Production of Gliotoxin in Unsterilized Soil
IT has long been recognized that microbial antagonisms exist in the soil, and the possibility that this might be due to production of antibiotics has been suggested although never actually proved.
Importance of antibiotic production in antagonism of selected Streptomyces species to two soil-borne plant pathogens.
Antagonism of ten Streptomyces spp., five of which produce antibiotics, to the plant pathogens Rhizoctonia solani and Phytophthora megasperma var. sojae was studied. Antibiotic activity was detected in culture for the five antibiotic producers. S. griseus, S. hygroscopicus var. geldanus, and S. noursei produced wide zones of inhibition to R. solani and P. megasperma var. sojae. Similar activity was found for S. reticuli var. protomycicus to P. megasperma var. sojae. S. cellulosae reduced Rhizoctonia root rot on pea when sterile soil was infested simultaneously with the antagonist and R. solani. S. hygroscopicus gave almost complete disease control when the streptomycete was added 7 days prior to infesting the soil with R. solani. Several of the Streptomyces spp. reduced Phytophthora root rot on soybean when the streptomycetes were added to soil at the same time as P. megasperma var. sojae or 7 days prior to adding the pathogen. S. herbaricolor and S. coeruleofuscus gave the most consistent control. No relationship was found between reported antibiotic activity or antagonism on agar media and reduction in disease severity. Only S. hygroscopicus var. geldanus gave both control of Rhizoctonia root rot and large zones of inhibition on agar media when the streptomycetes were preincubated in soil for 7 days.
Production of an Antibiotic Substance on Wheat Straw and other Organic Materials and in Soil
MANY soil micro-organisms produce under artificial conditions antibiotic substances which inhibit the growth of certain plant pathogens. On the assumption that a similar process may take place in the soil, investigations on this problem were commenced at the Research Station, Cheshunt, and an attempt made to devise a method whereby antibiotic substances will be produced abundantly in the soil for the purpose of controlling soil-borne diseases. Blair1, Garrett2, Millard and Taylor3., West and Hildebrand4., Sanford5, and others, have reported that organic manuring reduced the incidence of certain soil-borne diseases and have suggested that microbial antagonism may be one of the important factors.