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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.

1. In the vicinity of Kyoto I have isolated two species of Pythium from water. They were identified with Pythium aphanidermatum (EDS.) FITZP. having strong pathogenicity on various plants and with P. monospermum FITZP. having no pathogenicity on living plants respectively.2. Both fungi have some similar physiological characters. The optimum temperature for the growth of the mycelium of both fungi seems to lie at 34-36°C. They belong to the high temperature group in genus Pythium.3. Using the corn meal agar, the relation of pH value of culture media to the mycelial growth of the two fungi was studied. The results show that the optimum hydrogen-ion concentration for the growth of P. aphanidermatum was pH6.0 and for P. monospermum was pH7.0. They grow vigorously at pH9.0 yet, but there is no growth at pH4.0.4. When artificially inoculated, Pythium aphanidermatum forced to show the damping-off of seedlings of Cucumis sativus, Cucurbita pepo, Solanum lycopersicum, S. Melongena, Hibiscus Manihot, Pharbitus Nil, Vicia Faba f. ascendens etc. Pythium monospermum, however, did not show any injurious effect on the plants tested. Phaseolus vulgaris and Oryza sativa, when artificially inoculated with both fungi, did not show any significant symptoms. Cucurbita Pepo and Vicia Faba are more resistant than the other host plants tested.8. As above-stated, the seedlings of Phaseolus vulgaris and Oryza sativa showed no definite symptoms, when inoculated with both fungi. The germinating seeds, however, were much affected by the laboratory conditions.6. Generally high moisture content of soil increases the susceptibility of seedlings to fungal attack.

Rhizoctonia solani, Fusarium oxysporum and Pythium aphanidermatum in the saprophytic behaviour usually inhabited on debris in 0-20cm of soil depth, and P. aphanidermatum was in upper layer, R. solani in middle and F. oxysporum in deeper of soil, respectively. But, in overwetting soil, many of them immigrated into upper layer than in moderately moist soil. In each depth of soil phosphate and nitrogen decreased gradually with depth but carbon hydrate decreased suddenly at 30cm of depth. The survival ratio of R. solani inoculated in soil dug up from different depth decreased suddenly downwards of 30cm at 3 weeks after inoculation. It is considered that, carbon sources in soil determine the inhabitation of the fungi. P. aphanidermatum, inoculated in soil with rice straw, decreased in a half for 1 month, R. solani did for about 3.5 monthes and F. oxysporum did for about 5 monthes. Whereas P. aphanidermatum was lost after 3 monthes on straw in summer, a few of R. solani and F. oxysporum were surviving on it for 7 monthes. These 2 pathogens were dead more rapidly in submerged soil than in moderately moistened soil. P. aphanidermatum grew well on fresh straw in soil, but R. solani and F. oxysporum grew well on decomposed one by soil microben.From these results it is suggested that, though these 3 pathogens are alive in soil by utilization of plant debris, one of the factors determinating the colonized and active survival abilities of them are the components of debris on which they arrive and grow.

Pythium aphanidermatum zoospores in distilled water suspension showed differential responses towards a range of single compounds, and mixtures, diffusing from the ends of capillary tubes containing these materials in agar. All substances caused an initial disorientation of zoospore movement followed, according to the substance under test, by indifference, repulsion, attraction, trapping, and encystment, or, at extreme pH, by loss of motility and death. Of a wide range of substances and mixtures tested, including sugars, amino acids, inorganic salts, organic acids, auxins, and vitamins, only glutamic acid, after weak base adjustment, and mixtures of sugars combined with mixtures of amino acids, induced the pattern of response observed with roots and root materials. Comparison of the activity of glutamate and structurally related compounds indicated that the effectiveness of glutamate was dependent on the presence of several moieties of the glutamate ion.Short photographic exposures allowed counts to be made of zoospores and cysts around the capillary mouth and provided a method for comparing, quantitatively, the accumulation of zoospores in response to different substances over a period of time.The substances inducing activity were readily detected in pea root exudate and extract and are, in fact, of general occurrence in roots. The effectiveness of the active principle(s) in root exudate and extract was roughly proportional to the concentration of these root materials in terms of their content of carbon and nitrogen but no such relation could be established for glutamic acid and a joint mixture of amino acids and sugars, suggesting the existence in root materials of additional factor(s).

