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1.
Phytophthora root rot, caused byPhytophthora cinnamomi Rands, is the most important disease of avocado (Persea americana Miller). In an attempt to identify root rot-resistant rootstocks that could ultimately be used under conditions in southern Florida, we screened open-pollinated progeny of avocado from the National Germplasm Repository in Miami. From 1996 to 1998, a total of 2,355 seedlings from 51 accessions were examined in potting mix artificially infested withP. cinnamomi. Most seedlings developed severe root rot, but tolerance was observed in some families (i.e., progeny of certain accessions). Although the most susceptible families developed mean disease ratings of up to 97% root necrosis, mean ratings for the most tolerant families were less than 60%. There was also a strong relationship between the racial background of the female parent and the tolerance of seedlings. Seedlings of the West Indian race and hybrids between it and the Guatemalan race were significantly more tolerant than those from other parents (P< 0.05). Individuals in several families developed < 50% root necrosis, the arbitrary standard of tolerance in this study. Twelve families accounted for 82% (188 of 229) of the tolerant seedlings, and only two of these did not have a West Indian or Guatemalan × West Indian pedigree. Broad-sense heritability for PRR tolerance was 0.45. This is the first report on the inheritance of PRR tolerance in avocado and on the influence of genotype and racial pedigree under controlled conditions.  相似文献   

2.
Laurel wilt, caused by Raffaelea lauricola, threatens native and non‐native species in the Lauraceae in the south‐eastern USA. Avocado, Persea americana, is the most important agricultural suscept of laurel wilt. Grafted plants (clonal scions on seedling rootstocks) of 24 cultivars were screened against the disease in the field from 2008 to 2010. Disease was induced with either mycelial plugs or conidial suspensions of R. lauricola. There were significant differences in the severity of disease that developed on different cultivars, and West Indian cultivars were most susceptible (P < 0·05). Simmonds, a West Indian cultivar that comprises 35% of the commercial production in Florida, was consistently susceptible and was used as a standard genotype in different studies. Disease severity increased significantly on cv. Simmonds as plant size (stem diameter) increased (P < 0·0042). In greenhouse studies, internal (sapwood) and external disease severities on cv. Simmonds were correlated (P < 0·0001), and a threshold was evident, in that external symptoms developed only after moderately severe symptoms had developed internally. Latent infection was uncommon; R. lauricola was usually isolated on a semiselective medium or detected via qPCR only from discoloured xylem of inoculated cv. Simmonds. As basipetal movement of the pathogen was common, its movement among trees via root grafts is probable. Greater understanding is needed of the movement of R. lauricola in naturally and artificially infected trees, and whether sufficient tolerance exists in avocado to assist in the management of this important new disease.  相似文献   

3.
This work describes studies done on the Canary Islands in order to support the elaboration of quarantine and control legislation for potato cyst nematodes which take into account the special agroecological characteristics of the Mediterranean region. The interest of the islands for epidemiological studies is based on the occurrence of the oldest potato crops in the Old World and the use of several local cultivars and traditional management cropping systems. Also, the environmental conditions allow field experiments to be performed throughout the year. The phytonematological problems of the potato crop on the Canary Islands is reported and the absence of Ditylenchus destructor, D. dipsaci, Nacobbus aberrans, Rotylenchulus reniformis and trichodorids pointed out. The cyst nematodes, Globodera rostochiensis and G. pallida were found to cause severe damage to the crop and were studied in detail by field trials at Tenerife. Continuous growing of the cv. Cara, with the H1 gene conferring resistance to G. rostochiensis (pathotypes Ro1 and Ro4), exerted selection pressure for G. pallida. Under the edaphic and climatic conditions of Tenerife, nematicide application was found to be inefficient for controlling potato cyst nematodes. Alternative control techniques based on traditional management systems and on the use of environmentally adverse conditions were investigated.  相似文献   

