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1.
Ohne Zusammenfassung
With a summary: On corky root of tomato and the corky root fungus
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2.
In 1993, a serious epidemic of a tomato root disease resembling corky root rot occurred in commercial greenhouses throughout Canada. Pyrenochaeta lycopersici could not be isolated from diseased roots, but Humicola fuscoatra was commonly isolated. The objectives of our work were to determine if H. fuscoatra is able to infect roots of tomato and cause corky root rot symptoms. Humicola fuscoatra was found to infect the roots of tomato seedlings and older plants. We concluded that H. fuscoatra is not a pathogen of tomato, however, because infection of tomato roots with the fungus did not necessarily lead to development of corky root rot or any other disease symptoms. Populations of H. fuscoatra increased greatly in sterile water or sterile nutrient solution, which would help to explain why commercial greenhouse growers can find this fungus in recirculating nutrient solutions.  相似文献   

3.
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   

4.
Coffee corky-root disease, also called corchosis, was first detected in 1974 in a small area of Costa Rica where the root-knot nematode Meloidogyne arabicida is the dominant species. An epidemiological study revealed a constant association between Meloidogyne spp. and Fusarium sp. in cases of corky root. No corky root appears to have been reported in association with Meloidogyne exigua , which is the prevalent root-knot nematode on coffee in Costa Rica. Fusarium spp. are often cited as components of disease complexes in association with nematodes. Combined inoculations using M. arabicida or M. exigua with Fusarium oxysporum under controlled conditions showed that only the combination with M. arabicida produced corky-root symptoms on Coffea arabica cvs Caturra or Catuai. Fusarium oxysporum alone was nonpathogenic. Meloidogyne exigua or M. arabicida alone caused galls and reduction in shoot height, but no corky-root symptoms. When cultivars susceptible and resistant to M. arabicida were studied under field conditions for 5 years, all the susceptible cultivars exhibited corky-root symptoms on 40–80% of their root systems. Cultivars that were resistant to M. arabicida but not to M. exigua showed no corky root. These observations lead to the conclusion that corky-root disease has a complex etiology, and emphasize the dominant role of M. arabicida as a predisposing agent to subsequent invasion by F. oxysporum . Consequently, genetic resistance to M. arabicida appears to provide an effective strategy against the disease.  相似文献   

5.
Streptomyces scabies, causative agent of common scab of potato, produces the phytotoxins concanamycin and thaxtomin. In a potato tuber slice assay to study the contribution of concanamycins to lesion development, concanamycin A had weak necrosis-inducing activities; >10× the amount of thaxtomin A was needed to produce equivalent lesion severity. Concanamycins were detected in tubers inoculated with S. scabies, which caused deep-pitted lesions but not in those inoculated with Streptomyces acidiscabies, which caused corky, raised lesions. In field-grown, diseased potatoes, concanamycin content tended to be higher in tubers with deep-pitted lesions than in those with corky, raised lesions.  相似文献   

6.
Typical symptoms of corky root were observed on iceberg lettuce (Lactuca sativa L.) in the Netherlands and England, on prickly lettuce (Lactuca serriola L.) in Spain, and on sowthistle (Sonchus oleraceus L.) in Greece. Slow-growing bacteria with similar colonies as strains ofRhizomonas suberifaciens or otherRhizomonas species were isolated from soil surrounding plants with corky root symptoms using lettuce seedlings as bait. Crude lysate from all strains was tested for DNA homology with DNA fromR. suberifaciens strain CA1 (R. sub. CA1) andRhizomonas sp. strain WI4 (R. sp. WI4). Strains that had homology values higher than that ofR. sp. WI4 orR. sub. CA1 were tested for pathogenicity on 1-wk-old lettuce seedlings, cv. Salinas, Two strains from the Netherlands induced typical symptoms of corky root on lettuce. These strains tested negative with monoclonal antibody MAb-Rs1 specific forRhizomonas suberifaciens in an enzyme-linked immunosorbent assay (ELISA). They had low DNA homology withR. sub. CA1 (4–9%) and low to moderate DNA homology withR. sp. WI4 (4–17%). Some nonpathogenic strains had moderate to high levels of DNA homology withR. sub. CA1 orR. sp. WI4 (19–84%). All strains had fatty acid profiles similar to those ofRhizomonas species. This is the first report ofRhizomonas sp. causing corky root of lettuce in Europe.  相似文献   

