Physiological potential and health of peanut seed treated with ozone / Potencial fisiológico e sanidade de sementes de amendoim submetidas a ozonização

Peanut seed can be infected by pathogen diseases that adversely affect the oil crop's value chain. Ozone gas (O3) can be an alternative for the control of fungal diseases due to its high oxidizing potential. In this study, we investigated the effects of O3 exposure time on physiological and health characteristics of seed from three peanut cultivars. Seed from peanut cultivars Granoleico, IAC OL3, and IAC 503 were analyzed for their health (blotter test) and physiological potential (germination, first count, and seedling length) after exposure to O3 for 0, 1, 8, and 16 h. Peanut seed physiological quality and health differed among cultivars. Exposure of seed from peanut cultivars IAC OL3, IAC 503, and Granoleico to O3 at a rate of 600 mg h-1 did not affect the development of normal seedlings as measured by the first count and germination, but seedling length increased, decreased, or was not affected in cultivars Granoleico, IAC 503, and IAC OL3, respectively. Also, O3 did not eradicate fungal infections in peanut seed treated with O3 at a rate of 600 mg h-1 for up to 16 h, but the incidence of the fungus Rhizopus sp. in seed from cultivars IAC OL3, Granoleico, and IAC 503 increased, decreased or was not affected, respectively, after 8 h.(AU)

Sementes de amendoim são alvos de patógenos e geram problemas à cadeia produtiva da espécie oleaginosa. Uma alternativa de controle de microrganismos é a aplicação da ozonização devido seu alto potencial de oxidação. Portanto, o objetivo deste ensaio foi avaliar a aplicação do gás ozônio, em três cultivares de amendoim, nos atributos fisiológicos e sanitários de acordo com diferentes períodos de exposição das sementes ao O3. Neste ensaio, sementes de amendoim dos cultivares Granoloeico, IAC OL3 e IAC 503 foram analisadas quanto a sanidade (blotter test) e potencial fisiológico (germinação, primeira contagem e comprimento de plântulas) após submissão ao gás ozônio por 0, 1, 8 e 16 horas. De acordo com os cultivares, sementes de amendoim apresentam diferentes desempenhos fisiológicos e sanitários de qualidade. A exposição de sementes dos cultivares de amendoim IAC OL3, IAC 503 e Granoleico ao gás ozônio até 16 horas na taxa de 600 mg/h não interfere na formação de plântulas normais avaliada na primeira contagem de germinação e na germinação, entretanto há efeitos de incremento, decréscimo ou nulo no comprimento de plântulas para os cultivares Granoleico, IAC 503 e IAC OL3, respectivamente. Não há erradicação de fungos presentes em sementes de amendoim expostas ao gás ozônio numa taxa de 600mg/h até 16 horas, porém a incidência do fungo Rhizopus sp. aumenta, diminui ou é indiferente no período de 8h para os cultivares IAC OL3, Granoleico e IAC 503, respectivamente.(AU)

Acquisition of the physiological quality of peanut (Arachis hypogaea L.) seeds during maturation under the influence of the maternal environment.

The scarcity of information on the maturation physiology of the peanut seed (Arachis hypogaea L.; Virgínia group) makes harvesting high quality seeds a challenge for the seed industry. During two consecutive crop seasons, we studied the acquisition of physiological quality of peanut seeds during maturation in tropical conditions. We bring new insights about the period of late maturation of seeds and the influence of the maternal environment on physiological quality. We monitored water content, dry weight, ability of germination, desiccation tolerance, vigor and longevity. In addition, we monitored temperature and precipitation throughout plant growth. We demonstrate that the physiological quality of peanut seeds is acquired during development, with a maximum between 57 and 76 days after flowering in the late stage of maturation. This final period represents about 25% of the development, considered the best time to harvest peanut seeds with the highest quality. Our findings also support the idea that the adequate proportion of rainfall and thermal sum in the maternal environment are factors that favor the acquisition of peanut seed longevity.