4.
Rhynchohorus ferrugineus (red palm weevil) was first recorded in Cyprus in September 2006 on 4 palm trees (Phoenix canariensis) in a hotel garden in the coastal area of Lemesos. All infested plants from the first point of outbreak were removed and burned. Intensive monitoring showed that R. ferrugineus was present in the areas of Limassol, Larnaca and Paphos. In the Famagusta area a consignment of palm trees was found to be infested and measures for the destruction of the consignment were taken. From the results of monitoring, the areas of Limassol, Larnaca and Paphos were placed under close supervision and infested zones and buffer zones were created. In the area of Famagusta there was no trapping of adult insects, however a demarcated area was created and will remain under close supervision for a period of 3 years. The establishment of demarcated areas was carried out according to the provisions of the EU Decision 2007/365/EC. The measures taken in the infested and buffer zones were mainly the application of chemicals through the crown of the susceptible palm plants and the removal of heavily infested palms. Since burning proved not to be an efficient method, the heavily infested palm plants were buried in approved areas, after chemical spraying. In addition the NPPO, of Cyprus has taken measures in training all plant health inspectors in the identification and handling of infested palm trees and public awareness about R. ferrugineus. Surveys continue throughout Cyprus with the use of pheromone traps and eradication measures continue within the demarcated areas with the aim of eradicating of this pest.  相似文献   

5.
An indexing system for detectingTomato mosaic virus (ToMV) in commercial tomato seed lots is described. Factors associated with the procedure were analyzed and the following standard two-step working scheme is proposed: (i) mass screening by ELISA for the presence of the virus; (ii) evaluation of virus infectivity within the infested seed lots. A threshold of 10 ng ml−1 was determined for detection of purified ToMV by either ELISA or plant inoculation.Nicotiana tabacum cv. Xanthi NN was found to be a highly sensitive local lesion assay plant for the detection of ToMV. A positive ELISA threshold (1.3 times above the non-specific background) was set for seed samples taken from commercial seed lots by testing the same samples by both ELISA and a bioassay. http://www.phytoparasitica.org posting July 14, 2004.  相似文献   

6.
In Greece, the damage caused to trees and shrubs by termites has been increasing over the last 10 years. Local government and citizens have become interested in this pest due to frequent accidents caused by trees falling onto pavements, cars and people. This led the authors to carry out a survey to list the termite‐infested plant species, mainly on urban streets and in fields all over the country. The only termite species found was Kalotermes flavicollis (family Kalotermitidae). The present study highlights the current situation in Greece and provides a list of the fruit and ornamental trees and shrubs found to be infested by K. flavicollis, during the survey.  相似文献   

7.
The character of a bark beetle outbreak, planning system, and implementation of IPM measures in a forest affected by intensive decline connected with honey fungus (Armillaria sp.) is described. It is possible to distinguish two levels of outbreak in the study area. The first level is characterized by spruce mortality connected with yellowing of spruce and presence of plant pathogens, mostly Armillaria sp. Forest stands have disperse infestations of bark beetles. Identification of infested trees and salvage cutting in time are problematic. In case of late processing of infested trees, the second level of outbreak could become manifest. The populations of bark beetle increase. Beetles could attack relatively healthy trees. The classical outbreak with forest edges and spot infestations starts. The identification of infested trees is easier. The application of pheromone trap barriers is effective. Thus, the second level of outbreak could be easily managed. The planning of IPM measures is concerned with localization of various pheromone trap systems in particular forest stands. It is based on field survey, data acquisition, estimation of swarming bark beetle population, and information of pheromone system effectiveness.  相似文献   

8.
The character of a bark beetle outbreak, planning system, and implementation of IPM measures in a forest affected by intensive decline connected with honey fungus (Armillaria sp.) is described. It is possible to distinguish two levels of outbreak in the study area. The first level is characterized by spruce mortality connected with yellowing of spruce and presence of plant pathogens, mostly Armillaria sp. Forest stands have disperse infestations of bark beetles. Identification of infested trees and salvage cutting in time are problematic. In case of late processing of infested trees, the second level of outbreak could become manifest. The populations of bark beetle increase. Beetles could attack relatively healthy trees. The classical outbreak with forest edges and spot infestations starts. The identification of infested trees is easier. The application of pheromone trap barriers is effective. Thus, the second level of outbreak could be easily managed. The planning of IPM measures is concerned with localization of various pheromone trap systems in particular forest stands. It is based on field survey, data acquisition, estimation of swarming bark beetle population, and information of pheromone system effectiveness.  相似文献   

9.
Collaboration between the Plant Protection Services of France and the Channel Islands has helped to keep Jersey and Guernsey free of Colorado Beetle (Leptinotarsa decemlineata) for over 60 years. The Channel Islands lie close to the coast of the Cotentin peninsula where potato fields are still infested with Colorado Beetle. Joint surveys of the coastal potato fields of Cotentin provide valuable information on beetle populations. Beetle flight records together with local weather data provide the necessary information to issue Colorado Beetle alerts to the Channel Islands during the months of May–July. High risk alerts issued by French Plant Protection colleagues are acted on and inspectors are mobilised to search beaches in Jersey and Guernsey for adult beetles. Farmers are not obliged to control Colorado Beetle in France. However, there has been an agreement negotiated in the Cotentin that farmers will treat their fields if beetles are found, with monitoring carried out by staff from a local co‐operative. This co‐operation has proved essential in the Colorado Beetle campaign.  相似文献   

