Showing papers on "Mycelium published in 1972"

A morphological and genetic mapping study of white colony mutants of Streptomyces coelicolor.

Abstract: SUMMARY: Fifty whi mutants of Streptomyces coelicolor, having white instead of the wild-type grey colonies, were examined microscopically and genetically. The aerial mycelium structure of the mutants was broadly classified into six types, ranging from the complete absence of any stage of sporulation to the presence of apparently normal spores. Eight map locations were discovered for whi genes, all in previously well-marked regions of the map. Closely linked mutations possessed similar aerial mycelium structure, with few exceptions.

Release of Protoplasts from Schizophyllum commune by a Lytic Enzyme Preparation from Trichoderma viride

Abstract: SUMMARY: Spherical, osmotically sensitive protoplasts were liberated from the mycelium of Schizophyllum commune through the action of an extracellular enzyme preparation from the culture filtrate of Trichoderma viride grown on hyphal walls of the former organism. The conditions for obtaining stable protoplasts were determined. Maximum numbers of protoplasts were released from young growing mycelium by using MgSO4 or KCI at an osmotic potential between —12.8 and —17.8 atm in the presence of 0.05 M-maleic acid-NaOH at pH 5.8. Protoplasts were released through ruptures in the wall, initially at the apices, but later also from older parts of the hyphae.

The morphogenesis and possible evolutionary origins of fungal sclerotia

Abstract: Summary 1. Fungal sclerotia are able to survive adverse conditions for long periods and they are formed by many important plant pathogens. An understanding of the factors involved in their initiation and development may lead to a method of repressing their formation in nature, thereby reducing the chances of survival of fungi that depend on them as persistent resting stages in their life-cycles. Also, data on sclerotial morphogenesis may be applicable to other multihyphal fungal structures. 2. There are three types of sclerotial development. The most primitive and least common is the loose type, which is illustrated by Rhizoctonia solani. The sclerotium forms by irregular branching of the mycelium followed by intercalary septation and hyphal swelling. When mature, it consists of loosely interwoven hyphae that are rich in food reserves and darkly pigmented. The main types of development are terminal and lateral. The former develops from the coalescence of initials that are produced by a well-defined pattern of branching at the tip of a hypha or tips of closely associated hyphae, e.g. Botrytis cinerea. Lateral sclerotia are formed by the interweaving of side branches of one or several main hyphae. When only one main hypha is involved the sclerotium is of the lateral, simple type, e.g. Sclerotinia gladioli. If several main hyphae give rise to a sclerotium, the term strand type has been used. Sclerotium rolfsii is the classical example. 3. There is a considerable literature on the effects of environmental conditions on the initiation, development and maturation of sclerotia but few attempts have been made to interpret the data. Phenolics and/or polyphenol oxidases have been found to be connected with morphogenesis of the protoperithecium of Neurospora crassa, the perithecium of Podospora anserina and of Hypomyces sp. and the basidiocarp of Schixophyllum commune. A close correlation has been shown between melanin synthesis and microsclerotial development by Verticillium but there appears to be no literature on the role of phenolics and polyphenol oxidases in the morphogenesis of sclerotia. Possibly these substances may inhibit growth of the apices of main hyphae by changing the permeability of the membrane, by inducing a thickening of the cell wall at the tip or by reducing the plasticity of the wall. Such a check in growth could trigger-off the formation of initials close to the margin of the colony or elsewhere in the culture. Sulphydryl groups and disulphide bonds are of great significance in morphogenesis of organisms and are probably involved in sclerotial initiation. The formation of a large number of hyphal branches is a prerequisite for sclerotial initiation and mycelial branching is possible only if there is plasticity of hyphal walls. The ability of the wall to be moulded is possibly related to changes in the sulphur linkages of the protein of the protein-carbohydrate complexes of the cell wall and could be influenced by sulphur availability or the activity of specific enzymes. 4. After a sclerotial primordium has been initiated, further increase in size will depend on the continued, active translocation of nutrients to the site of development. Movement of nutrients to sclerotia is through a few translocatory hyphae. Presumably, nutrients will continue to move into the young sclerotium as long as a concentration or pressure gradient is maintained. Energy and substances for the formation of new branches are supplied in this way and as the requirements for hyphal branches are reduced, excess nutrients become available for conversion to inactive or insoluble reserves and for exudation. The exudates are often complex, consisting of proteins, including enzymes, lipids and carbohydrates. Many sclerotia have a mucilaginous matrix in which the medullary hyphae are embedded. Sclerotium-forming, fungal species that are not regarded as having such a matrix appear to secrete a layer of mucilage over the surface of sclerotial hyphae. This mucilage could have a morphogenetic function and serve as an adhesive which loosely binds hyphae together. More permanent unions are by hyphal fusions or anastomoses. 5. The sclerotium matures within a few days of attaining its maximum size. The rind effectively seals off the medullary hyphae from the surroundings and the translocatory hyphae cease to function. Thus the sclerotium is isolated both physiologically and nutritionally. The endogenous reserves enable the structure to exist in the absence of exogenous nutrients and then, when conditions become suitable, to germinate. 6. The sclerotium appears to provide an example of convergent evolution whereby analogous structures, which have become adapted to resist adverse conditions, have evolved. Data are available mainly for Typhula spp. and ScZerotinia spp. Sclerotia may be degenerate sexual reproductive structures, hyphal aggregates that have developed from closely interwoven conidiophores and undifferentiated conidia or they may be modified vegetative structures.

