Growth- and leaf-temperature effects on photosynthesis of sweet orange seedlings infected with Xylella fastidiosa

The effects of growth and leaf temperature on photosynthesis were evaluated in sweet orange seedlings ( Citrus sinensis cv. Pera) infected with Xylella fastidiosa (the bacterium that causes citrus variegated chlorosis, CVC). Measurements of leaf gas exchange and chlorophyll  a fluorescence were taken at leaf temperatures of 25, 30, 35 and 40°C in healthy and infected (without visible symptoms) seedlings submitted to two temperature regimes (25/20 or 35/20°C, day/night), not simultaneously. The CO₂ assimilation rates ( A ) and stomatal conductance ( g _s) were higher in healthy plants in both temperature regimes. Values for A and g _s of infected and healthy plants were higher in the 35/20°C regime, decreasing with leaf temperature increase. In addition, differences between healthy and infected plants were higher at 35/20°C, while no differences in chlorophyll  a fluorescence parameters were observed except for potential quantum efficiency of photosystem II, which was higher in infected plants. Low A values in infected plants were caused by low g _s and probably by biochemical damage to photosynthesis. The high alternative electron sink of infected plants was another effect of reduced A . Both high growth and high leaf temperatures increased differences in A between healthy and infected plants. Therefore this feature may be partially responsible for lower growth and/or productivity of CVC-affected plants in regions with high air temperature.     

Candidate genes underlying QTL for flowering time and their interactions in a wide spring barley (Hordeum vulgare L.) cross

Response to vernalization and photoperiod are the main determinants controlling the time to flowering in temperate cereals. While the individual genes that dete...     

Genetics of neotropical fish: from chromosomes to populations

The Neotropical freshwater fish fauna is very rich—according to the most recent catalogue 71 families and 4,475 species have been described. However, only a small amount of general information is available on the composition of Neotropical marine fishes. In Brazil, 1,298 marine species have been recorded. General analysis of available cytogenetic and population genetic data clearly indicates research has been mainly concentrated on freshwater fishes. Thus, today, cytogenetic information is available for 475 species of Characiformes, 318 species of Siluriformes, 48 species of Gymnotiformes, 199 freshwater species that do not belong to the superorder Ostariophysi, and only 109 species of marine fishes. For the species studied, only about 6% have sex chromosomes and about 5% have supernumerary or B chromosomes. A review of the cytogenetic studies shows that these data have provided valuable information about the relationships between fish groups, the occurrence of cryptic species and species complexes, the mechanism of sex determination and sex chromosome evolution, the distribution of nucleolus organizer regions, the existence supernumerary chromosomes, and the relationship between polyploidy and evolution. In relation to populations in Neotropical marine waters, the studies have shown the presence of cryptic species, which has important implications for fishery management. Different levels of genetic structuring can be found among Neotropical freshwater migratory fish species. This raises important implications for fish population genetic diversity and consequently its sustainable utilization in inland fisheries and aquaculture, specifically for conservation of ichthyo-diversity and survival.     

Technologies for the diagnosis and remediation of Fe deficiency

The objective of this paper is to review the developments in the last few years in two important issues related to Fe deficiency in plants. First, the current knowledge on the possible ways to carry out the diagnosis and prognosis of Fe deficiency in plants is discussed. This includes discussion on the best ways to carry out a meaningful analysis of Fe-containing compounds in different plant parts. We will also discuss other measurement techniques that can permit to assess the Fe nutritional status in plants, including leaf chlorophyll concentrations and others. Second, the new developments in management techniques to control and remediate iron deficiency are discussed. This includes possible improved ways to supply Fe compounds available to plants, both to the soil and to the irrigation water. We also discuss possible ways to supply directly the plant with Fe containing compounds, either to the foliage or to the stem. A particular emphasis is given throughout the paper to fruit tree crops growing in Mediterranean areas.     

