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1.
A leaf spot disease on wasabi plants grown in commercial greenhouses in the Fraser Valley of British Columbia was characterized. Mycelial growth and pycnidial formation were observed within lesions when leaves were incubated under conditions of high humidity. Isolation from diseased tissues consistently yielded colonies of a Phoma species. Sequence analysis of the rDNA internal transcribed spacer (ITS1‐5.8S‐ITS2) region of eight isolates showed 100% nucleotide sequence identity with Phoma wasabiae and Leptosphaeria biglobosa subspecies ‘occiaustralensis’ and 99.2% identity with L. biglobosa ‘canadensis’. Pathogenicity studies on wasabi leaves showed that wounding greatly facilitated infection and enhanced lesion development for most isolates but was not required for all isolates. Chlorotic areas appeared around the inoculation sites within 4 days, followed by necrosis. Isolates displayed a range of virulence, from weakly to highly virulent, on wasabi leaves. Similar results were observed on leaves of canola cultivar Westar, i.e. wounding significantly increased lesion size and isolates displayed a range of virulence. An isolate of Leptosphaeria maculans ‘brassicae’ from canola was highly virulent on wasabi and canola leaves, causing lesions similar to those of L. biglobosa ‘occiaustralensis’ while an isolate of L. biglobosa ‘canadensis’ from canola was weakly virulent on both hosts and required wounds to infect. These results demonstrate that isolates of L. biglobosa ‘occiaustralensis’ from wasabi are as virulent as L. biglobosa ‘canadensis’ on wasabi and canola leaves but in some cases were comparable in virulence to L. maculans ‘brassicae’. 相似文献
2.
ABSTRACT Dramatic changes occurred within populations of Phytophthora infestans in the United States and Canada from 1994 through 1996. Occurrence of the US-8 genotype, detected rarely during 1992 and 1993, increased rapidly and predominated in most regions during 1994 through 1996. US-7, which infected both potato and tomato and made up almost 50% of the sample during 1993, was detected only rarely among 330 isolates from the United States analyzed during 1994. It was not detected at all in more limited samples from 1996. Thus, ability to infect both potato and tomato apparently did not increase the fitness of this genotype relative to US-8, as predicted previously. US-1, the previously dominant genotype throughout the United States and Canada, made up 8% or less of the samples analyzed during 1994 through 1996. A few additional genotypes were detected, which could indicate the beginnings of sexual reproduction of P. infestans within the United States and Canada. However, clonal reproduction still predominated in all locations sampled; opportunities for sexual reproduction probably were limited, because the A1 and A2 mating types usually were separated geographically. The high sensitivity of the US-1 genotype to the fungicide metalaxyl also could have reduced opportunities for contact between the mating types in fields where this compound was applied. The previous correlation between metalaxyl sensitivity and genotype was confirmed and extended to a new genotype, US-17: all US-1 isolates tested were sensitive; all isolates of the US-7, US-8, and US-17 genotypes tested to date have been resistant. Isolates of P. capsici and P. erythroseptica, two other species often found on tomato and potato, could be easily distinguished from each other and from P. infestans using a simple allozyme assay for the enzyme glucose-6-phosphate isomerase. This technique could be useful for rapid identification of species, in addition to genotype of P. infestans. It generally was not possible to predict which genotypes would be present in a location from 1 year to the next. Long-distance movement of US-8 in seed tubers was documented, and this was probably the primary means for the rapid spread of this genotype from 1993 through 1996. 相似文献
3.
