A MICROSCOPICAL STUDY OF INFECTION OF THE ROOTS OF STRAWBERRY AND TOBACCO SEEDLINGS BY MICRO-ORGANISMS OF THE SOIL

1936 ◽  
Vol 14c (1) ◽  
pp. 11-26 ◽  
Author(s):  
A. A. Hildebrand ◽  
L. W. Koch
Keyword(s):  
Root Rot ◽  
Mycorrhizal Fungus ◽  
Microscopical Study ◽  
Thielaviopsis Basicola ◽  
Tobacco Seedlings ◽  
Living Root ◽  
Morphological Differences ◽  
Root Tissues ◽  
Micro Organisms ◽  
Different Soils

Similarity of organisms encountered in studies of black root of strawberry and of tobacco, respectively, carried out contemporaneously but independently, suggested the co-operative investigation, the results of which are embodied in this paper. Strawberry and tobacco seedlings growing (i) in seed-bed muck heavily infested with Thielaviopsis basicola (Berk.) Ferraris, and other organisms known to be pathogenic on tobacco, (ii) in soil from a commercial plantation where strawberry root rot had occurred in severe and typical form, and (iii) in greenhouse compost soil, were examined microscopically daily, commencing a few hours after germination and continuing throughout a period of four weeks. Organisms observed definitely within root tissues of both hosts included the "phycomycetous mycorrhizal" fungus, T. basicola (observed in plants grown in muck only), Rhizoctonia (Solani and endophytic orchid types), forms of Pythium, Asterocystis (Olpidiaster), certain unidentified fungi, a minute filamentous alga and nematodes. Organisms observed on the surface of roots included representatives of the genera Cylindrocarpon (Ramularia), Fusarium, Helminthosporium, Sphaeropsis, and Cephalothecium. The sequence of appearance, percentage occurrence, and parasitic capabilities of certain of the organisms varied in roots grown in the different soils. Because of early infection by, and ultimate almost universal occurrence of, the phycomycetous mycorrhizal fungus this organism received especial attention. Evidence based on certain morphological differences suggests the occurrence of strains of this organism. Of interest, too, is an alga invading living root tissue.From observations not limited alone to the examination of diseased roots of strawberry and tobacco, the authors are led to conclude, (1) that a root rot as it occurs in nature is extremely complex even in cases where a primary causal agent is recognized, and (2) that fungi representative of comparatively few groups or genera are "common factors" in root-rot complexes of different host plants.The technique described offers distinct advantages in that it permits a study of the sequence and severity of infection by the organisms involved in a root-rot complex; it reveals the occurrence of obligate parasites the presence of which would never be detected by the soil-plating, the Cholodny, or the tissue-isolation methods; and it is readily adaptable to the study of other root-rot complexes.

Induction of pigmentation of Thielaviopsis basicola and other fungi by a bacterium isolated from soil

1970 ◽  
Vol 48 (10) ◽  
pp. 1879-1886 ◽  
Author(s):  
Z. A. Patrick ◽  
Maury Schlifer
Keyword(s):  
Root Rot ◽  
Culture Media ◽  
Infested Soil ◽  
Thielaviopsis Basicola ◽  
Intimate Contact ◽  
Fungus Mycelium ◽  
Tobacco Seedlings ◽  
Viable Bacteria ◽  
Rhizopus Sp ◽  
Tobacco Roots

A blue-pigmented bacterium was isolated from soil and as a contaminant in cultures of Thielaviopsis basicola isolated from diseased tobacco roots. When the bacterium, a species of Pseudomonas, was grown in culture in association with T. basicola, a blue pigmentation was observed in the fungus. In addition to pigmentation of hyphae and conidia, other deleterious effects were induced in the fungus, including cytoplasmic granulation, vacuolation, contraction of cellular contents, reduced growth, and subsequent death of the affected cells. Other fungi, including Fusarium oxysporum f. sp. lycopersici, Botrytis convoluta, Rhizopus sp., and Mucor sp., were similarly affected. Hyphal pigmentation and other effects were observed only when viable bacteria were growing in intimate contact with the fungus mycelium. The pigment-inducing substance was not secreted into the culture media and was not obtained from lysed bacteria. Pigmentation and the other characteristic effects on T. basicola were not observed when the fungus and bacteria were added to soil. Similarly no significant reduction in severity of black root rot of tobacco seedlings was obtained when the blue bacteria were added to T. basicola infested soil.