In the present paper the writer has treated the taxonomical studies of seven species of Pythium causing damping-off disease of various crop seedlings. The fungi tested are as follows: Pythium aphanidermatum isolated from rotten fruits and from water of the drainage; Pythium deBaryanum isolated from diseased cucumber seedlings; P. vexans isolated from diseased tomato seedlings; P. ultimum isolated from wilted Hibiscus seedlings; P. monospermum isolated from water; P. zingiberum sp. nov. isolated from rotten roots of ginger; and P. Hemmianum sp. nov. isolated from wilted sponge-gourd seedlings (Luffa cylindrica).The sporangium formation is found abundantly in Pythium aphanidermatum and P. monospermum, but not in P. ultimum, P. deBaryanum and P. vexans. It is difficult to make clear the difference between P. ultimum and P. deBaryanum by the characters of sexual organs. In Pythium ultimum, however, one antheridium arising usually from oogonial stalk immediately below the oogonium, attaches to an oogonium, and in Pythium deBaryanum one to three androgenus antheridia attach usually to an oogonium.Butler described that antheridium of Pythium vexans was attached to an oogonium with its broad base. In my observations of P. vexans, such figures were not found, and no sporangium and few conidia were obtained.A new species of Pythium attacking roots of ginger was described as a new species under the name of Pythium zingiberum. It forms numerous oogonia and few conidia on agar culture. Sporangia are filamentous or irregularly inflated and are rarely formed. The oospore wall is smooth and usually filling the oogonium. Antheridia are usually diclinous, and wrap around the oogonium with antheridial branches.A Pythium isolated from wilted sponge-gourd seedlings was also studied. It forms no sporangia and only a few sexual organs, but numerous conidia are formed. The writer gave the name of Pythium Hemmianum to the present fungus as a new species in memory of the sixty first birthday of Dr. Takewo HEMMI.

In southern Ontario rootrot of sugar beets may be caused by Aphanomyces cochlioides Drechs., Pythium aphanidermatum (Edson) Fitz., Pythium ultimum Trow, or Rhizoctonia solani Kuehn. The distribution of these fungi was found to be limited to soil type rather than to locality, A. cochlioides thus being found in the clay soils and P. aphanidermatum only in the sand loam. They were not present in the subsoil and were most abundant in the top two or three inches of surface soil. A. cochlioides, which was found for the first time in Canada in 1946, causes the so-called blackroot of sugar beets, and is the most economically important pathogen encountered. Blackroot appears either as an early acute attack or a later chronic one, but the acute phase is of major importance and occurs in epiphytotics during seedling development, usually when the beet is from two to five weeks old. Weather records and experiments have shown that serious disease outbreaks only occur when moisture is abundant and soil temperature exceeds 60° F. Susceptibility is sharply correlated with the developmental rhythm of the seedling and ends when the cortex of the hypocotyl is sloughed off. A. cochlioides is homothallic, attacks the hypocotyl of the beet, and develops in the intercellular spaces of the cortex. It will not grow at relative humidities of less than 99% and this sensitivity to all but extremely high humidity is believed to limit its parasitic activity. Microbiological studies indicated that the number of organisms in the rhizosphere of diseased sugar beet roots is much larger than in that of healthy beet roots. Since parallel rhizosphere responses followed local artificial killing of roots, they are believed to be due in part at least to the utilization of necrotic tissues or substances released on their breakdown. Streptomycin, but not penicillin, was effective in controlling rootrot in greenhouse experiments. Control with Arasan is achieved in part through a direct fungicidal action, but the evidence suggests that it may be due to a shift in the microbiological balance of the soil flora unfavorable to the pathogen.

