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Efficacy of Bacillus thuringiensis (Berliner) in controlling the tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)
No full textThe tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is considered to be one of the most devastating pests affecting tomato crops in South America, where crop losses range from 60 to 100%. After its detection in the Spanish tomato-growing area at the end of 2006, it spread quickly to other European and northern African countries. Currently, T. absoluta management in these countries is mainly based on chemical treatments. Nonetheless, special emphasis is being placed on implementing environmentally safe strategies. Commercial formulates based on Bacillus thuringiensis may be a good alternative, as they have been used to control other insect pests successfully. The laboratory, greenhouse, and open-field experiments presented in this work are evidence that B. thuringiensis is highly efficient in controlling T. absoluta. First instar larvae were the most susceptible, while susceptibility was lower in second and third instar larvae. Our results have shown that the impact of T. absoluta can be greatly reduced by spraying only B. thuringiensis-based formulates, with no need for chemical insecticides. Furthermore, the integration of this technology with other biological control methods focused on T. absoluta eggs, such as the use of mirid predators or parasitoids, could reduce the number of B. thuringiensis treatments and the use of chemicals, with the consequent reduction of residues on fruits
Acta Horticulturae
No full textAn experiment was conducted in a vineyard planted with Vitis vinifera L. 'Riesling' in New York, USA. Vines were fully irrigated and were trained via vertical shoot positioning (VSP) giving a narrow curtain intercepting approximately 27% of the incident light. Vine rows were north-south oriented. In one experiment, the single curtain canopies were opened into a V-shape to increase light interception. Results showed that midday stem water potential decreased by approximately 20%, suggesting an increase in vine water use. In a second experiment, canopies were inclined towards the west for 20 min periods every 40 min in order to modify the daily pattern of vine light interception. The whole canopy gas exchange responses to these practices were measured with Mylar plastic chambers. During the afternoon, decreasing light interception by inclining the vine canopy towards the west, increased vine water use efficiency (WUE, canopy photosynthesis: transpiration) by 40% compared to when the vine canopy was in the vertical position. However, over the whole day WUE increased by only 8%. Overall this study supports the idea that vine gas exchange is driven more by vine light interception than by leaf area. Vines trained as VSP in north-south oriented rows offer a possibility for modifying daily patterns of gas exchange by changing canopy orientation to the sun. These strategies could be employed in order to either increase or decrease vine gas exchange depending on the environmental conditions and soil water status
Plant growth, yield and fruit quality of 'Lane Late' navel orange on four citrus rootstocks
Get PDFThis study analyses the influence of four citrus rootstocks, Citrus macrophylla Wester, Gou Tou Chen (Citrus hybrid), C. volkameriana Ten. & Pasq. and Cleopatra mandarin (C. reshni Hort. ex Tan.), on growth, yield and fruit quality on Lane Late navel orange. Trees were grown in a plot in Alicante (Spain), where the soil is clay loam, with pH 8.5 and electric conductivity in the 1/5 extract: 0.643 mmhos cm–1. Yield was weighed during four harvests, fruit quality was determined in 2007 and 2009. Cleopatra mandarin and Gou Tou Chen were found to be the most invigorating rootstocks for ‘Lane Late’ in heavy and calcareous soil. Trees on C. macrophylla rootstock produced the highest cumulative yield (328.81 kg tree–1), without significant differences compared to trees on Cleopatra mandarin (292.41 kg tree–1). Rootstock significantly affected fruit quality variables. C. macrophylla and C. volkameriana would appear to induce the highest fruit weight and ripening index
Phytochemical characterisation for industrial use of pomegranate (Punica granatum L.) cultivars grown in Spain
No full textBACKGROUND: The study of 15 pomegranate cultivars was carried out in order to demonstrate the wide diversity among the quality of Spanish pomegranates, and compared to 'Wonderful' cultivars, which are used worldwide for industrial purposes. Juice yield, quality parameters, organic acids and sugars, colour, vitamin C, ellagic acid, punicalagins, anthocyanins, total phenolic content, antioxidant capacity, and sensory properties were measured. RESULTS: A considerable variation was found between 'Wonderful' and pomegranates of Spanish origin, according to both cluster analysis and principal component analysis. 'Wonderful' juices displayed large antioxidant activity and a polyphenol content with very high acidity. In contrast, 'Mollar de Elche' showed fewer anthocyanins although it had very superior organoleptical properties. In addition to a high content in ellagitannins, 'Valenciana' juices had exclusive colour parameters. CONCLUSION: These useful results can be employed by the juice processing industry to select those properties more interesting for the development of pomegranate juices that are organoleptically attractive and rich in bioactive compounds. (C) 2011 Society of Chemical Industr
Two nucleotide positions in the Citrus exocortis viroid RNA associated with symptom expression in Etrog citron but not in experimental herbaceous hosts
Get PDFP>Citrus exocortis viroid (CEVd) is the causal agent of exocortis disease of citrus. CEVd has a wide host range that includes woody and herbaceous species. A new CEVd strain (CEVdCOL), phylogenetically clustering with CEVd variants of Class A inducing severe symptoms in tomato, was identified in Colombia and shown to induce only extremely mild symptoms in Etrog citron indicator plants. Using site-directed mutagenesis, two nucleotide substitutions (314A -> G and 315U -> A) in the lower strand of the P domain of the predicted CEVdCOL secondary structure resulted in a severe artificial CEVdMCOL variant. Conversely, two nucleotide exchanges (314G -> A and 315A -> U) in the same region of the severe variant CEVdE-117 resulted in a symptomless artificial CEVdME-117 variant. Infectivity assays conducted with the natural and mutated variants showed that all induced severe symptoms in Gynura aurantiaca, tomato and chrysanthemum. This is the first report of the identification of pathogenic determinants of CEVd in citrus, and shows that these pathogenicity determinants are host dependent
