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A large number of soilborne diseases that affect potato are important in the United States. In the Midwestern USA, early dying, involving Verticillium dahliae and Colletotrichum coccodes and the storage rots, pink rot and leak tub...
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A large number of soilborne diseases that affect potato are important in the United States. In the Midwestern USA, early dying, involving Verticillium dahliae and Colletotrichum coccodes and the storage rots, pink rot and leak tuber rot, caused by Phytophthora erythroseptica and Pythium ultimum are among the most serious. Various aspects of the biology and aetiology of these pathogens have been investigated to improve our understanding of the factors involved in disease development. These studies have addressed knowledge gaps and have assisted in the development of management strategies and tactics for each disease. Disease management integrates cultural practices, use of agrochemicals and to some degree, host resistance. Unfortunately, cultural management practices alone are currently inadequate to control these diseases, causing the potato industry to become over-reliant on the use of agrochemicals for effective management. Current research efforts are directed at the identification and incorporation of genetic resistance into cultivars with acceptable horticultural characteristics to provide more effective disease management..
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Worldwide exchange and trade of propagating material of ornamental crops is still a rapidly growing economic activity. New varieties are developed in all major production regions and can be of value to growers worldwide. To start ...
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Worldwide exchange and trade of propagating material of ornamental crops is still a rapidly growing economic activity. New varieties are developed in all major production regions and can be of value to growers worldwide. To start professional propagation and production, the highest quality and plant health is required. Users of plant material must be sure that they receive this material pathogen-free. In line with existing systems, it is proposed to distinguish 3 classes of certified material: prebasis (nuclear stock), basis (propagation stock) and certified stock material. It is concluded that it is up to virologists, mycologists etc. to draw up, in consultation with growers and propagators, standards and max. allowed tolerances for pathogens. Examples are given of certification systems of Dendranthema, Dianthus, Pelargonium and Petunia.
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Plant defensins represent a novel class of antimicrobial peptides showing structural and functional homology to their insect and mammalian defensin counterparts. Evidence is presented to support the idea that plant defensins are i...
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Plant defensins represent a novel class of antimicrobial peptides showing structural and functional homology to their insect and mammalian defensin counterparts. Evidence is presented to support the idea that plant defensins are important componentsof the defence system in plants and have roles in the protection of both seeds and vegetative tissues. Evidence includes the location of plant defensins at the periphery of different organs, and their induction under pathogenic stress. It is demonstrated that transgenic plants constitutively expressing a plant defensin show enhanced disease resistance.
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In 2002, Columbia Basin potato growers in Washington and Oregon began to experience serious outbreaks of potato purple top disease that have caused significant yield losses and reductions in tuber quality. It was determined that t...
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In 2002, Columbia Basin potato growers in Washington and Oregon began to experience serious outbreaks of potato purple top disease that have caused significant yield losses and reductions in tuber quality. It was determined that the beet leafhopper-transmitted virescence agent (BLTVA) phytoplasma is the causal agent of the disease in the Columbia Basin and that this pathogen is transmitted by the beet leafhopper. Little is known about the impact of purple top disease on potato in the Pacific Northwest. Trials were conducted in 2006, 2007, and 2008 to assess susceptibility of important potato cultivars grown in the Columbia Basin to purple top under field conditions. Eight potato cultivars were planted in small field plots and exposed to naturally occurring BLTVA-infected beet leafhoppers. Disease incidence was recorded at the end of the growing season. Purple top foliar symptoms were observed in all the tested cultivars, and plant samples collected and tested by PCR confirmed the presence of BLTVA. Results also indicated significant differences in susceptibility of the cultivars to purple top. Disease incidence in leafhopper-exposed plots ranged from 1.5 to 49.3% among cultivars. Russet Norkotah, Ranger Russet, and Umatilla Russet were relatively high in susceptibility to purple top, with average disease incidence of 33.5, 23.3, and 19.4%, respectively. Russet Burbank and FL1967 showed some resistance to purple top as they had the lowest plant disease incidence of 2.3 and 4.4%, respectively. Alturas, Shepody, and FL 1879 were moderately susceptible to purple top, with average disease incidence of 12.8, 8.0, and 9.3%, respectively. Information from this study will help potato growers reduce damage caused by potato purple top through selection of cultivars that are resistant to or tolerant of the disease and by protecting susceptible varieties against the beet leafhopper. (c)Potato Association of America 2009.
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Cornell 501 is a determinate, sieve 4 snap bean (Phaseolus vulgaris) with resistance to white mould, caused by Sclerotinia sclerotiorum. Cornell 501 was an F8 selection from the cross between 2 Cornell breeding lines, 5223x5813, t...
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Cornell 501 is a determinate, sieve 4 snap bean (Phaseolus vulgaris) with resistance to white mould, caused by Sclerotinia sclerotiorum. Cornell 501 was an F8 selection from the cross between 2 Cornell breeding lines, 5223x5813, the progeny of which had been evaluated for white mould resistance using the straw test procedure at the F3-F7 generations. Cornel 501 will provide breeders with a white mould resistant source to develop commercial cultivars of common bean.
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The mechanism of action of oligochitosan, which has shown great antifungal activity against Phytophthora capsici in vitro, was studied using 2-aminoacridone-labeled oligochitosan (2-AMAC-oligochitosan) and a gel-retardation experi...
