Ensaio de Proctor normal – análise metodológica e planilha para cálculo da densidade do solo máxima e teor de água ótimo

The definition of critical limits of soil density for development of plants is very complex, since it is dependent on the texture and organic matter content. The relative compaction, that is the percentage ratio of the bulk density to the maximum dry density as determined by the Proctor compaction test, has been presented as a parameter capable of standardizing and delimiting these critical limits. The aim of this study is to describe the procedures that have to be used for the implementation of a Proctor compaction test and make available an Excel worksheet that assists in the calculation of water content that the samples to be compacted must reach, besides calculating maximum dry density and optimum moisture content of soil from equation of degree 2 obtained by analytical form from an unbalanced data set.A definição de limites críticos de densidade do solo para o desenvolvimento das plantas é muito complexa, uma vez que é dependente da textura e do teor de matéria orgânica. A densidade relativa, que é a relação entre a densidade do solo no campo e a densidade do solo máxima obtida pelo ensaio de Proctor normal, tem sido apresentada como um parâmetro capaz de padronizar e delimitar esses limites críticos. O objetivo deste trabalho é descrever os procedimentos que devem ser adotados para a realização de um ensaio de Proctor normal e disponibilizar uma planilha eletrônica Excel. A planilha auxilia no cálculo do teor de água que as amostras a serem compactadas devem atingir, além de calcular a densidade do solo máxima e o teor de água do solo ótimo para compactação a partir de equação de 2° grau obtida de forma analítica a partir de um conjunto de dados não balanceados

Genome-Wide Association Study for Maize Leaf Cuticular Conductance Identifies Candidate Genes Involved in the Regulation of Cuticle Development.

The cuticle, a hydrophobic layer of cutin and waxes synthesized by plant epidermal cells, is the major barrier to water loss when stomata are closed at night and under water-limited conditions. Elucidating the genetic architecture of natural variation for leaf cuticular conductance (g c) is important for identifying genes relevant to improving crop productivity in drought-prone environments. To this end, we conducted a genome-wide association study of g c of adult leaves in a maize inbred association panel that was evaluated in four environments (Maricopa, AZ, and San Diego, CA, in 2016 and 2017). Five genomic regions significantly associated with g c were resolved to seven plausible candidate genes (ISTL1, two SEC14 homologs, cyclase-associated protein, a CER7 homolog, GDSL lipase, and β-D-XYLOSIDASE 4). These candidates are potentially involved in cuticle biosynthesis, trafficking and deposition of cuticle lipids, cutin polymerization, and cell wall modification. Laser microdissection RNA sequencing revealed that all these candidate genes, with the exception of the CER7 homolog, were expressed in the zone of the expanding adult maize leaf where cuticle maturation occurs. With direct application to genetic improvement, moderately high average predictive abilities were observed for whole-genome prediction of g c in locations (0.46 and 0.45) and across all environments (0.52). The findings of this study provide novel insights into the genetic control of g c and have the potential to help breeders more effectively develop drought-tolerant maize for target environments

Genome assembly and population genomic analysis provide insights into the evolution of modern sweet corn.

Sweet corn is one of the most important vegetables in the United States and Canada. Here, we present a de novo assembly of a sweet corn inbred line Ia453 with the mutated shrunken2-reference allele (Ia453-sh2). This mutation accumulates more sugar and is present in most commercial hybrids developed for the processing and fresh markets. The ten pseudochromosomes cover 92% of the total assembly and 99% of the estimated genome size, with a scaffold N50 of 222.2 Mb. This reference genome completely assembles the large structural variation that created the mutant sh2-R allele. Furthermore, comparative genomics analysis with six field corn genomes highlights differences in single-nucleotide polymorphisms, structural variations, and transposon composition. Phylogenetic analysis of 5,381 diverse maize and teosinte accessions reveals genetic relationships between sweet corn and other types of maize. Our results show evidence for a common origin in northern Mexico for modern sweet corn in the U.S. Finally, population genomic analysis identifies regions of the genome under selection and candidate genes associated with sweet corn traits, such as early flowering, endosperm composition, plant and tassel architecture, and kernel row number. Our study provides a high-quality reference-genome sequence to facilitate comparative genomics, functional studies, and genomic-assisted breeding for sweet corn

