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A rare case of a natural contact zone in Morocco between an autopolyploid and an allopolyploid of Centaurea aspera with sterile tetraploid hybrids
Get PDFA new contact zone between Centaurea aspera and Centaurea seridis was found in Morocco. Chromosome counts and flow cytometry showed that both taxa were tetraploid (4x = 44). A literature review and morphometric analysis established that C. aspera corresponds to the autopolyploid C. aspera subsp. gentilii and C. seridis corresponds to the allopolyploid C. seridis var. auriculata. This contact area was compared with the homologous contact zones in Spain formed by the diploid C. aspera subsp. stenophylla and the tetraploid C. seridis subsp. maritima. Natural hybrids between parental species were frequent in both areas. In Spain, hybrids were triploid (from reduced gametes A and gamete AB), highly sterile and exerted a ‘triploid block’. In Morocco, cytometry showed that hybrids were tetraploid and, therefore, probably fertile, but all the capitula lacked achenes. It is likely that the resulting genome of the new tetraploid hybrid (AAAB), through the fusion of reduced gametes AA (from subsp. gentilii) and AB (from var. auriculata), could explain irregularities in meiosis through formation of aneuploid gametes and, therefore, infertility of the hybrid. Moroccan sterile tetraploid hybrids develop, but have the identical irregularities to Spanish triploids, probably due to the odd number of homologous chromosomes. The new hybrid is first described as C. x subdecurrens nothosubsp. paucispinus. In addition, distribution and ecological traits are analysed
Acta Horticulturae
No full textThe citrus aphids Aphis spiraecola Patch. and Aphis gossypii Glover (Hemiptera: Aphididae) are key pests of citrus clementine in Spain. A rich complex of natural enemies (NE) exploits these two species. However, NE usually colonize citrus trees once aphid populations have exceeded economical thresholds. Hence, successful biological control should be based on anticipating the arrival of NE. Recently, our group has found that citrus orchards with a ground cover of grass (Poales: Poaceae) had less aphids per colony and these colonies lasted shorter than those colonies found in orchards with bare soil management. These differences were attributed to an earlier appearance of aphid NE in the grass cover which attracted NE to the citrus orchard. This early appearance of NE contributed to a successful control of aphids in the canopy
Acta Horticulturae
No full textCitrus triploid hybrids can be recovered by 2x x 2x hybridisations as a consequence of the formation of 2n gametes or by interploid hybridisation. Most of the tetraploid parents used are doubled-diploid (DD). The genetic structure of diploid gametes and particularly the rate of parental heterozygosity restitution (PHR) depend on the meiotic process by which they were originated. Second-division restitution (SDR) is the 2n gamete formation mechanism involved in 'Fortune' and clementines. With SDR, PHR is positively linked with the distance of each locus to the centromere. With DD parents, PHR depends of the rate of preferential pairing and thus the proportion of disomic versus tetrasomic segregations. We have compared the genetic structure of two populations of diploid gametes of clementine (one population of 2n gametes and one of 2x gametes produced by DD) with SNPs and SSRs markers covering the 9 citrus chromosomes. The DD displays mostly tetrasomic segregation; however three linkage groups present intermediate segregation and one display a tendency for disomy. The PHR in 2n gametes is 2/3 of the one obtained in 2x gametes produced by DD. The two methods of triploid production appear complementary in terms of genotypic variability. 4x x 2x hybridizations are more efficient than 2x x 2x for developing new cultivars phenotypically closer to the diploid parent of the DD. Conversely, 2x x 2x hybridisations provides the opportunity to select more innovative products
Visible-NIR reflectance spectroscopy and manifold learning methods applied to the detection of fungal infections on citrus fruit