7.
ABSTRACT Subsurface drip and furrow irrigation were compared on lettuce (Lactuca sativa) cvs. Salinas and Misty Day for yield and incidence and severity of three important diseases of lettuce in the Salinas Valley, CA. Experiments were conducted between 1993 and 1995 during the spring and fall seasons. The diseases examined included lettuce drop (Sclerotinia minor), downy mildew (Bremia lactucae), and corky root (Rhizomonas suberifaciens). Replicated plots of subsurface drip and furrow irrigation were arranged in a randomized complete-block design. All plants were inoculated with S. minor at the initiation of the experiment during the 1993 spring season. Plots were not inoculated for downy mildew and corky root during any season nor were the plots reinoculated with S. minor. During each season, all plots were sprinkler irrigated until thinning, and subsequently, the irrigation treatments were begun. The furrow plots were irrigated once per week, and the drip plots received water twice per week. The distribution of soil moisture at two soil depths (0 to 5 and 6 to 15 cm) at 5, 10, and 15 cm distance on either side of the bed center in two diagonal directions was significantly lower in drip-irrigated compared with furrow-irrigated plots. Plots were evaluated for lettuce drop incidence and downy mildew incidence and severity at weekly intervals until harvest. Corky root severity and yield components were determined at maturity. Lettuce drop incidence and corky root severity were significantly lower and yields were higher in plots under subsurface drip irrigation compared with furrow irrigation, regardless of the cultivar, except during the 1994 fall season. Incidence and severity of downy mildew were not significantly different between the two irrigation methods throughout the study. The differential microclimates created by the two irrigation treatments did not affect downy mildew infection, presumably because the mesoclimate is usually favorable in the Salinas Valley. Subsurface drip irrigation is a viable, long-term strategy for soilborne disease management in lettuce in the Salinas Valley.  相似文献   

8.
A collection of 241 isolates of Rhizoctonia solani obtained from potato plants grown in different areas in France was characterized for anastomosis grouping, symptomatology on tubers of different cultivars and sensitivity to three fungicides. Most isolates collected belonged to (anastomosis groups (AGs)) AG 3, but 2% and 4% of the isolates were AG 5 and AG 2-1. AG 3 and AG 2-1 isolates were mostly obtained from sclerotia on tubers, but all AG 5, some AG 3 and some AG 2-1 isolates were recovered from superficial tuber alterations, like deformations, corky or scabby lesions. Sclerotia were formed on tubers produced by healthy stem cuttings grown in soil artificially infested with AG 3, but not on tubers grown in soil infested with either AG 5 or AG 2-1. No variation in susceptibility to sclerotial formation was observed among five potato cultivars. In all cases, a large proportion of tubers showed superficial corky lesions, often associated with deformations. The proportion of tubers with lesions and deformations was highest in soil infested with AG 2-1 and significantly lower on cv. Samba in all treatments. All isolates were highly sensitive to flutolanil, iprodione and pencycuron, except the AG 5 isolates, moderately sensitive to pencycuron. These results show that, although AG 3 is the most common R. solani group on potato in France, AG 5 and AG 2-1 may be present. Isolates differed for pathogenicity. In vitro sensitivity to fungicides varied among AGs.  相似文献   

9.
N. Ioannou 《Phytoparasitica》2000,28(3):248-256
Preplant soil fumigation with methyl bromide (MB) is presently standard practice in greenhouse tomato production. Since this compound is scheduled to be phased out by 2005, the possibility of using solarization as an alternative soil disinfestation method was examined in four greenhouse tomato trials. Solarization was applied for 8 weeks in July-August, using transparent polyethylene sheets for soil mulching, and compared with MB fumigation applied in September, before planting, at 80 g/m2. Solarization raised the maximum soil temperature by 9°C and reduced the population density ofFusarium spp. in soil by 91–98%. Similar reductions of soil inoculum (95–99%) were obtained with MB fumigation. Both methods provided effective control of Fusarium wilt, Verticillium wilt and corky root rot on tomato plants. MB fumigation was in addition highly effective against root-knot nematodes, whereas nematode control with solarization did not exceed 50%. Both treatments resulted in similar fruit yield increases, ranging within 90–140% compared with plants grown in untreated soil. During the second cropping season following soil treatment, solarization exhibited two times higher residual effectiveness against vascular wilt diseases compared with MB fumigation. The latter treatment, however, was superior to solarization in its residual effectiveness against root-knot nematodes and to a lesser extent against corky root rot. Fruit yields from solarized and MB-fumigated soil during the second cropping season were higher than those obtained from untreated soil by approximately 35% and 60%, respectively. In Cyprus, solarization appears to be an effective alternative to MB fumigation in greenhouse tomato production, especially if integrated with other approaches enabling more effective nematode control.  相似文献   