Water content in peanut seeds according to conditions of the storage environment / Teor de água em sementes de amendoim em função das condições do ambiente de armazenamento

The conditions of the storage environment caninfluence the quality of seeds or grains in relation to commercial quality, deterioration and nutritional characteristics, mainly as a function of temperature and relative humidity. The objective of this study was to analyze the influence of temperature and relative humidity of storage on the water content of peanut seeds.The experiment was developed in a completely randomized designin factorial scheme5 x 9, with five temperatures (5, 10, 15, 20 and 25°C) and nine conditions of relative humidity, each condition had nine repetitions. The seeds were stored in airtight packaging with saturated solutions to maintain a constant condition.The water content in the seeds was evaluated in each condition. The data were subjected to analysis of variance, correlation, regression, multivariate analysis and adjustment with mathematical models. Relative humidity was more expressive in changing the equilibrium water content. The Chung-Pfost model was the most suitable to represent the sorption process in peanut seeds.

As condições do ambiente de armazenamento podem influenciar na qualidade desementes ou grãos em relação a qualidade comercial, deterioração e características nutricionais, principalmente em função da temperatura e umidade relativa. O estudo teve como objetivo analisar a influência da temperatura e umidade relativa de armazenamento sobre o conteúdo de água em sementes de amendoim. O experimento foi desenvolvido em delineamento inteiramente casualizadoem esquema fatorial 5 x 9, sendo cinco temperaturas (5, 10, 15, 20 e 25°C) e nove condições de umidade relativa. Cada condição apresentava nove repetições. As sementes foram armazenadas em embalagens herméticas com soluções saturadas para manter a condição constante. Foi avaliado o teor de água nas sementes em cada condição. Os dados foram submetidos a análise de variância, correlação, regressão, analise multivariada e ajuste com modelos matemáticos. A umidade relativa foi mais expressiva na alteração do teor de água em equilíbrio. O modelo de Chung-Pfost foi o mais adequado para representar o processo de sorção em sementes de amendoim.

Water content in peanut seeds according to conditions of the storage environment / Teor de água em sementes de amendoim em função das condições do ambiente de armazenamento

The conditions of the storage environment caninfluence the quality of seeds or grains in relation to commercial quality, deterioration and nutritional characteristics, mainly as a function of temperature and relative humidity. The objective of this study was to analyze the influence of temperature and relative humidity of storage on the water content of peanut seeds.The experiment was developed in a completely randomized designin factorial scheme5 x 9, with five temperatures (5, 10, 15, 20 and 25°C) and nine conditions of relative humidity, each condition had nine repetitions. The seeds were stored in airtight packaging with saturated solutions to maintain a constant condition.The water content in the seeds was evaluated in each condition. The data were subjected to analysis of variance, correlation, regression, multivariate analysis and adjustment with mathematical models. Relative humidity was more expressive in changing the equilibrium water content. The Chung-Pfost model was the most suitable to represent the sorption process in peanut seeds.(AU)

As condições do ambiente de armazenamento podem influenciar na qualidade desementes ou grãos em relação a qualidade comercial, deterioração e características nutricionais, principalmente em função da temperatura e umidade relativa. O estudo teve como objetivo analisar a influência da temperatura e umidade relativa de armazenamento sobre o conteúdo de água em sementes de amendoim. O experimento foi desenvolvido em delineamento inteiramente casualizadoem esquema fatorial 5 x 9, sendo cinco temperaturas (5, 10, 15, 20 e 25°C) e nove condições de umidade relativa. Cada condição apresentava nove repetições. As sementes foram armazenadas em embalagens herméticas com soluções saturadas para manter a condição constante. Foi avaliado o teor de água nas sementes em cada condição. Os dados foram submetidos a análise de variância, correlação, regressão, analise multivariada e ajuste com modelos matemáticos. A umidade relativa foi mais expressiva na alteração do teor de água em equilíbrio. O modelo de Chung-Pfost foi o mais adequado para representar o processo de sorção em sementes de amendoim.(AU)

Peanut cultivars display susceptibility by triggering outbreaks of Tetranychus ogmophallos (Acari: Tetranychidae).

