Pythium Myriotylum Research Articles

Evaluation of Amaranthus Accessions for Resistance to Damping-Off by Pythium myriotylum

Evaluation of Amaranthus Accessions for Resistance to Damping-Off by Pythium myriotylum

First Report of Pythium myriotylum on Sugarcane in Australia

First Report of Pythium myriotylum on Sugarcane in Australia

Peanut Pod Rot Complex: A Geocarposphere Nutrient Imbalance

Gypsum (CaSO4 · 2H2O), magnesium sulfate (MgSO4), potassium sulfate (K2SO4), ammonium nitrate (NH4NO3), and gypsum + magnesium sulfite, gypsum + potassium sulfate, and gypsum + ammonium nitrate were evaluated for their influence on the development of peanut pod rot in field test plots at Tifton, GA, in 1983–1984. Pythium myriotylum, Rhizoctonia sp., and Fusarium sp. were isolated from decaying pods, and fungal propagules from the soil were enumerated during the season. The involvement of these fungi in the disease was inconclusive. Peanut (Early Bunch) treated with gypsum tended to be higher in yield, lower in pod rot, and higher in percent sound mature kernels (%SMK) regardless of the accompanying treatment. Gypsum tended to ameliorate the harmful effects of potassium sulfate, magnesium sulfate, or ammonium nitrate by reducing concentrations of magnesium and nitrogen in the fruit compared with those found in peanuts treated with magnesium sulfate, potassium sulfate, or ammonium nitrate. Calcium in the fruit was negatively correlated (P = 0.01) with nitrogen, phosphorus, potassium, magnesium, other minor elements, and pod rot at harvest and was positively correlated with %SMK and yield. Evidence is presented for the hypothesis that the peanut pod rot complex is initiated by the same conditions that cause blossom-end rot of fruits.

Anatomical Traits Associated With Pod Rot Resistance in Peanut1

Abstract Peanut (Arachis hypogaea L.) cultivars resistant to Pythium myriotylum Drechs. and Rhizoctonia solani Kuhn, are needed for effective management of pod rotting diseases. The low efficiency of field screening for disease reaction in breeding for resistance has emphasized the need for improved evaluation methods. Anatomical examinations of roots, stems, leaves, pegs, and shells were made of six genotypes (TxAG-3, PI 341885, Toalson, Starr, Florunner, and Goldin I) with various degrees of resistance to pod rots in search of traits that might be used effectively in screening for disease reaction. The palisade mesophyll cells of 50-day old plants were arranged more compactly in pod rot resistant than in susceptible genotypes. An index representing total width (μm) of palisade cells/mm leaf blade was more discriminative in distinguishing among genotypes than average of either cell width or cell number alone. The distribution of lignin in peanut shells was correlated with pod rot resistance. The cell walls in the epicarp and sclerenchymatous mesocarp were thicker and more lignified in the resistant than in the susceptible genotypes. Genotypic differences in lignin distribution were readily apparent at 100x when shell sections were stained with phloroglucinol. Associations between anatomical traits of stems, pegs, roots, or juvenile plant leaflets and field pod rot reaction were not consistent among all genotypes. However, lignin-distribution in pods, and an index representing μm of palisade cells/mm of leaf blade individually or in combination, might be used effectively to supplement field evaluations in screening breeding lines for pod disease reaction.

Ｐｙｔｈｉｕｍ ｍｙｒｉｏｔｙｌｕｍによるクワイ茎腐病

Ｐｙｔｈｉｕｍ ｍｙｒｉｏｔｙｌｕｍによるクワイ茎腐病

Nursery diseases of Eucalyptus in Kerala1

AbstractSurvey of Eucalyptus (E, grandis and E. tereticornis) nurseries in Kerala State indicates that the most prevalent diseases are damping‐off, web blight and seedling blight in seedbeds and stem canker, leaf and shoot blights and Phaeoseptoria leaf spot in container plants. Cylindrocladium spp., Rbizoctonia solani and Pythium spp. arc the main serious pathogens. Pythium myriotylum, P. deliense, R. scilani, Cylindrocladium camellias, C. clavatum and Sclerotium rolfsii are recorded for the first time on Eucalyptus.

Evaluation of Six Peanut Genotypes for Pod Rot Resistance1

Abstract Six genotypes (TxAG-3, PI 341885, Toalson, Starr, Florunner, and Goldin 1) were evaluated for reaction to Pythium myriotylum Drechs, and Rhizoctonia solani Kuhn in the greenhouse to: 1) confirm field results as to the relative disease reactions of the entries; 2) ascertain whether peg versus pod exposure to pathogens confounds selection for pod rot resistance; 3) examine the utility of greenhouse inoculation in screening for pod rot resistance; and 4) evaluate simultaneous screening of plants for reaction to these fungi. Adult plants were exposed at two stages of fruit development. TxAG-3 had significantly less pod decay from each organism singly and in combination at both times of exposure to the pathogens than did the other entries. Exposure to the pathogens at the pegging and pod-filling stages of development produced similar results.