An automatic, multichamber soil-washing apparatus for removing fungal spores from soil

Abstract: An automatic soil-washing apparatus is described which enabled the washing of fungus spores out of large numbers of soil samples simultaneously. Tests of the apparatus indicated that superficial spores were removed from most of the soil particles. This allowed organisms growing in soil as vegetative mycelium to be isolated more readily without the serious competition commonly encountered from organisms sporulating heavily in the soil. Virtually no cross-contamination of soil samples occurred in the multichambered apparatus.

Carbohydrate metabolism in the fungus dendryphiella salina

Abstract: Summary When Dendryphiella salina was grown on non-saline media, mannitol and arabitol were the only polyols present in the mycelium. In media made up with sea-water or salinized by high concentrations of salts of potassium, sodium and magnesium, glycerol was also present. When mycelium grown in sea-water was transferred to distilled water, the glycerol content dropped very rapidly to zero. The amounts of mannitol and arabitol also declined. Transfer of similarly grown mycelium to sea-water alone reduced the rate of decline of glycerol, caused little change in the amount of mannitol and induced a rise in that of arabitol. These observations help to explain the absence of glycerol in mycelium in previous studies. The concentration (mol l−1) of solutes within mycelium were determined after 48 h growth in the presence of either sodium chloride, magnesium chloride, sodium sulphate, inositol or betaine at either 0.4 or 0.8 osmol kg−1water. There was a very similar total polyol concentration at each osmolality in the saline media irrespective of the salt, even though there could be different concentrations of individual polyols. With inositol in the medium, the same held if the endogenous concentration of that compound was included in the total. The same did not hold for betaine, in which medium growth was poor. The total polyol concentration increased in all cases with the osmolality of the medium. With respect to the total concentration of solutes present (excluding data for mycelium grown in betaine), polyols were 19 to 33 % of the total, α-amino nitrogen, 11 to 34% and organic acids, 0 to 8 %. These percentages take into account data obtained by 24Na-flux studies, which indicate that, in media containing sodium salts, much of the mycelial content of the cation may be located in the wall.

クルマエビの鰓黒病病原菌Fusarium sp.について

Abstract: A member of the imperfect fungi was isolated on a soytone-dextrose agar medium with chloramphenicol and cycloheximide from gill lesions of Penaeus japonicus BATE infected with black gill disease. Intramusculaly inoculation of conidia of the fungus caused invariably black gill disease in prawns, and the fungus could be isolated from gill lesions of artificially-infected prawns. The gills of healthy prawns were alway free of the fungus. Therefore the fungus was regarded as the pathogenic agent of black gill disease. The fungus produces mainly 4-celled, canoe-shaped macroconidia and 1-celled microconidia. Usually the mycelium is hyaline, but it characteristically produces a brown pigment when grown on the above-mentioned medium, salt Sabouraud's medium, and a salt potato-dextrose agar medium. On the basis of morphological criteria, this fungus fits best in the genus Fusarium.