10.
The isolation of Pyrenochaeta lycopersici, causal agent of corky root of tomato, is difficult because of its slow growth and poor sporulation. Identification is complicated due the existence of two morphologically similar forms, Types 1 and 2, that differ in several physiological and molecular features. For the rapid and unambiguous identification of isolates, two oligonucleotide primer pairs were designed using ITS region sequences. Specific PCR products of 147 and 209 bp were obtained for isolates of Type 1 and Type 2, respectively. Specificity of both primer pairs was verified using several fungal and bacterial species. As little as 0.7 pg of target DNA could be detected with the protocol. A nested PCR procedure was necessary for the detection of the fungus in plant tissue. This technique will be of use in epidemiological studies and in the implementation of control strategies.  相似文献   

11.
It was previously thought that Tobacco Rattle Virus (TRV) was self-eliminating from seed potato stocks and that the principal effects of the virus were the spraing symptoms (arcs or lines of corky brown tissue) formed in the tuber flesh. Recent work has clearly demonstrated that the virus can become fully and systemically established in some potato cultivars, with few, if any, tuber flesh symptoms. The studies reported here demonstrate that, in at least one such cultivar, an M-type strain of the virus can have a considerable effect on the growth and quality of the plant and its produce. When infected material was compared with healthy material, overall yield and yield components were severely affected by TRV, as were quality traits such as dry matter, after-cooking blackening and chemical components such as sugars, glycoalkaloids and chlorogenic acid. The results are discussed in terms of plant response to virus infection and plant protection mechanisms.  相似文献   

12.
Rhizopycnis vagum is a recently described coelomycetous fungus that contributes to vine decline of muskmelons in Honduras, Guatemala, Texas and California. This fungus has been associated with roots of muskmelon plants affected by vine decline in most Spanish muskmelon production areas. Isolates were collected from 1996 to 2000 and identified from their cultural and morphological characteristics and by sequencing the ITS region of the ribosomal coding nuclear DNA (rDNA) and phylogenetic analysis. A few isolates from muskmelon with growth characteristics similar to R. vagum were identified as Phoma terrestris . Watermelon, Cucurbita hybrids used as rootstocks for watermelon production, Amaranthus sp. and grapevine were also hosts for R. vagum . Based on disease reaction in muskmelon roots, the pathogenicity of 10 isolates of R. vagum from different hosts and geographical origins was verified. The fungus caused root discoloration, corky lesions, and eventually the presence of pink coloration on the roots. Rhizopycnis vagum appears to be a minor pathogen that contributes to muskmelon vine decline complex in Spain through infection of roots.  相似文献   

13.
Pathogenic isolates of Pyrenochaeta lycopersici, the causal agent of corky root rot of tomato, secrete cell death in tomato 1 (CDiT1), a homodimeric protein of 35 kDa inducing cell death after infiltration into the leaf apoplast of tomato. CDiT1 was purified by fast protein liquid chromatography, characterized by mass spectrometry and cDNA cloning. Its activity was confirmed after infiltration of an affinity-purified recombinant fusion of the protein with a C-terminal polyhistidine tag. CDiT1 is highly expressed during tomato root infection compared with axenic culture, and has a putative ortholog in other pathogenic Pleosporales species producing proteinaceous toxins that contribute to virulence. Infiltration of CDiT1 into leaves of other plants susceptible to P. lycopersici revealed that the protein affects them differentially. All varieties of cultivated tomato (Solanum lycopersicum) tested were more sensitive to CDiT1 than those of currant tomato (S. pimpinellifolium). Root infection assays showed that varieties of currant tomato are also significantly less prone to intracellular colonization of their root cells by hyphae of P. lycopersici than varieties of cultivated tomato. Therefore, secretion of this novel type of inducer of cell death during penetration of the fungus inside root cells might favor infection of host species that are highly sensitive to this molecule.  相似文献   