The peanut red spider mite, Tetranychus ogmophallos Ferreira and Flechtmann (Acari: Tetranychidae), is an important pest of peanut in Brazil and is considered a quarantine pest in other countries. This study investigates the development, reproduction, survival and life table parameters of T. ogmophallos on five peanut cultivars-three with high levels of oleic acid [high oleic] and recently released: Granoleico, IAC OL 3 and IAC 503; and two regular and previously used by farmers: Runner IAC 886, IAC Tatu ST 3-and two breeding lines (L. 8008 and L. 322) in the growth chamber. There were differences between the developmental times of all immature stages, the oviposition period, fecundity and adult longevity of T. ogmophallos reared on the peanut cultivars and breeding lines. The longest duration of the immature stage and lowest fecundity occurred on cultivars Granoleico and Runner IAC 886, and breeding line L. 322, which also displayed the lowest intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R0) and the shortest mean generation time (T). The highest fitness occurred on the IAC Tatu ST, IAC OL 3, IAC 503 and L. 8008. Our study shows that peanut cultivars belonging to the group with high oleic trait and recently released (IAC OL 3 and IAC 503) are susceptible to T. ogmophallos, except Granoleico, which is resistant. The regular and previously used cultivar Runner IAC 886 and breeding line L. 322 are resistant to the peanut red spider mite.

Can Bradyrhizobium strains inoculation reduce water deficit effects on peanuts?

Drought is one of the environmental factors that most affects peanut cultivation in semi-arid regions, resulting in economic losses to growers. However, growth promoting bacteria are able to reduce water deficit damage in some plant species. In this context, this study aimed to evaluate the interaction of Bradyrhizobium strains reducing water stress effects on peanut genotypes by antioxidant enzymes activities, leaf gas exchanges and vegetative growth, as well as to determine the taxonomic positioning of strain ESA 123. The 16S rRNA gene of ESA 123 was amplified by PCR and sequenced by dideoxy Sanger sequencing method. An experiment was performed in greenhouse with three peanut genotypes (BRS Havana, CNPA 76 AM and 2012-4), two Bradyrhizobium strains (SEMIA 6144 and ESA 123), a mineral source of N and an absolute control (without N) under two water regimes (with and without irrigation). Seeds of peanut were sown and the plants were grown until 30 days after emergence. On the 20th day, the water deficit plants group had their irrigation suspended for 10 days. At in silico analyzes, ESA 123 presented 98.97% similarity with the type strain of B. kavangense. Leaf gas exchange was affected by water deficit; as well as alteration of antioxidant activities and reduction of vegetative growth variables. However, some plants inoculated with SEMIA 6144 and ESA 123 strains presented lower reductions and increment of some evaluated variables, mainly the ones inoculated with the ESA 123 strain, Bradyrhizobium sp. from the semi-arid region of Northeast Brazil. This data suggests beneficial effects of the peanut-Bradyrhizobium interaction in a water stress condition, specially with the ESA 123 strain.

Resistance to thrips (Enneothrips flavens) in wild and amphidiploid Arachis species.

