Investigations on the tolerance of several trees to submergence in blackwater (igapó) and whitewater (várzea) inundation forests near Manaus, Central Amazonia

Physiological, cytological, and anatomical studies were carried out on the tolerance of trees to submergence in blackwater and whitewater inundation forests, locally called Igapó and Várzea, respectively. For this purpose, the leaves of several abundant tree species were investigated to determine their functional capability after submersion during the inundation phase. Their performance was compared with that of genetically identical leaves on the same branch that had sprouted after the flood water had receded. The studies showed that, in spite of submersion for up to several months and sometimes even in spite of the fact that they were still partially under water, these leaves had full functional capability at the beginning of the terrestrial phase, as determined by examination under the light and scanning electron microscope, the water potential, and the CO2 exchange

Isolation and characterization of high-efficiency Rhizobia from Western Kenya nodulating with common bean

Common bean is one of the primary protein sources in third-world countries. They form nodules with nitrogen-fixing rhizobia, which have to be adapted to the local soils. Commercial rhizobial strains such as Rhizobium tropici CIAT899 are often used in agriculture. However, this strain failed to significantly increase the common bean yield in many places, including Kenya, due to the local soils’ low pH. We isolated two indigenous rhizobial strains from the nodules of common bean from two fields in Western Kenya that have never been exposed to commercial inocula. We then determined their ability to fix nitrogen in common beans, solubilize phosphorus, and produce indole acetic acid. In greenhouse experiments, common bean plants inoculated with two isolates, B3 and S2 in sterile vermiculite, performed better than those inoculated with CIAT899 or plants grown with nitrogen fertilizer alone. In contrast to CIAT899, both isolates grew in the media with pH 4.8. Furthermore, isolate B3 had higher phosphate solubilization ability and produced more indole acetic acid than the other two rhizobia. Genome analyses revealed that B3 and S2 are different strains of Rhizobium phaseoli. We recommend fieldwork studies in Kenyan soils to test the efficacy of the two isolates in the natural environment in an effort to produce inoculants specific for these soils

The size of triangulations supporting a given link

Let T be a triangulation of S^3 containing a link L in its 1-skeleton. We give an explicit lower bound for the number of tetrahedra of T in terms of the bridge number of L. Our proof is based on the theory of almost normal surfaces.Comment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol5/paper13.abs.htm

Distribution, characterization and the commercialization of elite Rhizobia strains in Africa

Grain legumes play a significant role in smallholder farming systems in Africa because of their contribution to nutrition and income security and their role in fixing nitrogen. Biological Nitrogen Fixation (BNF) serves a critical role in improving soil fertility for legumes. Although much research has been conducted on rhizobia in nitrogen fixation and their contribution to soil fertility, much less is known about the distribution and diversity of the bacteria strains in different areas of the world and which of the strains achieve optimal benefits for the host plants under specific soil and environmental conditions. This paper reviews the distribution, characterization, and commercialization of elite rhizobia strains in Africa

Rhizobia contribute to salinity tolerance in common beans (Phaseolus vulgaris L.)

Rhizobia are soil bacteria that induce nodule formation on leguminous plants. In the nodules, they reduce dinitrogen to ammonium that can be utilized by plants. Besides nitrogen fixation, rhizobia have other symbiotic functions in plants including phosphorus and iron mobilization and protection of the plants against various abiotic stresses including salinity. Worldwide, about 20% of cultivable and 33% of irrigation land is saline, and it is estimated that around 50% of the arable land will be saline by 2050. Salinity inhibits plant growth and development, results in senescence, and ultimately plant death. The purpose of this study was to investigate how rhizobia, isolated from Kenyan soils, relieve common beans from salinity stress. The yield loss of common bean plants, which were either not inoculated or inoculated with the commercial R. tropici rhizobia CIAT899 was reduced by 73% when the plants were exposed to 300 mM NaCl, while only 60% yield loss was observed after inoculation with a novel indigenous isolate from Kenyan soil, named S3. Expression profiles showed that genes involved in the transport of mineral ions (such as K+, Ca2+, Fe3+, PO43−, and NO3−) to the host plant, and for the synthesis and transport of osmotolerance molecules (soluble carbohydrates, amino acids, and nucleotides) are highly expressed in S3 bacteroids during salt stress than in the controls. Furthermore, genes for the synthesis and transport of glutathione and γ-aminobutyric acid were upregulated in salt-stressed and S3-inocculated common bean plants. We conclude that microbial osmolytes, mineral ions, and antioxidant molecules from rhizobia enhance salt tolerance in common beans

