Endophytic bacterial systems governing red clover growth and development

Endophytic competent bacteria capable of promoting both beneficial and detrimental growth responses in red clover (Trifolium pratense L.) were recovered from three adjacent areas of farmland each having a different cropping history — continuous red clover, continuous potatoes (Solanum tuberosum L.) or a 2 yr rotation of red clover and potatoes. The population composition of these rhizobacteria was altered by the various crop sequences. The greatest instance of significant growth responses (beneficial or detrimental) occurred with those bacteria derived from the clover-potato soil, suggesting increased interactive ‘competition’ among bacterial populations at the ‘interface’ between different crop rotations. Whether bacterial strains promoted or inhibited growth appeared to depend on the cropping history and prior exposure of pre-bacterised clover plants to the natural microflora in the peat-based growing media. The interaction between bacterial colonists influenced plant trait expression to the degree that some characteristics were completely masked. Improvements in plant growth were interpreted as an allelopathic side-effect of the competition between endophytes for the same ecological niche, from which the plant inadvertently benefits.