10.
The red palm weevil Rhynchophorus ferrugineus (Olivier) is the most serious pest of palms in Turkey. Weevil infestation was first detected in Turkey in summer 2005 in parks and gardens of Mersin province, along the Mediterreanean coast of Turkey. Following the discovery of the pest, destruction of infested plant material, prophylactic insecticide chemical treatments, as well as adult weevil trapping were carried out on palm plantations. Traps containing a commercial aggregation pheromone were hung on palm trees at a high density, in order to monitor the pest infestation and reduce the weevil population by mass trapping. A significant decrease in the number of trapped beetles and destruction of infested plant material was observed in 2009 and continued in the following years in several cities in Turkey. Therefore, it has been observed that mass trapping and curative pesticide applications have played a significant role in the suppression of R. ferrugineus populations in palm plantations.  相似文献   

11.
Contaminant seeds in crop seed lots constitute a pathway for plant species introduction into new areas, and these non‐native weeds may be an environmental problem if they become invasive. Seed certification is a process that regulates and guarantees the quality of seed lots, including their purity. In this study, we assessed weed contamination in certified and non‐certified seed lots (n = 116) from 12 crop species commonly cultivated in the Balearic Islands. Contaminant seeds were separated using sieves, and then manually under a stereomicroscope, before they were germinated to confirm taxonomic identity. Weight, number and diversity of the contaminant seeds per kilogram of seed lot, number released per hectare according to sowing rate, and taxonomic identity and biogeographical origin of contaminant species were recorded. Although certification reduced the number of contaminant seeds in the seed lots, it did not entirely eliminate contaminants, because we found up to 2000 contaminant seeds kg?1 of certified ryegrass and sulla. Overall, contaminant seeds represented 118 taxa; of which, 82 were identified to species level, 70% of species were native, 19% were cultivated, and 11% were non‐native. Two of the identified taxa were first records for the Balearic Islands. In conclusion, contaminant seeds in imported crop seed lots represent a non‐negligible pathway for plant species introduction.  相似文献   

12.
“ Candidatus Liberibacter solanacearum” (Lso), transmitted by the potato psyllid (Bactericera cockerelli), is the causal agent of potato zebra chip, but can also infect other solanaceous plants, including peppers. Studies were conducted to investigate whether Lso could be transmitted to the next generation of plants through seeds from infected pepper plants. In 2014, jalapeno pepper plants were infested with psyllids carrying a mixture of Lso A and B (AB) at the AgriLife Research Station at Bushland. The study was again conducted in 2019 and pepper plants were infested with psyllids carrying Lso B or Lso AB. In each of the studies, noninfested plants served as controls. At harvest, fruits were collected and tested for the presence of Lso using quantitative PCR. Seeds from infected fruits were then tested for Lso. Overall, the percentage of seeds that tested positive for Lso ranged from 33% to 70%. However, Lso detection in embryos ranged only from 0% to 8%. Seed samples from Lso-positive fruits were planted in the greenhouse to determine the impact of Lso on emergence and the incidence of Lso in emerged plants. Although plant emergence differed between some of the seeds obtained from Lso-positive and -negative fruits, the overall impact of Lso on plant emergence was not consistent. However, of the 182 plants that emerged from seeds collected from infected fruits, none was positive for Lso, suggesting that seeds are unlikely to serve as sources for new Lso infections and their impact on disease epidemiology is negligible.  相似文献   

13.
Summary Raspberries and strawbereis planted several years after a previous crop of raspberries were found attacked byPratylenchus penetrans. Raspberries planted in places where appled trees had been taken out showed slightly stunted growth and a moderate attack of the roots byP. penetrans.The symptoms of heavily infested raspberries were: severely stunted growth of above ground parts without other particular symptoms; a very poor root system, parts of which are completely dead and blackened or show dead, blackened bark, and the absence of fine feeding roots. In cases of light attack the root system is more normal but there is a number of rather large black lesions.Raspberries should not be planted after raspberries, after fruit trees susceptible to attack byP. penetrans, after strawberries or on possibly infested soil (in general light soils) unless a determination of the degree of infestation in the plant sites has shown that the place is safe. In case of infestation suitable measures to eradicate the nematodes should be taken. It may be expected that a fairly light degree of infestation of the soil is sufficient to cause appreciable damage.  相似文献   

