize pre-harvest contamination with aflatoxigenic inoculum was not significant.     

Pterocarpenes elicited by Aspergillus caelatus in peanut (Arachis hypogaea) seeds

The substituted pterocarpenes named aracarpene-1 (1) and aracarpene-2 (2) were isolated from wounded peanut seeds challenged by a strain of Aspergillus caelatus. The structures of these putative phytoalexins were determined by interpretation of NMR and MS data. The aracarpenes were investigated for their antifungal and antibacterial activities as well as antioxidant, anti-inflammatory, and cytotoxic activities in mammalian cells. Aracarpene-2 demonstrated high antibacterial properties against tested gram-positive and gram-negative bacteria, whereas aracarpene-1 displayed low antibacterial properties against the same bacteria. Both compounds had no antifungal activity against Aspergillus flavus. Together with peanut stilbenoids that are also produced in the challenged seeds, these compounds may represent a class of low-molecular weight peanut metabolites with a defensive role(s) against pathogenic microorganisms.     

Aflatoxin-producing Potential of Isolates of the Aspergillus flavus-oryzae Group from Peanuts (Arachis hypogaea)

Seventy-eight samples of farmer stock peanuts, representing peanuts grown in nine different geographical areas during 1964, were assayed for aflatoxin and examined for associated microflora. Only two samples contained more than 50 ppb of aflatoxin. Infestation by members of the Aspergillus flavus-oryzae group varied from 35 to 100% of the kernels per area and from 1 to 100% of the kernels per sample. Aflatoxin production by individual isolates ranged from 0 to 349,143 ppb under the test conditions employed. In general, the isolates produced 8 to 10 times more B₁ than B₂, and no isolate producing aflatoxins G₁ or G₂ was found. The importance of proper postharvest handling of peanuts is emphasized by the prevalence of isolates of A. flavus-oryzae capable of producing aflatoxins on farmers stock peanuts.     

Response of Groundnut (Arachis hypogaea L.) to inoculation withRhizobium strains isolated from wild arboreal legumes

Summary The rhizobial strain isolated from wild arboreal legumes viz.Butea monosperma, Glyricidia sepium andAcacia nilotica effectively increased nodulation, shoot weight, pod weight, nitrogenase activity and also showed high competitive ability as compared to the homologous strains NC92 and G2 as well as chemical and absolute controls in groundnut. Thus, the findings of present study open a new field for exploring superior rhizobia from wild legumes, which can be used for improving the yield of cultivated legumes.

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Réponse de l'arachide (Arachis hypogaea L.) à l'inoculation par des souches de Rhizobium isolées de légumes arboricoles sauvages

Résumé Les souches rhizobiennes isolées de légumes sauvages arboricoles commeButea monosperma,Glyricidia sepium etAcacia nilotica ont effectivement augmenté la nodulation, le poids de la racine, le poids des cosses, l'activité de nitrogénase. Elles ont aussi montré une aptitude à la forte compétition par comparaison avec les souches homologues NC92 et G2 de même qu'un contrôle chimique et absolu de l'arachide. Aussi, les résultats de la présente étude ouvrent un nouveau champ pour l'exploration des rhizobia supérieurs de légumes sauvages, qui peuvent être utilisés pour l'amélioration du rendement de légumes cultivés.

     

Phylogeny and diversity of Bradyrhizobium strains isolated from the root nodules of peanut (Arachis hypogaea) in Sichuan, China.

Twenty-two rhizobial strains isolated from the root nodules of two Chinese peanut cultivars (Arachis hypogaea L. Tianfu no. 3 and a local cultivar) growing at four different sites in the Sichuan province, Southwest China, were characterized by growth rate, rep-PCR, PCR-RFLP of 16S rDNA, partial sequencing of ribosomal genes, and fatty acid-methyl ester analysis (FAME), and compared with strains representing Bradyrhizobium japanicum, B. elkanii and other unclassified Bradyrhizobium sp. All peanut isolates from Sichuan were bradyrhizobia. Dendrograms constructed using the rep-PCR fingerprints grouped the strains mainly according to their geographic and cultivar origin. Based on PCR-RFLP and partial sequence analysis of 16S rDNA it appears that peanut bradyrhizobial strains from Sichuan are similar to peanut strains from Africa and Israel, and closely related to B. japonicum. In contrast, analysis of FAME data using two-dimensional principal component analysis indicated that Bradyrhizobium sp. (Arachis) were similar to, but slightly different from other bradyrhizobia. The presence and level of fatty acid 16:1 w5c was the distinguishing feature. The results of PCR-RFLP of the 16S rRNA gene, the partial sequence analysis of 16S rDNA, and FAME were in good agreement.     