Hydraulic and Chemical Responses of Citrus Seedlings to Drought and Osmotic Stress
No full textIn this work we investigated the function of abscisic acid (ABA) as a long-distance chemical signal communicating water shortage from the root to the shoot in citrus plants. Experiments indicated that stomatal conductance, transpiration rates, and leaf water potential decline progressively with drought. ABA content in roots, leaves, and xylem sap was also increased by the drought stress treatment three- to sevenfold. The addition of norflurazon, an inhibitor of ABA biosynthesis, significantly decreased the intensity of the responses and reduced ABA content in roots and xylem fluid, but not in leaves. Polyethylene glycol (PEG)-induced osmotic stress caused similar effects and, in general, was counteracted only by norflurazon at the lowest concentration (10%). Partial defoliation was able to diminish only leaf ABA content (22.5%) at the highest PEG concentration (30%), probably through a reduction of the active sites of biosynthesis. At least under moderate drought (3-6 days without irrigation), mechanisms other than leaf ABA concentration were required to explain stomatal closure in response to limited soil water supply. Measurements of xylem sap pH revealed a progressive alkalinization through the drought condition (6.4 vs. 7.1), that was not counteracted with the addition of norflurazon. Moreover, in vitro treatment of detached leaves with buffers iso-osmotically adjusted at pH 7.1 significantly decreased stomatal conductance (more than 30%) as much as 70% when supplemented with ABA. Taken together, our results suggest that increased pH generated in drought-stressed roots is transmitted by the xylem sap to the leaves, triggering reductions in shoot water loss. The parallel rise in ABA concentration may act synergistically with pH alkalinization in xylem sap, with an initial response generated from the roots and further promotion by the stressed leaves
Compatiability of using 'Phytosiullus persimilis' and 'Neoseiulus californicus' (Acari; Phytoseiidae) to control Tetranychus urticae (Acari: Tetranuchidae) with drench applications of imidacloprid on clementine nurseries
No full textActivity of Cyt1Aa protein from 'Bacillus thuringiensis' (Berliner) subsp. israelensis against the Mediterranean fruit fly, 'Ceratitis capitata' (Wiedemann)
No full textThe pathogenicity determinant of Citrus tristeza virus causing the seedling yellows syndrome maps at the 3'-terminal region of the viral genome
Get PDFCitrus tristeza virus (CTV) (genus Closterovirus, family Closteroviridae) causes some of the more important viral diseases of citrus worldwide. The ability to map disease‐inducing determinants of CTV is needed to develop better diagnostic and disease control procedures. A distinctive phenotype of some isolates of CTV is the ability to induce seedling yellows (SY) in sour orange, lemon and grapefruit seedlings. In Florida, the decline isolate of CTV, T36, induces SY, whereas a widely distributed mild isolate, T30, does not. To delimit the viral sequences associated with the SY syndrome, we created a number of T36/T30 hybrids by substituting T30 sequences into different regions of the 3′ half of the genome of an infectious cDNA of T36. Eleven T36/T30 hybrids replicated in Nicotiana benthamiana protoplasts. Five of these hybrids formed viable virions that were mechanically transmitted to Citrus macrophylla, a permissive host for CTV. All induced systemic infections, similar to that of the parental T36 clone. Tissues from these C. macrophylla source plants were then used to graft inoculate sour orange and grapefruit seedlings. Inoculation with three of the T30/T36 hybrid constructs induced SY symptoms identical to those of T36; however, two hybrids with T30 substitutions in the p23‐3′ nontranslated region (NTR) (nucleotides 18 394–19 296) failed to induce SY. Sour orange seedlings infected with a recombinant non‐SY p23‐3′ NTR hybrid also remained symptomless when challenged with the parental virus (T36), demonstrating the potential feasibility of using engineered constructs of CTV to mitigate disease
Changes in predation and parasitism of the citrus leafminer Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) populations in Spain following establishment of Citrostichus phyllocnistoides (Hymenoptera: Eulophidae)
No full textThe citrus leafminer, Phyllocnistis citrella, is a pest native to Southeast Asia which threatened the citrus industry in the Mediterranean region upon its introduction in 1993. Immediately afterward, a classical biological control program was implemented in Spain. The exotic parasitoid Citrostichus phyllocnistoides was the only introduced parasitoid to become established. In 2006, data on both the incidence of P. citrella and the impact of its natural enemies were collected following the same protocols used in 1997-1999 when C. phyllocnistoides was not yet present. C. phyllocnistoides constituted 99.4% of the parasitoids collected in 2006 corresponding to a decrease in the incidence of P. citrella from 3.2-5.1 to 1.8-2.4 mines per leaf in 1997-1999 and 2006, respectively. Mortality caused by natural enemies on P. citrella in 2006 was 93.3% (18.0% parasitism, 40.8% feeding punctures and 34.5% predation). C. phyllocnistoides, which preferentially parasitizes P. citrella second instar larvae, has displaced most of the indigenous parasitoids that moved onto P. citrella mainly parasitizing third instar larvae, upon its introduction. Because C. phyllocnistoides is an idiobiont parasitoid and preferentially parasitizes P. citrella second instars, this stage has become dominant in the orchards. The shift in the relative abundance of P. citrella larvae has prompted generalist predators to prey mostly on second instars and has contributed to the displacement of the native non-specific parasitoids, which principally utilize third instars, from the system. Both indigenous predators and the introduced parasitoid are key players in the natural regulation of P. citrella. © 2009 Elsevier Inc. All rights reserved