THE ADVERSE INFLUENCE OF PHYTOTOXIC SUBSTANCES FROM DECOMPOSING PLANT RESIDUES ON RESISTANCE OF TOBACCO TO BLACK ROOT ROT

1963 ◽  
Vol 41 (6) ◽  
pp. 747-758 ◽  
Author(s):  
Z. A. Patrick ◽  
L. W. Koch
Keyword(s):  
Root Rot ◽  
Plant Residues ◽  
Thielaviopsis Basicola ◽  
Black Root Rot ◽  
Conditioning Factors ◽  
Root Diseases ◽  
Resistant Varieties ◽  
Important Host ◽  
Adverse Influence ◽  
Root Tissues

Exposure of tobacco plants to phytotoxic solutions obtained from decomposing rye and timothy residues increased their susceptibility to black root rot caused by Thielaviopsis basicola (Berk. & Br.) Ferraris. In greenhouse experiments 16 tobacco varieties, ranging from susceptible to highly resistant to black root rot in the field, were exposed to rye and timothy toxins and their relative resistance and severity of disease development were determined. Exposure to the toxins resulted in an apparent breakdown of resistance. There were no significant differences among the varieties and the disease was equally severe on roots of the resistant and the susceptible varieties after the toxin treatment. These results might explain in part, at least, the apparent breakdown of resistance that has at times been noted in the field with black root rot resistant varieties. The effect of the toxic compounds appears to be largely on the host rather than on the fungus. The precise biochemical and physiological changes which are induced in the root tissues by the toxins to make them more favorable for fungus invasion and colonization are at present not known. This study suggests, however, that phytotoxins may be important host-conditioning factors in the development of root diseases.

Management of Pythium myriotylum in Tobacco Transplant Production Greenhouses

2021 ◽  
Author(s):  
Xuemei Zhang ◽  
Chuck Johnson ◽  
David T Reed
Keyword(s):  
Root Length ◽  
Root Rot ◽  
Untreated Control ◽  
Copper Ion ◽  
Positive Control ◽  
Common Disease ◽  
Management Tools ◽  
Pythium Root Rot ◽  
Tobacco Seedlings ◽  
Root Tissues

Pythium root rot is a common disease that can threaten tobacco seedling production in greenhouses. However, management tools are limited in tobacco transplant production greenhouses. To identify additional Pythium control options, oomyceticide treatments (ethaboxam, mefenoxam, and copper ethanolamine complex) and non-oomyceticide (ultraviolet light and copper ion) water treatments were compared with etridiazole and an untreated control on TN 90LC tobacco seedlings inoculated with P. myriotylum in greenhouses. All the treatments in oomyceticide trials were applied to the bay water once before inoculation, when seedling roots had extended into the water. The inoculum was applied immediately before seeding in non-oomyceticide trials, where etridiazole was applied to bay water once, two weeks after seeding, as a positive control. Non-oomyceticide treatments were applied three times: 24 hours before, two weeks after, and four weeks after seeding. At the end of the tobacco transplant production season, ethaboxam and mefenoxam significantly (P<0.05) reduced root rot incidence and severity by as high as 100%, compared with the untreated control. Ethaboxam and mefenoxam also significantly (P<0.05) reduced oospores produced in infected root tissues, while significantly (P<0.05) increasing root length and weight. Ultraviolet radiation and copper ion treatments had no significant effects on tobacco seedling root length or weight compared with the untreated control, although the copper ion treatments significantly (P<0.05) reduced root rot severity and oospores produced in root tissues. Similar to etridiazole, ethaboxam and mefenoxam consistently reduced the AUDPC of Pythium root rot, but copper ion treatments only reduced AUDPC significantly (P<0.05) in one trial.

scholarly journals Gene Expression Profiling of a Compatible Interaction Between Douglas-Fir and the Root Rot Fungal Pathogen Phellinus sulphurascens

2013 ◽  
Vol 103 (6) ◽  
pp. 583-593 ◽  
Author(s):  
M. A. Islam ◽  
Rona N. Sturrock ◽  
Abul K. M. Ekramoddoullah
Keyword(s):  
Cdna Library ◽  
Root Rot ◽  
Douglas Fir ◽  
Coniferous Species ◽  
Elevated Expression ◽  
Plant Genes ◽  
Polymerase Chain ◽  
Fungal Genes ◽  
Root Tissues ◽  
Host Genes

