ReDivia - Repositorio Digital de l'Instit Valencià d'Investigacions Agràries
Not a member yet
2747 research outputs found
Sort by
Fifty Years of IOCV, 1957 to 2007: From Graft-Transmitted Citrus Agents to Viroids, Viruses and Endogenous Bacteria
Get PDFIn November, 1957, the well-known Citrus Experiment Station (CES) of the University of California at Riverside, USA, celebrated its 50th anniversary. This was a good opportunity to hold the first international conference on so-called “virus” diseases of citrus, of which many had been studied in California, if not in Florida. Maladies such as Tristeza, Psorosis, Concave Gum and Blind Pocket, Crinkly leaf and Infectious variegation, Stubborn, Xyloporosis and Cachexia, Exocortis, and Vein enation had been shown to be transmissible by graft-inoculation. and were, for this reason, thought to be of viral nature, but not a single causal agent had yet been identified, mechanically transmitted, purified, or even seen in the electron microscop
Intraguild interactions between Euseius stipulatus and the candidate biocontrol agents of Tetranychus urticae in Spanish clementine orchards: Phytoseiulus persimilis and Neoseiulus californicus
No full textSpanish clementine orchards are frequently infested by the two-spotted spider mte Tetranychus urticae. Natural control of T. urticae is insufficient despite the presence of Neoseiulus californicus and Phytoseiulus persimilis. The phytoseiid community is dominated by the generalist Euseius stipulatus which is poorly adapted to exploit T. urticae. Having the intention to promote biological control of T. urticae by augmentative releases we were interested whether P. persimilis and N. californicus are negatively affected by intraguild (IG) interactions with E. stipulatus. Two experiments were conducted. Firstly, we assessed female aggressiveness (quantified as combination of attack probability and latency) in IG predation on larvae. Secondly, we measured mortality, escaping rate and developmental time of immature IG prey in presence and absence of an adult IG predator female. Euseius stipulatus appeared the strongest IG opponent but microhabitat structure modulated the IG interactions and the advantage of E. stipulatus was partially offset when spider mite webbing was present. Implications of these IG interactions for natural and biological control of T. urticae in clementine orchards are discussed
Effects of post-teneral nutrion and ginger root oil exposure on longevity and mortality in bait treatments of sterile male 'Ceratitis capitata'
No full textThe aconitate hydratase family from Citrus
Get PDFBackground: Research on citrus fruit ripening has received considerable attention because of the importance of citrus fruits for the human diet. Organic acids are among the main determinants of taste and organoleptic quality of fruits and hence the control of fruit acidity loss has a strong economical relevance. In citrus, organic acids accumulate in the juice sac cells of developing fruits and are catabolized thereafter during ripening. Aconitase, that transforms citrate to isocitrate, is the first step of citric acid catabolism and a major component of the citrate utilization machinery. In this work, the citrus aconitase gene family was first characterized and a phylogenetic analysis was then carried out in order to understand the evolutionary history of this family in plants. Gene expression analyses of the citrus aconitase family were subsequently performed in several acidic and acidless genotypes to elucidate their involvement in acid homeostasis. Results: Analysis of 460,000 citrus ESTs, followed by sequencing of complete cDNA clones, identified in citrus 3 transcription units coding for putatively active aconitate hydratase proteins, named as CcAco1, CcAco2 and CcAco3. A phylogenetic study carried on the Aco family in 14 plant species, shows the presence of 5 Aco subfamilies, and that the ancestor of monocot and dicot species shared at least one Aco gene. Real-time RT-PCR expression analyses of the three aconitase citrus genes were performed in pulp tissues along fruit development in acidic and acidless citrus varieties such as mandarins, oranges and lemons. While CcAco3 expression was always low, CcAco1 and CcAco2 genes were generally induced during the rapid phase of fruit growth along with the maximum in acidity and the beginning of the acid reduction. Two exceptions to this general pattern were found: 1) Clemenules mandarin failed inducing CcAco2 although acid levels were rapidly reduced; and 2) the acidless "Sucreña" orange showed unusually high levels of expression of both aconitases, an observation correlating with the acidless phenotype. However, in the acidless "Dulce" lemon aconitase expression was normal suggesting that the acidless trait in this variety is not dependent upon aconitases. Conclusions: Phylogenetic studies showed the occurrence of five different subfamilies of aconitate hydratase in plants and sequence analyses indentified three active genes in citrus. The pattern of expression of two of these genes, CcAco1 and CcAco2, was normally associated with the timing of acid content reduction in most genotypes. Two exceptions to this general observation suggest the occurrence of additional regulatory steps of citrate homeostasis in citrus
