Date of Award

1964

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Advisor

Frank L. Howard

Abstract

Fairy Rings caused by Marasmius oreades Fr. and other fungi cause considerable damage to turfgrasses. The recommended control measures for this disease are either soil fumigation or digging up the affected turf and replacing it with noninfested soil. Both methods require subsequent reseeding or resodding of the area. Results of two years' experimentation indicate that chemical control of fairy ring disease is not practical at the present. Hence, the possibilities of biological control were explored.

This investigation has shown that Pythium aartotrogus and other Pythium species will inhibit the mycelial growth of M. oreades and Agaricus bisporus. Pythium artotrogus was more antagonistic to A. bisporus than was other Pythium species tested. Pythium ultimum and an isolate of P. irregulare were more antagonistic to M. oreades mycelium was shown to be due to the toxic metabolites of P. artotrogus completely inhibited the growth of the agaric hyphal tips within twenty minutes. The biological activity of the filtrate was not reduced when kept at 7° C for prolonged periods, but it was shown to be thermolabile.

Studies on the effect of temperature on mycelial growth showed that M. oreades and P. artotrogus had the same minimum temperature requirement. The optimum temperature for growth was about 27° C for both fungi. Growth of P. artotrogus occurred at higher temperatures than M. oreades. At all temperatures P. artotrogus had a growth rate of two to ten times that of M. oreades.

Marasmius oreades grew over a pH range of about 3.0 to 7.5 with an optimum of about 5.5. Growth of P. artotrogus occured from pH 2.5 to above 7.7 with an optimum at 5.5.

Pythium artotrogus was not parasitic to A. bisporus or M. oreades. However, this Pythium species was shown to parasitize the hyphae of P. aphanidermatum, P. debaryanum, P. irregulare, P. splendens and P. ultimum. When encountering susceptible hyphae, the hyphal tip of P. artotrogus coiled around the host hypha followed by the formation of an appressorium on the hyphal surface of the host. Following penetration, the infection hypha grew lengthwise in that of the host, degenerating the cellular contents as it advanced. Although not parasitic, the hyphae of P. artotrogus formed coils around the hyphae of P. arrhenomanes. Pythium artotrogus did not form coils and was not parasitic in its own or in the hyphae of P. graminicolum.

Of the many Pythium species that were shown to be antagonistic to A. bisporus and M. oreadnes, only P. artotrogus was shown to cause no injury to four species of Agrostis in laboratory pathogenicity tests.

The data indicate that P. artotrogus has the potential to be used as a biological control agent for fairy ring caused by M. oreades. However, since it was shown that P. artotrogus would not grow among the mycelial mass of either A. bisporus or M. oreades, the antagonistic Pythium species will have to be applied to the turf on the outer edge and in advance of the fairy ring if it is to be a successful biological control agent.

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