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Induced resistance in sweet orange against 'Xanthomonas citri' subsp. 'citri' by hexanoic acid
Get PDFAbstract Citrus canker, caused by Xanthomonas citri subsp. citri, is a serious and wide-spread disease of citrus, causing losses in fruit yield and quality. There are no highly effective citrus canker disease control measures. Repeated spray applications of copper are often employed to protect fruit from bacterial infection with consequences for copper phytotoxicity and accumulation in the soil. Alternatively, innate plant defense mechanisms can be enhanced by plant treatments with specific natural and synthetic inducers for control of bacterial diseases. In this study, hexanoic acid applied as a soil drench or foliar spray on 9-month-old potted citrus trees reduced lesions on leaves by 50% compared with control plants. Disease-reducing activity lasted up to 50 days after application. Induction of resistance mediated by hexanoic acid was demonstrated by enhanced expression of Pathogenesis-related (PR) genes and callose deposition in treated and infected plants. These findings indicated that hexanoic acid applications trigger a defensive response in the plants. The application of this natural compound may have potential for management of citrus canker in conjunction with other disease control measures and may reduce the frequency or rate of copper bactericides
Seasonal trends, sampling plans and parasitoid complex of the Chinese wax scale, Ceroplastes sinensis Del Guercio (Hemiptera: Coccidae), in Mediterranean citrus groves
No full textSeasonal trends and the parasitoid complex of Chinese wax scale (Ceroplastes sinensis) was studied from July 2010 to February 2013. Six commercial citrus groves located in northeastern Spain were sampled fortnightly. Chinese wax scale completed a single annual generation. Egg oviposition started in May and continued until mid-July. Egg hatching began in mid-June, and in the first quarter of August, the maximum percentage of hatched eggs was reached. In the same groves, the parasitoid species of C. sinensis were determined together with their seasonal trends, relative abundance and occurrence on C. sinensis. Four hymenoptera were found parasitizing C. sinensis, mainly on third instars and females: Coccophagus ceroplastae (Aphelinidae), Metaphycus helvolus (Encyrtidae), Scutellista caerulea (Pteromalidae) and Aprostocetus ceroplastae (Eulophidae). The most abundant species was A. ceroplastae, corresponding to 54% of the parasitoids emerged. Coccophagus ceroplastae and M. helvolus represented 19%, whereas S. caerulea comprised 8% of the total. This study is the first published record of C. ceroplastae in Spain and the first record of M. helvolus on C. sinensis in Spain. Concerning the economical thresholds normally used, sampling plans developed for the management of C. sinensis in citrus groves should target population densities of around 12-20% of invaded twigs, equivalent to 0.2-0.5 females per twig. The sample size necessary to achieve the desired integrated pest management precision is 90-160 twigs per grove for the enumerative plan and about 160-245 twigs per grove for the binomial plan
Involvement of the Redox System in Chilling Injury and Its Alleviation by 1-Methylcyclopropene in 'Rojo Brillante' Persimmon
No full textA treatment with 1-methylcyclopropene (1-MCP) is known to reduce softening to the flesh of ‘Rojo Brillante’ persimmon, which is the main chilling injury (CI) symptom that occurs after storage at low temperature. However, very little is known about the mechanism by which 1-MCP confers persimmon tolerance to chilling. The aim of this study was to investigate the changes in the redox system associated with CI and its reduction by 1-MCP during storage at 1 °C and after shelf life period. Our results showed that during cold store, both control and 1-MCP treated fruit underwent gradual oxidative stress (accumulation of H2O2, increment in APX, CAT, LOX, and slight increase in SOD activity) but no CI was manifested. During shelf life conditions, ethylene production was slightly higher in control than in 1-MCP treated fruit. Besides, the CI manifestation of control fruit was associated with oxidative burst [major H2O2 accumulation and sharp increase in catalase (CAT), peroxidase (POD), and lipoxygenase (LOX) activity], while 1-MCP treatment greatly reduced the CI symptoms. The 1-MCP treated fruit showed down-regulated POD activity and up-regulated CAT activity, which resulted in slower H2O2 accumulation. The reduction of the flesh softening as the main manifestation of CI in ‘Rojo Brillante’ persimmon by 1-MCP was associated with the modulation of the redox state of the fruit during the shelf life period that follows low-temperature storage
Mature seeds for in vitro sanitation of the Grapevine leafroll associated virus (GLRaV-1 and GLRaV-3) from grape (Vitis vinifera L.)
