SOIL MICROORGANISMS ASSOCIATED WITH FLAX ROOTS
The root microflora of Bison flax, resistant to wilt caused by Fusarium oxysporum f. lini, was compared with that of the wilt-susceptible variety Novelty. Plants grown in "disease-free" soil show that the susceptible variety harbors not only the most numerous, but also the most metabolically active bacterial flora on its roots. Generic classification of bacterial isolates shows a higher incidence of more active organisms, represented by Pseudomonas and Flavobacterium on roots of the susceptible crop, whereas the more slowly growing pleomorphic types such as Arthrobacter were most abundant on roots of the resistant variety. Fungi were also more numerous on roots of the susceptible crop, but the generic composition of rhizosphere populations of both varieties was similar to that of the soil itself. Fusarium oxysporum dominated the flora occurring in an active mycelial state on roots of the susceptible variety, whereas F. oxysporum and Phoma sp. were codominants in the active flora of the resistant crop. Tests with other soils showed that dominance of specific genera varies with soil type. The results indicate a selective action on the root microflora, particularly the bacteria, and suggest both quantitative and qualitative differences in root environments of the two flax varieties.