Suppression of Take-All of Wheat by Seed Treatments with Fluorescent Pseudomonads

Abstract

Strains of fluorescent Pseudomonas spp. applied to wheat seeds suppressed take-all in both greenhouse- and field-grown winter and spring wheat. The effective strains were originally isolated from roots of wheat grown in soil naturally suppressive to take-all and were selected on the basis of in vitro antibiosis to Gaeumannomyces graminis var. tritici. Isolate 2-79, alone or combined with isolate 13-79, suppressed take-all in 5 of 6 field tests conducted in nonfumigated soil infested with inoculum of G. graminis var. tritici. The combination treatment was more suppressive than 13-79 alone in all field tests, and was slightly more suppressive than 2-79 alone in 3 of 6 field tests. Suppression of take-all by the bacteria was expressed in the field as fewer plants with foliage symptoms of take-all and taller plants, more heads, greater yield and less root disease than those grown from nontreated seed. Tests in field plots fumigated with methyl bromide, with and without the reintroduction of G. graminis var. tritici, established that the bacteria do not promote plant growth other than by control of take-all. The seed treatment resulted in increased yields of up to 147% in fumigated soil and up to 27% in natural soil. An antibiotic-resistant strain of 2-79 was isolated from the roots of wheat in the field following germination of bacteria-treated seed. The population of the introduced bacterium exceeded 106 colony-forming units/0.1 g of root tissue 3 wk after planting. The populations of strains 2-79 and 13-79 applied on wheat seeds with methylcellulose were stable for 21 days at 5 or 15.degree. C, but declined rapidly at 25.degree. C.