Douglas-fir (DF) (Pseudotsuga menziesii) is one of the largest and most economically important coniferous species in western North America. Its productivity is greatly affected by the root rot fungus Phellinus sulphurascens Pilát. Evidence of resistance by DF to fungal root pathogens such as P. sulphurascens has been reported but mechanisms of resistance in this compatible pathosystem are not yet known. To better understand the DF–P. sulphurascens interaction, especially at the molecular level, we selected 12 diverse plant genes already identified as defense-related from a cDNA library constructed using root tissues from P. sulphurascens-infected DF seedlings. Using quantitative reverse-transcriptase polymerase chain reaction on infected DF root samples collected at five different time points after inoculation, we found that P. sulphurascens infection significantly elevated expression of the 12 selected genes. In most cases the highest expression level was recorded within 2 to 3 days after inoculation. The constructed cDNA library, which is enriched with defense-related host genes and a number of fungal genes, will continue to serve as a useful resource for future larger-scale gene discovery and functional research on the P. sulphurascens and DF pathosystem.

On the Fixation of Atmospheric Nitrogen by Phoma Radicis Callunae, including a New Method for Investigating Nitrogenfixation in Micro-Organisms

1928 ◽  
Vol 6 (2) ◽  
pp. 167-189
Author(s):  
W. NEILSON JONES ◽  
M. LLEWELLYN SMITH
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogen Starvation ◽  
Molecular Nitrogen ◽  
Mycorrhizal Fungus ◽  
Growth Period ◽  
Calluna Vulgaris ◽  
Atmospheric Nitrogen ◽  
Free Medium ◽  
New Apparatus ◽  
Micro Organisms

(1) Evidence from chemical analyses of seeds of Calluna mdgaris and of seedlings grown on a nitrogen-free medium confirms the view that this plant can obtain nitrogenous supplies from the air, probably in the form of molecular nitrogen, in sufficient amount to prevent the advent of any symptoms of nitrogen starvation. (2) A new apparatus for the investigation of nitrogen-fixation by micro-organisms is described. (3) Using the above apparatus, experiments on the mycorrhizal fungus of Calluna vulgaris are described in which this organism was grown in pure culture on a nitrogen-free medium with and without a supply of molecular nitrogen. The evidence obtained indicates that the amount of glucose used by the fungus during growth, and the amount of nitrogen contained in the culture at the end of the growth period are greater under the former condition. It is concluded that the fungus in question can utilise the molecular nitrogen of the air in some degree under the conditions of the experiments, although these were not the most favourable possible for nitrogen-fixation. It is considered that the results obtained justify an extension of these experiments using a strain of the fungus freshly extracted from the Calluna plant.

scholarly journals Black Root Rot Caused by Thielaviopsis basicola on Lettuce in California

Plant Disease ◽  
2008 ◽  
Vol 92 (9) ◽  
pp. 1368-1368 ◽  
Author(s):  
S. T. Koike
Keyword(s):  
Root Rot ◽  
Disease Incidence ◽  
Control Plant ◽  
Pathogenic Fungi ◽  
Plant Roots ◽  
Peat Moss ◽  
Thielaviopsis Basicola ◽  
Black Root Rot ◽  
Iceberg Lettuce ◽  
Salinas Valley

