Growth of Gaeumannomyces graminis var. tritici in soil: Effects of temperature and water potential

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Abstract

The effects of temperature and water on the growth of the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt), were examined in two factorial experiments. The first examined the effects of temperature and water potential on the growth of two isolates of Ggt on agar media, using osmotically-adjusted water potentials. The second experiment was concerned with the growth of the Ggt isolates in one sterile and two natural soils at two water regimes in the absence of a living host. Three temperatures (10, 18 and 26°C) were used in these experiments. A third experiment determined growth through soil.

Growth was greatest at high temperatures and low water potential in axenic culture, but in unsterile soil growth at different temperatures and water potentials was strongly influenced by competition from the soil biota. The best temperature for growth in unsterile soil was 18°C. Growth at 26°C in unsterile soil was greatly reduced, this being attributed to more intense microbial competition. In sterile soil Ggt grew equally well at 18 and 26°C. At 10°C, both isolates of Ggt grew better in unsterile soil than in sterile soil.

Under suitable conditions Ggt grew out readily from infected straw into unsterile soil (up to 5 cm in 10 days) in the absence of a host plant, forming melanized, hyaline and branched hyphae. These hyphae were infectious after dry storage for 5 months in the laboratory. Ggt thus appears to be a more successful soil inhabitant than is widely believed. Our experiments could explain many of the host-based concepts related to field expression of disease.

The technique presented here could be of value for testing the suppressiveness or conduciveness of soils by measuring fungal growth in soil.

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