Effects of a number of 3-hydroxyisoxazole derivatives substituted at 4 and/or 5 position of isoxazole ring on cucumber Fusarium wilt (Fusarium oxysporum f. cucumerinum) and cucumber seedling damping-off (Corticium rolfsii, Pythium aphanidermatum), and their antimicrobial activities on potato-sucrose-agar (PSA) medium and in soil were studied.Greenhouse evaluation (in vivo)-Compounds substituted with alkyl groups or hydrogen atom at 5-position of isoxazole ring were generally more effective than the derivatives substituted with aryl groups under greenhouse conditions. The effectiveness decreased in the following order:methyl>ethyl>propyl>butyl>hydrogen.Replacement of hydrogen atom at 4-position of isoxazole ring by nitro or methyl group or by chlorine or bromine atom reduced effectiveness against Fusarium wilt or seedling damping-off.Laboratory evaluation (in vitro)-Inhibitory effects of these derivatives on PSA medium against R. solani, C. rolfsii and P. debaryanum were generally strengthened in proportion to increase in the number of carbon atoms of alkyl groups at 5-position with the exception of activities against F. oxysporum. The growth inhibition of C. rolfsii by these derivatives in soil was not proportional to increase in the number of carbon atoms of alkyl groups at 5-position, and 3-hydroxy-5-methylisoxazole (hymexazol) showed the highest activity in soil. On the other hand, replacement of alkyl groups at 5-position by phenyl group enhanced inhibitory effect on PSA medium, but reduced it in soil. Effect of hymexazol thus selected as the most effective soil-fungicide in this series of compounds was studied extensively by large scale tests in a greenhouse.

In searching for a method to isolate Pythium aphanidermatum (Edson) Fitzp. from soil, it was found that streptomycin inhibited growth of some Pythium spp. but not others. It was also found that pimaricin at relatively high rates did not affect growth of 5 Pythium spp. but was inhibitory to several other representative soil fungi. This knowledge was used in designing a technique to selectively isolate P. aphanidermatum from soil which will be reported elsewhere. Streptomycin, although primarily effective against gram-negative bacteria (3), has shown in-vivo activity against several plant pathogenic fungi including Phytophthora infestans (Mont.) D. By. (7), Pseudooperonospora cubensis (Berk. & Curt.) Rostow (1), P. humnuli (Miy. & Tak.) G. W. Wils. (6), and Peronospora tabacina Adam (4). Pimaricin has been successfully used to isolate Phytophthora spp. from roots (2) and fruit (5). It has been incorporated with pentachloronitrobenzene to give quantitative enumeration of Pythium debaryanum Hesse and an undescribed Pythium sp. using dilution-plate and soil-plate techniques (9). The object of this paper is to report the effects of streptomycin and pimaricin on growth and respiration of several Pythium spp. and other representative soil fungi.

Maha Pancha Gavya (MPG), a concoction made from five cow products was tested for its toxicity against Pythium aphanidermatum (Edson) Fitz. and its antagonists at 5, 10, 25, and 50% concentration in in vitro to find out if it can be used in integration for the control of damping-off in tomato in nursery beds. MPG was very effective inihibiting the growth of P. aphanidermatum . At the highest concentration, the growth of the pathogen was negligible. Isolates of Trichoderma viride , T harzianum , and T. viren s were also sensitive to MPG at all the concentrations. Their radial growth decreased, but it was fluffy in nature and sporulated profusely. MPG was not toxic against two bacterial antagonists i.e., Bacillus subtilis and Pseudomonas fluorescens . Soil application of 10% MPG to nursery beds improved seedling stand and gave upto 48.27% tlisease control, which was more than that given by individual antagonists. However, MPG improved disease control efficacy of all the antagonists when it was used in combination with them. Integrated treatment with MPG and B. subtilis gave maximum disease control (65.33%). MPG enhanced seedling growth and it was more in combination with T. viride and B. subtilis . MPG in integration with neem cake and neem leaf extract gave complete control of damping-off and maxium increase in height of the tomato seedlings. Keywords: Maha Panch Gavya (MPG); Trichoderma ; Pythium aphanidermatum ; integrated control; neem products; tomato; damping-off. DOI: 10.3329/bjar.v35i1.5862 Bangladesh J. Agril. Res. 35(1) : 11-16, March 2010