In 2005 and 2006, field-grown iceberg lettuce (Lactuca sativa) in California's coastal Salinas Valley (Monterey County) was affected by a previously unreported disease. Symptoms were observed on iceberg lettuce at the post-thin rosette stage (8 to 12 leaves). Plants were stunted and slightly chlorotic. Fine feeder roots had numerous, small (4 to 8 mm long), elongated, dark brown-to-black lesions. Larger secondary roots and taproots lacked lesions. No vascular discoloration was present. Isolations from root lesions consistently resulted in gray fungal colonies that formed catenulate, cylindrical, thin-walled, hyaline endoconidia and catenulate, subrectangular, thick-walled, dark aleuriospores. The fungus was identified as Thielaviopsis basicola (2). Conidial suspensions (5.0 × 105) of eight isolates from iceberg lettuce were used for pathogenicity tests. Iceberg cv. Ponderosa and romaine cv. Winchester were grown for 3 weeks in soilless peat moss rooting mix. Roots of 20 plants per cultivar were washed free of the rooting mix and soaked in conidial suspensions for 5 min. Plants were repotted and grown in a greenhouse. Control plant roots were soaked in sterile distilled water (SDW). After 3 weeks, inoculated iceberg exhibited slight chlorosis in comparison with control plants. Feeder roots of all iceberg plants inoculated with the eight isolates exhibited numerous black lesions and T. basicola was reisolated from these roots. Romaine lettuce, however, did not show any foliar symptoms. Small segments of roots had tan-to-light brown discoloration and T. basicola was occasionally reisolated (approximately 40% recovery). Roots of control iceberg and romaine showed no symptoms. Results were similar when this experiment was repeated. To explore the host range of T. basicola recovered from lettuce, two isolates were prepared and inoculated as described above onto 12 plants each of the following: iceberg lettuce (cv. Ponderosa), bean (cv. Blue Lake), broccoli (cv. Patriot), carrot (cv. Long Imperator #58), celery (cv. Conquistador), cotton (cv. Phy-72 Acala), cucumber (cv. Marketmore 76), green bunching onion (cv. Evergreen Bunching), parsley (cv. Moss Curled), pepper (cv. California Wonder 300 TMR), radish (cv. Champion), spinach (cvs. Bolero and Bossanova), and tomato (cv. Beefsteak). Control plant roots of all cultivars were soaked in SDW. After 4 weeks, only lettuce and bean roots had extensive brown-to-black lesions, from which the pathogen was consistently resiolated. Roots of cotton, pepper, spinach, and tomato had sections of light brown-to-orange discoloration; the pathogen was not consistently recovered from these sections. All other species and the control plants were symptomless. This experiment was repeated with similar results except that inoculated peppers were distinctly stunted compared with control plants. To my knowledge, this is the first report of black root rot caused by T. basicola on lettuce in California. Disease was limited to patches along edges of iceberg lettuce fields; disease incidence in these discrete patches reached as high as 35%. Affected plants continued to grow but remained stunted in relation to unaffected plants and were not harvested. Black root rot of lettuce has been reported in Australia (1); that report also showed that lettuce cultivars vary in susceptibility to T. basicola and isolates from lettuce were highly aggressive on bean but not on many other reported hosts of this pathogen. References: (1) R. G. O'Brien and R. D. Davis. Australas. Plant Pathol. 23:106, 1994. (2) C. V. Subramanian. No. 170 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1968.

scholarly journals First Report of a Phytopythium litorale Species Causing Crown and Root Rot on Rhododendron pulchrum in China

Plant Disease ◽  
2021 ◽  
Author(s):  
Yaxing Li ◽  
Yangfan Feng ◽  
Cuiping Wu ◽  
Junxin Xue ◽  
Binbin Jiao ◽  
...  
Keyword(s):  
Root Rot ◽  
Morphological Characters ◽  
Morphological Features ◽  
Crown Rot ◽  
Sterile Water ◽  
First Report ◽  
Inoculation Method ◽  
Platanus Orientalis ◽  
Crown And Root Rot ◽  
Root Tissues

