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Helleri holly were grown in 100% sand, 50% bark-50% sand, and 100% bark media and inoculated with Pythium irregulaye Buis. Pythium populations were determined at 4, 10 and 17 cm depths at planting date and every two weeks thereafter. After 7 weeks fresh weight of plants and populations of bacteria, actinomycetes, and total fungi were determined. P. irregulare was highest at the 4 and 10 cm depths, with bark media reaching their highest Pythium levels 4 weeks after inoculation. Pythium peaked in 100% sand 6 weeks after inoculation and declined thereafter.

The genus Pythium includes a number of readily recognized species with wide distributions and host ranges. The taxonomic position of the genus and its relationship to other Phycomycetes were well established during the latter part of the 19th century. In the early 1900s pathologists found Pythium spp. consistently associated with root diseases and it soon became apparent that these fungi were important plant pathogens. Certainly, while 1),ot all isolates of Pythium species are capable of causing diseases of plants, many are soil­ borne pathogens that cause serious economic loss on a wide variety of hosts, while others are more limited in host and geographic range or affect plants only under special environmental conditions. New species are being discov­ ered as pathologists investigate soil organisms associated with plant growth problems. Rands & Dopp (123) in their classic investigation of sugarcane root dis­ eases established the symptoms and determined the conditions needed for these fungi to become destructive. This work, and others of a similar nature, are part of the extensive literature on diseases caused by species of Pythium. This review will concentrate on examples of the readily available literature of the past 50 years and will emphasize the pathology of the genus, with only brief treatment of other aspects such as taxonomy and control. It will be con­ fined to Pythium spp. as they affect economic plants and will not deal with those affecting algae, other marine plants, fungi, and unusual hosts.

Pairings of 5 heterothallic isolates of Pythium sylvaticum in all possible combinations revealed the existence of 2 sexually compatible groups of isolates.Tracings of gametangial hyphae leading to ...

By the use of selective media and techniques which favor the isolation of Phycomycetes, 85 soil samples from four old growth forest sites in Kentucky, North Carolina and Tennessee were assayed for ...

In studies of Pythium species common to forest and agricultural soils of the Southeast, numerous assays for these fungi have been made on Hendrix and Kuhlman's modification of Kerr's Pythium medium (Hendrix and Kuhlman, 1965; Kerr, 1963). A frequently isolated Pythium produced only globose, terminal or intercalary sporangia or chlamydospores on corn meal and hempseed agar plates. These bodies failed to form zoospores when agar blocks bearing mycelium were flooded or continuously irrigated with distilled water or with soil leachate. A few isolates from several soil samples produced well-developed oogonia and oospores. The globose sporangia which were also present failed to produce zoospores on flooding or irrigation. Apparently the oospore-producing isolates were closely related to those producing only sporangia or chlamydospores. Extensive pairings of the sporangial isolates on hempseed agar2 plates demonstrated that well-formed oospores were produced when the mycelium of certain isolates made contact. The oospores so formed were similar to those produced by the homothallic isolates. The existence of a Pythium species normally heterothallic is of mycological interest, and because this fungus is morphologically different from other named species it is described here as a new species. The nature of the heterothallic reaction will be discussed in a separate paper.

Pythium heterothallicum is described as a new species. The species designation “heterothallicum” was chosen to emphasize the absence of homothallic isolates, in contrast to P. sylvaticum in which i...

(1974). Taxonomy of Pythium Sylvaticum and Related Fungi. Mycologia: Vol. 66, No. 6, pp. 1049-1053.

Oospores and oogonia of P. dissotocum, P. myriotylum, P. irregulare, and one isolate of P. ultimum increased in diameter after being subcultured for 30 mo. Oospores and oogonia of P. aphanidermatum and one isolate of P. ultimum decreased in diameter during this period. Sporangia of P. irregulare increased in diameter and of two isolates of P. ultimum decreased in diameter during this period. The taxonomic value of reproductive cell diameter in the genus Pythium is discussed.

Pythium dimorphum, a new species, is characterized by oogonia partially to completely covered with blunt irregularly spaced projections averaging 3 / in length and aplerotic to nearly plerotic oospores averaging 30 / diam. Antheridia may be hypogynous or monoclinous but are frequently absent. Prominent ovoid to elongate thin-walled, spherical chlamydospores averaging 64 L in diam with dark contents are a distinguishing feature of this fungus. Ovoid or club-shaped sporangia, averaging 28 X 54 1A, are present.