14.
Apple mosaic ilarvirus (ApMV) was detected in all (160) hazel ( Corylus avellana ) cv. Negret orchards assayed in Catalonia, north-east Spain, during 1997 and 1998. In a preliminary survey, using enzyme-linked immunosorbent assay (ELISA), only 9 of the 320 samples collected appeared free from ApMV and three of these individuals indexed ELISA positives when re-tested. The spread of ApMV was studied in a plantation of Negret hazel in which virus-free trees were randomly interspersed with graft-inoculated individuals. When tested by ELISA 10 years after planting, 15% of the ungrafted trees contained ApMV. At that time, 8% of seeds on ungrafted and virus-free trees and 54% of seeds on ApMV-inoculated trees indexed ApMV-positive. These results are discussed in terms of pollen-mediated inoculation.  相似文献   

15.
Burkholderia cepacia (syn. Pseudomonas cepacia) strain PHQM100 applied as a seed coating was tested in growth chamber experiments for its ability to suppress preemergence damping-off, and postemergence damping-off in corn induced by Pythium and Fusarium spp. The symptoms observed in bioassays with soils naturally infested with the fungal pathogens were seed rot with Pythium spp. and mesocotyl and root tissue necrosis in the presence of Fusarium spp. Three corn cultivars that differed in their susceptibility to damping-off pathogens were used. Cultivar L was susceptible to pre- and postemergence damping-off, whereas cv. LPDP and cv. LG11 were moderately resistant and resistant to the damping-off diseases respectively. In the presence of Pythium spp., seed treatment with B. cepacia reduced seed rot, as compared to the untreated seeds, and this reduction was more consistent in the cv. LPDP than in the resistant cv. LG11 or the susceptible cv. L. In soils infested with Fusarium spp., seed treatment significantly reduced root and mesocotyl necrosis as compared to the untreated seeds, and this reduction was more consistent in the resistant cultivars LG11 and LPDP than in the susceptible cv. L. Root colonization levels by B. cepacia were similar in the three corn cultivars tested. Biocontrol efficiency of B. cepacia varied among cultivars mainly due to the differences in their susceptibility to the fungal pathogens. In spite of variability and also irrespective of the soil characteristics, B. cepacia increased seedling emergence and decreased mesocotyl and root necrosis when used as a seed coating.  相似文献   

16.
To examine whether the pathogenic bacterium, Erwinia carotovora subsp. carotovora, causal agent of soft rot of Chinese cabbage (Brassica campestris L., pekinensis group), can overwinter in plant debris and soil and serve as inoculum the following year, we monitored field populations of rifampicin-resistant, phage-sensitive strains of the bacterium. Chinese cabbage (cv. Matsushima Kohai W1116) were planted in field soil in pots that were sunk into the field on Aug. 2, 1996 and eventually reduced to one plant per pot. Outer petioles of the plants were inoculated with mixture of 13 bacterial strains of E. carotovora subsp. carotovora on Sept.5, 1996. After the soft rot spread throughout the plant, the diseased plant was buried in the potted soil. New seeds were sown in the pots on April 30, 1997, and the disease was observed in June and July. The bacterial strains were re-isolated from the potted soil, diseased tissue and rhizosphere soil by the dilution plating method on modified Drigalski's medium containing 100 ppm rifampicin and by the enrichment technique. In addition to rifampicin resistance, phage sensitivities of some of the re-isolated strains were identical to those of the strains buried in the soil with the diseased plant in the previous year. From these results, some of the 13 strains overwintered in the soil and infested plant tissue and acted as primary inoculum the following year. The frequency of re-isolation varied among the strains, perhaps because of competition among the strains, differences in epidemiological behavior and stabilizing selection among the strains, and the presence of different ecotypes of the organism. Received 21 July 2000/ Accepted in revised form 19 September 2000  相似文献   