During a survey of pathogenic oomycetes in Nanjing, China from June 2019 to October 2020, at least ten adjacent Rhododendron pulchrum plants at a Jiangjun Mountain scenic spot showed symptoms of blight, and crown and root discoloration . Symptomatic root tissues collected from three 6-year-old plants were rinsed with water, cut into 10-mm pieces, surface sterilized with 70% ethanol for 1 min, and plated onto 10% clarified V8 PARP agar (cV8A-PARP) containing pimaricin (20 mg/liter), ampicillin (125 mg/liter), rifampicin (10 mg/liter), and pentachloronitrobenzene (20 mg/liter). Four Pythium-like isolates were recovered after three days of incubation at 26°C, and purified using hyphal-tipping. Ten agar plugs (2×2 mm2) of each isolate were grown in 10 mL of 10% clarified V8 juice (cV8) in a 10 cm plate at 26°C for 3 days to produce mycelial mats, and then the cV8 was replaced with sterile water. To stimulate sporangial production, three to five drops of soil extract solution were added to each plate. Sporangia were terminal, ovoid to globose, and the size is 24 to 45.6 (mean 34.7) (n=10.8) in length x 23.6 to 36.0 (mean 29.8) (n=6.2) in width. Gametangia were not observed in cV8A or liquid media after 30 days. For colony morphology, the isolates were sub-cultured onto three solid microbial media (cV8A-PARP, potato dextrose agar, corn meal agar) . All isolates had identical morphological features in the three media. Complete ITS and partial LSU and cox2 gene regions were amplified using primer pairs ITS1/ITS4, NL1/NL4, and FM58/FM66 , respectively. The ITS, LSU, and cox2 sequences of isolate PC-dj1 (GenBank Acc. No. MW205746, MW208002, MW208003) were 100.00% (936/936 nt), 100.00% (772/772 nt), and 99.64% (554/556 nt) identical to those of JX985743, MT042003, and GU133521, respectively. We built a maximum-likelihood tree of Phytopythium species using the concatenated dataset (ITS, LSU, cox2) to observe interspecific differences. Based on the morphological characters and sequences, isolate PC-djl was identified as Phytopythium litorale . As the four isolates (PC-dj1, PC-dj2, PC-dj3 and PC-dj4) tested had identical morphological characters and molecular marker sequences, the pathogenicity of the representative isolate, PC-dj1, was tested using two inoculation methods on ten one-year-old R. pulchrum plants. For the first inoculation method, plants were removed from the pot, and their roots were rinsed with tap water to remove the soil. Each of these plants was placed in a glass flask containing 250 mL of sterile water and 10 blocks (10 x 10 mm2) of mycelial mats harvested from a three-day-old culture of P. litorale, while the other plant was placed in sterile water as a control, and incubated at 26°C. After three days, symptoms including crown rot, root rot and blight was observed on the inoculated plants whereas the control remained asymptomatic. For the second inoculation method, ten plants were dug up to expose the root ball. Ten three-day-old cV8A plugs (5×5 mm2) from a PC-dj1 culture or sterile cV8A plugs were evenly insert into the root ball of a plant before it was planted back into the original pots. Both plants were maintained in a growth chamber set at 26°C with a 12/12 h light/dark cycle and irrigated as needed. After 14 to 21 days, the inoculated plant had symptoms resembling those in the field , while the control plant remained asymptomatic. Each inoculation method was repeated at triplicate and the outcomes were identical. Phytopythium isolates with morphological features and sequences identical to those of PC-dj1 were recovered from rotted crown and root tissues of all inoculated plants. Previously, P. litorale was found causing diseases of apple and Platanus orientalis in Turkey, fruit rot and seedling damping-off of yellow squash in southern Georgia, USA. This is the first report of this species causing crown and root rot on R. pulchrum, an important ornamental plant species in China. Additional surveys are ongoing to determine the distribution of P. litorale in the city of Nanjing.

STUDIES ON FOOT AND ROOT ROT OF WHEAT: II. CULTURAL RELATIONSHIPS ON SOLID MEDIA OF CERTAIN MICRO-ORGANISMS IN ASSOCIATION WITH Ophiobolus graminis SACC.

1933 ◽  
Vol 8 (6) ◽  
pp. 545-552 ◽  
Author(s):  
W. C. Broadfoot
Keyword(s):  
Root Rot ◽  
Potato Dextrose Agar ◽  
Wheat Seedlings ◽  
Reliable Indication ◽  
Solid Media ◽  
Metabolic Products ◽  
Growth Reaction ◽  
Bacteria And Fungi ◽  
Micro Organisms ◽  
Pot Culture

The antagonistic and compatible growth relationships of 66 cultures of bacteria and fungi, most of which were from the soil, towards O. graminis on potato dextrose agar and Molisch's salt peptone agar, were compared with the effect of each on the virulence of this pathogene on wheat seedlings in open soil culture.Of the 21 cultures which controlled the virulence of O. graminis in the soil, only 15 of these were antagonistic on potato dextrose agar, while of the 45 cultures which gave intermediate or no control, 17 were compatible and 28 were decidedly antagonistic. From data secured indirectly, the antagonism or compatibility of the micro-organisms toward O. graminis, observed on potato dextrose agar, did not seem to depend on active alkali or acid more than on other metabolic products. The study apparently demonstrates that the growth reaction of various micro-organisms and O. graminis, associated on the two solid media used, is not a reliable indication that the same micro-organism will or will not suppress the virulence of this pathogene on wheat in soil in open pot culture.

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