Influence of Potassium on Spore Germination in the Nematophagous Fungus, Hirsutella rhossiliensis.

The nematophagous fungus Hirsutella rhossiliensis Minter and Brady produces adhesive spores that ge rmina te direct ly through the cuticle of host nematodes (3). When juveni les o f the plant-parasi t ic nematode Criconemella xenoplax (Raski) Luc and Raski were inoculated with spores of this fungus and incubated in water, only a small pe rcen tage became infec ted (3). Nematodes that were heat stressed or heat killed, however, were invaded and colonized by the fungus in water. These results indicate that H. rhossiliensis is a parasite of nematodes under stress, but later experiments (4) showed that addition of certain solutes including K + stimulated parasitism of unstressed individuals. Furthermore, the level o f parasitism in soil extracts was positively correlated with conductivity measurements of the soil extract, which is a measure of salt content. Many reports demonstrate increases in spore germination or more rapid fungal growth in response to cations in the medium. For example, Fusarium oxysporum f. sp. vasinfectum and Verticillium albo-atrum grew more rapidly on agar adjusted to 10 or 2 0 bars with salts than with no salt amendment or on a medium adjusted to the same osmotic potential with sucrose (5). Macroconidia and chlamydospores Fusar-