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1.
Ochrobactrum CSL 2573, Rhizobium CSL 2411 and Sinorhizobium CSL 2611 strains harbouring the Agrobacterium cucumopine Ri plasmid (pRi), previously were shown to induce root-mat symptoms in an in vitro cucumber cotyledon assay. In whole-plant, rockwool-grown cucumber host tests Rhizobium CSL 2411 was shown to be as efficient an inducer of root-mat symptoms as the virulent Agrobacterium radiobacter strain NCPPB 4042, which also harbours a cucumopine pRi. Conjugal transfer of pRi to ingressing, avirulent Agrobacterium isolates was observed within root tissues with symptoms. Ochrobactrum CSL 2573 and Sinorhizobium CSL 2611 were not able to induce root-mat symptoms on plants. Rhizobium CSL 2411 and Ochrobactrum CSL 2573 were reisolated from inoculated plants, but Sinorhizobium CSL 2611 was not detected or isolated from inoculated plants 68 days after inoculation. It was postulated that the differences in pathogenicity observed between the in vitro and in situ host tests were caused by a lack of proper attachment to inoculated root tissues by pRi-harbouring Ochrobactrum and Sinorhizobium in the whole-plant host tests.  相似文献   

2.
Pythium spp. that cause damping-off of seedlings also can cause root rot of older plants and lead to yield reductions. This can be especially severe in soilless cultures where the fungus can spread easily with the nutrient solution. 39Pythium isolates obtained from discolored roots were assayed for their ability to cause damping-off on cucumber seedlings in sand-peat and for their pathogenicity in soilless culture of cucumber in rockwool or hydroponic solution. Isolates ofPythium aphanidermatum, P. irregulare, P. sylvaticum andP. ultimum were highly pathogenic in sand-peat, but onlyP. aphanidermatum strains were pathogenic in soilless conditions and led to root decay, plant death in rockwool culture and growth reduction in hydroponic culture. One strain ofP. aphanidermatum significantly reduced the yield of cucumber grown in rockwool under conditions similar to those of commercial cultures.  相似文献   

3.
The aim of this study was to isolate, identify and analyze the diversity of the causative agents of crown galls and hairy roots from symptomatic plants of Vaccinium corymbossum by means of biological, biochemical and molecular tools. All the bacteria isolated from blueberries (n?=?78) were found to be Agrobacterium since they grew on three differential media, provoked cell and/or root proliferation on Kalanchoe, and contained a 730?bp partial sequence that codes for virulence genes within the virC operon found on Ti and/or Ri plasmids. Isolates were highly variable considering the ERIC-PCR patterns as well as biochemical reactions and were all represented by 7 different restriction patterns of the 16SrDNA. While most of the isolates belonged to Agrobacterium bv. 1 (n?=?33) or Agrobacterium bv. 2 (n?=?31) only fourteen were Agrobacterium rubi. A representative isolate of each of these three groups was further identified by sequencing the approximately 400?bp 16SrDNA. We concluded that Vaccinium plants are particularly susceptible to Agrobacterium bv. 1, Agrobacterium bv. 2, and also to Agrobacterium rubi. To our knowledge this is the first survey of Agrobacterium affecting blueberries in Argentina.  相似文献   

4.
Substrates made from rockwool, coir dust, pumice and perlite were compared for conduciveness to Pythium root and crown rot in cucumber under near-commercial conditions. Rockwool slabs of 7 cm height were more conducive to the Pythium disease than coir dust slabs, pumice or perlite under these conditions. Temperature, oxygen concentration and water content were determined in the substrates to explain differences in conduciveness between the inorganic substrates rockwool, pumice and perlite by differences in the physical conditions. Temperature and oxygen concentration could not explain the differences but the higher disease level on rockwool was associated with a much higher water content of this substrate as compared to coir dust, pumice and perlite. Increasing the height of the substrate from 7 to 14 cm greatly decreased the percentage of diseased plants due to the Pythium disease on rockwool but had no effect on the level of disease on perlite when the substrate had been infested 4 cm below the planting hole. This difference in response in substrate height between rockwool and perlite could be explained by a much larger decrease in water content with substrate height in the rockwool than in the perlite substrate. Temperature in the substrates were above 30 °C for more than 6 h on sunny days in June and reached maximum values of 35 °C or more. These temperatures are highly favourable for the pathogen P. aphanidermatum but will have adverse effects on most biocontrol strains.  相似文献   