Zoospore cysts of Pythium aphanidermatum germinated well without external nutrient supply, but pea root exudate increased percentage germination and germ tube growth. Zoospore cyst germination and growth varied with different concentrations of the substrate supplied. Alone, the neutral fraction (sugars) increased percentage germination but had little effect on germ tube growth; the cationic fraction (amino acids) suppressed germination and growth somewhat, except at very low concentrations; the anionic fraction (organic acids) mildly stimulated both processes. Neutral and anionic fractions combined approached the stimulatory effect of root exudate. Amongst the components of root exudate tested as pure chemicals, fructose, histidine, homoserine, proline, and tartaric acid promoted germination and growth at low concentrations. Alpha-alanine, glutamine, serine, and valine became stimulatory at high concentrations. A combination of glucose with one of the organic acids was more effective than either alone.

The effects of herbicides on the growth of soi-lborne plant pathogens and on the occurrence of damping-off of cucumber seedlings inoculated with the causal fungi were studied.Among ten sorts of herbicides used, dinoseb, pentachlorophenol, linuron, and chloropropham inhibited the mycelial growth of Fusarium oxysporum, Rhizoctonia solani and Pythium aphanidermatum on culture medium, while 2, 4-D, MCPA, prometryne, and simazine seemed to promote the development of aerial hyphae of R. solani or P. aphanidermatum.The effect of antifungal herbicides among above-described on the occurrence of pre- or post-emergence damping-off in cucumber was examined. Pythium+dinoseb, Pythium+linuron, and Fusarium+dinoseb combinations resulted in the increase in healthy seedlings compared with Pythium or Fusarium alone. This is probably due to the antifungal effect of herbicides. Rhizoctonia+dinoseb, Rhizoctonia+linuron, Pythium+pentachlorophenol, and Rhizoctonia+pentachlorophenol combinations, however, resulted in an appreciable reduction in cucumber stand due to damping-off compared with Rhizoctonia or Pythium alone. At present, it is not clear whether the herbicides acted on the pathogens or on the host.It is possible that the herbicides affected the physiology of host plant, so that the susceptibility of emerging seedlings to the pathogens increased. The results may suggest the importance of secondary effects of herbicide.

Zoospores of Pythium aphanidermatum in distilled water suspension responded to intact pea roots by massing in large numbers at the sites of elongation behind the root tips. They showed preferential attraction to wounds made by puncturing the epidermis, and to the stele exposed at the cut ends of roots. Massing of zoospores was followed, almost immediately, by encystment and early germination, the germ tubes being directed towards the source of stimulation. The phenomenon was non-specific over a wide range of plants examined. Root exudate and extract, diffusing from the ends of capillary tubes containing these materials in agar, caused identical zoospore responses. Analysis of zoospore movement under stimulation revealed a sequence of responses—initial disruption of the typical course of movement, attraction, trapping, and early cessation of movement by encystment. Attraction was equated with chemotaxis, whilst trapping showed features of kineses.