Get PDFThe conservation of old grapevine varieties is important since they are adapted to specific climate conditions and may carry genes interesting to breeders. As virus infection is common in grapevine varieties, the use of virus free materials is of great importance. In this work, we used somatic embryogenesis for the sanitation of GLRaV-1 and GLRaV-3 viruses that were found after analyzing the putative presence of the five most common, economically important grape viruses by real-time multiplex RT-PCR in the old cultivar "Grumet Negre". Unopened and opened inflorescences, fecundated ovaries, and, also, mature seeds were used as starting explants. Explants were cultured on plates with two embryogenesis induction media (Nitsch & McCown Woody plant medium) that contained the growth regulator thidiazuron and differed in their salt and vitamin compositions. One half of each kind of explant was cut prior to being cultured. After five months of culture, embryos had only developed from seeds that were cut previous to sowing. To the best of our knowledge, this is the first time that mature seeds have been used for inducing embryogenesis in grape. A total of 42% of the embryos transferred to tubes for germination regenerated into normal plantlets. The absence of both the GLRaV-1 and GLRaV-3 viruses in all regenerated plants was confirmed by real-time uniplex RT-PCR. So, this protocol can be used for sanitation and also for micropropagation
Some rootstocks improve pepper tolerance to mild salinity through ionic regulation
Get PDFGrafting has been proposed as an interesting strategy that improves the responses of crops under salinity. In pepper, we reported increased fruit yield of the commercial ‘Adige’ cultivar under salinity when grafted onto accessions Capsicum chinense Jacq. ‘ECU-973′ (12) and Capsicum baccatum L. var. pendulum ‘BOL-58′ (14), whereas no effect was observed when grafted onto accession Capsicum annuum L var. ‘Serrano’ (5). We also analysed the physiological and biochemical mechanisms related to the tolerance conferred by these rootstocks. Responses to salinity (40 mM NaCl) were studied in the different plant combinations for 30 days by determining water relations, mineral content, proline accumulation, photosynthetic parameters, nitrate reductase activity and antioxidant capacity. Higher salt tolerance was achieved when the ‘Adige’ cultivar was grafted onto the 12 genotype, which allowed not only lower Na+ and Cl− accumulation in the scion, but also ion selectivity maintenance, particularly Na+/K+ discrimination. These traits led to a minor negative impact on photosynthesis, nitrate reductase activity and lipid peroxidation in grafted scion leaves. This work suggests that using tolerant pepper rootstocks that maintain the scion's ion homeostasis is a promising strategy to provide salinity tolerance and can consequently improve crop yield
Draft Genome Sequences of Dickeya sp. Isolates B16 (NIB Z 2098) and S1 (NIB Z 2099) Causing Soft Rot of Phalaenopsis Orchids
Get PDFThe genus Dickeya contains bacteria causing soft rot of economically important crops and ornamental plants. Here, we report the draft genome sequences of two Dickeya sp. isolates from rotted leaves of Phalaenopsis orchid
Acta Horticulturae
No full textSSRs have been considered as almost ideal markers for genetic diversity analysis. With the increasing availability of sequencing data, SNPs and InDels become major classes of codominant markers with genome wide coverage. We have analyzed the respective values of SSRs, InDels, and SNPs for intra and interspecific Citrus genetic diversity analysis. Moreover, we have compared the diversity structure revealed by markers mined in a single heterozygous genotype (clementine) and markers mined from a large interspecific survey. A random set of markers was selected for each marker class to genotype 48 citrus accessions. SSRs were the most polymorphic markers at the intraspecific level allowing complete varietal differentiation within basic taxa (C. reticulata, C. maxima, C. medica). However, SSRs gave the lowest values for interspecific differentiation, followed by SNPs and InDels, that in average displayed low intraspecific variability but high interspecific differentiation. A clear effect of the discovery panel was observed for SNPs and InDels. The ascertainment biases associated with the clementine heterozygosity mining resulted mainly in an over estimation of within C. reticulata diversity and an underestimation of the interspecific differentiation. In conclusion pluri-allelic SSRs are very useful for intraspecific structure analysis but have limitations for interspecific and phylogenetic studies. SNPs and InDels mined in large discovery panels appear to allow efficient selection of more specialized markers with high potential for phylogenetic diagnosis and to decipher the interspecific mosaic structure of secondary cultivated species or to analyze intraspecific diversity. Several SNP genotyping methods are available for different analysis scales, from high throughput genotyping to small set of data production. With the ongoing resequencing projects, SNPs markers will soon be the most important class of markers for citrus genetics