5.
Glasshouse experiments were conducted to study infection and disease development in rockwool-grown rose plants inoculated with Ralstonia pseudosolanacearum. A R. pseudosolanacearum strain isolated from rose plants was more aggressive than strains from anthurium or curcuma. The three rose cultivars tested, Avalanche, Red Naomi, and Armando, differed in susceptibility. At 20°C, the rose strain caused hardly any symptoms over a 6-week period, whereas at 28°C typical wilt symptoms were observed within 2 weeks after stem inoculation of Armando, the most susceptible cultivar. Inoculating roots with the rose strain resulted only in weak atypical symptoms. Nevertheless, inoculating roots of cv. Armando at a relatively low inoculum dose of 104 cfu/ml led to high densities in the base of stems in one out of two experiments. R. pseudosolanacearum occasionally spread from stem inoculated plants with symptoms in rockwool slabs. This limited spread resulted in a low infection incidence, and only of plants directly adjacent to the plants with symptoms.  相似文献   

6.
ABSTRACT The capacity of the microflora in rockwool to suppress Pythium aphanidermatum, the causative agent of root and crown rot in cucumber, was assessed. Disease development of cucumber (Cucumis sativus) grown on rockwool was evaluated in an "ebb-and-flood" system with a recirculating nutrient solution after inoculation with P. aphanidermatum. In five independent experiments from 1995 to 1998, 11 batches of used rockwool were tested. All batches without P. aphanidermatum problems in the preceding cucumber crop had significantly lower numbers of diseased plants in nonautoclaved than in autoclaved used rockwool; the disease incidence was reduced by 52 to 100%. Suppressiveness also was present in rockwool previously used to grow other vegetable crops. Rockwool originating from a cucumber crop that was severely attacked by Pythium resulted in a high disease incidence. Previously unused (new) rockwool had higher or similar percentages of diseased plants than did nonsterilized used rockwool. Disease suppression in used rockwool could also be measured in a smaller test system. In both systems, autoclaved rockwool became suppressive to Pythium after recolonization with the indigenous microflora. Population sizes of total culturable aerobic bacteria as well as of fluorescent pseudomonads did not correlate with disease suppressiveness, as numbers of bacteria and pseudomonads were similar or lower in nonautoclaved (suppressive) than in autoclaved (nonsuppressive) rockwool. Differences in the structure of the bacterial populations could be visualized by using eubacterial polymerase chain reaction (PCR) followed by denaturing gradient gel electrophoresis (DGGE). Interestingly, the nonautoclaved and the recolonized used rockwool, which were both suppressive, showed different dominating bacterial groups as compared with the autoclaved rockwool. PCR-DGGE patterns obtained at different sampling times showed that the composition of the bacterial populations changed during plant growth. Fungal populations were present in the treatments that yielded suppressive rockwool, i.e., the nonautoclaved and the recolonized rockwool, but they were absent or present in low numbers in the autoclaved rockwool, which permitted a high disease incidence. Suppressiveness of rockwool to Pythium root and crown rot is a hitherto undescribed phenomenon, and knowledge of the mechanism and microorganisms involved will stimulate the development of microbially balanced soilless growing systems.  相似文献   