Thrips (Enneothrips flavens) is a pest that causes severe damage and yield losses to peanut crop if not properly controlled. The main control method currently used by farmers is bi-weekly application of insecticides during crop development, which, in addition to its toxicity, is very costly. Thus, new sources of resistance must be identified in order to reduce the use of insecticides and effectively manage the pest. This study aimed to evaluate the occurrence and symptoms of E. flavens infestations in 12 accessions of 10 wild species of Arachis and nine amphidiploids, as well as to compare their morphoagronomic characteristics to those of commercial cultivars. To this end, we conducted experiments during two summer seasons, using a randomized block design with four replications. We conducted evaluations of the severity of infestation, noting visual symptoms of E. flavens and morphological and reproductive characteristics of the Arachis plants. Results indicated that wild accessions V 7635 (A. vallsii), V 13250 (A. kempff-mercadoi), K 9484 (A. batizocoi), Wi 1118 (A. williamsii), V 14167 (A. duranensis) and V 13751 (A. magna) are the most promising for obtaining useful new amphidiploids. Among the amphidiploids, An 12 (A. batizocoi x A. kempff-mercadoi)4x, An 9 (A. gregoryi x A. stenosperma) 4x, and An 8 (A. magna x A. cardenasii)4x showed high level of resistance to E. flavens. The identified thrips resistant wild and amphidiploid Arachis species may be used in future breeding program to produce thrips resistant peanut cultivars.

An oxidative burst and its attenuation by bacterial peroxidase activity is required for optimal establishment of the Arachis hypogaea-Bradyrhizobium sp. symbiosis.

AIMS: The main purpose of this study was to determine whether the Arachis hypogaea L. root oxidative burst, produced at early stages of its symbiotic interaction with Bradyrhizobium sp. SEMIA 6144, and the bacterial antioxidant system are required for the successful development of this interaction. METHODS AND RESULTS: Pharmacological approaches were used to reduce both plant oxidative burst and bacterial peroxidase enzyme activity. In plants whose H2 O2 levels were decreased, a low nodule number, a reduction in the proportion of red nodules (%) and an increase in the bacteroid density were found. The symbiotic phenotype of plants inoculated with a Bradyrhizobium sp. SEMIA 6144 culture showing decreased peroxidase activity was also affected, since the biomass production, nodule number and percentage of red nodules in these plants were lower than in plants inoculated with Bradyrhizobium sp. control cultures. CONCLUSIONS: We demonstrated for the first time that the oxidative burst triggered at the early events of the symbiotic interaction in peanut, is a prerequisite for the efficient development of root nodules, and that the antioxidant system of bradyrhizobial peanut symbionts, particularly the activity of peroxidases, is counteracting this oxidative burst for the successful establishment of the symbiosis. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results provide new insights into the mechanisms involved in the development of the symbiotic interaction established in A. hypogaea L. a legume infected in an intercellular way.

New hybrids from peanut (Arachis hypogaea L.) and synthetic amphidiploid crosses show promise in increasing pest and disease tolerance.

The primary gene pool of the cultivated peanut (Arachis hypogaea L., allotetraploid AABB) is very narrow for some important characteristics, such as resistance to pests and diseases. However, the Arachis wild diploid species, particularly those from the section Arachis, still have these characteristics. To improve peanut crops, genes from the wild species can be introgressed by backcrossing the hybrids with A. hypogaea. When diploid species whose genomes are similar to those of the cultivated peanut are crossed, sterile hybrids result. Artificially doubling the number of chromosomes of these hybrids results in fertile synthetic polyploids. The objectives of this study were: 1) to obtain progenies by crossing amphidiploids with the cultivated peanut, and 2) to characterize these two groups of materials (amphidiploids and progenies) so that they may be efficiently conserved and used. Using morphological, molecular, and pollen viability descriptors we evaluated one cultivar of A. hypogaea (IAC 503), eight synthetic amphidiploids, and the progenies resulting from four distinct combinations of crossing between IAC 503 and four amphidiploids.

