Root-infecting Fungi Research Articles

Effects of root-infecting fungi on wheat transport processes and growth

Aurtobasidium bolleyi and Gaeumannomyces graminis damaged transport processes and decreased shoot growth of sand-grown wheat plants only if they colonized the stele and disrupted the phloem of most roots. One week after planting in sand infested by A. bolleyi the phloem of most roots was disrupted and no 14C-labelled assimilates were detected in them. K uptake, shoot water content and shoot growth were decreased. However, plants rapidly recovered because A. bollayi did not penetrate beyond the epidermis of new roots. G. graminis disrupted the phloem of some roots within the first week, but shoot growth was unaffected. During the next 4 weeks the phloem of most roots was disrupted and K uptake, shoot water content and shoot growth were severely decreased. Uptake of Ca and Mg was affected less. Phialophora radicicola, Pythium scleroteichum and Wojnomicia graminis did not penetrate root steles and did not affect transport processes or shoot growth. When wheat was planted in sand infested by Cochliobolus sativus or Fusarium culmorum, K uptake, shoot water content and shoot growth were decreased after 1 week although root steles were not colonized until 3 or 4 weeks later. Tests for phytotoxins revealed the presence of inhibitory substances in culture filtrates of C. sativus, but not F. culmorum.

Effect of urea on Poria weirii and soil microbes in an artificial system

Poria weirii (Murr.) Murr. (an important root-infecting fungus of conifers in western North America) grown in alder stem sections and buried in soil at 15°C survived better when urea was not added to the soil. Survival over a 32 week period was inversely related to rate of urea applied. Fungus populations were greatest at 4 weeks after which numbers of Trichoderma began to increase. This corresponded with decreased survival of P. weirii; Trichoderma was the fungus isolated almost exclusively from alder sections when P. weirii was not. Increasing soil populations of actinomycetes with time may have had some effect on survival as well.

Root-Infecting Fungi Isolated from Sorghum Seedlings

Fungi were isolated from roots of sorghum seedling, and tested for pathogencity. The isolations included species of Aspergillus, Alternaria, Fusarium, Fusidium, Humicola, Mucor, Penicillium, Rhizoctonia, Trichoderma, Verticillium and some unidentified fungi. Isolates varied from non-pathogenic to highly pathogenic in pathogenicity tests on sorghum seedlings in fruit jars at 21oC and 27oC using vermiculite, but in grernhouse tests isolats did not exhibit pathogenicity

Root Fungi Pathogenic Root-Infecting Fungi S. D. Garrett

Root Fungi Get access Pathogenic Root-Infecting Fungi, by Garrett S. D., Cambridge University Press, London & New York, 1970, 294 p., illus., $12.50 (72-10024). Thor Kommedahl Thor Kommedahl University of Minnesota, St. Paul Search for other works by this author on: Oxford Academic Google Scholar BioScience, Volume 21, Issue 11, June 1971, Pages 547–548, https://doi.org/10.2307/1295849 Published: 01 June 1971

Diseases of Root Systems

Pathogenic Root-infecting Fungi By S. D. Garrett. Pp. xi + 294. (Cambridge University: London, July 1970.) 75s; $12.50.

Survival of root-infecting fungi in soil. 13. Decomposition of flavonoids and other phenolics in soil and their effects on Fusarium root rot of bean.