G. Rodríguez Z. K. Punja 《European journal of plant pathology / European Foundation for Plant Pathology》2009,124(3):483-493
Wasabi (Wasabia japonica) is grown for its highly-valued rhizome which is used as a condiment in Japanese food. Symptoms of vascular blackening in
the rhizome were first observed in 2005 in plants grown in British Columbia, Canada. Microscopic observations and microbial
isolation from infected tissues revealed that most of the xylem tracheid cells were blackened and bacteria were consistently
associated with symptomatic plants. The bacterium most frequently recovered was identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) using BioLog™ and sequencing of a specific ~510 bp IGS region. Pathogen-free plants obtained using meristem-tip micropropagation
were inoculated with a wasabi isolate of Pcc. Vascular blackening symptoms developed in the rhizome after 8 weeks when the rhizome was first wounded by stabbing or cutting,
or if the roots were pre-inoculated with Pythium species isolated from rhizome epidermal tissues, followed by inoculation with Pcc at 1 × 108 cells ml−1. Xylem tracheid cells were blackened and Pcc was reisolated from all diseased tissues. The highest frequency of rhizome vascular blackening occurred at 22°C and 27°C
and these tissues occasionally succumbed to soft rot at higher temperatures, but not when inoculated tissues were incubated
at 10°C. The rooting medium used by growers for vegetative propagation of wasabi was shown to contain Pcc but the pathogen was not recovered from the irrigation water. Entry of Pcc through wounds on wasabi rhizomes and the host tissue response result in symptoms of vascular blackening. 相似文献
4.
ABSTRACT Cylindrocarpon root rot, caused by Cylindrocarpon destructans, is an important disease on ginseng (Panax quinquefolius) in Canada. We studied the effects of iron (Fe) on disease severity and pathogen growth. When Hoagland's solution was amended with Fe at 56 and 112 mug/ml compared with 0 mug/ml, disease initiation and final severity on hydroponically maintained ginseng roots was significantly (P<0.0001) enhanced. Under field conditions, wounding of roots with a fine needle followed by application of 0.05% FeNaEDTA to the rhizosphere of treated plants significantly enhanced Cylindrocarpon root rot in 2003 and 2004 compared with unwounded roots with Fe or wounded roots without Fe. Foliar applications of Fe (as FeNaEDTA) to ginseng plants three times during the 2002 and 2003 growing seasons significantly increased Fe levels in root tissues. These roots developed larger lesions following inoculation with C. destructans in vitro. When radioactive Fe ((59)Fe) was applied to the foliage of ginseng plants, it was detected in the secondary phloem and in cortical and epidermal tissues within 1 week. Artificially wounded areas on the roots accumulated more (59)Fe than healthy areas. Diseased tissue also had threefold higher levels of phenolic compounds and Fe compared with adjoining healthy tissues. High-performance liquid chromatography analysis revealed enhanced levels of protocatechuic acid, chlorogenic acid, caffeic acid, ferulic acid, cinnamic acid, phloridizin, and quercetin. Phenolic compounds produced in diseased and wounded tissues sequestered Fe in vitro. The effects of Fe on mycelial growth, conidial germ tube length, and secondary branching of germ tubes of C. destructans were examined in vitro. When grown on Chrome-azurol S medium, Fe also was sequestered by C. destructans through siderophore production, which was visualized as a clearing pigmented zone at the margin of colonies. Mycelial dry weight was significantly increased in glucose/ yeast broth containing Fe at 56 or 112 mug/ml. Conidial germ tube length and secondary branching of hyphae also were enhanced after 8 and 16 h by Fe. Colony growth of C. destructans was not enhanced by Fe, but significantly greater spore production was observed with Fe at 56 and 112 mug/ml compared with no Fe in the medium. Although these levels of Fe had no effect on fungal pectinase enzyme activity, polyphenoloxidase (PPO) activity was significantly (P <0.0001) enhanced. We conclude that Fe enhances Cylindrocarpon root rot through enhanced pathogen growth, sporulation, and PPO enzyme activity. Fe sequestered by phenolic compounds produced in wounded tissues can enhance Fe levels at the site of infection. The pathogen also has the ability to sequester Fe at these sites. 相似文献
5.
Inoculum prevalence, host infection and biological control of Colletotrichum acutatum: causal agent of blueberry anthracnose in British Columbia 总被引:1,自引:1,他引:0
To identify the causal organism of anthracnose (ripe-rot), which reduces yield and postharvest quality of blueberries grown in British Columbia, Canada, 80 isolates were recovered from diseased fruits collected from commercial blueberry fields during 2002–04 and identified as Colletotrichum acutatum using colony morphology, growth rate and species-specific PCR primers. In vitro incubation of replicated sets of inoculated detached berries at various temperatures produced infection at temperatures of 7–30°C, with an optimum at 20°C. Colletotrichum acutatum could not survive on the soil surface as mummified berries but the pathogen was detected mostly within flower buds and less so in blueberry twigs and fruit trusses. Infection of developing flower buds in May–June of the preceding growing season gave the highest inoculum recovery in the following year. Two commercial fungal biocontrol agents, Prestop ( Gliocladium catenulatum ) and PlantShield ( Trichoderma harzianum ), each reduced anthracnose development in 2003 and 2004 by up to 45% when sprayed three times onto plants between flowering and fruit ripening. 相似文献
6.