GENETIC BASIS OF VITAMIN AND MINERAL LEVELS IN FRESH SWEET CORN KERNELS

Supplemental file(s) description: Chapter1_SuppFigures, Chapter1_SuppTables, Chapter2_SuppFigures, Chapter2_SuppTables, Chapter3_SuppFigures, Chapter3_SuppTablesNutritional deficiencies affect more than two billion people worldwide, with iron, zinc, vitamin E, and non-provitamin A carotenoids at risk of deficiency in the US. Sweet corn is widely consumed and does not usually provide significant amounts of these compounds. We assessed the natural variability of tocochromanols (vitamin E and antioxidants), carotenoids (provitamin A, lutein, zeaxanthin), and 15 minerals in fresh kernels (~21 DAP) of a sweet corn association panel. For each phenotype, we performed a genome-wide association study to identify the genes involved in the genetic control of their quantitative variation and genomic prediction to provide insights into how best to enhance genetic gains in a sweet corn biofortification program. We identified significant associations of α-tocopherol (highest vitamin E activity) with vte4, as well as content and composition of tocotrienols (antioxidants) with hggt1 and vte1, respectively. We also reported that β-carotene (provitamin A) was associated with crtRB1, and the relative flux between α- and β-branches of the carotenoid pathway was controlled by lcyE. For tocotrienols, we identified associations with two starch biosynthetic genes (su1 and sh2) specific to sweet corn, and reported evidence for the involvement of sh2. Of the 15 studied minerals, iron and zinc were associated with nas5 and cadmium with hma3. Weaker-effect associations specific for a location were observed for calcium (WI) and nickel (NY), and these markers were within ± 250 kb of the genes ras2 and ptr2, respectively. Whole-genome prediction models had moderate prediction abilities for most of the phenotypes measured in the three studies, indicating that these models may be used for developing sweet corn lines with nutrient-dense kernels. Smaller marker datasets that target genes or quantitative trait loci associated with carotenoids or tocochromanols resulted in lower prediction abilities compared to the whole-genome set, but the inclusion of endosperm mutation type in the models increased the abilities for tocotrienols and certain carotenoids. Together, these studies represent the most extensive assessment of natural variation for vitamins and minerals in fresh sweet corn kernels and constitute a key step for improving the nutritional quality of sweet corn for human health

Indicadores da qualidade física de um Latossolo Vermelho distrófico típico sob plantio direto escarificado Physical quality indicators in Latosol under no tillage chiseled