Physiological quality of peanut forage seeds submitted to different storage times and environments / Qualidade fisiológica de sementes de amendoim forrageiro submetidas a diferentes tempos e ambientes de armazenamento

The successful establishment and production of pasture depends on a good seed quality, and the seed represents only about 10% of the total cost of the pasture formation. Considering this fact, the aim of the present study was to compare different times (0; 4; 8 and 12 months) of storage (BOD set at 10ºC), (Refrigerator 00ºC ± 5C) and (Lab at 26ºC ± 3ºC) in seeds of Arachis pintoi cv. Amarillo. The seeds used were treated with the fungicide Vitavax-Thiram ® [Active Ingredient (carboxin + thiram): 200 + 200g / L] at a dosage of 300ml of fungicide diluted in 500mL of water to 100kg of seeds. The experimental design was in completely randomized blocks (DBC), arranged in a 4x3 factorial scheme with four storage times (0; 4; 8 and 12 months), three environments (Lab, Refrigerator and B.O.D.) with four repetitions. The results were submitted to analysis of variance, the regression and the means were compared by the Tukey test and F, at 5% probability. The seeds stored at low temperatures, even in the highest storage time studied, maintain their physiological quality, indicating that low temperatures have a positive effect on seed conservation.(AU)

O sucesso no estabelecimento e produção de pastagens depende de uma boa qualidade da semente, sendo que a semente representa apenas cerca de 10% do custo total de formação da pastagem. Diante deste fato o objetivo do presente trabalho foi comparar diferentes tempos (0; 4; 8 e 12 meses) de armazenamento em (B.O.D regulada a 10ºC); (Geladeira 00ºC ± 5C) e Laboratório a 26ºC ± 3 ºC não há necessidade de parênteses para separar os tratamentos em sementes de Arachis pintoi cv. Amarillo. As sementes utilizadas foram tratadas com fungicida Vitavax-Thiram® [Ingrediente Ativo (carboxina + tiram): 200 + 200g/L], na dosagem de 300mL de fungicida diluídos em 500mL de água para 100kg de sementes. O delineamento experimental utilizado foi em blocos inteiramente casualizado (DBC), dispostos em um esquema fatorial 4x3 sendo quatro tempos de armazenamento (0, 4, 8 e 12 meses), três ambientes (Laboratório, Geladeira e incubadora B.O.D) com quatro repetições. Os resultados foram submetidos à análise de variância, regressão e as médias comparadas pelo teste de Tukey e F, a 5% de probabilidade. As sementes armazenadas em baixas temperaturas, mesmo no maior tempo de armazenamento estudado, mantêm sua qualidade fisiológica, indicando que baixas temperaturas exercem efeito positivo na conservação das sementes.(AU)

Physiological quality of peanut forage seeds submitted to different storage times and environments / Qualidade fisiológica de sementes de amendoim forrageiro submetidas a diferentes tempos e ambientes de armazenamento

The successful establishment and production of pasture depends on a good seed quality, and the seed represents only about 10% of the total cost of the pasture formation. Considering this fact, the aim of the present study was to compare different times (0; 4; 8 and 12 months) of storage (BOD set at 10ºC), (Refrigerator 00ºC ± 5C) and (Lab at 26ºC ± 3ºC) in seeds of Arachis pintoi cv. Amarillo. The seeds used were treated with the fungicide Vitavax-Thiram ® [Active Ingredient (carboxin + thiram): 200 + 200g / L] at a dosage of 300ml of fungicide diluted in 500mL of water to 100kg of seeds. The experimental design was in completely randomized blocks (DBC), arranged in a 4x3 factorial scheme with four storage times (0; 4; 8 and 12 months), three environments (Lab, Refrigerator and B.O.D.) with four repetitions. The results were submitted to analysis of variance, the regression and the means were compared by the Tukey test and F, at 5% probability. The seeds stored at low temperatures, even in the highest storage time studied, maintain their physiological quality, indicating that low temperatures have a positive effect on seed conservation.