The pentaflurobenzyl esters of acids related to chrysanthemic acid are active insecticides. Formal substitution of one or more of the fluorines in pentafluoro-benzyl alcohol has led to a new series of insecticidal compounds. The synthesis of these esters has some novel aspects. Key factors contributing to the insecticidal activity of these esters in soil, particularly against corn root worm, are discussed, including rates of degradation and vapour pressure. 相似文献
7.
Kievitone, phaseollinisoflavan and phaseollin were detected in roots of bean seedlings (Phaseolus vulgaris L.) grown in natural soil. Comparison of phytoalexin production by roots grown in different media indicated that these phytoalexins were probably induced by microorganisms in soil. The influence of common root rot pathogens of bean, Pythium spp., on phytoalexin production was determined. Pythium ultimum elicited kievitone, phaseollinisoflavan and phaseollin in roots grown in sterilized silica sand. P. sylvaticum induced only kievitone and phaseollin in the same growth medium. Glyphosate did not significantly affect the accumulation of phytoalexins within 3 days. However, by day 5, significantly more phaseollin was detected in the roots of Pythium inoculated plants treated with glyphosate than in Pythium inoculated plants not treated with glyphosate. In a hydroponic system, both Pythium spp. elicited accumulation of kievitone and phaseollin in root tissue, and both phytoalexins were exuded into the bathing solution. Glyphosate application did not significantly affect accumulation or exudation of phytoalexins by bean roots in the hydroponic system. The results from this study illustrate the nature and extent of phytoalexin production by bean roots in the absence and presence of microbes. 相似文献
8.
Factors Influencing Development of Root Rot on Ginseng Caused by Cylindrocarpon destructans 总被引:1,自引:0,他引:1
ABSTRACT The fungus Cylindrocarpon destructans (Zins) Scholten is the cause of root rot (disappearing root rot) in many ginseng production areas in Canada. A total of 80 isolates of C. destructans were recovered from diseased roots in a survey of ginseng gardens in British Columbia from 2002-2004. Among these isolates, 49% were classified as highly virulent (causing lesions on unwounded mature roots) and 51% were weakly virulent (causing lesions only on previously wounded roots). Pectinase and polyphenoloxidase enzymes were produced in vitro by C. destructans isolates when they were grown on pectin and phenol as a substrate, respectively. However, highly virulent isolates produced significantly (P < 0.001) higher enzyme levels compared with weakly virulent isolates. Histopathological studies of ginseng roots inoculated with a highly virulent isolate revealed direct hyphal penetration through the epidermis, followed by intracellular hyphal growth in the cortex. Subsequent cell disintegration and accumulation of phenolic compounds was observed. Radial growth of highly and weakly virulent isolates on potato dextrose agar was highest at 18 and 21 degrees C, respectively and there was no growth at 35 degrees C. Mycelial mass production was significantly (P = 0.01) lower at pH 7.0 compared with pH 5.0. To study the effects of pH (5.0 and 7.0) and wounding on disease development, ginseng roots were grown hydroponically in Hoagland's solution. Lesions were significantly larger (P < 0.001) at pH 5.0 compared with pH 7.0 and wounding enhanced disease by a highly virulent isolate at both pHs. In artificially infested soil, 2-year-old ginseng roots were most susceptible to Cylindrocarpon root rot among all root ages tested (1 to 4 years) when evaluated using a combined scale of disease incidence and severity. Root rot severity was significantly (P < 0.002) enhanced by increasing the inoculum density from 3.45 x 10(2) CFU/g of soil to 1.86 x 10(3) CFU/g of soil. Disease severity was higher at 20 degrees C compared with 15 and 25 degrees C and at -0.02 MPa soil moisture compared with -0.005 and -0.001 MPa. A significant interaction between soil moisture and temperature was observed for root rot severity. 相似文献
9.
