Abstract Intercropping is a sustainable practice becoming increasingly popular in the Canadian Prairies. However, its long‐term impact on diseases in subsequent sole crops is not well understood. We examined root rot and associated fungal communities in durum wheat Triticum turgidum L. ssp. durum (Desf.) Husn., following different ratios of lentil ( Lens culinaris Medik.)–yellow mustard ( Sinapis alba L.), and field pea ( Pisum sativum L.)–oat ( Avena sativa L.) intercrops, and respective monocultures, in a semiarid region of the Canadian Prairies (2018–2019). The previous crop(s) impacted disease severity in durum wheat and had a significant impact on the composition of fungal communities. Durum grown after the mustard monoculture and its high‐ratio intercrop had 15% less severe root rot than after the lentil monoculture and its high‐ratio intercrop, while durum following the oat monoculture and its intercrops had 16% more severe root rot than after mustard and its intercrops. Fusarium species were the most frequent fungal isolates, accounting for 70% of total isolations. The main Fusarium cereal pathogens were >1.7x–25.5x higher following the oat than the mustard monoculture and 2x–3x higher after the pea–oat than the lentil–mustard intercrops. In turn, isolation of the main fungi with biocontrol potential (antagonists) was 4.3x–5x higher after the mustard than oat monoculture, and 2x higher after lentil–mustard than pea–oat. The prevalence of antagonists in mustard‐containing treatments, and their negative correlation with disease levels, suggest a dual mechanism of disease suppression: a direct pathogen inhibition through the mustard's allelopathy and enhanced populations of indigenous microbial antagonists.
Fernandez et al. (Thu,) studied this question.