Seedling blight. II. Soil in relation to seedling blight of opium poppy and peas

Abstract

Three steamed soils, limed and not limed, two hosts, and one isolate of Pythium ultimum were used in an experiment. The organism, isolated from peas germinating in limed Belanglo soil, was pathogenic to both hosts. The incidence of seedling blight of peas in the three reinfested soils varied significantly. On poppy, on two of the reinfested soils, it also varied significantly, but inversely to the incidence on peas. On peas in the first sowing it was not affected by liming the soil; on poppy it was significantly reduced. Seedling blight of both hosts was associated with one organism. The contrasting results could not be correlated with the uniform conditions of soil temperature, air temperature, and soil moisture; on any one soil or soil treatment they could not be ascribed to the prevailing uniform aeration, reaction, microflora, and microbial antagonism The only conditioning factor that was varied was the steamed soil, or steamed soil modified by adding lime. Differences in the incidence of disease were associated with variation of the conditioning factor and the host. Seedling blight of peas, resulting from natural reinfestation, occurred in earlier resowings in limed than in unlimed soils. Physiogenic seedling blight of poppy also occurred, causing total loss on one soil and smaller percentages of loss on the other soils.