The rot-disease of seedlings in nursery-beds is one of the most serious diseases of the rice plant in Japan. This disease had been recognized by some investigators to be caused by a water mould, Achlya prolifera (NEES) DEBARY (Achlya prolifera NEES). However, in 1931 and 1933, ITO and his coworkers reported that the disease is caused by some species of Saprolegniaceae, Pythiomorpha and Pythium.The present paper deals with the results of the writer's inoculation experiments of some aquatic fungi on rice seedlings, in which seven species belonging to Saprolegniaceae and nine species of Pythium were used. The names of these sixteen fungi, which were isolated by the writer from water in Kyoto, are as follows: Saprolegnia Thureti DEBARY, S. mixta DEBARY, S. monoica PRINGSH. var. glomerata TIESENHAUSEN, Achlya racemosa HILDEBRAND, A. imperfecta COKER, A. Oryzae ITO et NAGAI, Aphanomyces helicoides v. MINDEN, Pythium tenue GOBI, P. angustatum SPARROW, P. torulosum COKER et PATTERSON, P. aphanidermatum (EDSON) FITZPATRICK, P. helicum ITO, P. proliferum DEBARY, P. marsipium DRECHSLER, P. polypapillatum ITO, and P. pleroticum ITO.The writer's inoculation experiments were carried out using the seedlings grown on SACHS' solution containing 2% agar or the sterilized field soil covered with water. In the experiments each fungus to be tested were inoculated on the seeds as soon as they were sown.The pathogenicity of Pythium aphanidermatum and P. helicum was extremely strong and that of the other seven species of Pythium seemed to be moderate, but all the species tested, which belong to Saprolegniaceae, showed a very weak pathogenicity. The pathogenicity of these aquatic fungi was suggested to be more destructive when the rice plants were cultivated at lower temperatures.Judging from the writer's experiments Pythium species seem to be more important than the fungi belonging to Saprolegniaceae as the causal organisms of the rot-disease of rice-seedlings.

The anterior flagellum of the zoospores of Phytophthora fragariae, P. megasperma, P. cambivora, Saprolegnia parasitica, Achlya americana, and Pythium aphanidermatum projects straight in front of the zoospore and never moves except during encystment whereas the posterior flagellum is active during the swimming period. In the secondary zoospore the anterior and posterior flagella are attached a short distance apart in the center of the depression on the concave side and respectively pass forward and backward through a groove and form a central axis about which the zoospore rotates. Hyaline vesicles which also have been called beads or paddles form at the base of the flagella at the beginning of encystment and glide part or all the way down the flagella. Movement of flagella after they are released from the zoospore is reported for the first time. Encystment may result from contact stimulus except in the case of Allomyces anomalus. A filament on which vesicles may occur may be secreted or retracted by the Allomyces zoospore.

Nuclear divisions taking place in the hyphae ofPythium aphanidermatum have been described. Typical prophase type of nuclei with elongate chromatin fibres have been observed. Achromatic structures resembling spindle fibres with well defined poles during anaphase configuration have been noticed. A mild pretreatment with acenaphthene vapours proved instrumental in arresting the progress of nuclear division. Stages similar to early and late anaphase and telophase with deeply staining chromosomal masses have been observed. A high concentration of acenaphthene treatment resulted in the formation of giant nuclei.

Pythium aphanidermatum (Edson) Fitzpatrick has been associated with seed decay and severe stem rot of cowpea in Nigeria. The symptoms produced on both seedlings and established cowpea plants are described. Fungus-induced losses of 0.94 per cent as seed decay and 11.10 per cent damage to adult cowpea plants have been recorded.

Fifteen wheat germplasm, namely BAW-1033, BAW-l045, BAW-1056, BAW1061, BAW-1064, BAW-1004, BAW-l008, BAW-1027, BAW-1035, Sonalika, Gourob, Protiva, Shatabdi, Sourov and Kanchan (check) were screened against different seedling diseases in two consecutive years under inoculated condition. Before sowing, the soils of the experimental field were inoculated with five fungal pathogens, namely Sclerotium rolfsii , Biplaris sorokiniana , Fusarium oxysporum , Pythium aphanidermatum , and Rhizoctonia solani . Considering the lower percent of diseased seedling and higher vigour index, four wheat germplasrn, namely Shatabdi, BAW-1045, BAW-1004 and Protiva were selected as tolerant materials against seedling diseases. Key Words: Screening; wheat germplasm; seedling diseases DOI: 10.3329/bjar.v34i4.5842 Bangladesh J. Agril. Res. 34(4) : 673-681, December 2009

Oxygen uptake by Pythium aphanidermatum zoospores during motility, encystment, and germination was measured. Addition of glucose or fructose had no appreciable effect on motile zoospore respiration. The effects of various substrates on the respiratory rate of germinating cysts were as follows: glucose, glucose-6-phosphate, xylose, acetate, citrate, glutamate, and 6-phosphogluconate did not increase the respiratory rate; whereas fructose, fructose-6-phosphate, iructose-l,6-diphosphate, sucrose, alphaketoglutarate, pyruvate, and dilute pea root exudate all significantly increased cyst respiration.