The flavonoids rutin and quercetin and two of their decomposition products, phloroglucinol and protocatechuic acid, were rapidly degraded in soil. Less than 10% of their phenolic nuclei were detected in soil, and from 27 to 57% of their structural carbons remained in soil after 9 weeks of incubation. Phenolic intermediates were not detected in soils amended with rutin or quercetin. There were no differences in the decomposition of any of the substrates in noninfested soil and in soils infested with F. solani f. sp. phaseoli. In pure culture, two virulent isolates of the pathogen could effectively metabolize a glucose–rhamnose mixture and protocatechuic acid, but only one of the isolates could use phloroglucinol and rutin to any great extent. When incorporated into soil at a rate of 0.1% and 0.3%, rutin, phloroglucinol, protocatechuic acid, and a glucose–rhamnose mixture significantly increased propagule numbers of the pathogen over that of the control. From 1 week, to the termination of the experiment after 9 weeks, more than 80% of the propagules of F. solani f. sp. phaseoli existed in the soils as chlamydospores. Propagule numbers were higher in soils amended with 0.3% substrate than in soils amended with 0.1% substrate, and the numbers 1 week after amendment addition were similar to those obtained 9 weeks after amendment addition. In the first and second crops of beans (planted 3 and 6 weeks after amendment incorporation), protocatechuic acid and phloroglucinol, at a concentration of 0.3%, were very effective in reducing root-rot severity. The other amendments, except quercetin, were effective in suppressing disease to various degrees. The effectiveness of the various amendments depended upon amendment concentration and time of planting. Quercetin, added to soil at either concentration, did not increase inoculum density but did increase disease severity.

Survival of Root-infecting Fungi in Soil XI. Survival of Rhizoctonia solani as affected by inoculum concentration and various soil amendments

Survival of Root-infecting Fungi in Soil XI. Survival of Rhizoctonia solani as affected by inoculum concentration and various soil amendments

Rigidoporus lignosus . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Rigidoporus lignosus . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Hevea and over 40 other tropical genera icluding cacao, coconut, coffee, tea and bamboo. DISEASE: White root rot. Common on rubber where it destroys the tap root so that diseased trees are easily blown over. The foliage turns yellow and this is accompanied by die-back in Asia, but these symptoms are absent in West Africa (45, 1166). Also parasitic on other perennial crops. GEOGRAPHICAL DISTRIBUTION: Africa (Cameroon, Congo, Ethiopia, Fernando Po I., 'French Equatorial Africa', Ghana, Ivory Coast, Kenya, Mauritius, Nigeria, Sierra Leone, Uganda), Asia (Brunei, Burma, Ceylon, India, Indo- China, Indonesia, Japan, Malaysia, Philippines, Thailand); Australasia & Oceania (New Guinea, New Hebrides); North America (Mexico); Central America & West Indies (Costa Rica, Dominica); South America (Argentina, Brazil, Guyana). (CMI Map 176, ed. 2, 1966). TRANSMISSION: Rigidoporus lignosus is a rhizomorphic root-infecting fungus with an ectotrophic growth habit. The rhizomorph requires a food base, generally the tree stump on which it originated, until it encounters other dead wood or living or moribund tree roots which it can invade. Epiphytic growth of rhizomorphs may extend 5-15 feet ahead of actual penetration of live rubber roots (Napper, 1938) and descend the full length of the tap root to a depth of 181 feet (45, 1161d). Air-borne spores may also infect tree stumps immediately after felling (45, 201) and thus provide foci for the spread of rhizomorphs, as was earlier postulated by Petch (1921). This source of infection, however, is regarded as less important than root-infection (46, 1089).

Survival of Root-infecting Fungi in Soil VII. Decomposition of Tannins and Lignins in Soils and their Effects on Fusarium Root Rot of Bean

Survival of Root-infecting Fungi in Soil VII. Decomposition of Tannins and Lignins in Soils and their Effects on Fusarium Root Rot of Bean

Fixation and staining of fungus hyphae and host plant root tissues for electron microscopy.

A deuteromycetous root-infecting fungus (Pyrenochaeta terrestris) and one of its hosts (Allium cepa) were fixed in OsO4, OsO4 vapor, KMnO4, glutaraldehyde followed by OsO4, acrolein followed by OsO4 and a glutaraldehyde-acrolein mixture followed by OsO4. The fungus was also fixed in LiMnO4. Three procedures were selected for routine comparisons because they provided suitable detail of organelles within cells of both the host and the pathogen; they were as follows: (1) 1% OsO4 for 2 hr in an ice bath; (2) 3% glutaraldehyde with 3% acrolein or 3-6% acrolein for 1-2 hr at room temperature then 1% OsO4 for 2 hr in an ice bath; and (3) 3% KMnO4 for 2 hr at room temperature. These fixatives were buffered with 0.2 M sodium cacodylate at pH 7.2-7.4. Fixation was followed by soaking the tissue blocks for a few hours to 2 days in 0.5% uranyl acetate, then by dehydration and embedding. Sections were stained with Reynolds' lead citrate. Glutaraldehyde-acrolein or acrolein provided the most detail of different organel...