Multiple molecular forms of enzymes in barley leaves infected with Erysiphe graminis f.sp. hordei

Abstract: Multiple molecular forms of 14 enzymes (isoenzymes) from near-isogenic barley lines inoculated with powdery mildew were studied by polyacrylamide disk electrophoresis. Following inoculation of the susceptible line (ml-g) the number of isozyme bands of acetylesterase, acid phosphatase, malate dehydrogenase (NADP), succinate dehydrogenase and peroxidase increased. These new bands were not detected in extracts of healthy tissue or mycelium and conidia from infected leaves; their intensity was not reduced by removing mycelium and conidia before preparing extracts. Only the new peroxidase band appeared within one day after inoculation. Eleven enzymes from inoculated susceptible lines showed an increase in intensity of one or more bands within 7 days; four enzymes showed a decrease. A hypersensitive line (Ml-k) showed changes after inoculation that were similar to those of the susceptible line. With a resistant line (Ml-g) there was an intensity increase in one or more bands of seven enzymes within 7 days after inoculation. Such changes in the multiple molecular forms and activity of enzymes are biochemical symptoms of disease, may be a basis for the increased metabolism associated with infection and suggest profound interactions between parasite and host.

In vitro and in vivo production of cell wall degrading enzymes by Botrytis cinerea from tomato

Abstract: The production and activity of pectolytic and cellulolytic enzymes byBotrytis cinerea in tomato plants, as well as by conidia of this fungus in some nutrient media was studied. In inoculated tomato plants, the activity of these enzymes varied. PME, endo-PG and exo-PG were produced in petioles and fruits, while cellulase was only found in those parts which were softened by the invading mycelium. PGTE could only be detected in the softened parts of the petiole stumps. In suitble substrates, PME, endo-PG and exo-PG are produced rapidly with the onset of germination of the conidia. At some temperatures, endo-PG activity was found before germination could be observed. Some endo- and exo-PG was detected in washing water of conidia. The significance of the production of these enzymes by germinating conidia in relation to the infection process on tomato plants is discussed.

The nutrition of the subcuticular mycelium of Rhynchosporium secalis (barley leaf blotch): permeability changes induced in the host

Abstract: The fungus Rhynchosporium secalis grows for 10 to 14 days after infection beneath the cuticle of barley leaves. Soluble nutrients which are present in the free space of the leaf are available for utilization by the fungus. Within 3 days after infection, and at least 7 days before the first disease symptoms appear, the fungus causes an increase in the permeability of the underlying host cells so that the concentration of nutrients in the free space is increased. The increase is greater in a susceptible than in a resistant host variety. Evidence is presented that R. secalis does not produce, in vitro , toxic metabolites which specifically affect host membranes.

Trisporic acid synthesis in mated cultures of the fungus Blakeslea trispora

Abstract: 1. At least part of trisporic acid (TA) synthesis in a mated culture of the fungus Blakeslea trispora proceeds by secretion of mating-type-specific precursor molecules by both mating types, and conversion of these molecules to TA by the mating partner. 2. The contribution of the minus strain to TA synthesis is dependent on the amount of plus mycelium present. On the other hand, the contribution of the plus strain is influenced by the biosynthetic activity of the minus mycelium 3. This mutual stimulation of both sexual partners is abolished by 5-fluorouracil.

Mushroom virus disease in the Netherlands : symptoms, etiology, electron microscopy, spread and control

Abstract: During the 1960s, Dutch mushroom farmers suffered severe losses from an infectious disease. Three types of virus particles were associated with the disease: isometric particles 25 and 34 run in diameter and bacilliform particles 19 run wide and 50 nm long. Symptoms were highly variable. Two, possibly three types of particle, were demonstrated in ultrathin sections of diseased fruiting bodies; one type, the 34-nm particle, was observed in sections of virus-infected mycelium from a nutrient medium and of basidiospores from diseased mushrooms. The disease spread with viable mycelium and spores from infected mushrooms. The time of infection governed loss of yield: earlier infection considerably reduced yield, whereas later infection did not. Results of the trials were used in drawing up control measures, which have been implemented among Dutch growers and have considerably reduced national losses, as shown by annual returns from the growers.

Filobasidum capsuligenum nov. comb.

Abstract: Leucosporidium capsuligenum Fell et al. is classified in the genusFilobasidium Olive sinceTilletia-like basidia were discovered growing out from a dicaryotic mycelium with clamp connections. The speciesFilobasidium floriforme andFilobasidium capsuligenum are compared morphologically and physiologically.