Plasmon divergence in peanuts (Arachis hypogaea): A third plasmon and locus affecting growth habit

Summary In a series of reciprocal crosses between peanut (Arachis hypogaea L.) cultivars from different regions and known testers, the cultivar HG1 from India was shown to have a third plasmon type, designated [G]. HG1 also has a third locus, Hb₅ , which interacts with the plasmons and the loci described earlier. In the [G] plasmon, Hb₁ and Hb₅ are additive: plants having three or four dominant alleles have a trailing habit while the other nuclear genotypes produce in [G] erect plants. In the [V4] plasmon, Hb₂ and Hb₅ are complementary, [V4] Hb₂-, Hb₅-plants being trailing, the others erect. In the [G] plasmon, Hb₂ and Hb₅ are complementary, while in the [O] plasmon they are additive.     

Inadequate iron supply and high bicarbonate impair the symbiosis of peanuts (Arachis hypogaea L.) with different Bradyrhizobium strains

In the present study, we examined the effects of iron deficiency in an acid solution and in an alkaline solution containing bicarbonate on the growth and nodulation of peanuts inoculated with different bradyrhizobial strains or supplied with fertilizer nitrogen.Inadequate iron supply in acid solution decreased the number of nodule initials, nodule number and nodule mass. Alleviating the iron deficiency increased acetylene reduction but not bacteroid numbers in nodules. Nitrogen concentrations in shoots of inoculated plants increased as iron concentrations in solution increased when determined at day 30 but not at day 50. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic nitrogen fixation than for those receiving fertilizer nitrogen.Adding bicarbonate to the solution with 7.5 M Fe markedly depressed nodule formation. This effect was much more severe than that of inadequate iron supply alone. Bicarbonate also decreased nitrogenase activity but did not decrease bacteroid concentrations in nodules.Both NC92 and TAL1000 nodulated peanuts poorly when bicarbonate was present. However, an interaction between iron concentrations in acid solutions and Bradyrhizobium strains on nodulation of peanuts was observed. Alleviating iron deficiency increased the number of nodule initials and nodules to a much greater extent for plants inoculated with TAL1000 than for plants inoculated with NC92.     

Ethylene and the geotropic response of lateral branches in peanuts (Arachis hypogaea L.)

The prostrate growth habit of runner-type peanut plants changedwhen treated with the ethylene-releasing compound CEPA: thehorizontal branches became plagiotropically oriented and theplant assumed a bushy form. Treatment with CEPA caused a markedincrease in ethylene evolution for about a week, which thendecreased to the level of the control. Nevertheless, the branchesmaintained their newly assumed plagiotropic orientation. Ethylene evolution from isolated branch tips correlated withtheir age and orientation, being highest in old plagiotropicand lowest in old diatropic branches. Light intensity and qualitywhich caused plagiotropic orientation of branches also causedan increase in ethylene evolution, while ethylene evolutionwas lowest under light conditions favouring diatropic orientation.Along with the changes to plagiotropic orientation by CEPA,an increase in GA-like substances and a decrease in growth inhibitorswas observed in extracts from treated plants. (Received October 7, 1975; )     

Phytohormones and light regulation of the growth habit in peanuts (Arachis hypogaea L.)