Assessment of Ceratitis capitata (Diptera, Tephritidae) pupae killed by heat or cold as hosts for rearing Spalangia cameroni (Hymenoptera: Pteromalidae)
No full textIn this work, we study the suitability of using dead medfly Ceratitis capitata pupae, killed by heat- or cold-shock, for the mass rearing of Spalangia cameroni, a pupal parasitoid of key pests. 100% mortality of medfly pupae could be accomplished with cold-shock at -20 degrees C for 60 min or with heat-shock at 55 degrees C for 30 min. Neither parasitism percentage nor sex ratio of the offspring differed significantly among heat-shocked, cold-shocked and untreated pupae. In addition, there was no significant difference in the percentage of parasitoids that aborted (male male or female female) among pupal treatments. Some of the pupae were covered with peat because the third larval instar of the medfly buries itself before pupation. However, the buried pupae were not parasitised at a greater or lesser rate than those not covered with peat. The percentage of parasitism was also unaffected by whether the pupae had been killed recently or had been stored at between 4 degrees C and 6 degrees C over 15 or 30 days. The use of dead hosts and later storage permitted the following: (a) the use of hosts over long periods of time; (b) a rapid increase in parasitoid numbers and (c) the availability of pupae killed at the most suitable postpupation times for the production of parasitoids. Furthermore, in biological control projects, the use of dead parasitised pupae in the field avoids the risk of enhancing the pest and allows an increase in parasitism in the field through the use of pupae treated with cold- or heat-shock
Susceptibility of Prunus rootstocks to natural infection of Plum pox virus and effect of mineral oil treatments
No full textThe use of rootstocks that are less susceptible or resistant to natural Plum pox virus (PPV) infection and/or the application of mineral oil treatments are two possible strategies to reduce viral incidence in nursery plots. We evaluated the susceptibility of Prunus rootstocks used in the Spanish stone fruit industry and the effect of mineral oil treatment (Sunspray Ultrafine at 1%) on the spread of the virus at two different localities in Valencia, Spain, under different natural PPV inoculum pressures (high inoculum pressure, 2006-08; low inoculum pressure, 2006-07). Samples from both plots were analysed by double-antibody sandwich indirect enzyme-linked immunosorbent assay (DASI-ELISA) and spot real-time RT-PCR. Under high inoculum pressure, the assayed rootstocks exhibited significant differences in their susceptibility to natural infection. The most susceptible rootstocks at the end of the experiment were Adesoto 101 and Mariana GF8-1. Cadaman and Garnem rootstocks presented the fewest PPV-infected plants; these infections could be detected only by spot real-time RT-PCR. No differences among the assayed rootstocks were found under low PPV inoculum pressure. Aphid species were monitored using Moericke yellow water traps and sticky-plant methods at both localities in May 2006 and 2007. Aphis spiraecola was the most abundant aphid species monitored by both methods at both localities. The average percentage of A. spiraecola carrying PPV PCR-amplifiable targets was 30.37% in the plot with high PPV inoculum pressure and only 7.98% in the plot with low inoculum pressure. We found significant differences in PPV incidence between Mariana GF8-1 plots that were treated with mineral oil and those that were not treated after one year under natural conditions and high PPV inoculum pressure
An empirical equation to calculate soil solution electrical conductivity at 25 degrees C from major ion concentrations