O sucesso no estabelecimento e produção de pastagens depende de uma boa qualidade da semente, sendo que a semente representa apenas cerca de 10% do custo total de formação da pastagem. Diante deste fato o objetivo do presente trabalho foi comparar diferentes tempos (0; 4; 8 e 12 meses) de armazenamento em (B.O.D regulada a 10ºC); (Geladeira 00ºC ± 5C) e Laboratório a 26ºC ± 3 ºC não há necessidade de parênteses para separar os tratamentos em sementes de Arachis pintoi cv. Amarillo. As sementes utilizadas foram tratadas com fungicida Vitavax-Thiram® [Ingrediente Ativo (carboxina + tiram): 200 + 200g/L], na dosagem de 300mL de fungicida diluídos em 500mL de água para 100kg de sementes. O delineamento experimental utilizado foi em blocos inteiramente casualizado (DBC), dispostos em um esquema fatorial 4x3 sendo quatro tempos de armazenamento (0, 4, 8 e 12 meses), três ambientes (Laboratório, Geladeira e incubadora B.O.D) com quatro repetições. Os resultados foram submetidos à análise de variância, regressão e as médias comparadas pelo teste de Tukey e F, a 5% de probabilidade. As sementes armazenadas em baixas temperaturas, mesmo no maior tempo de armazenamento estudado, mantêm sua qualidade fisiológica, indicando que baixas temperaturas exercem efeito positivo na conservação das sementes.

Contribution of phytochelatins to cadmium tolerance in peanut plants.

Cadmium (Cd) is a well known heavy metal considered as one of the most toxic metals on Earth, affecting all viable cells that are exposed even at low concentration. It is introduced to agricultural soils mainly by phosphate fertilizers and causes many toxic symptoms in cells. Phytochelatins (PCs) are non-protein thiols which are involved in oxidative stress protection and are strongly induced by Cd. In this work, we analyzed metal toxicity as well as PCs implication on protection of peanut plants exposed to Cd. Results showed that Cd exposure induced a reduction of peanut growth and produced changes in the histological structure with a deposit of unknown material on the epidermal and endodermal cells. When plants were exposed to 10 µM Cd, no modification of chlorophyll, lipid peroxides, carbonyl groups, or hydrogen peroxide (H2O2) content was observed. At this concentration, peanut leaves and roots glutathione (GSH) content decreased. However, peanut roots were able to synthesize different types of PCs (PC2, PC3, PC4). In conclusion, PC synthesis could prevent metal disturbance on cellular redox balance, avoiding oxidative damage to macromolecules.

Detection, characterization, and biological effect of quorum-sensing signaling molecules in peanut-nodulating bradyrhizobia.

Bacteria of the genus Bradyrhizobium are able to establish a symbiotic relationship with peanut (Arachis hypogaea) root cells and to fix atmospheric nitrogen by converting it to nitrogenous compounds. Quorum sensing (QS) is a cell-cell communication mechanism employed by a variety of bacterial species to coordinate behavior at a community level through regulation of gene expression. The QS process depends on bacterial production of various signaling molecules, among which the N-acylhomoserine lactones (AHLs) are most commonly used by Gram-negative bacteria. Some previous reports have shown the production of QS signaling molecules by various rhizobia, but little is known regarding mechanisms of communication among peanut-nodulating strains. The aims of this study were to identify and characterize QS signals produced by peanut-nodulating bradyrhizobial strains and to evaluate their effects on processes related to cell interaction. Detection of AHLs in 53 rhizobial strains was performed using the biosensor strains Agrobacterium tumefaciens NTL4 (pZLR4) and Chromobacterium violaceum CV026 for AHLs with long and short acyl chains, respectively. None of the strains screened were found to produce AHLs with short acyl chains, but 14 strains produced AHLs with long acyl chains. These 14 AHL-producing strains were further studied by quantification of ß-galactosidase activity levels (AHL-like inducer activity) in NTL4 (pZLR4). Strains displaying moderate to high levels of AHL-like inducer activity were subjected to chemical identification of signaling molecules by high-performance liquid chromatography coupled to mass spectrometry (LC-MS/MS). For each AHL-producing strain, we found at least four different AHLs, corresponding to N-hexanoyl-DL-homoserine lactone (C(6)), N-(3-oxodecanoyl)-L-homoserine lactone (3OC(10)), N-(3-oxododecanoyl)-L-homoserine lactone (3OC(12)), and N-(3-oxotetradecanoyl)-L-homoserine lactone (3OC(14)). Biological roles of 3OC10, 3OC12, and 3OC14 AHLs were evaluated in both AHL-producing and -non-producing peanut-nodulating strains. Bacterial processes related to survival and nodulation, including motility, biofilm formation, and cell aggregation, were affected or modified by the exogenous addition of increasing concentrations of synthetic AHLs. Our results clearly demonstrate the existence of cell communication mechanisms among bradyrhizobial strains symbiotic of peanut. AHLs with long acyl chains appear to be signaling molecules regulating important QS physiological processes in these bacteria.