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The mechanism of action of oligochitosan, which has shown great antifungal activity against Phytophthora capsici in vitro, was studied using 2-aminoacridone-labeled oligochitosan (2-AMAC-oligochitosan) and a gel-retardation experiment. Internalization of 2-AMAC-oligochitosan in cysts, germtubes and sporangia of P. capsici was confirmed by confocal laser scan microscopy (CLSM), and the degree of uptake depended on the incubation concentration. 2-AMAC-oligochitosan localized mainly in the cytoplasm and showed no binding to both cell wall and cell membrane. Mannose, an inhibitor for oligochitosan uptake by macrophages, could not inhibit the internalization of oligochitosan in P. capsici. The gel-retardation experiment showed that oligochitosan bound strongly to DNA and RNA of P. capsici. These results indicate that oligochitosan exerts its antifungal activity by penetrating the cell membrane and putative binding to intracellular targets such as DNA and RNA..
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Grapevine leafroll-associated virus 3 (GLRaV-3) is a mealybug-transmissible ampelovirus. Though the transmission mechanism has been described as semipersistent on the basis of temporal parameters, definitive proof of this mechanis...
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Grapevine leafroll-associated virus 3 (GLRaV-3) is a mealybug-transmissible ampelovirus. Though the transmission mechanism has been described as semipersistent on the basis of temporal parameters, definitive proof of this mechanism has never been provided. In the present study, we carried out preliminary assays to establish the location of the virus in its vector, Planococcus citri. After dissecting the insects, GLRaV-3 was detected by means of IC-RT-PCR in the salivary glands, intestine and Malpighian tubes, but not in the sucking apparatus. Immunogold labelling of the capsid protein revealed the presence of the virus in some cells of the primary salivary glands, but not in the alimentary channel of the stylet, or in the accessory salivary glands. The strong labelling of the electron-dense secretion vesicles in some cells of the primary salivary glands, together with the non-detection of the virus in the sucking apparatus suggests that the transmission mechanism may be different from that previously described. We propose a circulative transmission mechanism based on a specific transportation route for the viral particles from the midgut or hindgut to the salivary glands. As the transmission mechanism is generally a common feature of a viral genus, the existence of a circulative transmission mechanism for other mealybug-transmitted ampeloviruses is expected. Organ by organ analysis of GLRaV-1, another ampelovirus not transmissible by P. citri, showed the absence of the virus in the salivary glands, thus providing further, though indirect, evidence in favour of circulative transmission for this virus genus..
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The acquisition, incubation and transmission of Watermelon silver mottle virus (WSMoV) by T. palmi were investigated by examining symptoms developed on Benincasa hispida. An acquisition threshold period of 30 minutes was required ...
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The acquisition, incubation and transmission of Watermelon silver mottle virus (WSMoV) by T. palmi were investigated by examining symptoms developed on Benincasa hispida. An acquisition threshold period of 30 minutes was required when 5 first-instar nymphs as a group were used to transmit the virus. The efficiency of transmission increased by 2-fold when the acquisition access period increased to 24 h. Nymphs were able to transmit WSMoV within 2 h after a 2-h acquisition access feeding on diseased plants. Of the 64 thrips given a 6-h acquisition feeding at the nymph stage, approximately 63% transmitted the virus at either nymph or adult stage, or at both stages. Sixteen thrips transmitted the virus on the 1st day. Among the transmitters, approximately one fifth of the insects transmitted only once in their lifetime, and, 22, 5 and 3 individuals transmitted WSMoV 2, 3, and 4 times in their lifetime, respectively. Approximately 30, 15 and 22% thrips transmitted the virus only at the nymph stage, only at the adult stage, and at both stages, respectively. Approximately 25% of the transmitters were able to make a successive 2-day transmission. The results showed that once becoming viruliferous, T. palmi may or may not transmit WSMoV later in life. The results also showed an erratic pattern of WSMoV transmission by T. palmi. Our observations suggest that there may be two mechanisms involved in the transmission of WSMoV by T. palmi, a non-circulative styler-borne transmission at the very early stage and the other the propagative-circulative form at a later stage..
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摘要 :
The acquisition, incubation and transmission of Watermelon silver mottle virus (WSMoV) by T. palmi were investigated by examining symptoms developed on Benincasa hispida. An acquisition threshold period of 30 minutes was required ...
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The acquisition, incubation and transmission of Watermelon silver mottle virus (WSMoV) by T. palmi were investigated by examining symptoms developed on Benincasa hispida. An acquisition threshold period of 30 minutes was required when 5 first-instar nymphs as a group were used to transmit the virus. The efficiency of transmission increased by 2-fold when the acquisition access period increased to 24 h. Nymphs were able to transmit WSMoV within 2 h after a 2-h acquisition access feeding on diseased plants. Of the 64 thrips given a 6-h acquisition feeding at the nymph stage, approximately 63% transmitted the virus at either nymph or adult stage, or at both stages. Sixteen thrips transmitted the virus on the 1st day. Among the transmitters, approximately one fifth of the insects transmitted only once in their lifetime, and, 22, 5 and 3 individuals transmitted WSMoV 2, 3, and 4 times in their lifetime, respectively. Approximately 30, 15 and 22% thrips transmitted the virus only at the nymph stage, only at the adult stage, and at both stages, respectively. Approximately 25% of the transmitters were able to make a successive 2-day transmission. The results showed that once becoming viruliferous, T. palmi may or may not transmit WSMoV later in life. The results also showed an erratic pattern of WSMoV transmission by T. palmi. Our observations suggest that there may be two mechanisms involved in the transmission of WSMoV by T. palmi, a non-circulative styler-borne transmission at the very early stage and the other the propagative-circulative form at a later stage..
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