14.
The investigations on the cause of the “Lent disease” of mother plants as well as cuttings ofPelargonium zonale have indicated, that these troubles are due to faulty cultural methodes combined with an infection byCorynebacterium fascians and “weakness parasites”. The bacteria cause the axillary buds to develop leafy galls on the stem under the soil level and small tumorous growths on the cortex of the stem above, the socalled corky spots. The infected plants may not wither, but galls and spots are more easily infected by pathogens than healthy plants. FrequentlyBotrytis cinerea infects these tissues and causes the black base rot. Spraying the mother plants with streptomycin (Fytostrep 60: 2.5 ml/l) and thiram (0.2%) decreased the base rot, but markedly inhibited the rooting of the cuttings. Moreover, the inocula of bothC. fascians andB. cinerea are present in such a large quantity, that full control is impossible. Reduction of losses may be achieved by improvement of cultural methods and soil disinfection.  相似文献   

15.
Isolates of Pyrenochaeta lycopersici, the causal agent of corky root rot on tomato plants, were assessed for physiological and genetic characteristics using conventional and molecular techniques. All isolates were able to produce necrosis on tomato roots and classified into temperature group according to the optimal growth temperatures. Specific-PCR assays and DNA sequence analysis of the ribosomal DNA (rDNA) internal transcribed spacer region confirmed the existence of both types (Type 1 and Type 2) of the pathogen among the isolates tested. All isolates were identified as Type 2 except for isolate Pl-4, which was classified as Type 1. Restriction fragment length polymorphism (RFLP) analysis with six enzymes resulted in three distinct banding patterns among the isolates depending on the length and restriction profiles of the rDNA intergenic spacer region. Inter-simple sequence-repeat analysis revealed a high level of genetic diversity among the isolates in agreement with the data of RFLP analysis. These results indicated that there were three different intraspecific groups among Turkish isolates of P. lycopersici. The presented study is the first attempting to characterize Turkish isolates of P. lycopersici. The results obtained will be useful in screening of tomato seedlings for resistance to P. lycopersici.  相似文献   

16.
Common and netted scabs are two disfiguring bacterial diseases of potato tubers, caused by various groups of Streptomyces species. Common scab, caused primarily by Streptomyces scabies and Streptomyces europaeiscabiei , is characterized by more or less deep pustules on the tuber surface, while symptoms of netted scab, caused mainly by Streptomyces reticuliscabiei , are superficial, corky alterations of the tuber periderm. Some isolates of S. europaeiscabiei are able to induce both common and netted scab symptoms, and therefore constitute a third pathogenicity group. Like most bacterial diseases, potato scabs would be best controlled by using resistant cultivars. Repeated experiments with soil artificially infested with isolates of three species representative of the three pathogenicity groups showed the level and stability of cultivar resistance, as well as the existence of a range of aggressiveness among different isolates. The distribution of scab severity indexes recorded on a collection of 16 potato cultivars and 27 breeding clones grown in soil infested with common scab-inducing isolates was continuous, suggesting isolate nonspecific quantitative resistance. Least susceptible cultivars were Nicola, BF15, Sirtéma, and Charlotte, while Urgenta, Désirée, Ondine and Bintje were very susceptible. The same genotypes proved either highly susceptible (e.g. cvs Bintje, Désirée or Carmine) or highly resistant (e.g. cvs Charlotte, Sirtéma, Monalisa, BF15 or Belle de Fontenay) to isolates forming netted scab symptoms, suggesting isolate-specific qualitative resistance. The ability was confirmed of some isolates of S. europaeiscabiei to induce one or the other type of symptoms depending on cultivar and soil temperature.  相似文献   

17.
We report the results of a 3-year study in which we collected and analyzed soil and yield data from experimental plots in six commercial processing tomato fields in Yolo and Solano counties in California. Our objective was to assess the effect of soil chemistry and soil-delivered nutrients and fungicides on tomato plant health and fruit yield at harvest. Marketable yield, leaf necrosis, and fruit loss due to sunburn differed significantly between individual fields, with averages ranging from 81.2–138.5 Mg ha?1, 32–72% leaf necrosis and 1.9 to 8.8% sunburnt fruit, respectively. Higher-yielding fields showed significantly lower levels of leaf necrosis and sunburn damage and a positive correlation with pre-plant soil parameters such as potassium concentration and cation exchange capacity (CEC). Interestingly, soil amendments of composted poultry manure or other nutrient supplements in low-CEC fields, but not high-CEC fields, resulted in higher fruit yield and less leaf necrosis. While all fields showed symptoms typical of Verticillium wilt and some fields showed symptoms of Fusarium wilt, Fusarium crown and root rot, corky root, and root knot nematode, none of our soil amendments, including chemical and biological fungicides, significantly or consistently reduced incidence or severity of these diseases. We discuss our findings in the context of premature vine decline of tomato, an emerging phenomenon in production fields in the Sacramento Valley, which is characterized by the loss of plant vigor and canopy cover at the onset of fruit ripening and for which causative agent(s) and management options in California remain elusive. (247 words).  相似文献   