Origin of triploid Arachis pintoi (Leguminosae) by autopolyploidy evidenced by FISH and meiotic behaviour.

BACKGROUND AND AIMS: Polyploidy is a dominant feature of flowering-plant genomes, including those of many important crop species. Arachis is a largely diploid genus with just four polyploid species. Two of them are economically important: the cultivated peanut and A. glabrata, a tropical forage crop. Even though it is usually accepted that polyploids within papilionoid legumes have arisen via hybridization and further chromosome doubling, it has been recently suggested that peanut arose through bilateral sexual polyploidization. In this paper, the polyploid nature of the recent, spontaneously originated triploid cytotype of the tropical lucerne, A. pintoi, was analysed, and thereby the mechanism by which polyploids may arise in the genus. METHODS: Chromosome morphology of 2x and 3x A. pintoi was determined by the Feulgens technique and the rDNA sites were mapped by FISH. To investigate whether polyploidization occurred by means of unreduced gametes, a detailed analysis of the microsporogenesis and pollen grains was made. KEY RESULTS: The 2x and 3x plants presented 9m + 1sm and a satellited chromosome type 2 in each haploid genome. Physical mapping revealed a cluster of 18S-26S rDNA, proximally located on chromosome 6, and two 5S rDNA loci on chromosomes 3 and 5. Diploid plants presented 10II in meiosis while trivalents were observed in all triploids, with a maximum of 10III by cell. Diploid A. pintoi produced normal tetrads, but also triads, dyads and monads. Two types of pollen grains were detected: (1) normal-sized with a prolate shape and (2) large ones with a tetrahedral morphology. CONCLUSIONS: Karyotype and meiotic analysis demonstrate that the 3x clone of A. pintoi arose by autopolyploidy. The occurrence of unreduced gametes strongly supports unilateral sexual polyploidization as the most probable mechanism that could have led to the origin of the triploid cytotype. This mechanism of polyploidization would probably be one of the most important mechanisms involved in the origin of economically important species of Arachis, either by triploid bridge or bilateral sexual polyploidization.

Interaction among Arachis hypogaea L. (peanut) and beneficial soil microorganisms: how much is it known?

The leguminous crop Arachis hypogaea L. (peanut) is originally from South America and then was disseminated to tropical and subtropical regions. The dissemination of the crop resulted in peanut plants establishing a symbiotic nitrogen-fixing relationship with a wide diversity of indigenous soil bacteria. We present in this review, advances on the molecular basis for the crack-entry infection process involved in the peanut-rhizobia interaction, the diversity of rhizobial and fungal antagonistic bacteria associated with peanut plants, the effect of abiotic and biotic stresses on this interaction and the response of peanut to inoculation.

Experimental evidences of pSym transfer in a native peanut-associated rhizobia.