A Technique for Evaluating Peanut Germ Plasm for Resistance toPythium myriotylum

Peanut seedlings expressed stunt, wilt, and necrosis 6 days after inoculation with Pythium myriotylum zoospores. The amount of seedling disease was positively and significantly correlated with the degree of Pythium pod rot in maturing plants of peanut genotypes PI 365553, PI 378012, Toalson, Tamnut 74, and Florunner.

Underrow Ripping of Peanuts in Virginia1

Abstract The effects of underrow ripping on peanut yields have been studied for several years along with other tillage production practices. In this study, tillage treatments included no ripping and ripping under the plant row in combination with four methods of seedbed preparation. The bed preparations were prepared flat (conventionally), with a rotary tiller and bed shaper, with a disk bedder, and with a rolling cultivator. Test plots were planted at different locations each year to assess different soil conditions. To evaluate these tillage treatments, yield, grade, value, and incidence of pod breakdown were recorded. Results indicated that underrow ripping compared to not ripping directly under the plant row adversely affected crop yield and value in some soil conditions but had no effect in other soil conditions. Peanut roots penetrated the subsoil region even in soil types with an A2 layer. Under-row ripping appeared to enhance the incidence of pod breakdown, caused by Pythium myriotylum and Rhizoctonia solani. It does not appear to be an advantageous tillage operation to use in peanut production systems for southeast Virginia based on these responses and the additional energy required to perform the operation.

ダイズの連作障害とＰｙｔｈｉｕｍ ｓｐｐ．の関係

The soybean plants in monoculture plots in Hokkaido Prefectural Kitami Agricultural Experiment Station showed severe necrosis of roots, and their growth was retarded. Pythium myriotylum and Pythium sp., pathogenic to soybean plants, were isolated only from the necrotic root tissues in monoculture. When ridomil, N-(2, 6-dimethylphenyl)-N-(methoxyacetyl) alanine methyl ester, was drenched to the soil collected from the monoculture plots, the roots of soybean seedlings grown in the soil remained healthy. These results suggest that the symptoms of soybean plants in monoculture are caused by the infections of P. myriotylum and Pythium sp.

Effects of gibberellin A 3 and 2,4-D on plant and root exudate lipids and susceptibility to Pythium myriotylum

Gibberellin A 3 or 2,4-dichlorophenoxyacetic acid were applied to the foliage of peanut plants under axenic culture and in the greenhouse. Leaves, roots and exudates from axenically grown plants were analyzed for total lipids, free sterols, free fatty acids and paraffinic hydrocarbons. The total lipid concentrations of leaves, roots and root exudates were not altered. The free sterol of roots, and the paraffinie hydrocarbon concentrations of both leaves and roots increased, but the free fatty acid of root exudates decreased. Plants treated in the greenhouse were rated for disease severity after soil infestation with Pythium myriotylum. Roots of treated plants exhibited less rot than roots of non-treated plants. We believe there are possibilites of altering disease susceptibility using foliar applications of growth regulators through their effects on root lipids and root-lipid exudation patterns.

Nonparasitic pathogenesis of germinating tomato by Pythium myriotylum

Surface-disinfested seed of pepper, cowpea, sorghum, and three cultivais of tomato were placed onto petri dishes containing water agar amended with powdered, lyophilized mycelium of Pythium myriotylum cultured on a liquid, glucose–glutamate medium. Only the germinating seed of tomato cultivais were adversely affected. Hypocotyl length and root length of seedlings were reduced more than 42 and 74%, respectively, when grown on water agar amended with 25 μg/mL of P. myriotylum mycelium. At 250 μg/mL of mycelium, root tips and hypocotyls became necrotic, roots were discolored, and seedlings were killed. When we autoclaved the mycelium-amended water agar at pH values at or above 6.0, the activity of the mycelial toxin(s) was significantly decreased. Roots were affected more than hypocotyls by the toxin(s). Mycelial suspensions which were sterilized by sonication were more toxic than suspensions that were autoclaved. The data support the report that P. myriotylum produces toxin(s) active on tomato and suggest that P. myriotylum mycelium contains toxin(s) that may play a role in preemergence damping-off of tomato. Toxin(s) from soil-borne fungi may be involved in poor crop performance.

Parasitic and nonparasitic pathogenesis of tomato plants by Pythium myriotylum

Tomato plants grown in soil infested with Pythium myriotylum or in soil containing nonviable mycelium were severely stunted. Mycelium of P. myriotylum was produced on a glucose–glutamate–cholesterol medium, separated from the medium, lyophilized, and ground into a fine powder in a Waring blendor. Tomato plants transplanted into steam-pasteurized soil with the addition of 200 mg of the nonviable mycelium developed foliar necrosis and were severely stunted. Seedlings with roots immersed in an autoclaved aqueous suspension of the mycelium (100 μg/ml) developed laminar collapse and dehydration within 12 h and were killed within 24 h. Detached tomato leaves behaved similarly. On autoclaving, the toxin associated with the mycelium of P. myriotylum was relatively stable below pH 6 but labile at pH values above 6. Treated leaves lost more fresh weight at 35 °C than at 27 or 22 °C. Evidence for variability in toxin production within P. myriotylum was obtained. Toxin(s) in the mycelium of P. myriotylum may be involved in reduced growth and death of tomato plants. This is the first known report of toxin production by P. myriotylum.