7.
ABSTRACT The root pathogen Pythium aphanidermatum induced lower levels of disease in cucumber (Cucumis sativus) plants on unsterilized, re-used rockwool slabs than on heat-sterilized, re-used rockwool. Several recolonization treatments of the sterilized rockwool enhanced the suppressiveness of the rockwool. Microbial community structures in the different rockwool treatments were investigated by plate counts on selective media. Disease suppressiveness in the different rockwool treatments showed the highest correlation with the culturable number of filamentous actinomycetes in both experiments (r = 0.79 and 0.94), whereas the numbers of Trichoderma spp. correlated with suppression only in the first experiment (0.86). The numbers of total culturable bacteria, fluorescent pseudomonads, Bacillus spores, and fungi all showed lower correlations with disease suppressiveness. The filamentous actinomycetes enumerated with the plate counts were mainly Streptomyces spp., of which 10% were antagonistic toward P. aphanidermatum in dual culture. The composition of the bacterial and actinomycete populations was studied with polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). Multivariate analyses of these patterns with canonical correspondence analysis showed significant correlations between the microbial composition and the disease suppressiveness. However, none of the bands in PCR-DGGE patterns occurred exclusively in the treatments that had enhanced disease suppressiveness. Bands extracted from the actinomycete-specific DGGE gels showed closest similarity with members of several actinomycete genera, i.e., Streptomyces, Mycobacterium, Microbacterium, Rhodococcus, Curtobacterium, and Tsukamurella. The possible mechanism of disease suppressiveness in used rockwool slabs, based on the results obtained with culture-dependent and culture-independent detection methods, is discussed.  相似文献   

8.
Tomatoes grown in soilless systems can be seriously damaged byFusarium oxysporum Schlect f.sp.radicis lycopersici (Forl) causing Fusarium crown and root rot (FCRR). FCRR suppression can be achieved through the use of chemicals, selected substrates, composts and artificially introduced antagonistic microorganisms. This study evaluated the natural capacity of a used rockwool to suppress FCRR infections. New and used rockwool, sampled from closed soilless systems, was either autoclaved or not, either artificially inoculated withForl or not and, finally, sown with tomato seeds cv. ‘Cuore di Bue’. The effects of autoclaved/non-autoclaved and used/new rockwool on FCRR incidence were assessed by evaluating the symptoms of crown rot on the root — shoot transition zone of tomato seedlings. Non-autoclaved and inoculated used rockwool significantly reduced FCRR incidence when compared with non-autoclaved and inoculated new rockwool. Autoclaved and inoculated used rockwool did not suppress FCRR, similarly to new and inoculated rockwool. These findings are in accordance with other research that, on a cucumber/Pythium host/pathogen complex in a closed rockwool soilless system, demonstrated the key role of resident microflora in suppressing the root rot disease. http://www.phytoparasitica.org posting Dec. 8, 2006.  相似文献   

9.
Crown gall was previously reported on grape in Israel but the pathogen was not isolated and characterized. The three recognized biovars ofAgrobacterium tumefaciens can be tumorigenic on grape, but biovar 3 is the most important world wide. A single occurrence of tumors in a vineyard yielded bacteria which incited galls on grape,Nicotiana glauca and tomato, but not on bryophyllum. The bacteria were confirmed asA. tumefaciens because they contained DNA which hybridized with T-DNA from a Ti plasmid. Biochemical and physiological tests, octopine production and utilization, and agrocin 84 insensitivity conformed with those of bv. 3. Subsequent occurrences of the grape disease have not been found, but the presence ofA. tumefaciens bv. 3 in Israel is a potential threat to nurseries and vineyards.  相似文献   

10.
A wilt disease including severe root rot and corky rot was observed near the end of the growing season in glasshouse tomato (Lycopersicon esculentum) plants, growing in soilless systems. Numerous aleuroconidia of the common soil-borne fungusHumicola fuscoatra var.fuscoatra were always present in the cells of affected roots. The pathogenicity ofH. fuscoatra was not established, but inoculation with previously used rockwool from a crop with corky root symptoms reproduced the disease. It is suggested that near the end of the growing season the artificial substrate offers favourable conditions for the development of a complex root disease in whichH. fuscoatra may play a role.  相似文献   