Comparison of Techniques for the Isolation of Root-infecting Fungi

MANY techniques have been devised to study the microflora of the root-surface. Washing techniques have been devised and used by various workers1–7 for certain specific purposes. A clear demonstration of the effectiveness of the washing techniques was provided only by Harley and Waid5. In a study of the root-surface fungal population of beech, they made serial washings in sterile water and estimated the degree of completeness of the removal of fungi by the dilution plate method. They found that most of the detachable fungal units were removed in the first 10 washes. A fairly constant number of isolations were obtained thereafter by plating 0.5-cm root fragments. These isolations were thought to represent the fungal population of the root surface living in an active mycelial state.

Inoculum Potential and the Fusarial Wilt of Cotton

THE importance of inoculum potential of a pathogen in overcoming host resistance and causing infection is now well recognized1. This is particularly so with root-infecting fungi which have to overcome not only host resistance but also competition from soil saprophytes. As pointed out by Sanford2, “The importance to disease incidence of serious competition between the pathogen and saprophytes associated in general soil habitat or in the rhizosphere seems to be undetermined”. A fungus like Fusarium oxy-sporum f. vasinfectum (Atk.) Snyd. and Hans., having a high degree of competitive saprophytic ability3, can be expected to build up sufficient inoculum in soil by colonizing saprophytic substrates. Whether such a change in its inoculum, potential will cause any alteration in its infective capacity is not understood. A study of infective behaviour of the fungus with changes in inoculum potential was therefore undertaken by us.

Violet-Pigmented Pseudomonads With Antifungal Activity From the Rhizosphere of Beans

Bean rhizosphere bacteria antagonistic to four root-infecting fungi and an antibiotic produced by these bacteria were studied. The bacteria were violet-pigmented gram-negative rods, probably belonging to the genus Pseudomonas . The antibiotic, which was localized largely in the bacterial cell mass, was easily extracted with acetone. It was selectively active against a wide variety of plant-pathogenic and saprophytic fungi tested in vitro but was relatively inactive against bacteria. The compound, partially purified by chromatography, was soluble in all organic solvents tried, but nearly insoluble in water. It demonstrated no characteristic ultraviolet- or visible-absorption spectrum and was chemically unidentified. The antagonistic bacteria or crude antibiotic applied to buried buckwheat segments suppressed the colonization of this substrate by Rhizoctonia spp. The data suggested that the bacteria or the antibiotic may play a role in the suppression of root-infecting fungi in soil.

The Ecology of Soil-Borne Fungal Disease

The behaviour in soil of root-infecting fungi is sometimes considered to be a complex subject, and the inherent principles and implications are indeed commonly misunderstood by plant pathologists not specialist in this field. There has, of course, been no shortage of reviews recently on various aspects of the ecology of fungi in soil. Yet despite, or perhaps even because of the extent of this literature, confusion is still common. From the large field avail­ able two works can best be recommended. Firstly Garrett's 1956 book (1), which provides a considered and balanced account of the relative importance of work up to that date and presents the theoretical concepts important in fully understanding the subject. Secondly the account of the 1958 Liverpool International Symposium (2) since it includes much recent work that indi­ cates the trend of current work and thought, some of it more controversial than others. The apparent complexity of the biology in soil of plant pathogens is partly the result of the soil's opacity, which makes observations difficult and necessitates the use of indirect methods, the interpretation of which is some­ times ambiguous. But another potent source of difficulty is the presence in the soil of an established population of microorganisms with their own biology without any necessary connection with a host plant. This situation contrasts markedly with the simple one existing for most air-borne diseases, in which not only is observation of the host-pathogen interaction relatively easy but also the system is a simple two-component one with two pathways of interac­ tion, and can be represented: H;:=P. This biological system is affected by the inorganic environment acting directly on both components which can then adjust the equilibrium as indicated by the arrows. The variations within this system are limited, and, using the symbolic signs for neutral, positive and negative effects (3), the pathogen may show 0 or towards the suscept, and the suscept +,0, or towards the pathogen. Little difficulty attends under­ standing the possibilities in such a system. Occasionally air-borne diseases may involve more than two components as in the synergistic production of disease in the white blister rust of cabbage, and there is also the possibility that the phyllosphere (4) might affect the outcome as has been recorded by Bamberg (5) and Koch (6), but there is no indication that such phenomena are either general or generally considered in air-borne disease. In soil, by contrast, it is the simple condition, H;:=P, that is uncommon, even rare. It occurs occasionally, owing to bad technique in hydroponics or in plant culture in sterilized composts. Where such a situation is allowed to develop disease is often exceptionally severe, and even organisms not

