INTERACTIONS AMONG STREPTOMYCES-GRISEOVIRIDIS, FUSARIUM ROOT DISEASE,AND DOUGLAS-FIR SEEDLINGS

In a laboratory experiment, Douglas-fir (Pseudotsuga menziesii var. gl auca [Beissn.] France) seedlings had similar disease ratings when trea ted with known Fusarium isolates or concurrently with Fusarium and Str eptomyces griseoviridis. When tested under greenhouse conditions and a gainst known Fusarium isolates, more seeds germinated and survived as seedlings in control medium than survived in S. griseoviridis-inoculat ed medium or when S. griseoviridis and Fusarium were added together. A series of applications of S. griseoviridis as a soil drench to a crop of Douglas-fir seedlings did not affect seedling morphology. However, against resident levels of Fusarium, S. griseoviridis reduced Fusariu m infection by 16%, but increased infection by F. oxysporum and F. pro liferatum, two potentially pathogenic fungi, by 40%.