11.
An isolate of Trichoderma viride from the surface of an apparently healthy tomato root was found to be pathogenic to seedlings of cucumber, pepper and tomato in laboratory and greenhouse experiments. In laboratory experiments, when seeds of each host species were inoculated with conidia of the pathogen, the subsequent growth of seedlings was decreased and they developed light-brown water-soaked lesions on their roots and crowns. The pathogen could be re-isolated from lesions on the seedlings, and microscopic examination of inoculated seedlings demonstrated that the fungus invaded the vascular tissues of the young seedlings. Culture filtrates of T. viride were found to contain a heat-stable factor that caused a decrease in the growth of the roots of young cucumber, pepper and tomato seedlings. In greenhouse experiments, the fungus did not affect germination or seedling fresh weight of young cucumber seedlings in soil- peat- or rockwool-based germinating media, but 10% of seedlings germinated in rockwool showed signs of infection. This is the first report of T. viride being pathogenic on pepper and tomato.  相似文献   

12.
Pink root rot of squash (Cucurbita moschata) caused by Setophoma terrestris was found in Maebashi, Gunma Prefecture, Japan in July 2007. Cucumber grafted on the squash first developed wilt and finally blight. These symptoms followed a severe pink root rot of the squash rootstock. The fungal isolates from diseased roots were identified as S. terrestris based on morphological characteristics and nucleotide sequences. One isolate induced a similar pink root rot but not entire wilting of the cucumber vine. We propose the name “pink root rot” (koshoku-negusare-byo in Japanese) of squash for the new disease.  相似文献   

13.
A detached leaf assay was developed to determine the pathogenicity of Pythium isolates to cut‐flower chrysanthemum roots. Leaves from young plants were excised and inoculated by insertion of a plug of mycelium into a slit cut in the excised petiole. After incubation leaves were assessed for presence and extent of necrosis. Necrosis indicated pathogenicity and was consistently confirmed by comparisons with whole plant inoculations. The rate of necrosis spread also gave some indication of virulence. Isolates of Pythium sylvaticum, P. ultimum and HS group were the most virulent, with a mean rate of spread of 14·6 mm per day, significantly (P < 0·05) faster than the mean rate of spread, 1·6 mm per day, of less virulent isolates. Less virulent isolates included P. irregulare, P. oligandrum and P. aphanidermatum. The latter was unexpected, as P. aphanidermatum is an important species in pythium root rot epidemics in chrysanthemums elsewhere. The value of the detached leaf assay for screening large numbers of isolates was demonstrated in a survey of isolates from clinic samples from chrysanthemum nurseries and in a series of dilution‐plating experiments looking at numbers of Pythium propagules in commercial chrysanthemum beds showing root rot. In the survey, the predominant pathogenic species was identified as P. sylvaticum and the most likely source of infection was contaminated soil as opposed to blocking media or irrigation water, whilst in soil colonization studies the use of detached leaf assays demonstrated a relationship between pathogenic inoculum concentration in soil and the expression of root rot symptoms.  相似文献   

14.
A survey of symptoms of phytophthora root and collar rot of common ( Alnus glutinosa ) and grey alder ( A. incana ) in riparian and forest stands in Bavaria was conducted by the Bavarian State Forestry and river authorities. Symptoms were seen in 1041 out of 3247 forest alder stands. The majority of the affected stands (80·9%) were less than 21 years old; 46% of these young stands were growing on nonflooded sites and 92% had been planted. The riparian survey showed that symptoms were widespread along more than 50% of the river systems. Along some rivers the disease incidence exceeded 50%. The 'alder Phytophthora ' was recovered from 166 of 185 riparian and forest alder stands with symptoms. In 58 of the 60 rivers and streams investigated in detail, the source of inoculum was traced back to infested young alder plantations growing on the river banks or on forest sites that drain into the rivers. Once introduced to a river system, the 'alder Phytophthora ' infects alders downstream. Baiting tests showed that the 'alder Phytophthora ' was present in rootstocks of alders from three out of four nurseries which regularly bought in alder plants for re-sale, but not in rootstocks from four nurseries that grew their own alders from seed. In addition, the infected nurseries used water from infested water courses for irrigation. The Bavarian State Ministry for Agriculture and Forestry has developed a code of practice for producing healthy alder plants in forest nurseries. This includes a 3-year fallow period between bare-rooted alder crops because of poor survival of the 'alder Phytophthora ' in soil.  相似文献   