M. McCullagh R. Utkhede J. G. Menzies Z. K. Punja T. C. Paulitz 《European journal of plant pathology / European Foundation for Plant Pathology》1996,102(8):747-755
Three strains ofPseudomonas fluorescens (63-49, 63-28, and 15), one strain ofPseudomonas corrugata (13) and one strain ofSerratia plymuthica (R1GC4) were tested on rockwool-grown cucumbers for their ability to reduce Pythium root-rot caused byPythium aphanidermatum. These strains were previously selected for biocontrol ability from collections of >4000 bacteria. Strains 63-49 and 63-28 were tested on cucumber plants grown in rockwool in two replicatedPythium-inoculated trials conducted in British Columbia (B.C). Another inoculated, replicated trial was conducted in Quebec with all five strains. Cucumber yields (fruit number and weight) were measured over a ten-week harvest period. Strain 63-49 caused an early promotion of plant growth and increased cucumber yields at early harvests. No measurable effect ofPythium inoculation on disease development was observed in the Quebec trial, due to unfavourable cool weather. However, 63-49 significantly increased the total number of cucumbers (12%) and cucumber weight (18%), compared to the non-treated control. Strains 13, 15 and R1GC4 slightly increased the cumulative cucumber yields, but strain 63-28 had no effect. In the B.C. trial, inoculation withP. aphanidermatum reduced the number and weight of cucumbers by 27%. Treatments ofPythium-inoculated cucumbers with 63-49 significantly increased fruit number and weight by 18%, compared to thePythium-inoculated control. Strain 63-28 increased the cumulative number of cucumbers over time, compared to thePythium-inoculated control, but the increase was less than with 63-49. The use ofPseudomonas spp. in rockwool-grown cucumbers can increase yields, both in the presence and absence of Pythium root rot, and with variable seasonal conditions and disease pressures. 相似文献
10.
Owen Wally Jayaraman Jayaraj Zamir Punja 《European journal of plant pathology / European Foundation for Plant Pathology》2009,123(3):331-342
Genes encoding an acidic wheat class IV chitinase (383), an acidic wheat β 1,3-glucanase (638) and a rice cationic peroxidase
(POC1) were introduced into ‘Nantes Coreless’ carrot (Daucus carota) by Agrobacterium-mediated transformation. The genes were introduced singly or in various combinations followed by selection imposed by the
herbicide phosphinothricin. Regenerated plantlets were screened for presence and expression of the three transgenes using
PCR, Southern and Northern hybridisations. Eighteen transgenic lines expressing a single transgene and 2 lines each co-expressing
638/383 and 383/POC1 were assessed for resistance to the necrotrophic fungal pathogens Botrytis cinerea and Sclerotinia sclerotiorum. Percentage leaf area diseased was measured 4 and 7 days after inoculation (dai) and compared to non-transformed control
plants. Six lines expressing β-1,3-glucanase 638 alone had no enhanced resistance to B. cinerea at 4 dai and only slight resistance to S. sclerotiorum; there was no effect at 7 dai. Two out of the six lines expressing 383 alone had enhanced tolerance to both pathogens with
a 20–50% reduction in disease development at 7 dai. Two lines co-expressing 638/383 had slight reductions in disease by (10–20%)
similar to that of the lines expressing chitinase 383 alone. Highest levels of disease resistance were seen in transgenic
lines expressing POC1, alone or in combination with chitinase 383. Disease symptoms were slower to develop and symptoms were
reduced by up to 90% for B. cinerea and 70% for S. sclerotiorum. The 383/POC1 co-expressing plants developed disease at levels similar to that of POC1 alone. Petioles of plants over-expressing
POC1 had higher levels of lignin accumulation constitutively compared to control plants, which was greatly enhanced following
inoculation with S. sclerotiorum. These results indicate that peroxidase over-expression can lead to significant disease reduction against necrotrophic pathogens
in transgenic carrot plants. 相似文献