ReDivia - Repositorio Digital de l'Instit Valencià d'Investigacions Agràries
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The predatory mirid Dicyphus maroccanus as a new potential biological control agent in tomato crops
No full textThe first record of the omnivorous predator Dicyphus maroccanus Wagner (Hemiptera: Miridae) inhabiting tomato crops in the Valencia region (East Coast of Spain) was in 2009. Since then, D. maroccanus has often been found preying on the eggs of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in this area. To evaluate this predator’s potential as a biological control agent, its life-history traits in the presence and absence of prey [(eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae)] on tomato plants were studied under laboratory conditions. Immature stages that preyed on eggs of E. kuehniella developed successfully. However, no nymph completed development on the plant without the addition of E. kuehniella eggs. To reach adulthood, male and female D. maroccanus nymphs consumed 267 and 312 E. kuehniella eggs, respectively. The net reproductive rate (R0) was estimated to be 34.52 female eggs per female, the generation time (T) was 40.48 days, and the estimated intrinsic rate of increase (rm) was 0.0868 females per female per day at 25 °C. In a second experiment, the capacity to detect plants infested or not infested with T. absoluta was studied using a Y-tube olfactometer. Female D. maroccanus were strongly attracted to the odor of T. absoluta-infested plants. In a third experiment, the capacity of D. maroccanus to control T. absoluta on tomato plants was investigated under extended laboratory conditions. Dicyphus maroccanus significantly reduced the number of T. absoluta-infested leaves in over 90 % of cases relative to control conditions. These results suggest that D. maroccanus could play a significant role in T. absoluta management. The potential of this zoophytophagous predator as a biocontrol agent on tomato crops is discussed
Tissue-print and squash real-time PCR for direct detection of 'Candidatus Liberibacter' species in citrus plants and psyllid vectors
No full textHuanglongbing (HLB) disease is seriously threatening and/or damaging the citrus industry worldwide. Accurate detection of the three species associated with HLB disease, Candidatus Liberibacter asiaticus', Candidatus Liberibacter africanus' and CandidatusLiberibacter americanus', is essential for the preventive control of the disease. Real-time PCR is a useful tool for bacterial detection. However, nucleic acid purification steps limit the number of samples that can be processed by PCR. Universal detection of Ca.Liberibacter' species was achieved by direct tissue-printing and spotting of plant leaf petiole extracts or squashing of individual psyllids onto paper or nylon membranes. Primers were designed and used with TaqMan chemistry for accurate detection of the bacterium in immobilized targets (prints of 10 overlapping leaf pedicels per tree, or squashed single vectors), by extraction with water and direct use for real-time PCR. This simplified method was validated and could detect HLB-liberibacters in 100% of leaves with symptoms and 59% of symptomless leaves collected from HLB-infected trees. The use of direct assays as template showed good agreement with use of purified DNA (=076 +/- 0052). The squash assay allowed detection of the bacterium in 40% of mature Diaphorina citri that fed on leaves of HLB-infected trees with or without symptoms. A commercial ready-made kit based on this technology showed 96% accuracy in intra-laboratory performance studies. The simplified direct methods of sample preparation presented herein can be effectively adopted for use in rapid screening of HLB agents in extensive surveys, certification schemes or for epidemiological and research studies
Optimised computer vision system for automatic pre-grading of citrus fruit in the field using a mobile platform
Get PDFThe mechanisation and automation of citrus harvesting is considered to be one of the best options to reduce production costs. Computer vision technology has been shown to be a useful tool for fresh fruit and vegetable inspection, and is currently used in post-harvest fruit and vegetable automated grading systems in packing houses. Although computer vision technology has been used in some harvesting robots, it is not commonly utilised in fruit grading during harvesting due to the difficulties involved in adapting it to field conditions. Carrying out fruit inspection before arrival at the packing lines could offer many advantages, such as having an accurate fruit assessment in order to decide among different fruit treatments or savings in the cost of transport and marketing non-commercial fruit. This work presents a computer vision system, mounted on a mobile platform where workers place the harvested fruits, that was specially designed for sorting fruit in the field. Due to the specific field conditions, an efficient and robust lighting system, very low-power image acquisition and processing hardware, and a reduced inspection chamber had to be developed. The equipment is capable of analysing fruit colour and size at a speed of eight fruits per second. The algorithms developed achieved prediction accuracy with an R-2 coefficient of 0.993 for size estimation and an R-2 coefficient of 0.918 for the colour index
Addressing the Threat of Huanglongbing in the Mediterranean Region: a Challenge to Save the Citrus Industry
