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

Abstract

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.

Untangling the Pea Root Rot Complex Reveals Microbial Markers for Plant Health

“…Repeated experimental evidence supports the importance of pathogen complexes for the pea (Kerr, 1963;Shehata et al, 1983;Oyarzun and Van Loon, 1989;Xue, 2003;Wille et al, 2020) and other plant pathosystems (Lamichhane and Venturi, 2015;Abdullah et al, 2017). Notably, interactions of pathogens have significant implications for disease aetiology (Kerr, 1963;Willsey et al, 2018), plant resistance (Kankanala et al, 2019), and disease management (Gossen et al, 2016;You and Barbetti, 2019). Our results demonstrated that the composition of key microbial taxa of the PRRC in diseased pea roots was determined by conjoint effects of the soil and plant genotype.…”

Plant genotype and temperature impact simultaneous biotic and abiotic stress‐related gene expression in Pythium‐infected plants

“…This is despite such soilborne diseases displaying a range of characteristic symptoms including widespread pre‐emergence damping‐off, and severe root rotting of seedlings and mature plants (Wong et al , ; Barbetti et al , ; O'Rourke et al , ); this leads to failure of subterranean clover forages to persist and consequent serious reductions in the capacity to carry livestock and whole‐farm profitability (You and Barbetti, ; ; You et al , ; ). Previous studies of subterranean clover root diseases included causal pathogens, varietal resistance screening, environmental effects on disease severity, and impact of cultural practices and fungicides on root diseases as well as expression of resistance/susceptibility (e.g., Barbetti, ; ; Barbetti and MacNish, ; You et al , ; You et al , ; ; Ma et al , ; You and Barbetti, ; You et al , ).…”