SOIL RECEPTIVITY TO FUSARIUM-SOLANI F SP PISI AND BIOLOGICAL-CONTROL OF ROOT-ROT OF PEA

Potential antagonists of Fusarium solani f. sp. pisi (Fsp) were selected from soil samples with varying degrees of receptivity to this pathogen. They were tested against Fsp isolate 48 (Fs48), in increasingly complex systems. Most species tested in vitro were able to antagonize Fs48. No relation could be established in vitro between the receptivity of the soil from which an isolate originated and its antagonism to Fs48. In soils naturally infested with pea root rot pathogens, which were stored humid at 4 degrees C for a period longer than a year, various isolates of Fusarium, Gliocladium and Penicillium spp. were able to reduce root rot. After sterilization of these soils, only Gliocladium roseum isolates, added at 10(5) conidia g(-1) dry soil, significantly reduced disease severity and prevented root weight losses caused by Fs48 at 10(4) conidia g(-1) dry soil. In soils in which the biota were activated by growing peas before the assays, doses of 10(6) and 10(7) of G. roseum were required to reduce root rot. In these soils, the antagonistic effects of fluorescent pseudomonad strains from soil of low receptivity to Fsp were variable. Some strains of fluorescent pseudomonads, from soil moderately receptive to Fsp and from highly infested soils, were also able to reduce root rot. Disease suppression by pseudomonad strains was more evident in the absence than in the presence of Aphanomyces euteiches in the root rot pathogen complex. The role of receptiveness of the soil with regard to potential antagonists is discussed.