18.
Potato common scab caused by the actinobacterium Streptomyces scabiei is characterized by the formation of corky lesions on tubers that reduce their marketability. Management of common scab is very complex and often ineffective under various environmental conditions. Using potato varieties that are more resistant to common scab remains one of the most efficient strategies to control this disease. However, very little is known about the factors associated with resistance to common scab. Somaclone RB9 regenerated from thaxtomin A-habituated potato Russet Burbank calli produced tubers more resistant to common scab than the original variety. Comparison of the RB9 tuber proteome with that of Russet Burbank using label-free quantitative proteomic analysis revealed changes in the accumulation of defence-related proteins from the patatin and lipoxygenase (LOX) families, which are involved in the metabolism of lipids, and of two miraculins of the Kunitz-type protease inhibitors family. The implication of LOX during common scab infection was studied using synchronized minitubers developed from leaf-bud cuttings. S. scabiei infection stimulated the accumulation of LOX in both Russet Burbank and RB9 minitubers, but this accumulation was intensified in RB9 minitubers. Infection also increased LOX activity in Russet Burbank and RB9 minitubers. However, LOX activity measured in noninfected RB9 minitubers was similar to that of infected Russet Burbank minitubers, indicating endogenous activation of LOX activity in RB9 minitubers. We discuss how increased LOX abundance and activity in the somaclone RB9 may contribute to improving tuber defence against common scab.  相似文献   

19.
The aflatoxigenic fungi, Aspergillus flavus and A. parasiticus infect a wide variety of crops, all of which produce oil-rich seed. A histological study of the host–pathogen interaction between peanut,Arachis hyphogea , and A. parasiticus was performed in a system where peanuts remained attached to the plant and were inoculated without wounding. For infection studies, a genetically-tagged strain of A. parasiticus, G5, was engineered to harbor the β-glucuronidase (GUS) reporter gene under control of the nor-1 promoter from the aflatoxin biosynthetic pathway. There was a similar temporal pattern of aflatoxin B1 production and appearance of GUS activity in cultures ofA. parasiticus G5. This strain was used to follow infection and aflatoxin production during colonization of undamaged, drought-stressed peanuts. The fungus colonized all tissues of the peanut pod and appeared to gain ingress through the corky layer of the pericarp. Both intra- and inter-cellular colonization were observed. Fungal colonization of the cotyledons resulted in visible depletion of storage bodies within cells. Two morphologically distinct types of hyphae, wider hyphae and narrower hyphae, were seen throughout the pod tissues. Statistical analysis revealed that the narrower hyphae were significantly more likely to produce GUS activity than wider ones. GUS activity was found in hyphae infecting the pericarp, embryo and cotyledons indicating expression of aflatoxin biosynthetic genes in these tissues. Interestingly, GUS activity was not observed in the hyphae colonizing the testa.  相似文献   

20.
Pyrenochaeta lycopersici is the causal agent of corky root rot, which is a serious disease worldwide that attacks the roots of tomato. A total of 139 isolates were sampled from eight locations in Italy and Israel and assigned to two molecular types (type 1 and type 2) based on internal transcribed spacer (ITS) sequences. These isolates were genotyped using amplified fragment length polymorphisms (AFLPs) to decipher the population structure. Based on this population structure analysis, three groups of P. lycopersici were identified. One group correlated to ITS type 1, while the other two correlated to ITS type 2. amova indicated high genetic divergence (FST = 0·40) between the Italian types 1 and 2. These data support the view that the two ITS types represent significant evolutionary entities, although there might be incomplete lineage sorting present. Some isolates of different ITS type were observed to have very similar multilocus AFLP profiles, and some genotypes were intermediate between the two ITS types. This suggests that parasexual hybridization between the two types has had a significant role in shaping the population structure of P. lycopersici. Finally, the average divergence among the populations within the ITS types was very high (FSC = 0·710, P < 10?5), probably due to strong genetic drift and founder effects combined with restricted migration.  相似文献   

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