Kinetics of Zinc Uptake and Anatomy of Roots and Leaves of Coffee Trees as Affected by Zinc Nutrition

Abstract

The influence of silicon (Si) (2.5 mM), sodium chloride (NaCl) (100 mM), and Si (2.5 mM) + NaCl (97.5 mM) supply on chlorophyll content, chlorophyll fluorescence, the concentration of malondialdehyde (MDA), H₂O₂ level, and activities of superoxide dismutase (SOD; E.C.1.15.1.1.), ascorbate peroxidase (APx; E.C.1.11.1.11.), catalase (CAT; E.C.1.11.1.6.), guaiacol peroxidase (G-POD; E.C.1.11.1.7.) enzymes, and protein content were studied in tomato (Lycopersicon esculentum Mill c.v.) leaves over 10-day and 27-day periods. The results indicated that silicon partially offset the negative impacts of NaCl stress with increased the tolerance of tomato plants to NaCl salinity by raising SOD and CAT activities, chlorophyll content, and photochemical efficiency of PSII. Salt stress decreased SOD and CAT activities and soluble protein content in the leaves. However, addition of silicon to the nutrient solution enhanced SOD and CAT activities and protein content in tomato leaves under salt stress. In contrast, salt stress slightly promoted APx activity and considerably increased H₂O₂ level and MDA concentration and Si addition slightly decreased APx activity and significantly reduced H₂O₂ level and MDA concentration in the leaves of salt-treated plants. G-POD activity was slightly decreased by addition of salt and Si. Enhanced activities of SOD and CAT by Si addition may protect the plant tissues from oxidative damage induced by salt, thus mitigating salt toxicity and improving the growth of tomato plants. These results confirm that the scavenging system forms the primary defense line in protecting oxidative damage under stress in crop plants.     

Free amino acid composition of quince (Cydonia oblonga Miller) fruit (pulp and peel) and jam

Twenty-one free amino acids present in several samples of quince fruit (pulp and peel) and quince jam (homemade and industrially manufactured) were analyzed by GC/FID. The analyses showed some differences between quince pulps and peels. Generally, the highest content in total free amino acids and in glycine was found in peels. As a general rule, the three major free amino acids detected in pulps were aspartic acid, asparagine, and hydroxyproline. For quince peels, usually, the three most abundant amino acids were glycine, aspartic acid, and asparagine. Similarly, for quince jams the most important free amino acids were aspartic acid, asparagine, and glycine or hydroxyproline. This study suggests that the free amino acid analysis can be useful for the evaluation of quince jam authenticity. It seems that glycine percentage can be used for the detection of quince peel addition while high alanine content can be related to pear addition.     

ADVERSE EFFECTS OF HUMIC SUBSTANCES FROM DIFFERENT ORIGIN ON LUPIN AS RELATED TO IRON SOURCES

Humic substances improve the efficiency of different iron (Fe) sources overcoming Fe deficiency chlorosis of plants. However, applied at high rates, they can promote negative effects on plants. The main objective of this work was to study the potential adverse effect of three humic acids from different origin when they were applied with two effective Fe sources for plants: Fe- ethylenediaminedihydroxyphenylacetic acid (EDDHA) and Vivianite. To this end, an experiment with lupin (Lupinus albus L.) was performed involving two factors: (i) Fe source, and (ii) humic substances from three different origin (composted cork, leonardite, and compost obtained from a mixture of olive husk with cotton gin trash) applied at 0, 0.1, and 0.5 g organic carbon (C) kg^?1 of growing media. At the rates used, humic substances promoted adverse effects on plant development, chlorophyll meter readings, and Fe content in lupin grown in calcareous media. Overall, the effect on dry matter and Fe content in plants was more relevant when Fe was supplied with Vivianite, the effect on chlorophyll meter readings being more significant when Fe was applied as Fe-EDDHA. Differences were also observed depending on the source of humic substances, those from leonardite promoting the greatest decrease in dry matter in roots and shoots. These humic substances possessed the highest values of spectroscopy index for aromaticity (A₂₅₄ ). On the other hand, the application of humic substances from olive husk compost, which exhibited the lower aromaticity index, resulted in the smallest decrease in dry matter production and chlorophyll meter readings. Dry matter in roots decreased logarithmically with increased values of the estimates of the amounts of aromatic compounds accumulated in the growing media (R² = 0.92; P < 0.01) with Vivianite as Fe source. Thus, the effects decreasing dry matter production, particularly in roots, and chlorophyll meter readings can be ascribed at least partially to the presence of phytotoxic aromatic compounds in humic substances.     

