Influence of a volatile inhibitor in natural or limed soil on fungal spore and seed germination

Seed germination on sterilized moist filter or blotting papers resting on natural soils in stacked “Nalgene” plastic specimen dishes was inhibited particularly in alkaline soils in comparison with controls under similar conditions but without soil. The same response was observed when seeds were suspended on filter or blotting papers above the soils, suggesting the influence of an inhibitory volatile factor. Seed germination was not affected in Good's buffers over the pH range of the soil samples tested indicating that inhibition on filter or blotting papers in contact with soils was not due to the direct effect of pH. The observed inhibition of seed germination is similar to that found in the germination of conidia of common soil fungi; a volatile fungistatic factor was also detected in these soils. Liming of moderately acid soils increased conidial inhibition on indirect soil contact or from volatiles: germination of seeds, however, was not affected by liming in five of six soils tested. These results indicate that seeds of higher plants as well as fungal conidia are affected by some natural soils and volatiles are at least partially responsible for inhibition.