Violet-Pigmented Pseudomonads With Antifungal Activity From the Rhizosphere of Beans

Bean rhizosphere bacteria antagonistic to four root-infecting fungi and an antibiotic produced by these bacteria were studied. The bacteria were violet-pigmented gram-negative rods, probably belonging to the genus Pseudomonas. The antibiotic, which was localized largely in the bacterial cell mass, was easily extracted with acetone. It was selectively active against a wide variety of plant-pathogenic and saprophytic fungi tested in vitro but was relatively inactive against bacteria. The compound, partially purified by chromatography, was soluble in all organic solvents tried, but nearly insoluble in water. It demonstrated no characteristic ultraviolet- or visible-absorption spectrum and was chemically unidentified. The antagonistic bacteria or crude antibiotic applied to buried buckwheat segments suppressed the colonization of this substrate by Rhizoctonia spp. The data suggested that the bacteria or the antibiotic may play a role in the suppression of root-infecting fungi in soil.

Factors affecting competitive saprophytic colonization of the agar plate by various root-infecting fungi

Growth rates of fourteen root-infecting fungi in the presence of competing soil micro-organisms were measured on Cellophane film overlying plates of Czapek-Dox + 0·05% yeast-extract agar, which were inoculated with unsteri-lized soil at 0–48 hr. before inoculation of the overlying Cellophane with the fungus under test. The results obtained were not significantly affected either by the pH of the agar or by the incorporation of 0·005% streptomycin to check growth of bacteria. Results reported by Rao (1959) in these Transactions , using an agar plate modification of the “Cambridge method” for estimating competitive saprophytic colonization, were confirmed and extended, particularly with respect to the effect of age of the pure-culture inocula employed for making up inoculum/soil mixtures. Integration of results obtained by the Cellophane technique and by Rao's method suggests that the success of a fungus in colonizing the agar plate from a mixed inoculum can be predicted simply from a measurement of its linear growth rate in pure culture. No correlation was found between success in saprophytic colonization and tolerance of a fungus to antibiotic effects. It is therefore concluded that the outcome of the struggle for colonization of the agar plate is largely decided by the relative linear growth rates of the competitors before significant antibiotic effects are produced.

COMPARATIVE RESPONSE OF TWO SAPROPHYTIC AND TWO PLANT PARASITIC SOIL FUNGI TO TEMPERATURE, HYDROGEN-ION CONCENTRATION, AND NUTRITIONAL FACTORS