NITROGEN USE EFFICIENCY IN DRY BEAN GENOTYPES

Dry bean is an important legume crop for Latin American people and nitrogen is one of the most yields limiting nutrients for bean crop. A greenhouse experiment was conducted to evaluate nitrogen (N) use efficiency of 20 dry bean genotypes. Genotypes were grown on an Oxisol and two N levels used were without N application (low level) and an application of 400 mg N kg^?1 (high level). Shoot dry weight, grain yield and yield components, N concentration and uptake in shoot and grain were significantly affected by N and genotype treatments. Grain yield had a highly significant (P < 0.01) association with shoot dry weight, pod number, grains per pod and 100 grain weight. Among the 20 genotypes tested, Perola, CNFR 7847, CNFR 7865, CNFP 7777 and CNFM 6911 were found to produce reasonably good yield at low N rate as well as responded well to applied N. Whereas, some genotypes like BRS Radiante, CNFP 7624, CNFM 7875, CNFM 7886, CNFC 7813, CNFC 7827, CNFP 7677 and CNFP 7775 produced very good yields at higher N rate but very low yields at lower N rate. Hence, these genotypes are good for farmers using higher technology. Nitrogen concentration and uptake were higher in dry bean grains compared with shoot and 63% of N accumulated at zero N rate and 75% N accumulated at 400 mg N rate were translocated to grain across 20 genotypes. Nitrogen uptake efficiencies were having highly significant (P < 0.01) quadratic relationship with grain yield. This indicates that improving N uptake in dry bean plants can increase grain yield.     

Cross-crop effects on larval growth,survivorship and fecundity of <Emphasis Type="Italic">Helicoverpa armigera</Emphasis>

The cotton bollworm Helicoverpa armigera is a destructive pest that affects a variety of crop plants. Because of its polyphagous feeding habit, mobility as adults, and high fecundity, the expanding infestations of H. armigera in different crops have caused economic losses and difficulties for pest population management. In Brazil, a sequence of different crop systems in the same area and crop rotation during the year can create a spatio-temporal mosaic of crops where H. armigera can persist. However, the consequences of the simultaneous and/or alternating presence of host plants for H. armigera populations through generations are unknown. In this study, we simulated, in the laboratory, hypothetical situations for the availability of soybean and cotton crops in the landscape. We evaluated the effects of: (1) the number of generations during which a population feeds on a host-plant species; (2) the succession of host-plant species on which populations have fed for two generations; and (3) the parental host plant on the fitness of H. armigera populations. Only the current host plant on which larvae fed affected the performance of the H. armigera populations. Decrease of mortality rates during the immature period was slowed when the larvae fed on soybean. The lowest value of reproductive potential (R ₀) was found for individuals originating from mating between females and males reared in cotton. Our results indicated that pest-management and biological-control plans for H. armigera should be developed on a regional scale rather than for just a specific crop area.     

Chromoplast morphology and beta-carotene accumulation during postharvest ripening of Mango Cv. 'Tommy Atkins'

Accumulation of beta-carotene and trans-cis isomerization of ripening mango mesocarp were investigated as to concomitant ultrastructural changes. Proceeding postharvest ripening was shown by relevant starch degradation, tissue softening, and a rising sugar/acid ratio, resulting in a linear decrease (R (2) = 0.89) of a ripening index (RPI(KS)) with increasing ripening time. A modest accumulation of all-trans-beta-carotene and its cis isomers resulted in a slight pigmentation of the mango chromoplasts, because ambient temperatures of 18.2-19.5 degrees C provided suboptimal ripening conditions, affecting color development and beta-carotene biosynthesis. The ultrastructures of chromoplasts from mango mesocarp and carrot roots were comparatively studied by means of light and transmission electron microscopy. Irrespective of the ripening stage, mango chromoplasts showed numerous plastoglobuli varying in size and electron density. They comprised the main part of carotenoids, thus supporting the partial solubilization of the pigments in lipid droplets. However, because different pigment-carrying tubular membrane structures were also observed, mango chromoplasts were assigned to the globular and reticulotubular types, whereas the crystalline type was confirmed for carrot chromoplasts. The large portions of naturally occurring cis-beta-carotene in mango fruits contrasted with the predominance of the all-trans isomer characteristic of carrots, indicating that the nature of the structure where carotenoids are deposited and the physical state of the pigments are crucial for the stability of the all-trans configuration.