Search for potential vectors of 'Candidatus Liberibacter solanacearum': population dynamics in host crops
Get PDF'Candidatus Liberibacter solanacearum' has recently been reported to be associated with vegetative disorders and economic losses in carrot and celery crops in Spain. The bacterium is a carrot seedborne pathogen and it is transmitted by psyllid vector species. From 2011 to 2014 seasonal and occasional surveys in carrot, celery and potato plots were performed. The sticky plant method was used to monitor the arthropods that visited the plants. The collected arthropods were classified into Aphididae and Cicadellidae, and the superfamily Psylloidea was identified to the species level. The superfamily Psylloidea represented 35.45% of the total arthropods captured on celery in Villena and 99.1% on carrot in Tenerife (Canary Islands). The maximum flight of psyllid species was in summer, both in mainland Spain and the Canary Islands, reaching a peak of 570 specimens in August in Villena and 6,063 in July in Tenerife. The main identified psyllid species were as follows: Bactericera trigonica Hodkinson, B. tremblayi Wagner and B. nigricornis Forster. B. trigonica represented more than 99% of the psyllids captured in the Canary Islands and 75% and 38% in 2011 and 2012 in Villena, respectively. In addition, Trio:a urticae Linnaeus, Bactericera sp., Ctenarytaina sp., Cacopsylla sp., Trio:a sp. and Psylla sp. were captured. 'Ca. L. solanacearum' targets were detected by squash real-time PCR in 19.5% of the psyllids belonging to the different Bactericera species. This paper reports at least three new psyllid species that carry the bacterium and can be considered as potential vectors
Acta Horticulturae
No full textPostharvest degreening treatment with exogenous ethylene application is widely used in Mediterranean growth area to improve the external coloration of the early-season citrus varieties in which internal maturity is achieved when the peel is still green. Nevertheless this treatment can induce physiological disorders overall related to calyx senescence. In previous studies it has been reported that the application of 3,5,6-trichloro-2-pyridyloxyacetic acid (TPA) reduces calyx senescence associated to ethylene exposure. However it is important to know the effect of this auxin under commercial industrial conditions. The purpose of this study was to evaluate the effect of postharvest application of TPA on the reduction of disorders associated to degreening in clementines in different commercial postharvest applications (by drencher and by low volume spraying in the handling line). The application of TPA by drencher significantly reduced the disorders of calyx senescence associated to degreening treatment in clementines, recommending 40 ppm of TPA as the most effective dose. The application of TPA by low volume spraying in the handling line treatments was effective on the reduction of calyx disorders, obtaining the best results with 100 ppm of TPA; nevertheless in the trials clementines exhibited low susceptibility to calyx disorders after degreening process. The results suggest that this auxin could be a good option to control disorders of citrus fruit during degreening treatment
Transmission of 'Candidatus Liberibacter solanacearum' in carrot seeds
No full textA protocol for the specific detection and quantification of ‘Candidatus Liberibacter solanacearum’ in carrot seeds using real‐time PCR was developed. The bacterium was detected in 23 out of 54 carrot seed lots from 2010 to 2014, including seeds collected from diseased mother plants. The average total number of ‘Ca. L. solanacearum’ cells in individual seeds ranged from 4·8 ± 3·3 to 210 ± 6·7 cells per seed from three seed lots, but using propidium monoazide to target live cells, 95% of the cells in one seed lot were found to be dead. Liberibacter‐like cells were observed in the phloem sieve tubes of the seed coat and in the phloem of carrot leaf midrib from seedlings. The bacterium was detected as early as 30 days post‐germination, but more consistently after 90 days, in seedlings grown from PCR positive seed lots in an insect‐proof P2 level containment greenhouse. Between 12% and 42% of the seedlings from positive seed lots tested positive for ‘Ca. L. solanacearum’. After 150 days, symptoms of proliferation were observed in 12% of seedlings of cv. Maestro. ‘Candidatus Liberibacter solanacearum’ haplotype E was identified in the seeds and seedlings of cv. Maestro. No phytoplasmas were detected in seedlings with symptoms using a real‐time assay for universal detection of phytoplasmas. The results show that to prevent the entry and establishment of the bacterium in new areas and its potential spread to other crops, control of ‘Ca. L. solanacearum’ in seed lots is required