Seedling blight. 6. The effect of mixtures of unsterilized soils, and of reinfesting steamed soils, on seedling blight of poppies and peas

Abstract

Soils of different seedling blight potential were used in various combinations in pot experiments to ascertain the effect of the mixtures on the incidence of seedling blight. The species of Pythium associated with seedling blight of peas and poppies were widely and well distributed throughout the soils, three of which had never before been sown to these or related crops. Four grams of each of three soils were added in turn as inoculum to 2.5 kg. of each of the other two soils. Stands of peas and poppies were generally unaffected by such small additions, but in one instance the stand of peas was reduced. Similar experiments were made with four unsteamed soils as inoculum, each added to the same four soils which had previously been steamed. The soil inoculum which caused seedling blight of peas on an unsteamed soil caused much greater reduction in stands of peas on all four steamed soils. Percentage stands of poppies were reduced in two soils. In another series of experiments, unsteamed soils of contrasting seedling blight potential each mixed in three proportions. The transition from good to poor stands of poppies was gradual, and tended to be directly proportional to the percentage of one of the component soils, whereas with peas the transition was abrupt, a high percentage of seedling blight being obtained by incorporating in the mixture the soil which had a high disease potential to peas. It appears that the stand of peas in the soil which was common to both mixtures was influenced principally by the pathogens, whereas the stand of poppies was influenced almost wholly by the conditioning factor, which was the general character of the soil itself.