Pythium aphanidermatum, with an optimum temperature for growth at 35C, grew well and was readily isolated from soil on pimaricin–vancomycin medium (MPVM) when incubated for24 h at 38–40C. The pH of the medium affected recovery; maximum numbers developed above pH 6.0. Other Pythium spp. were recovered on MPVM at 20–25C, but were excluded by incubation at 38–40C. These Pythium spp. included P. ultimum, P. paroecandrum, P. irregulare, P. mamillatum, and an unidentified Pythium sp. These species grew well and were readily isolated from soil on gallic acid medium (GAM) when incubated for 24–48 h at 20C. P. aphanidermatum and P. myriotylum grew from mycelium on GAM, but their oospores did not germinate nor could they be isolated from soil on this medium. P. myriotylum grew well on MPVM, but was only rarely isolated, even from soils with known high potential for disease caused by P. myriotylum. Propagules of Pythium were enumerated by a plate-dilution frequency method or by a smear-plate method in serial dilutions of soil in 0.3% water agar. This differential isolation method is valuable for studies on the ecology, survival, and inoculum potential in soils with mixed populations of P. aphanidermatum and other Pythium spp.

Culture filtrates of Trichoderma harzianum Rifai have been found to inhibit zoospore germination, germ tube elongation and mycelial growth of Pythium aphanidermatum causing the damping-off disease of tobacco in Nigeria. Further, the invasion of the hyphae of P. aphanidermatum by hyphae of T. harzianum has been demonstrated in mixed cultures of the two fungi. The results of investigations on the role of T. harzianum as an agent of biological control of the damping-off disease in sterilized and unsterilized soils are reported and discussed.

A description is provided for Pythium aphanidermatum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On a wide range of hosts, often similar to those attacked by P. butleri , but inducing different symptoms, represented in the following families: Amaranthaceae, Amaryllidaceae, Araceae, Basellaceae, Bromeliaceae, Cactaceae, Chenopodiaceae, Compositae, Coniferae, Convolvulaceae, Cruciferae, Cucurbitaceae, Euphorbiaceae, Gramineae, Leguminosae, Linaceae, Malvaceae, Moraceae, Passifloraceae, Rosaceae, Solanaceae, Umbelliferae, Violaceae, Vitaceae, Zingiberaceae . DISEASES: Damping-off of various seedlings; 'cottony-leak' of cucurbit fruit in storage; 'cottony blight' of turf grasses; root and stalk rot of maize. Other hosts: tobacco, sugar-beet, sugar-cane, papaw, pineapple, ginger, bean and cotton. GEOGRAPHICAL DISTRIBUTION: Africa (Central African Republic, Fernando, Ghana, Kenya, Malawi, Mali, Nigeria, Sierra Leone, South Africa, Southern Rhodesia, Sudan, Togo, Zambia); Asia (Ceylon, China, Formosa, India, Indonesia, Israel, Japan, Java, Malaya, Philippines, Sumatra); Australasia & Oceania (Australia, Hawaii, New Caledonia); North America (Canada, Mexico); Central America & West Indies (Antilles, Jamaica, Puerto Rico); South America (Argentina, Brazil, Peru, Venezuela); Europe Austria, Cyprus, Czechoslovakia, Great Britain, Greece, Holland, Italy, Poland, U.S.S.R., Yugoslavia). (CMI Map 309) TRANSMISSION: Soil-borne. Eggplant fruit become infected when blossom end is in contact with soil (5: 465). Readily isolated from soil using fresh potato cubes treated with streptomycin and pimaricin as baits (43, 1519; 43, 46) or seedling papaw roots in soil containing papaw tissue (43, 1720). Also recorded as seed-borne on tomato and cucurbits but doubtful whether seed-transmitted (see Noble et al., An Annotated List of Seed-Borne Diseases , 1958, pp. 23, 25, 124).

