SPORE POPULATIONS OF HELMINTHOSPORIUM SATIVUM IN SOILS IN RELATION TO THE OCCURRENCE OF COMMON ROOTROT OF WHEAT

Abstract

The relationship of the spore population of Helminthosporium sativum in soils and the occurrence of common rootrot of wheat in the greenhouse and field was studied in 1959 and 1960. Results appeared to be similar in both years. In the 47 fields studied in 1960, numbers of viable spores of H. sativum ranged from < 8 to 253 per gram of soil. Disease ratings ranged from 1 to 33 for seedlings grown in the greenhouse in soils from these fields, and from 2 to 36 for seedlings and 7 to 56 for mature plants grown in the fields. H. sativum was isolated more frequently from mature field plants than from either greenhouse or field seedlings. Isolates of Fusarium spp. were obtained more often from mature field plants than from greenhouse seedlings.Disease rating of seedlings in the greenhouse and the field tended to vary as the logarithm of the population of spores in the soil. No such relationship was found for mature plants. However, fairly good correlations were found between spore populations and frequency of H. sativum isolated from all of these sources. Spore populations of H. sativum were negatively related to the frequency of isolation of Fusarium spp. from mature field plants, but were not related to the incidence of Fusarium in greenhouse seedlings.