The behavior of two soil saprophytes, Trichoderma viride and Trichocladium asperum, and two root-infecting fungi, Ophiobolus graminis and Fomes annosus, was compared under various conditions in laboratory culture.On an agar-solidified organic medium optimum temperatures for growth were approximately: T. viride 25–30 °C, T. asperum 20–25 °C, O. graminis 20–25 °C, F. annosus 25 °C. T. viride rapidly outgrew the other fungi in the optimum range but this relationship changed at lower temperatures, its growth rate being equalled by that of O. graminis at 10 °C. T. viride was the only fungus to grow at 35 °C. In a synthetic liquid medium adjusted to pH values from 3.0–7.0 with a citrate–phosphate buffer, growth of O. graminis and F. annosus was sharply reduced at pH values below 5.0. T. viride made good growth at pH 3.1 and reduction in growth of T. asperum occurred only below pH 4.0. Both parasites required thiamine for growth in a synthetic medium and O. graminis also required biotin; in addition they showed a preference for organic as opposed to inorganic nitrogen sources. T. viride and T. asperum grew well with KNO3 as nitrogen source and neither required vitamins. D-Glucose, D-fructose, and D-mannose were readily utilized, and D-arabinose poorly utilized, by all four fungi. Utilization of other hexoses, pentoses, disaccharides, and polysaccharides varied considerably between the fungi.The relationship of the results obtained to the observations of others on the ecology of soil fungi is discussed and the possibility that combinations of physical and nutritional factors may favor specific fungi in the soil is considered.

Strain Differentiation in a Root-infecting Fungus

IN various fields of mycology it has long been realized that, for certain purposes, the orthodox descriptive method of systematic classification is by no means adequate. Fungal strains grouped together on the bais of similar physiological reactions have been found to cut right across species of diverse taxonomie affinities, and it appears that in such disciplines as, for example, clinical medicine, agriculture, and forest pathology, the strain rather than the species is frequently of importance.

A comparative study of competitive saprophytic ability in twelve root-infecting fungi by an agar plate method

The agar plate method is a modification of the ‘Cambridge method’ for the estimation of competitive saprophytic ability, as developed by F. C. Butler and R. L. Lucas. A pure culture of the fungus to be tested is grown upon maizemeal-sand medium and mixed with an unsterilized soil in a series of dilutions. From these inoculum-soil mixtures, solidified by impregnation with water agar, disks are cut out and plated upon Czapek-Dox + 0·05% yeast-extract agar, acidified to pH 4·0. By this method, the following were classed as vigorous saprophytes: Fusarium culmorum, F. avenaceum, F. oxysporum f. cubense, F. oxysporum f. vasinfectum, F. caeruleum and Curvularia ramosa . Saprophytes of intermediate ability were Helminthosporium sativum (isolate 1) and Macrophomina phaseoli . The following behaved as poor saprophytes: Verticillium dahliae, H. sativum (isolate 2), Rhizoctonia solani, Fomes annosus and Ophiobolus graminis . These results agree well enough with earlier observations by other methods, except for the poor saprophytic performance on the agar plate of M. phaseoli and R. solani , which can certainly colonize, as competitive saprophytes, certain substrates in the soil. It seems, therefore, that the agar plate method provides conditions of competition more intense than those associated with some natural substrates in the soil.

A Technique for the Investigation of the Competitive Saprophytic Ability of Soil Fungi by the Use of Easily Decomposed Substrates

THE method commonly used to determine the competitive saprophytic ability of soil fungi consists of exposing suitable substrates to colonization by the fungus in non-sterile soil. A serious disadvantage of this method is that only relatively resistant substrates, for example, wheat straw, can be used effectively because of the manipulation to which the substrate has to be subjected after incubation. Less-resistant substrates such as portions of non-woody roots, rhizomes and cylinders or disks of storage parenchyma of carrots or potatoes, etc., are so softened by the action of soft-rotting organisms in the soil that it becomes difficult to cleanse them adequately of adhering soil, and hence to state with confidence that fungi isolated from them have actually colonized the substrate in competition with the general soil microflora. It is very important to test the suitability of any potential substrate, for, as Garrett1 has pointed out in the case of root-infecting fungi, one is usually trying to demonstrate a negative character, that is, inability to compete as a soil saprophyte, and to obtain the strongest circumstantial evidence the killed host must be used as the substrate. A substrate such as wheat straw can probably only yield evidence relevant to fungi pathogenic to wheat or at most to cereals; hence the need to be able to employ any substrate that suggests itself. Since the chief obstacle to the use of soft tissues as substrates is the difficulty of removing the unwanted soil, the present method has been designed to prevent all unnecessary contact with the soil.