Spore germination and ribosomal activity in the rust fungi I. Comparison of a bean rust fungus and a culturable wheat rust fungus

Abstract: Ribosomes from uredospores of the as-yet-uncultured bean rust fungus ( Uromyces phaseoli ) and the culturable Australian wheat rust fungus race 126-ANZ-6,7 ( Puccinia graminis f. sp. tritici ) were compared for transferase activity, capacity to bind polyuridylic acid and capacity to incorporate leucine into ribosomes in vivo . While the ribosome activities in bean rust uredospores declined before the germ tube was formed, these activities were maintained by ribosomes from the Australian wheat rust fungus. Mycelium derived from uredospores of the wheat rust fungus, and continuously subcultured for 4 years, had ribosomes that were three times more active in the transferase assay than ribosomes from uredospores.

The effect of aromatic compounds on cellulase and xylanase production of fungi schizophyllum commune and chaetomium globosum

Abstract: This study of the effect of phenolics and higher aromatic compounds on cellulase and xylanase production by wood-destroying fungi, showed an interference with the induction of enzymes. The mycelium age also influences the extracellular enzyme production.

Effects of various soil fungi and insecticides on the capacity of Mucor alternans to degrade DDT.

Abstract: Pure cultures of the fungus Mucor alternans, isolated from DDT-contaminated soils, were able to degrade DDT to water-soluble metabolites. After the addition of fungal spores to DDT-contaminated soils, however, the insecticide-degrading capacity of the fungus was no longer evident. Since under field conditions many species of fungi are simultaneously exposed to mixed residues of pesticidal chemicals, the effects of various species of soil fungi and of various insecticides on DDT degradation by M. alternans were investigated. Experiments were conducted to study the effect of nine fungal species, their stale cell-free media, and various insecticides and related compounds on the capacity of M. alternans to degrade 14C-DDT to water-soluble metabolites. It was found that several pure fungal cultures or some cell-free media, in which mycelia had grown, could also degrade the insecticide. In most cases, however, addition of one of the various fungi to 14C-DDT-treated M. alternans cultures resulted in a total depr...

The character of endogenous growth regulators in the course of development in the fungus Lentinus tigrinus.

Abstract: The character of endogenous growth regulators in different stages of growth and development ofLentinus tigrinus was followed by means of bioassays. The methanolic extract of differently old mycelium and fruiting body was chromatographically separated and tested for auxins by means of Avena coleoptile segments, for gibberellins by using lettuce seedlings and for cytokinins by measuring the content of chlorophyl in leaf segments of barley. Auxins were found only in young vegetative mycelium and in the growing young stalk. The level of gibberellins is more significant and it reaches the highest values in the vegetative mycelium, in the growing young stalk and in the differentiated cap. The content of auxin and gibberellin substances did not increase even in the medium after cultivation of mycelium. Bioassays of cytokinins show a slight stimulation in the vegetative mycelium and in the primordia of caps. Significant inhibition was ascertained in the fully developed stalk. The high quantities of cytokinins were found in caps when basidiospores were formed. The results show a close connection of endogenous growth substances with the growth and the development of the fungus and indicate their participation in differentiation processes.

Changes in Total Soluble Proteins and in Some Enzymes during Morphogenesis of Sclerotium rolfsii

Abstract: SUMMARY: Patterns of soluble proteins and enzymes were studied in the normal mycelium of the fungus Sclerotium rolfsii and at three stages of sclerotial formation. Significant changes in total soluble proteins were found during the morphogenetic process, as detected by gel isoelectric focusing. While no changes could be detected in acid phosphatase activity, peroxidase activity was higher in mature sclerotia than at other stages. Polyphenol oxidase activity was demonstrated with dihydroxy-phenylalanine, catechol and tyrosine as substrates. While only one active isozyme of the latter enzyme was found in the mycelium, six different isozymes were detected in the mature sclerotia. Esterase isozymes, on the other hand, decreased significantly during morphogenesis.

Dependence of Fruit-Body Elongation on the Mycelium in Flammulina Velutipes

Abstract: Flammulina velutipes (Curt, ex Fr.) Sing, fruit bodies were grown on potato dextrose agar. Their fresh and dry weights increased during the elongation phase up to a length of 13–14 cm which was clo...