15.
Thick root is a relatively new disorder of cucumber grown in artificial substrates. Plants of cucumber, tomato, sweet pepper, lupin, anthurium, Cucurbita ficifolia , C. maxima and two lines from crosses between C. maxima and C. moschata were grown in thick root disease (TRD)-infested nutrient solutions containing the TRD agent. Plants from each species or line, except anthurium, developed TRD symptoms. Growth of diseased plants, except those of the line C. maxima  × C. moschata RS841, was significantly reduced compared with the nondiseased controls. Two weeks after infestation, by adding TRD-affected nutrient solution to fresh nutrient solution, the presence of the infective TRD agent was shown in each of the nutrient solutions in which the plants had been grown, including anthurium. No infective TRD agent could be shown in nutrient solution that had not been in contact with roots of living plants. The minimum pH for thick root formation was shown to be between 5·0 and 5·5. Nutrient solutions with pH values ranging from 4·0 to 6·5 and infested with the TRD agent lost their infectivity within 8 days. The infective period decreased with decreasing pH (pH 4·0–6·5) and a pH effect on the infectivity of a nutrient solution was shown within 1 h of infestation. The data show that the risk of TRD can be reduced by decreasing the pH of the nutrient solution.  相似文献   

16.
Fusarium crown and root rot of tomatoes in the UK   总被引：1，自引：0，他引：1  
Fusarium crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici was found in the UK in 1988 and 1989 mainly in rockwool-grown tomato crops. Up to 14% of plants were affected in individual crops. In experiments, leaf and stem symptoms did not appear until the time of first fruit harvest even when the plants were inoculated at planting, first flowers or fruit set. Conidial inoculum at 106 spores/plant applied at seed sowing killed 70–83% of tomato seedlings, whereas similar levels of inoculum applied to young plants caused root and basal stem decay, and eventually death but only after fruit harvest began. Disease incidence and symptom severity increased with inoculum concentration. Experimentally, the disease was more severe in peat- or compost-grown plants than in rockwool. Disease spread was only a few centimetres in 50 days in experimental rockwool-grown plants. All tomato cultivars tested were highly susceptible. Prochloraz-Mn was highly effective against the pathogen in vitro and controlled the disease in the glasshouse, but only when applied preventively. Non-pathogenic Fusarium oxysporum isolates and Trichoderma harzianum also reduced FCRR disease levels.  相似文献   

17.
Rhizogenic Agrobacterium biovar 1, harbouring an Ri‐plasmid (root‐inducing plasmid), is the causative agent of hairy root disease (HRD) in the hydroponic cultivation of tomato, cucumber and aubergine. The disease is characterized by extensive root proliferation leading to strong vegetative growth and, in severe cases, substantial losses in marketable yield. Agrobacterium biovar 1 is a heterogeneous group of agrobacteria and includes at least 10 genomospecies, among which at least four (G1, G3, G8 and G9) have been associated with HRD in hydroponically grown vegetables. This review has synthesized the current knowledge on rhizogenic Agrobacterium biovar 1, including infection process, current taxonomic status, genetic and phenotypic diversity, detection methods and strategies for disease control. With regard to the latter, symptom reduction and prevention of infection through cultivation methods and chemical disinfection (e.g. by the use of chlorine‐based disinfectants and hydrogen peroxide) are discussed and biocontrol strategies are elaborated on. Recent research has led to the identification of a phylogenetically related clade of Paenibacillus strains that have antagonistic activity against rhizogenic Agrobacterium biovar 1 strains, holding great potential for HRD control. Finally, possible directions for future research are proposed.  相似文献   