No full textThe development of systems for automatically detecting decay in citrus fruit during quality control is still a challenge for the citrus industry. The feasibility of reflectance spectroscopy in the visible and near infrared (NIR) regions was evaluated for the automatic detection of the early symptoms of decay caused by Penicillium digitatum fungus in citrus fruit. Reflectance spectra of sound and decaying surface parts of mandarins cv. 'Clemenvilla' were acquired in two different spectral regions, from 650 nm to 1050 nm (visible NIR) and from 1000 nm to 1700 nm (NIR), pointing to significant differences in spectra between sound and decaying skin for both spectral ranges. Three different manifold learning methods (principal component analysis, factor analysis and Sammon mapping) were investigated to transform the high-dimensional spectral data into meaningful representations of reduced dimensionality containing the essential information. The low-dimensional data representations were used as input feature vectors to discriminate between sound and decaying skin using a supervised classifier based on linear discriminant analysis. The best classification results were achieved by employing factor analysis on the NIR spectra, yielding a maximum overall classification accuracy of 97.8%, with a percentage of well-classified sound and decaying samples of 100% and 94.4%, respectively. These results lay the foundation for the future implementation of reflectance spectroscopy technology on a commercial fruit sorter for the purpose of detecting decay in citrus fruit
Sampling Methods for Detection and Monitoring of the Asian Citrus Psyllid (Hemiptera: Psyllidae)
No full textThe Asian citrus psyllid (ACP), Diaphorina citri Kuwayama is a key pest of citrus due to its role as vector of citrus greening disease or “huanglongbing.” ACP monitoring is considered an indispensable tool for management of vector and disease. In the present study, datasets collected between 2009 and 2013 from 245 citrus blocks were used to evaluate precision, sensitivity for detection, and efficiency of five sampling methods. The number of samples needed to reach a 0.25 standard error-mean ratio was estimated using Taylor’s power law and used to compare precision among sampling methods. Comparison of detection sensitivity and time expenditure (cost) between stem-tap and other sampling methodologies conducted consecutively at the same location were also assessed. Stem-tap sampling was the most efficient sampling method when ACP densities were moderate to high and served as the basis for comparison with all other methods. Protocols that grouped trees near randomly selected locations across the block were more efficient than sampling trees at random across the block. Sweep net sampling was similar to stem-taps in number of captures per sampled unit, but less precise at any ACP density. Yellow sticky traps were 14 times more sensitive than stem-taps but much more time consuming and thus less efficient except at very low population densities. Visual sampling was efficient for detecting and monitoring ACP at low densities. Suction sampling was time consuming and taxing but the most sensitive of all methods for detection of sparse populations. This information can be used to optimize ACP monitoring efforts
User concerns about sprayer inspections in the Comunidad Valenciana (Spain). Importance of adequate communication for the higher involvement of stakeholders
Get PDFLa fertilización y el riego de la sandía al aire libre
Get PDFLa sandía, al igual que la mayoría de los cultivos hortícolas, vegeta mejor en los suelos de textura media, profundos, con buen drenaje, bien provistos de elementos fertilizantes y materia orgánica, con pH ligeramente ácido o moderadamente alcalino, presentando una tolerancia media a la salinidad. La fertilización es la práctica de cultivo que tiene como finalidad suministrar
al suelo o a la planta directamente las cantidades de nutrientes necesarias para la obtención de producciones altas y frutas de buena calidad: pero, además se debe procurar que esta se realice de la forma más eficiente posible con la finalidad de reducir el costo económico y su impacto ambiental
Acta Horticulturae
No full textProduction of seedless citrus fruits is required for the fresh market because consumers do not accept seedy fruits. Development of new seedless mandarin cultivars has a high priority for many citrus industries worldwide. The recovery of triploid hybrids is the most promising approach to achieve this goal, since triploids have a very low pollen and ovule fertility. They are seedless or produce very low numbers of seeds and do not induce the formation of seeds in other cultivars by cross pollination. In Spain we are carrying a triploid breeding program since 1996 based on 2x × 2x, 2x × 4x and 4x × 2x sexual hybridizations followed by embryo rescue and flow cytometry, together with the use of different approaches to produce