Mycoparasitism of oospores of Pythium and Aphanomyces species by Hyphochytrium catenoides

Oospores of Pythium myriotylum in nonsterile soil extracts became invaded by a fungus that was isolated and identified as Hyphochytrium catenoides. Sporangia of H. catenoides formed as spherical or ovoid lobes within the Pythium oospore and as radial catenulate swellings on agar media. In water, these sporangia formed short exit tubes through which anteriorly monoflagellated zoospores were released. Oospores of P. myriotylum and Aphanomyces euteiches placed in suspensions of motile zoospores of H. catenoides became extensively invaded within 48 h. Oospores of Pythium aphanidermatum and P. ultimum were also attacked, but these species were less susceptible to invasion than was P. myriotylum. Sporangia, hyphae, and zoospores of the Pythium spp., A. euteiches, and several other phycomycetes were not observed to be invaded. Zoospores of H. catenoides were formed and released in water adjusted to pH 5.0–7.0 and at temperatures of 10–35 °C, but were produced most abundantly and were most highly motile at pH 6.0–7.0 and at 20–30 °C. The roots of several crop plants did not appear to be parasitized by H. catenoides. Oospores of P. myriotylum, P. aphanidermatum, and P. ultimum in moist soil artificially infested with these species and H. catenoides were destructively invaded by the mycoparasite. Its presence in several soils and its ability to reproduce quickly in its parasitic stage suggest that H. catenoides may play a role in the natural decline of susceptible Oomycetes in soil.

Pathogenicity of Pythium myriotylum isolated from strawberry roots in Japan.

Pathogenicity of Pythium myriotylum isolated from strawberry roots in Japan.

Comparative Pathogenicity of Pythium myriotylum and P. irregulare to the Soybean Cultivar Bragg

Comparative Pathogenicity of Pythium myriotylum and P. irregulare to the Soybean Cultivar Bragg

Pathogenicity of Pythium myriotylum and Other Species of Pythium to Caladium Derived From Shoot-Tip Culture

Pathogenicity of Pythium myriotylum and Other Species of Pythium to Caladium Derived From Shoot-Tip Culture

Histopathology of infection of bean with Pythium myriotylum compared with infection with other Pythium species

Clusters of abundant appressoria formed from branching hyphae of mycelial inoculum of Pythium myriotylum on the surface of bean hypocotyls and roots. Pythium aphanidermatum usually produced single appressoria, but sometimes small clusters of appressoria. Pythium ultimum produced only single appressoria. Early pathogenesis of all species was characterized by rapid radial growth of hyphae in the epidermal cells, which was more rapid than in the cortex. These hyphae were constricted at the host cell walls. Invaded tissue and adjacent cells stained differently from healthy cells with all isolates. Aerial hyphae were produced from vesicles below the cuticle or within epidermal cells soon after infection was established. Safranin-staining materials were observed in the xylem, phloem, and tannin sacs. Zoospores of P. myriotylum and P. aphanidermatum germinated and produced long prepenetration hyphae, which branched and formed single appressoria. Oospores of P. myriotylum, P. aphanidermatum, and P. ultimum, after germination, produced branched hyphae and single appressoria. Penetration, rapid advance through epidermal cells, and ramification of cortical and vascular tissue were identical with those of mycelial inoculum. Sporangia of all three species formed intercellularly and intracellulary within 48 h and predominantly in the epidermis and upper cortex. Oogonia were produced intercellularly and intracellularly in 4 day s throughout the tissue, but mainly in the inner two thirds of the cortex. Sporangia of P. myriotylum and P. aphanidermatum in infected bean hypocotyls germinated within 3 h when flooded with tap water and produced zoospores within 6 h. When similar tissue was air-dried for 3 days or rapidly dried for 3 h. there was neither germination nor zoospore production.

Eradication of plant pathogenic fungi in soil and nursery potting mixtures with a mobile continuous soil pasteurizer

A mobile continuous soil pasteurizer was evaluated for the eradication of soil-borne plant pathogenic fungi by assaying soil or infested potting mixture after treatment by selective cultural plating techniques and by host infection. Population of Pythium spp., Rhizoctonia solani, Fusarium spp., and other plant pathogenic fungi were eliminated from field soil after exposure to 80 ± 2°C for 30 min. Phytophthora parasitica, Pythium myriotylum, and Rhizoctonia solani were eliminated from an infested potting mixture treated at 60, 70, or 80°C. Aspergillus niger was recovered from the infested potting mixture at all of the temperatures tested. No papaya, peanut, rye, or tomato seedlings survived in potting mixture treated at a temperature below 40°C, but all seedlings survived in potting mixture exposed to 60, 70, or 80°C. No symptoms of phytotoxicity were noted in any of the plants at any of the treatments employed in this study.

Density of Pythium myriotylum Oospores in Soil in Relation to Infection of Rye

Density of Pythium myriotylum Oospores in Soil in Relation to Infection of Rye