No full textThe electrical conductivity at 25 degrees C (EC(25)) of soil solutions or irrigation waters is the standard property for assessing salinity. Many models for soil salinity prediction calculate the major ion composition of the soil solution. The electrical conductivity of a solution can be determined from its composition through several different empirical equations. An assessment of these equations is necessary to incorporate the most accurate and precise equations in such models. Twelve different equations for the EC(25) calculation were calibrated by means of regression analyses with data from 133 saturation extracts and another 135 1: 5 soil-to-water extracts from a salt-affected agricultural irrigated area. The equations with better calibration parameters were tested with another data set of 153 soil solutions covering a wide range of salt concentrations and compositions. The testing was conducted using the standardized difference t-test, which is a rigorous validation test used in this study for the first time. The equations based on the ionic conductivity decrement given by Kohlrausch's law presented the poorest calibration parameters. The equations founded on the hypothesis that EC(25) is proportional to analytical concentrations had worse calibration and validation parameters than their counterparts based on free-ion concentrations and ionic activities. The equations founded on simpler mathematical relationships generally gave improved validation parameters. The three equations based on the specific electrical conductivity definition presented a mean standardized difference between observations and predictions indistinguishable from zero at the 95% confidence level. The inclusion of the charged ion-pair concentrations in the equation based on free-ion concentrations improved its predictions, particularly at large electrical conductivities. This equation can be reliably used in conjunction with chemical speciation software to assess EC(25) from the ion composition of soil solutions
Replacement of CTV-susceptible sour orange rootstock by CTV-tolerant ones may have triggered outbreaks of Tetranychus urticae in Spanish citrus
No full textThe two spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) is a major pest of citrus in Spain. Commercial citrus plants are always propagated asexually by bud-grafting onto a seedling rootstock. During the last 70 years, millions of citrus trees grafted on sour orange have been destroyed because of Citrus tristeza virus (CTV). Therefore other rootstocks are nowadays predominant. The aim of this study was to asses the influence of the rootstock on selected life history parameters of T. urticae. Mites were reared on leaves of Citrus unshiu trees grafted on six different rootstocks: sour orange, Troyer citrange, trifoliate orange, Volkamer lemon, Alemow and Cleopatra mandarin. Some parameters (sex ratio, egg hatching and survival) were not affected by the rootstock, whereas many other important ones were (fecundity, oviposition rate, lifespan and development time). These differences may explain the diversity found in the selected life history parameters (net fecundity, generation time and intrinsic rate of increase, rm). Sour orange appeared as the worst rootstock for T. urticae (rm = 0.140). It was closely followed by Troyer citrange and trifoliate orange (6% and 9% increase in rm, respectively), then by Alemow (35.3% increase in rm), Volkamer lemon (77.6% increase in rm) and finally Cleopatra mandarin which yielded an rm 89.1% higher than sour orange. These results can explain, at least partially, the increasing prevalence of T. urticae as a pest in Spanish citrus orchards. Furthermore, problems could become much more severe on salt-tolerant rootstocks because of global warming, which is expected to exacerbate the threat of salinity, especially in areas with a semi-arid climate. © 2010 Elsevier B.V. All rights reserved
Acta Horticulturae
No full textIn the present study a commercial solution of chitosan was applied to 'Oronules' mandarins to investigate its effect when applied as a coating at different solids content (0.6, 1.2 and 1.8%). Additionally, one group of mandarins was coated with a commercial wax, and another group remained uncoated. Mandarins were stored at 5°C for up to 30 d followed by 7 d at 20°C simulating retail conditions. All coatings restricted gas exchange and modified the internal atmosphere of the fruit compared to uncoated mandarins, with a greater effect at higher chitosan concentration. Chitosan-coated mandarins at higher solids content had the highest internal CO2 content and the highest ethanol content. Even though chitosan applied at 0.6% increased the internal level of CO2 of the mandarins, this coating did not increase the amount of ethanol compared to uncoated mandarins. Chitosan application did not decrease mass loss of mandarins during storage, whereas the commercial wax decreased mass loss compared to uncoated control fruit. The internal quality of mandarins was not affected by coating application. All coatings increased the gloss of the fruit. In order to improve the water barrier properties of the chitosan coating, it would be necessary to add hydrophobic components to the formulation