Diageotropic side branches in runner type peanuts assume anorthotropic position when grown in the dark but return to aplagiotropic postition when transferred back to light. The effectof light on the trailing habit of lateral branches depends onthe quality and intensity of the light taking place under blue+farred light, but not under blue alone. Light intensity below 28Kergs.cm^–2.sec^–1 changed the growth of the runner'slaterals from trailing to erect. Inhibitors of both GA and auxinactivity were higher in the laterals of runners than in thoseof the erects. Along with the change in the trailing habit bylow light intensity, a decrease in inhibitor level was observed.Gibberellin-like activity was smaller in both extracts and diffusatesof the growing tip of lateral branches than in the main axis.An inhibitor found only in lateral branches of runner type plantscould be detected in erect plants in the presence of auxin.The predominant factor controlling differences in the growthhabit of side branches of the erect and runner types is thepresence of an inhibitor; while, within each type, levels ofgibberellin seem to account for the different growth habit ofthe axis and laterals. (Received January 23, 1973; )     

The Deamidase of Groundnut Plants (Arachis hypogaea)

The deamidase enzyme system present in extracts of groundnutplant tissues has been studied. The distribution of the enzymewithin the different organs of the plant were determined, andsome of the properties of the enzyme present in leaf extractsare recorded. From its substrate specificity the enzyme is probablybest regarded as a -methyleneglutaininase, although it catalysesthe hydrolysis of glutamine at about one-fifth of the rate of-methyleneglutamine. The enzyme may play an important role inthe over-all nitrogen metabolism of the plant, as well as controllingthe relative concentrations of -methyleneglutamine and -methyleneglutamicacid in the different organs. The properties of the enzyme havebeen compared with those recorded in the literature of glutaminasesand asparaginases, and certain common features are apparent.The new deamidase was, however, more stable to certain denaturingtreatments than were the other types of deamidase.     

Osmotic and matric potential effects on growth, sugar alcohol and sugar accumulation by Aspergillus section Flavi strains from Argentina

AIMS: The effect of osmotic and matric potential stress on growth and sugar alcohols (polyols: glycerol, erythritol, arabitol and mannitol) and sugars (trehalose and glucose) accumulation in toxigenic and nontoxigenic colonies of Aspergillus flavus and A. parasiticus was evaluated. METHODS AND RESULTS: Growth of Aspergillus section Flavi with significant reductions at 20 and 30 degrees C was more sensitive to changes in matric potential, between 60 and 100% in the range of -7 to -14 MPa. No significant differences were found between toxigenic and nontoxigenic strains for both species. Total polyol accumulation in unamended maize meal agar medium (-0.75 MPa water potential) was higher at 30 than 20 degrees C. The major change in concentrations of endogenous sugars and total polyols was in matrically amended medium (with PEG 8000) at -7 and -10 MPa. Accumulation of glucose, arabitol, mannitol and erythritol content of A. flavus and A. parasiticus mycelial colonies was greater in normal unstressed maize meal agar medium (-0.75 Mpa) at 20 degrees C. This was modified by solute and matric stress. CONCLUSIONS: The data showed relative sensitivity to osmotic and matric potential, and temperature, and the impact on growth rates, polyol and sugar accumulation in mycelia of A. flavus and A. parasiticus. SIGNIFICANCE AND IMPACT OF THE STUDY: The matric potential effects on growth may be of particular importance for growth and survival in environments with low-matric potential stress. The tolerance of spoilage fungi such as Aspergillus section Flavi to such modifications could increase the potential for spoilage and mycotoxin production in such substrates. This knowledge is important for understanding the relative ecological fitness of these aflatoxigenic species and in the development of prevention strategies for their control.     

花生成熟花粉的超微结构

花生（Arachis hypogaea L．）成熟花粉为二细胞型,具3个萌发沟,少数有4个。外壁呈蜂窝状。花粉壁由覆盖层、基粒棒、外壁内层及内壁构成。线粒体嵴密集、相互平行,脂体被粗面内质网包围。粗面内质网与外核膜相连,亦与线粒体相连。高尔基体甚少。营养核无核仁及染色质,与生殖细胞相连形成雄性生殖单位（male germ unit）。生殖细胞锤形、有壁,见一末端延伸成长尾状（长8μm）。细胞质含核糖体、线粒体、微管,未见体。在有些生殖细胞核内观察到具双层膜、少量嵴及深色内含物的球形结构,其米来源及本质尚不知,有待进一步研究确定。