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Experiments were carried out to determine the effect of decomposition of oil cakes, used as organic manures in India, on the population of Pythium aphanider-matum in soil. Low quantities (0.1 to 1.0% w/w) of castor and peanut cakes stimulated the growth of the fungus at 20° to 30 °C but in presence of higher quantities of these cakes the growth of the fungus in soil was inhibited. Inhibition was more conspicuous and was caused by lesser amounts of these cakes at high temperatures than at low temperatures. On the other hand, margosa cake (Azadirachta indica) was highly stimulatory to the fungus in all concentrations of 0.1 to 5% at 20°–30 °C, but caused inhibition at 36 °C. Washing of margosa cake with alcohol made it as inhibitory as the other two cakes. It has been suggested that the three cakes affected P. aphanidermatum in soil differently because of their chemical nature and the nature of their decomposition products which may (i) directly suppress the fungus through toxic effect, (ii) stimulate it through nutritional effect, (iii) stimulate or inhibit actinomycetes lytic to the pathogen. Temperature and pH of soil during.decomposition, as well as C:N ratio of the cakes, do not play any major role in the suppression of the fungus.

1. Davies, M. E. 1959. The nutrition of Phytophthora fragariae. Trans. Brit. Mycol. Soc. 42: 193-200. 2. Erwin, D. C. 1968. The effect of calcium on mycelial growth of Phytophthora mlegasperma and P. cinnamomli. Mycologia 60: 1112-1116. 3. Hendrix, J. W. 1965. Influence of sterols on growth and reproduction of Pythium and Phytophthora spp. Phytopathology 55: 790-797. 4. . 1966. Inability of Pythium aphanidermatum and Phytophthora palmivora to incorporate acetate into digitonin-precipitable sterols. Mycologia 58: 307-312. 5. , S.-M. Guttman, and D. L. Wightman. 1969. Cation and sterol effects on growth of Phytophthora parasitica var. nicotianae. Phytopathology 59: 1620-1624. 6. , C. Norman, and J. L. Apple. 1966. Chemical and physical factors influencing growth of Phytophthora parasitica var. nicotianae on vegetable oils. Physiol. Plantarum 19: 159-166. 7. Ingraham, J. L., and R. Emerson. 1954. Studies on the nutrition and metabolism of the aquatic phycomycete, Allomyces. Amer. J. Bot. 41: 146-152.

THIS report describes the use of serological techniques to distinguish two morphologically similar pathogenic fungi in soil. Pythium aphanidermatum (Edson) Fitzp. causes damping-off in many plants, including the tobacco (Nicotiana tabacum L.) and tomato (Lycopersicon esculentum Mill.) plants1. Recently Dukes et al. reported that this fungus also causes dark brown to black stem cankers on tomato seedlings grown in fields in South Georgia2. Phytophthora parasitica (Dast.) var. nicotianae (B. de Haan) Tucker [ = Phytophthora nicotianae var. nicotianae3] causes black shank of tobacco in this same area of South Georgia4, and has been reported to cause damping-off of tobacco seedlings, as well as a disease of eggplant, tomato and other plants5. It is difficult to differentiate quickly between these two indigenous soil-borne fungi in the vegetative state, whether in culture or in host tissues. To identify these pathogens in host tissue when reproductive structures are lacking, it is necessary to isolate and grow them in culture on media suitable for production of asexual bodies. Some isolates of both species may produce reproductive structures very slowly or not at all6,7. Proper identification of these species thus may require considerable time and effort, especially by workers not familiar with this group of fungi.

The use of chemical techniques as an aid in taxonomy has received considerable attention in the last few years. Paper chromatography has been used by many workers to determine quantitative or qualitative differences, or both, in fungi (1, 2, 3, 4). The object of this work was to determine if differences existed in the free amino acid content between isolates of Pythium aphanidermatum (Edson) Fitzpatrick, Pythium arrhenomanes Drechsler, Pythium debaryanum Hesse, and Pythium ultimum Trow.