A avaliação da qualidade física dos solos agrícolas tem assumido importância cada vez maior, principalmente em áreas sob sistema plantio direto, uma vez que nesse sistema de manejo ocorrem importantes alterações na estrutura do solo. A resistência mecânica do solo à penetração (RP), o intervalo hídrico ótimo (IHO) e a densidade relativa (DR) têm sido apresentados como opções para essa avaliação. Os objetivos deste trabalho foram avaliar e modelar a RP em função da umidade e densidade do solo e determinar o IHO em função da DR em dois sistemas de manejo. Amostras de solo com estrutura preservada foram coletadas na camada de 0-5cm, em solo sob plantio direto (PD) e plantio direto escarificado (PDE) há seis meses. Em laboratório, determinou-se a RP utilizando penetrômetro eletrônico e efetuou-se um ajuste estatístico individual para cada manejo à equação de Busscher. No PDE, para uma mesma densidade e umidade do solo, a RP foi menor que no PD, e a diferença na RP foi maior entre os dois manejos quando a umidade do solo no campo foi menor. O IHO foi maior no PDE até a DR 0,9. Os resultados permitem concluir que a RP é um parâmetro sensível para determinar a qualidade estrutural do solo e que o PDE reduziu significativamente a RP e aumentou o IHO, o que proporcionará melhores condições para o desenvolvimento radicular das plantas por um período de tempo maior.The assessment of the physical quality of agricultural soils has taken on added importance, especially in areas under no tillage, as important changes to soil structure occur as a result of this type of management. Soil resistance to penetration (RP), the least limit water range (LLWR) and relative density (RD) have been used as evaluation parameters. The aim of this study was to assess and model RP as a function of soil moisture and density and to determine the LLWR as a function of RD under two management systems. Samples of soils under no tillage (NT) and chiseled no tillage (CNT) for six months and whose structure had been preserved were collected at a depth of 0 to 5cm. In the laboratory, RP was assessed using an electronic penetrometer and each management system was statistically adjusted to Busscher's equation. In CNT soils, RP was lower for the same density and moisture, and lower than the PD, whereas the difference in RP was larger between the two management systems when soil moisture in the field was lower. The LLWR was higher under CNT up to an RD of 0.9. Results allow us to conclude that RP is a sensitive parameter for determining the physical quality of the soil and that CNT significantly reduced RP and increased the LLWR, providing favorable conditions for root growth for a longer time period

Textura do solo e a estimativa do teor de água no ponto de murcha permanente com psicrômetro Soil texture and the estimation by Dewpoint Potential Meter of water retention at wilting point

A determinação do volume de água disponível às plantas é fundamental para o correto manejo da irrigação e definição quanto ao uso dos solos agrícolas. Os principais fatores que exercem influência na retenção e disponibilidade de água às plantas são a textura e a estrutura do solo. O objetivo deste trabalho foi quantificar a influência da textura na retenção da água, na condição de ponto de murcha permanente (PMP) das plantas (-1,5MPa), sendo utilizado um psicrômetro modelo WP4-T. Determinaram-se a textura de 100 amostras de solo e o teor de água no PMP. Os resultados indicaram que, em potenciais maiores que -1,0MPa, o psicrômetro mostrou-se pouco preciso, não se recomendando a sua utilização nessa condição. O PMP aumentou de 0,059 para 0,29g g-1, quando o teor de argila aumentou de 120 para 779g kg-1. Obteve-se um bom ajuste dos resultados do teor de água no PMP em função do teor de argila do solo, e 91% da variação do teor de água no PMP puderam ser atribuídos à variação no teor de argila. Conclui-se que o psicrômetro é um equipamento que pode ser utilizado para determinar o PMP, e a equação PMP (g g-1)=0,0003*Argila (g kg-1)+0,0118 pode ser utilizada para estimar o PMP.<br>The determination of the available water to plants is essential to right irrigation management and definition regarding the use in agricultural soils. The main factors that exert influence on retention and availability of water to plants are texture and soil structure. The aim of this study was to quantify the influence of the texture on water retention in the condition of permanent wilting point (PWP) of plants (-1,5MPa) using a WP4-T Dewpoint Potentia Meter. The texture of 100 soil sample and soil moisture at PWP was determined. Results indicated that, in potentials higher than -1,0MPa, WP4-T seemed not very precise, therefore its use is not recommended in this condition. PWP increased from 0,059 to 0,29g g-1, while the clay content increased from 120 to 779g kg-1. It was obtained a good adjustment of the results of water content at PWP based on clay content of soil, being that 91% of variation in water content at PWP could be attributed to variation in clay content. It was concluded that WP4-T is an equipment that can be used to determine PWP and the equation PWP (g g-1)=0,0003 * Clay(g kg-1)+0,0118 can be used to estimate PWP

Τι είπαν ξένοι ερευνητές και επιστήμονες για τον Ελληνισμό και τους λαούς της Ν.Α. Ευρώπης (3) [Αρθρο]

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