new tetraploid parents. The objective is to obtain new high quality easy peeling and seedless mandarin cultivars. More than thirty spontaneous autotetraploid apomictic genotypes to be used as male parents have been selected from seedbeds by flow cytometry. Also nine autotetraploid non apomictic genotypes, mainly to be used as female parents, have been obtained by chromosome duplication with treatments of micrografted shoot tips with colchicine or oryzalin. Symmetric protoplast fusion is also being used to produce allotetraploid genotypes. So far, we have obtained more than 5,500 triploid hybrids from 130 parental combinations by 2x × 2x pollinations, more than 4,300 triploid hybrids from 100 parental combinations by 2x × 4x pollinations, and more than 5,600 triploid hybrids from 103 parental combinations by 4x × 2x pollinations. In 2008 we released the first cultivars originated in the program, the seedless late maturing mandarins ‘Garbí’ and ‘Safor’, obtained from 2x × 2x crosses. More than 400,000 trees of these cultivars have been planted by growers during the last three years
Determination of an efficient irrigation schedule for the cultivation of rose cv. Freedom under greenhouse conditions in Colombia
Get PDFAn experiment on rose (Rosa sp.) cv. Freedom was performed in a greenhouse on the Bogota Plateau, Colombia, to identify an efficient irrigation regime for this crop. The tested treatments were based on three irrigation doses, applying different fractions of the estimated crop evapotranspiration (ETc), calculated using a class A evaporation tank: i) 100% ETc (ETc100), ii) 80% ETc (ETc80) and iii) 70% ETc (ETc70). During the entire experimental period, from mid-May to early September, the crop had a constant production of floral stems. In all of the irrigation treatments, the soil and plant water status were monitored using tensiometers and the midday stem water potential, respectively (ystem). In the fully irrigated roses, the actual water use was determined using a drainage lysimeter in order to obtain the local crop coefficients (Kc) by means of a water balance. From June to August, the obtained monthly Kc values varied between 1.10 and 1.26. Compared to the ETc100 treatment, 14.5 and 21.8% less water was applied in treatments ETc80 and ETc70, respectively. Despite this fact, no statistically significant differences were found among the treatments for rose production or quality. Finally, in the more irrigated roses, tight relationships between the stem water potential and vapor pressure deficit were obtained. The reported base-line equations can be used for predicting the optimum rose plant water status, depending on the environmental conditions. Overall, the reported results can be used for an efficient irritation schedule for rose crops under greenhouse conditions, using the local Kc and direct determinations of plant water status corrected for the evaporative demand
Laboratory evaluation of the compatibility of a new attractant contaminant device containing Metarhizium anisopliae with Ceratitis capitata sterile males
Get PDFLaboratory experiments were conducted to evaluate the compatibility of using the entomopathogenic fungus Metarhizium anisopliae, to be dispensed in a new attractant contaminant device (ACD), jointly with sterilized Ceratitis capitata males, as an integrated approach to control this major pest. The exposure of sterile Vienna 8 (V8) strain and wild type (WT) males to the contaminating part (infective dish) of the ACD showed similar susceptibility levels to the fungal strain (LT50 value of 4.52 and 4.72 days, respectively). Sterile V8 males were significantly less attracted to the infective dish (18.4%) than WT males (28.5%). As the success of Sterile Insect Technique (SIT) heavily relies on the mating success of sterile males in the field, mating performance of infected males was assessed. Around 85% of the females were mated, independently of the male strain and treatment (fungus-treated or untreated males) indicating that mating performance was unaffected by the fungus under laboratory conditions. Females showed a greater tendency to remate if previously mated to fungus-treated males, either V8 or WT. Our data suggest that this M. anisopliae based-ACD does not impair the performance of C. capitata sterile males and, therefore, it could be used combined with area wide SIT-based programs, providing that these results are validated in field conditions. The implications of this combined strategy to control C. capitata are discussed. (C) 2014 Elsevier Inc. All rights reserved