Specialized 16SrX phytoplasmas induce diverse morphological and physiological changes in their respective fruit crops

The host-pathogen combinations-Malus domestica (apple)/`Candidatus Phytoplasma mali´, Prunus persica (peach)/`Ca. P. prunorum´ and Pyrus communis (pear)/`Ca. P. pyri´ show different courses of diseases although the phytoplasma strains belong to the same 16SrX group. While infected apple trees can survive for decades, peach and pear trees die within weeks to few years. To this date, neither morphological nor physiological differences caused by phytoplasmas have been studied in these host plants. In this study, phytoplasma-induced morphological changes of the vascular system as well as physiological changes of the phloem sap and leaf phytohormones were analysed and compared with non-infected plants. Unlike peach and pear, infected apple trees showed substantial reductions in leaf and vascular area, affecting phloem mass flow. In contrast, in infected pear mass flow and physicochemical characteristics of phloem sap increased. Additionally, an increased callose deposition was detected in pear and peach leaves but not in apple trees in response to phytoplasma infection. The phytohormone levels in pear were not affected by an infection, while in apple and peach trees concentrations of defence- and stress-related phytohormones were increased. Compared with peach and pear trees, data from apple suggest that the long-lasting morphological adaptations in the vascular system, which likely cause reduced sap flow, triggers the ability of apple trees to survive phytoplasma infection. Some phytohormone-mediated defences might support the tolerance

Influencia de la profundidad de la tosca sobre los parámetros edáficos y la productividad de los cultivos

En la región Semiárida Pampeana se presenta la tosca a diferentes profundidades, probablemente impidiendo el normal desarrollo de los cultivos. Por esta razón en el presente trabajo se analiza el efecto que la profundidad del manto calcáreo produce sobre la acumulación de agua sobre el perfil, la producción de los cultivos y la evolución del suelo. Durante un año y en tres sitios con puntos con tosca a 3 profundidades distintas, se tomaron valores de humedad en el perfil mensualmente y de materia seca durante el ciclo de crecimiento de alfalfa, pasto llorón y maíz. Del análisis morfológico de los perfiles se pone de manifiesto que el desarrollo del horizonte A es mayor cuanto mayor es el espesor efectivo del perfil hasta la tosca. Se concluyó que la mayor profundidad de tosca se corresponde con más agua acumulada en el perfil. Sin embargo, la profundidad mayor de tosca no va acompañada de producción de. materia seca, al menos en años húmedos como el estudiado (precipitaciones 40% superiores a la media de los últimos 60 años).Director: Ing. Agr. Daniel Buschiazzo y Codirector: Ing. Agr. Alberto Quiroga. Cátedra de Edafología, Manejo, Conservación y Fertilidad de Suelos

Light regimes in three aquatic ecosystems of different physico-chemical properties. 1. Attenuation, irradiance reflectance and comparison between downwelling, upwelling and scalar irradiances (PAR)

In two tropical lakes, one of the white water floodplain with an amount of suspended solids (tripton) of 100 mg/l, and one of the black water floodplain stained by humic substances (gilvin) of 130 - 170 HAZEN, situated in Central Amazonia, measurements of the light regime were made. Mainly two types of collectors were used measuring the hemispherical (cosine) and the spherical (scalar) incident solar radiation in the PAR wave band (photosyntethetically active radiation). From these data the coefficients for the irradiance reflectance, extinction for downward irradiance, and the depth of the euphotic zone were calculated for the so-called Várzea (white water) and lgapó (black water) lakes and all values compared to those obtained in the water body of an oligotrophic lake in Northern Germany. Besides comments concerning methodological details, remarks are given on the consequences of the very extreme light regimes for the biota in the two tropical lakes