Microbial Colonization of Plant Roots

TL;DR: After a long period devoted largely to isolation of organisms from roots, there is new impetus into finding mechanisms of colonization of the root; also, ex­ perimental approaches to the population dynamics of microorganisms on roots are emerging.

Abstract: Research in microbial growth and interactions on roots is like ly to increase in the future as the need for integration of plant pathology and soil microbiology is recognized. On the one hand, some diseases are suppressed by soil microorgan­ isms (4) and on the other hand, the soil microflora can also.suppress beneficial root symbionts; for example, the establishment of a selected mycorrhizal fungus is easier in sterile than in n onsterile soil (21, 143) . Also, poor responses to Rhizobium inoculation may result from competition from less effective indige­ nous strains and antagonists in soi l . Interest in controlling the rhizosphere comes also from the effects of certain rhizosphere microorgan isms themselves on plant growth; many organisms in the general soil microflora may be subclinical pathogens reducing root and root hair growth or acting directly on the plant (8 , 19). Inoculation of many plant species with certain soil bacte ria sometimes in­ creases yield, advances flowering, or increases internode extension (27, 93, 117). After a long period devoted largely to isolation of organisms from roots, there is new impetus into finding mechanisms of colonization of the root; also, ex­ perimental approaches to the population dynamics of microorganisms on roots are emerging. In this review we summarize the present information and suggest possible future research . Good data are sparse and conclusions have necessarily often been made on the basis of very few experiments.