Abstract. The Intergovernmental Technical Panel on Soils has completed the first State of the World's Soil Resources Report. Globally soil erosion was identified as the gravest threat, leading to deteriorating water quality in developed regions and to lowering of crop yields in many developing regions. We need to increase nitrogen and phosphorus fertilizer use in infertile tropical and semi-tropical soils – the regions where the most food insecurity among us are found – while reducing global use of these products overall. Stores of soil organic carbon are critical in the global carbon balance, and national governments must set specific targets to stabilize or ideally increase soil organic carbon stores. Finally the quality of soil information available for policy formulation must be improved – the regional assessments in the State of the World's Soil Resources Report frequently base their evaluations on studies from the 1990s based on observations made in the 1980s or earlier.

Abstract. The Intergovernmental Technical Panel on Soils has completed the first State of the World's Soil Resources report. Globally soil erosion was identified as the gravest threat, leading to deteriorating water quality in developed regions and to lowering of crop yields in many developing regions. We need to increase nitrogen and phosphorus fertilizer use in infertile tropical and semi-tropical soils – the regions where the most food insecure among us are found – while reducing global use of these products overall. Stores of soil organic carbon are critical in the global carbon balance, and national governments must set specific targets to stabilize or ideally increase soil organic carbon stores. Finally the quality of soil information available for policy formulation must be improved – the regional assessments in the SWSR report frequently base their evaluations on studies from the 1990s based on observations made in the 1980s or earlier.

During a pathogen attack, cells triggers the overproduction of reactive oxygen species causing oxidative stress and physiological damage. Plants develop strategies using these reactive molecules for protection against pathogen attack. Phytoplasma are bacteria lacking cell walls that inhabit plant phloem and reduce yield, tuber quality, and commercial harvest value. Sprayed salicylic acid (SA) activated plant defense response against phytoplasma attack and reduced infection symptoms, favored photosynthate translocation, and improved tuber quality. Low levels of exogenous SA (0.001 mM) induced higher biological activity. Damage reduction was associated with high hydrogen peroxide and ascorbic acid contents together with reduction of peroxidase activity, suggesting an important SA role regulating these molecules counteracting pathogen effects.Resumen Durante un ataque patogénico las células presentan una sobreproducción de especies reactivas de oxígeno. Esto provoca estrés oxidativo y daño fisiológico. Las plantas aprovechan éstas moléculas reactivas para desarrollar estrategias que conducen a la autoprotección contra el patógeno atacante. Los fitoplasmas son bacterias sin pared celular que habitan el floema de las plantas y disminuyen el rendimiento, la calidad de los tubérculos y el valor comercial de las cosechas, entre otros daños. El ácido salicílico (SA) asperjado activó la respuesta de defensa de la planta contra el ataque del fitoplasma, redujo los síntomas de la infección, favoreció la translocación de fotosintetizados e incrementó la calidad de los tubérculos. Bajos niveles de SA exógeno (0.001 mM) mostraron mayor actividad biológica. La reducción de daño estuvo asociada a altos contenidos de peróxido de hidrógeno y ácido ascórbico acompañada de reducción de la actividad peroxidasa, lo que sugiere un papel importante del SA en la regulación de éstas moléculas contrarrestando los efectos dañinos del patógeno.

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The classification of Mexican maize (Zea mays L.) begun since the early 20th century, it was consolidated during the middle of this century, but recent additions and rearrangements have been performed by several authors employing new methods of analysis and collections from diverse origin; nevertheless, maize from the State of Michoacan, Mexico has received little attention in regard to its systematic classification. Maize populations from the Tarasca Mountain Chain in Michoacan are commonly considered in literature, as belonging to the Chalquen˜o race; however, closer observations indicate that significant differences do exist, suggesting the necessity of performing an in-depth study on this respect. Thirty nine native maize populations from the Tarasca Mountain Chain region were evaluated along with 19 typical populations of the Chalquen˜o, Celaya and Conico races coming from the States of Mexico, Puebla, Hidalgo, Quere´taro and Oaxaca. Populations were evaluated in Aranza, Michoacan and Montecillo, Mexico State. Seventeen morphological characters were scored and analyzed by one-way analyses of variance and multivariate techniques. Populations were also genetically analyzed through 17 isozyme loci. Native populations had some alleles not found either in the Chalquen˜o, Celaya or Conico races, and possess larger genetic diversity. Local populations were congregated into a discrete group apart from the typical Chalquen˜o populations, suggesting that landraces from the Tarasca Mountain Chain region might not be considered as belonging to the Chalquen˜o race, but they integrate by themselves a different race.

ABSTRACT. Salt stress affects crop growth and productivity. In this study, we determined the growth, yield of photosystem II (PSII), and K + and Na + concentration in root, stem, old leaves, and young leaves of two Mexican varieties of rice, Tres Ríos and Cotaxtla. In addition, the K + /Na + ratio in stem and root of both varieties was determined. The experiment was conducted in a growth chamber under controlled conditions, under a completely randomized distribution, with a 2 x 2 (Variety x Salinity) factorial arrangement and 12 replications. Plants were grown in a hydroponic solution for 15 days and then some of them were treated with 100 mM NaCl; control plants (without NaCI treatment) were grown in parallel. Salt stress caused 20 and 15% reductions in stem and root length, respectively, in the variety Tres Ríos, while in the variety Cotaxtla no significant differences were observed in these variables compared to the control. Dry matter weight decreased by 24% in the variety Tres Ríos. The quantum yield of PSII decreased by 30% the third day of treatment application, in both varieties. Na + concentration was significantly (p ≤ 0.05) higher in NaCI-treated plants. In the variety Tres Ríos, the yield of PSII was completely eradicated six days after treatment implementation, while the K+ concentration in stem and older leaves also decreased and the lowest K + / Na + ratio in stem was recorded, which could indicate that it is more susceptible to salinity than the variety Cotaxtla.

We studied morphological changes over time by nodules formed on the root system of the common bean (Phaseolus vulgaris L.). Two cultivars, Bayomex and Cacahuate 72 with growth habit Type I and the Rhizobium etli strain CE-3 were used. The results showed the collapse of the infected zone, degradation of the cell walls and membranes, changes in the number and distribution of the starch granules, appearance of protein granules, and disintegration of the central tissue of the nodule with ageing. Additionally, we describe the influence of time on the progress of the nodular senescence.