Universidade Federal de Viçosa

About: Universidade Federal de Viçosa is a education organization based out in Viçosa, Brazil. It is known for research contribution in the topics: Population & Dry matter. The organization has 16012 authors who have published 26711 publications receiving 353416 citations.

Photosynthesis impairment in cassava leaves in response to nitrogen deficiency

Abstract: Plants of cassava (Manihot esculenta Crantz cv Cigana Preta) grown in a sand root medium were watered with nutrient solutions containing either 3 mM nitrate (low N) or 12 mM nitrate (high N) Chlorophyll concentration, chlorophyll a/b ratio, stomatal conductance, photorespiration rate and net carbon assimilation rate (on an area and a mass basis, but not on a chlorophyll basis) all decreased in low-N plants as compared with high-N ones By contrast, photosynthetic nitrogen-use efficiency increased in low-N plants As indicated by chlorophyll a fluorescence data, these plants exhibited increases in both excitation pressure on Photosystem II and thermal energy dissipation, with a corresponding decrease in quantum yield of electron transport, when contrasted with high-N plants This decrease paralleled an unchanged maximal Photosystem II photochemical efficiency, suggesting a down-regulation of the Photosystem II photochemistry It is proposed that decline in biochemical capacity for carboxylation, rather than stomatal limitation or electron transport, were the major constraints associated to the reduced photosynthetic rates induced by nitrogen deficiency in cassava plants

Effects of ozone treatment on postharvest carrot quality

Abstract: Ozone (O3) is a powerful oxidant and is used in water treatment, pest disinfection and the removal of pesticides, mycotoxins and other contaminants from fruits and vegetables. However, the treatment conditions should be specifically determined for all types of products for the effective and safe use of ozone. The aim of this study was to evaluate the effect of ozone applied as gas (0–5 mg L−1) and dissolved in water (0–10 mg L−1) on the quality of carrots. The exposure of carrots to ozone as gas and dissolved in water did not alter the weight loss percentage, firmness and the color of the vegetable. The O3 treatments as gas also did not affect the pH of the carrots. However, in treatments with O3 dissolved in water, the ozone concentrations and its interaction with temperature temporarily affected the pH of carrots. Moreover, O3 as gas prevented the sharp increase in soluble solids during storage for five days (18 ± 2 °C, 80 ± 5% RH), thereby increasing the shelf-life of carrots.

Influence of a compacted loam subsoil layer on growth and yield of irrigated cotton in Southern Spain

Abstract: Subsoil compaction, which may occur naturally or be a consequence of machinery traffic, causes reductions in crop yields. The aim of this work was to characterize the effects of subsoil compaction on growth and yield of cotton (Gossypium hirsutum L.) under field conditions. Two field experiments were carried out in Cordoba, Spain, on an Eutric Fluvisol with loam texture. A treatment with a compacted layer (bulk density of 1.6–1.7 Mg m−3) at 0.2–0.4 m depth was compared with a control treatment with maximum bulk density of about 1.4 Mg m−3. Soil resistance to penetration was related to soil bulk density and water content. The compaction provoked reductions in root length (40% in 1996 and 33% in 1997), leaf area index (26% in 1996 and 12% in 1997), evapotranspiration (12% in 1996 and 7% in 1997) and seed cotton yield (28% in 1996 and 10% in 1997). Average resistance to penetration in the compacted layer was above 3 MPa (a threshold for cotton root growth according to the literature) but root growth was observed below this layer. It was speculated that spatial variation of soil bulk density and resistance and temporal variation of soil water content allowed the roots to find weaker path-ways to cross the compacted layer. The effect of the subsoil compaction on the soil characteristics and the root growth remained during the second experimental year but it was less pronounced on the above ground plant growth, development and yield. It was concluded that subsoil compaction influences significantly growth and yield of cotton, but successive cropping may alleviate the effects of the compaction.

Revisiting the classification of curtoviruses based on genome-wide pairwise identity

Abstract: Members of the genus Curtovirus (family Geminiviridae) are important pathogens of many wild and cultivated plant species. Until recently, relatively few full curtovirus genomes have been characterised. However, with the 19 full genome sequences now available in public databases, we revisit the proposed curtovirus species and strain classification criteria. Using pairwise identities coupled with phylogenetic evidence, revised species and strain demarcation guidelines have been instituted. Specifically, we have established 77 % genome-wide pairwise identity as a species demarcation threshold and 94 % genome-wide pairwise identity as a strain demarcation threshold. Hence, whereas curtovirus sequences with >77 % genome-wide pairwise identity would be classified as belonging to the same species, those sharing >94 % identity would be classified as belonging to the same strain. We provide step-by-step guidelines to facilitate the classification of newly discovered curtovirus full genome sequences and a set of defined criteria for naming new species and strains. The revision yields three curtovirus species: Beet curly top virus (BCTV), Spinach severe surly top virus (SpSCTV) and Horseradish curly top virus (HrCTV).