In previous works we have characterized the native bacterial diversity associated with root nodules of peanut grown in Córdoba province, Argentina. Studies performed in the isolate Rhizobium sp. NET30 revealed a phylogenetic incongruence between housekeeping and nodulation genes. This discrepancy could be explained by the horizontal transfer of nodulation genes from the native peanut isolate Rhizobium sp. NCHA22, a bacterium that showed high identity percentages with Rhizobium tropici IIB strains in the basic and symbiotic genes analyzed. In this work, we demonstrate that, in R. sp. NCHA22, genes required for nodule formation in common bean (Phaseolus vulgaris L.) are plasmid-borne. A symbiotic plasmid capable of conjugal transfer to different genetic backgrounds was identified in this isolate. The mechanism involved in the plasmidic transfer differs from that described for R. tropici CIAT899 (R. tropici IIB type strain). The transfer of a symbiotic plasmid, and the subsequent homologous recombination of nodulation genes in R. sp. NET30 genetic background could account for the phylogenetic incongruence determined in this isolate. Results are also indicating that the transfer of the R. tropici NCHA22 pSym may be a frequent event in native conditions.

Streptomyces sp. ASBV-1 reduces aflatoxin accumulation by Aspergillus parasiticus in peanut grains.

AIMS: To evaluate the ability of Streptomyces sp. (strain ASBV-1) to restrict aflatoxin accumulation in peanut grains. METHODS AND RESULTS: In the control of many phytopathogenic fungi the Streptomyces sp. ASBV-1 strain showed promise. An inhibitory test using this strain and A. parasiticus was conducted in peanut grains to evaluate the effects of this interaction on spore viability and aflatoxin accumulation. In some treatments the Streptomyces sp ASBV-1 strain reduced the viability of A. parasiticus spores by c. 85%, and inhibited aflatoxin accumulation in peanut grains. The values of these reductions ranged from 63 to 98% and from 67% to 96% for aflatoxins B(1) and G(1), respectively. CONCLUSIONS: It was demonstrated that Streptomyces sp. ASBV-1 is able to colonize peanut grains and thus inhibit the spore viability of A. parasiticus, as well as reducing aflatoxin production. SIGNIFICANCE AND IMPACT OF THE STUDY: The positive finding for aflatoxin accumulation reduction in peanut grains seems promising and suggests a wider use of this actinobacteria in biological control programmes.

Signal molecules in the peanut-bradyrhizobia interaction.

Main nodulation signal molecules in the peanut-bradyrhizobia interaction were examined. Flavonoids exuded by Arachis hypogaea L. cultivar Tegua were genistein, daidzein and chrysin, the latest being released in lower quantities. Thin layer chromatography analysis from genistein-induced bacterial cultures of three peanut bradyrhizobia resulted in an identical Nod factor pattern, suggesting low variability in genes involved in the synthesis of these molecules. Structural study of Nod factor by mass spectrometry and NMR analysis revealed that it shares a variety of substituents with the broad-host-range Rhizobium sp. NGR234 and Bradyrhizobium spp. Nodulation assays in legumes nodulated by these rhizobia demonstrated differences between them and the three peanut bradyrhizobia. The three isolates were classified as Bradyrhizobium sp. Their fixation gene nifD and the common nodulation genes nodD and nodA were also analyzed.

Adaptational changes in lipids of Bradyrhizobium SEMIA 6144 nodulating peanut as a response to growth temperature and salinity.

Phospholipids provide the membrane with its barrier function and play a role in a variety of processes in the bacterial cell, as responding to environmental changes. The aim of the present study was to characterize the physiological and metabolic response of Bradyrhizobium SEMIA 6144 to saline and temperature stress. This study provides metabolic and compositional evidence that nodulating peanut Bradyrhizobium SEMIA 6144 is able to synthesize fatty acids, to incorporate them into its phospholipids (PL), and then modify them in response to stress conditions such as temperature and salinity. The fatty acids were formed from [1-(14)C]acetate and mostly incorporated in PL (95%). Phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL) were found to be the major phospholipids in the bacteria analyzed. The amount and the labeling of each individual PL was increased by NaCl, while they were decreased by temperature stress. The amount of PC, PE, and PG under the combined stresses decreased, as in the temperature effect. The results indicate that synthesized PL of Bradyrhizobium SEMIA 6144 are modified under the tested conditions. Because in all conditions tested the PC amount was always modified and PC was the major PL, we suggest that this PL may be involved in the bacteria response to environmental conditions.