Manipulating the ecosystem enables management of soilborne pathogen complexes in annual legume forage systems

Studies were undertaken to examine the potential for manipulating the ecosystem by altering forage species composition, intensity of grazing or by adding Rhizobium, to enhance productivity of subterranean clover (Trifolium subterraneum) forages affected by the soilborne pathogens Pythium irregulare and Rhizoctonia solani. Levels of tap and lateral root disease on clover and its productivity were differentially and significantly affected by the relative proportions of clover to annual ryegrass (Lolium rigidum). In the presence of P. irregulare, both tap and lateral root disease decreased as percentage clover composition increased (R² = 0.58, 0.59, respectively); there was no such significant effect in the presence of R. solani (R² = 0.08, 0.18, respectively). Increasing and maintaining high clover content in forage offers a means to both reduce root disease and increase productivity and forage legume stand persistence. With simulated grazing studies, continuous (i.e. intensive) grazing in the presence of P. irregulare resulted in the most severe tap and lateral root disease, poorest nodulation and smallest roots and shoots compared with intermittent grazing. Hence, reducing grazing intensity also offers potential for significantly increasing productivity of root-rot-affected clover forage. For Rhizobium studies, nodulation was reduced in the presence of P. irregulare or R. solani; the extent of this was dependent upon which pathogen and the clover variety. Overall, these different studies highlight significant potential for manipulating the ecosystem to better manage soilborne pathogen complexes and improve productivity and persistence in annual legume forage systems adversely affected by soilborne oomycete and fungal pathogens.