17.
After causing damage in Asia and the USA, Dryocosmus kuriphilus Yasumatsu recently established in Europe on Castanea. The first outbreak in Europe occurred at a C. sativa nursery for production of plants for planting in Cuneo (Piemonte, Italy) in 2002. The Piemonte official service notified Slovenia that a consignment originating from an infested nursery was sold to Slovenia. Prompt phytosanitary action was taken in Slovenia in 2005 in order to trace back plants from this consignment and prevent establishment of the pest. In the period 2006–2009, intensive surveys of forests and fruit production areas showed absence of the pest in the majority of the Slovenian territory, including the demarcated area from 2005. An earlier introduction of infested plants from Cuneo in January 2004 remained undiscovered until 2007. Despite the radical measure of eliminating the infested orchard and removing infested Castanea trees in the forest bordering this orchard, the pest was not eradicated in this outbreak area. Individual infested trees in the forest were confirmed at a distance of up to 10–34 km in 2008, and a further 15 km in 2009. The results of annual surveys, eradication campaigns based on generic contingency elements and the change of strategy after the finding of infested forests are presented.  相似文献   

18.
Initial experiment on the reactions of five Japanese cultivars of cucumber toColletotrichum orbiculare infection in the greenhouse revealed that cv Suyo and Gibai were susceptible and moderately susceptible, respectively, while cv Shogoin fushinari and Sagami hanjiro were resistant to infection byC. orbiculare; cv Ochiai fushinari was moderately resistant. The ability of 16 plant growth promoting fungi (some isolates belonged to species ofPhoma and some non-sporulating isolates) isolated from zoysiagrass rhizospheres to induce systemic resistance in the above five cucumber cultivars was tested by growing plants in potting medium infested with barley grain inocula of PGPF in the greenhouse. The second true leaves of 21-day-old plants were challenge inoculated withC. orbiculare and disease assessed. Nine, out of 16 isolates, caused significant reduction of disease caused byC. orbiculare in at least two cultivars.Phoma isolates (GS8-1 and GS8-2) and non-sporulating isolates (GU21-2, GU23-3, and GU24-3) significantly reduced the disease in all the five cultivars. The disease suppression in cucumber was due to the induction of systemic resistance, since the inducer(s) and the pathogen were separated spatially and that the inducer did not colonize aerial portions. The resistance induced by certain isolates in a susceptible cultivar was less than that in a resistant cultivar. Disease suppression caused by isolate GU21-2 was similar to theC. orbiculare induced control in certain cultivars. The average rate of expansion of lesion diameter on leaves due toC. orbiculare was slower due to induction with the selected plant growth promoting fungi compared to the uninduced control plants. Roots of four cultivars were colonized by only three isolates, however, roots of one cultivar (Suyo) was colonized by five isolates suggesting the cultivar-specific root colonization ability.Abbreviations cv cultivar(s) - PGPF plant growth promoting fungal isolates - PGPR plant growth promoting rhizobacteria  相似文献   

19.
Indian citrus ringspot disease is an important viral disease in kinnow mandarin orchards where disease incidence up to 100% has been recorded. The disease is caused by Indian citrus ringspot virus (ICRSV), a positive sense flexuous RNA virus. The transmission of ICRSV is generally through budwood. Association of ICRSV with pollens of naturally infected flowers from cv. ‘Kinnow’ mandarins has been shown previously and this study demonstrates the presence of ICRSV in seed tissues. DAC-ELISA revealed the presence of virus in seed coats but not in embryo and endosperm of seeds collected from the fruits of ICRSV-infected Kinnow plants. Of the infected seed coats, 18% were found to harbor the virus. The seedlings in the grow-out test did not show any symptom for 2 years and the virus could not be detected in seedlings by DAC-ELISA and RT-PCR. The present study indicated that ICRSV could be localized in the testa of seeds but its transmission to progeny was not observed.  相似文献   

20.
Using quantitative PCR, DNA of Plasmodiophora brassicae, the causal agent of clubroot, was detected and quantified on canola, pea and wheat seeds, as well as on potato tubers, all harvested from clubroot‐infested fields in Alberta, Canada. Quantifiable levels of infestation were found on seven of the 46 samples analysed, and ranged from <1·0 × 103 to 3·4 × 104 resting spores per 10 g seeds; the vast majority (80–100%) of resting spores on these samples were viable, as determined by Evan’s blue vital staining. However, the levels of infestation found were generally lower than that required to cause consistent clubroot symptoms in greenhouse plant bioassays. While the occurrence of P. brassicae resting spores on seeds and tubers harvested from clubroot‐infested fields suggests that seedborne dissemination of this pathogen is possible, practices such as commercial seed cleaning may be sufficient to effectively mitigate this risk.  相似文献   

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