Distribution of Wall-bound Invertase during the Asexual Life-cycle of Neurospora crassa

Abstract: Summary: The association of invertase with Neurospora wall was studied biochemically in six cytologically distinct stages of the Neurospora asexual life-cycle: (i) conidia, (ii) mid-log phase [10 h old], (iii) post-log phase hyphae [18 h old], (iv) aerial mycelium [4 days old], (v) submerged mycelium [4 days old], and (vi) mycelium [2 days old] induced to form conidiophores. The percentages of total invertase activity found in the wall fraction were 8, 18, 23, 8, 21 and 17, respectively. The specific activities of the wall fraction were 3, 85, 120, 40, 24, and 74 units of invertase activity per milligram protein, respectively. Histochemical localization of invertase with an indirect immunofluorescent technique also showed that conidiophores had strong activity in their walls as well as in the cytoplasm and that vacuoles were devoid of any activity.

Mechanism of translocation of potassium in mycelium of Phycomyces Blakesleeanus in an aqueous environment

Abstract: Measurements of rates of translocation of potassium in mycelium of Phycomyces blakesleeanus suggest that the movement of potassium in this system may occur by diffusion alone. It is not necessary to involve bulk flow of cytoplasm as a contributory factor. The forces causing the translocation of potassium are the intracellular concentration gradient of potassium and an intracellular electrical potential gradient. The latter gradient is the sum of two contributions: one is an indigenous electric potential gradient in the mycelium (negative towards the apices); the other is an induced potential gradient caused by the extracellular concentration gradient of potassium.

Changes Produced by Botrytis Cinerea Pers. in Finished Wines

Abstract: Lyophilized Botrytis cinerea Pers. mycelium was added to three varietal white wines: Sauvignon blanc, French Colombard, and Thompson Seedless. Changes in headspace composition with time were monitored by gas chromatography (GC). Three components (acetaldehyde, l-,l-diethoxyethane, and 2,4,5-trimethyl-1,3-dioxolane) underwent major increases in concentration, while a number of other compounds changed in concentration to lesser extents. Thirty-five headspace constituents were identified by GC-mass spectrometry. Compositional changes were shown to be dependent upon the presence of viable mycelium in the wine samples; heat-inactivated mold caused no corresponding aroma changes.

The infection and perennation of the bitter rot fungus, Gloeosporium album, on apple leaves

Abstract: SUMMARY In the period from late spring to leaf-fall (May-November) Gloeosporium album Osterw. was regularly isolated from leaves of the apple variety Cox's Orange Pippin affected by the disorder called ‘Cox-spot’. The fungus grew epiphytically on healthy apple leaves, producing a network of mycelium which developed sporulating pustules when in contact with damaged or moribund tissues. Both the imperfect and perfect stages of the fungus were found on overwintered leaves; isolates from ascospores and conidia proved pathogenic on wood and fruit.

Histology of infection and sporulation by saprophytic cultures of Melampsora lini inoculated onto flax cotyledons in sterile culture

Abstract: Saprophytic mycelium of the rust fungus Melampsora lini (Ehrenb.) Lev., race 3, invaded the wounded ends of detached cotyledons of Bison variety flax placed on suitable agar media. A normal parasitic relationship was established within 4 weeks, as shown by the presence of numerous haustoria. The rust mycelium invaded intercellular spaces in the cotyledons as well as in well-established adventitious roots. Uredosori formed mainly on thickened parts of the cotyledons, adjacent to callus tissue. Nuclei in uredospores were difficult to observe but in general there seemed to be two per spore. Teliosori formed infrequently under the conditions used but in some cultures they did develop on the cotyledons and on the oldest parts of adventitious roots. Teliospores were uninucleate.

Nutrient-dependent inhibition of perithecial development due to sequential crosses on the same mycelium of Neurospora tetrasperma.

Abstract: An explanation of perithecial inhibition in the second of two sequential crosses at different locations on the same mycelium of Neurospora tetrasperma was sought by (1) assaying media that had supported inhibited and uninhibited portions of the mycelium which contained no developing perithecia, (2) determining the effect of these media on perithecial development, (3) adding nutrients to inhibited portions of the mycelium, and (4) assaying carbon sources in media that had supported portions of the mycelium which contained developing perithecia, and portions, both inhibited and uninhibited, which contained no developing perithecia. Different kinds and volumes of media and various intervals of time between sequential crosses were used to aid in determining limits of perithecial inhibition. Perithecial inhibition was observed to be independent of volatile metabolites and pH, independent of non-volatile metabolites, reversible by addition of nutrients, dependent upon nutrient volume, and correlated with the concentration of the carbon source in the medium. It is proposed that second crosses are inhibited because of a previous lowering of the concentration of nutrients in the medium in second-cross locations, owing to prior demand upon those nutrients by the developing perithecia in first-cross locations. The possibility of an activation signal between first- and second-cross locations is discussed. No inhibitory substance in inhibited locations was detected.