No full textEven though Citrus huanglongbing (HLB), caused by Candidatus Liberibacter spp., is not yet present in the Mediterranean basin, this devastating disease is threatening the very survival of citrus in most parts of the world. In the framework of an international course on “Emerging and Quarantine Diseases of Mediterranean Fruit and Vegetable Crops”, the participants were asked to hold group discussions to define measures for prevention and management of HLB in the Mediterranean Region. Following an introduction on the present situation of HLB in the world and emphasizing the facts that: (i) the African citrus psyllid, Trioza erytrae, is already present in the Canary and Madeira islands and threatens the western Mediterranean area and (ii) Asian HLB, with Candidatus Liberibacter asiaticus and the Asian citrus psyllid, Diaphorina citri, are present in Iran and the Arabian Peninsula and threaten the eastern Mediterranean area, a general discussion defined: (I) measures for prevention, including awareness, monitoring and surveillance, pest risk analysis, the establishment of quarantine measures, and practicing PCR detection methods for liberibacters in citrus and psyllids; (II) action plans taking into consideration the presence of insect vectors and/or HLB-like symptoms; and (III) future actions that must include the development of genetically modified citrus cultivars resistant to the causal liberibacter agents or to infection by the psyllid vectors. As management of HLB would be difficult in the Mediterranean area, in particular because of the small size of most citrus orchards, all efforts should be concentrated towards preventing HLB entrance and spread in the area
Effect of antifungal hydroxypropyl methylcellulose- beeswax edible coatings on gray mold development and quality attributes of cold-stored cherry tomato fruit
Get PDFEdible composite coatings based on hydroxypropyl methylcellulose (HPMC), beeswax (BW), and food preservatives with antifungal properties, were evaluated on cherry tomatoes during cold storage. Food preservatives selected from previous research work included sodium propionate (SP), potassium carbonate (PC), ammonium phosphate (APh) and ammonium carbonate (AC). Cherry tomatoes artificially inoculated with Botrytis cinerea were coated and stored up to 15 d at 5 degrees C followed by 7 d of shelf-life at 20 degrees C. All antifungal HPMC-BW coatings significantly reduced gray mold development on inoculated and cold-stored cherry tomatoes, the SP-based coating being the most effective. Analytical and sensory fruit quality was also evaluated after cold storage and shelf-life. The AC-based coating was the most effective to control weight loss and maintain the firmness of coated cherry tomatoes. Respiration rate, firmness, color, sensory flavor, off-flavor, and fruit appearance were not adversely affected by the application of the antifungal coatings. Overall, the application of HPMC-BW edible composite coatings containing AC could be a promising treatment to extend the postharvest life of cherry tomatoes. Further studies should focus on the modification of some physical characteristics of the coatings in order to enhance the general performance and provide higher peel gloss. (C) 2014 Elsevier B.V. All rights reserved
The use of agricultural substrates to improve methane yield in anaerobic co-digestion with pig slurry: Effect of substrate type and inclusion level
No full textAnaerobic co-digestion of pig slurry with four agricultural substrates (tomato, pepper, persimmon and peach) was investigated. Each agricultural substrate was tested in co-digestion with pig slurry at four inclusion levels: 0%, 15%, 30% and 50%. Inclusion levels consisted in the replacement of the volatile solids (VS) from the pig slurry with the VS from the agricultural substrate. The effect of substrate type and inclusion level on the biochemical methane potential (BMP) was evaluated in a batch assay performed at 35 degrees C for 100 days. Agricultural substrate's chemical composition was also analyzed and related with BMP. Additionally, Bacteria and Archaea domains together with the four main methanogenic archaeal orders were quantified using quantitative real-time TaqMan polymerase chain reaction (qPCR) at the end of the experiment to determine the influence of agricultural substrate on sludge's microbial composition. Results showed that vegetable substrates (pepper and tomato) had higher lipid and protein content and lower carbohydrates than fruit substrates (persimmon and peach). Among substrates, vegetable substrates showed higher BMP than fruit substrates. Higher BMP values were obtained with increasing addition of agricultural substrate. The replacement of 50% of VS from pig slurry by tomato and pepper increased BMP in 41% and 44%, respectively compared with pig slurry only. Lower increments in BMP were achieved with lower inclusion levels. Results from qPCR showed that total bacteria and total archaea gene concentrations were similar in all combinations tested. Methanomicrobiales gene concentrations dominated over the rest of individual archaeal orders. (C) 2013 Elsevier Ltd. All rights reserved
Development of models to predict product deposition from coverage obtained on artificial collectors and their practical applications