18.
In the current study, the performance of three endophytic actinomycetes identified as Actinoplanes campanulatus, Micromonospora chalcea and Streptomyces spiralis previously shown to reduce seedling damping-off, and root and crown rots of mature cucumber (Cucumis sativus) caused by Pythium aphanidermatum in pots under greenhouse conditions were further evaluated to determine their potential as biological control agents and as plant growth promoters in the field under the conditions of commercial production of cucumbers in the United Arab Emirates (UAE). When applied individually or in combination to cucumber seedlings, the three isolates significantly promoted plant growth and yield and reduced seedling damping-off and root and crown rots of mature cucumber plants. Individually the performance level of S. spiralis was relatively the best followed by A. campanulatus and then by M. chalcea. The three isolates (which were not inhibitory to each other) performed better, both as biological control agents as well as plant growth promoters, when applied together than when they were inoculated individually. The ability of these three isolates to colonize the internal tissues of roots, stems and leaves under field conditions, and to persist up to 8 weeks after seedling inoculation, showed that they can easily adapt to an endophytic habit systemically within healthy cucumber plants. As the three endophytic actinomycete isolates also colonized the rhizosphere and showed outstanding rhizosphere competency it is clear that they are facultative and not obligate endophytes. The success with the three inoculants indicated that they could well be used in place of the fungicide metalaxyl which is currently recommended for the management of Pythium diseases in the UAE. This is the first successful field use of endophytic actinomycetes as promising plant growth promoters and biological control agents against Pythium diseases of cucumber.  相似文献   

19.
A total of 651 isolates of cucumber corynespora leaf spot fungus ( Corynespora cassiicola ) collected from cucumber in Japan, either with (438 isolates) or without (213 isolates) a prior history of boscalid use, were tested for their sensitivity to boscalid by using a mycelial growth inhibition method on YBA agar medium. Additionally, seven isolates of C. cassiicola obtained from tomato, soybean, eggplant (aubergine) and cowpea in different locations in Japan were tested before boscalid registration. Minimum inhibitory concentration (MIC) and 50% effective concentration (EC50) values for 220 isolates from crops without a prior history of boscalid use ranged from 0·5 to 7·5 μg mL−1 and from 0·04 to 0·59 μg mL−1, respectively. Two hundred and fourteen out of 438 isolates collected from ten cucumber greenhouses in Ibaraki Prefecture, Japan, which received boscalid spray applications showed boscalid resistance, with MIC values higher than 30 μg mL−1. Moreover, resistant isolates were divided into two groups: a moderately resistant (MR) group consisting of 189 isolates with EC50 values ranging from 1·1 to 6·3 μg mL−1, and a very highly resistant (VHR) group consisting of 25 isolates with EC50 values higher than 24·8 μg mL−1. MR isolates were detected from all ten greenhouses, but VHR isolates were detected from only three. As a result of fungus inoculation tests which used potted cucumber plants, control failures of boscalid were observed against resistant isolates. Efficacy of boscalid was remarkably low against VHR isolates in particular. This is the first known report on boscalid resistance in Japan.  相似文献   

20.
A study was conducted to investigate the effect of salinity on pythium damping-off and tolerance to salinity among Pythium aphanidermatum isolates from different geographical origins, genetic backgrounds and saline/non-saline soils. Increasing irrigation-water salinity from 0·01 to 5 dS m−1 significantly increased mortality in cucumber seedlings inoculated with P. aphanidermatum and reduced dry weight of non-inoculated seedlings. In vitro tests in culture media amended with different concentrations of NaCl showed that growth of P. aphanidermatum, P. spinosum and P. splendens isolates was stimulated or unaffected at salinity levels stressful for cucumber (electrical conductivity = 5 dS m−1). Significant differences were found in tolerance to salinity among 47 P. aphanidermatum isolates obtained from different greenhouses. The concentration of NaCl required to reduce growth of P. aphanidermatum isolates by 50% varied from 23 to 62 dS m−1, with an average of 46 dS m−1, however, oospore production was more sensitive to salinity and no oospores were produced above 20 dS m−1. Analysis of tolerance of P. aphanidermatum isolates to salinity showed no relationship between tolerance to salinity and geographical origins or genetic data. Isolates of P. aphanidermatum from greenhouses with no salinity problems were as tolerant to salinity as isolates obtained from salinity-affected greenhouses, suggesting lack of evidence for ecological adaptation within P. aphanidermatum in Oman. Increased mortality in cucumber seedlings at higher salinity levels may imply a synergistic interaction between salinity stress and salinity-tolerant Pythium species on cucumber seedlings, resulting in greater seedling losses.  相似文献   

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