Influence of light on hülle cell and aleuriospore formation in Aspergillus

Abstract: Hulle cell formation was directly dependent on darkness in strains of Aspergillus versicolor, A. ustus, A. flavipes, and A. niveus. On four different nutrient media hulle cells were observed exclusively or more abundantly in colonies grown in the dark. Aleuriospores in one strain of A. flavipes, although present in colonies cultivated in light, were produced in significantly greater quantities in cultures grown in the dark. Such effects are similar to those in other Aspergillus species where Sclerotium and cleistothecium formation are influenced by dark. Two divergent chains of events seem operative: one, affected by light, is conducive to early differentiation of hyphae and formation of the conidial apparatus; the other, affected by darkness, favours the normal development of mycelium and the successive events which lead to the production of such structures as sclerotia, aleuriospores, hulle cells, and cleistothecia.

Presence of carotenoids and ergosterol inMucor azygospora and inMucor inaequisporus

Abstract: The yellow-orange mycelia ofMucor azygospora andM. inaequisporus were analyzed for the presence of carotenoids.Mucor azygospora contained 7 carotenoids with γ-carotene as the principal pigment andMucor inaequisporus the same carotenoids with Β-carotene predominating. The steroid ergosterol was obtained in a crystalline state from the unsaponifiable fraction of both fungi.

[Breeding experiments with strain 59 c, a strain of mushrooms having a new type of fruiting body : II. Cytological investigations].

Abstract: 1 Cytological examinations of mycelia of strains 59b and 59c were made in order to determine whether the nuclei in the mycelia of strains 59b and 59c differ in number and size Cultures of strain 59c, which form large, massive fruiting bodies, degenerate easily into the low-yielding puffball-like ancestral form 59b when the mycelium is propagated by transfer 2 Strain 59c has been propagated by several methods (tissue cultures, cultures of pieces of hyphae, and direct transfer of mycelia) For the 59c-type propagation culture "SS 585, 1V" was used a culture of pieces of hyphae New tissue cultures and the mycelium of a monospore culture which forms normal, white fruiting bodies, were examined also 3 The nuclei were stained by a slightly modified "HCL-Giemsa" method 4 Strain 59c showed a statistically significant increase in the number of nuclei when compared to strain 59b The latter strain showed the least variation as regards numbers of nuclei 5 Strain 59c furthermore showed a statistically significant increase in the size of nuclei when compared to strain 59b Whereas most of the nuclei of strain 59c measured from 172-782, almost all of the nuclei of strain 59b fell within the 015-393 size range 6 The mycelium of new tissue cultures of fruiting bodies of type 59c was examined after different treatments In hyphal cultures we try to obtain cells without nuclei of strain 59b, the influence of the environment on the number of nuclei is therefore of interest 7 The number of nuclei increased with increasing temperature The mycelia grown at 28 °C and at 24 °C had a statistically significant higher number of nuclei than the mycelia grown at 20 °C No statistically significant differences were found between the 24 °C and the 28 °C cultures 8 Mycelia grown on wheat-agar showed a statistically significant decrease in the number of nuclei when compared with mycelia grown on compost-agar

The reaction of near-isogenic lines of flax to the rust fungus melampsora lini i. host-parasite interface

Abstract: Two near-isogenic lines of the flax cultivar Redwing, differing in their reaction to M. lini (Pers.) Lev. f. sp. liniperda Koern race '300', were studied to elaborate on the nature of the resistance in flax. In the susceptible line (rr) the fungus developed normally, producing extensive mycelium and haustoria and finally uredospores. However, in line S-66-53 (RR) no haustoria were formed, but a hypersensitive reaction was induced upon inoculation. The fungus did not appear to establish any nutritional relationship in S-66-53. The genetic control of resistance as regulated by the R locus is discussed and a hypothesis is proposed to explain the induction of the hypersenitive reaction.