Get PDFModels to relate the observed coverage on artificial collectors used in field tests (water-sensitive paper, WSP) and in laboratory bioassays of citrus pests (pieces of polyvinyl chloride sheets, PVC) with product deposition are described. Different solutions of plant protection products commonly used for pest control in citrus were sprayed in a Potter Tower on PVC and WSP under the same controlled conditions. These experiments led to the formulation of different basic models to relate coverage and deposition depending on the products and collectors. The best fitting model was selected from among those that had highest coefficients of determination (R-2) and lowest estimation error (RMSEP), and at the same time resulted in a normal distribution of residuals. Finally, coverage on pieces of PVC sheets was related with coverage obtained on WSP by different equations depending on the product being applied. Such equations can be used to link laboratory and field results in order to assess the quality of a spray application in citrus cultivation
Estimating SIT-driven population reduction in the Mediterranean fruit fly, Ceratitis capitata, from sterile mating
No full textArea-wide sterile insect technique (SIT) programs assume that offspring reduction of the target population correlates with the mating success of the sterile males released. However, there is a lack of monitoring tools to prove the success of these programs in real-time. Field-cage tests were conducted under the environmental conditions of the Mediterranean coast of Spain to estimate: (a) the mating success of sterile Vienna-8 (V8) Ceratitis capitata males using molecular markers and (b) their efficacy to reduce C. capitata populations under six release ratios of wild females to wild males to V8 males (1:0:0, 1:1:0, 1:1:1, 1:1:5, 1:1:10, and 1:1:20). Statistical models were developed to predict: (a) the number of females captured in traps, (b) sperm ID (sterile or not) in spermathecae of the trapped females, and (c) the viable offspring produced, using release ratio and temperature as predictors. The number of females captured was affected by relative humidity. However, its influence in the model was low. Female captures were significantly higher in ratios 1:0:0 compared to ratios where V8 males were released. The proportion of V8 sperm in spermathecae increased with temperature and with the number of V8 males released, but leveled off between ratios 1:1:10 and 1:1:20. In all seasons, except winter (no offspring), viable offspring increased with temperature and was lowest for ratio 1:1:20. For the first time, a strong negative relationship between proportion of V8 sperm detected by molecular tools and C. capitata offspring was established. The models obtained should contribute to enhance the efficacy of SIT programs against this pest
A comparative life history study of two mirid bugs preying on Tuta absoluta and Ephestia kuehniella eggs on tomato crops: Implications for biological control
No full textThe omnivorous predators Nesidiocoris tenuis (Reuter) and Macrolophus pygmaeus Rambur (Hemiptera: Miridae) are indigenous natural enemies that commonly inhabit tomato crops in the Mediterranean basin. Both predators are mass-reared and primarily released to control whiteflies, although recently they have also contributed to the control of the invasive tomato pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). The life history traits of these two predators have been studied in the laboratory under the conditions of being fed exclusively the eggs of T. absoluta or the eggs of the factitious prey Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae). Immature stages of both predator species successfully developed while preying on eggs of T. absoluta. However, the mature M. pygmaeus females produced significantly lower numbers of offspring in comparison to the offspring produced when preying on E. kuehniella eggs. This resulted in higher than expected demographic indexes for N. tenuis when compared to M. pygmaeus (e.g., the intrinsic rates of increase were 0.127 and 0.005, respectively). Our results support previous studies on the potential of N. tenuis has as biological control agent of T. absoluta, and indicate that the role of M. pygmaeus in controlling T. absoluta in the absence of other food sources is possibly limited. © 2013 International Organization for Biological Control (IOBC)
Genetic structure of a phytophagous mite species affected by crop practices: the case of Tetranychus urticae in clementine mandarins
No full textTetranychus urticae Koch is a cosmopolitan mite considered as the most polyphagous species among spider mites. This mite is a key pest of clementine mandarins in Eastern Spain, where Spanish clementine production concentrates. Crop management practices can affect the population dynamics of this mite and, consequently, its impact on the orchard. Microsatellite markers were used to study mite population genetics from two commercial orchards which had been managed differently following Integrated Pest Management (IPM) or Organic Pest Management (OPM) schemes during four consecutive years. A multiplex system including 20 microsatellite loci was designed specifically and allowed an efficient and inexpensive genotyping of individual mites. We found that the IPM population had a stronger fluctuation of population structure and higher genetic diversity compared to OPM population. Thus, our study concludes that crop management has an impact on the population genetics of T. urticae which may be related to the alternation of some acaricides under IPM