Impact of cropping practices on dry root rot and soil microbial diversity in durum wheat in semi-arid regions of Morocco

Dry root rot is one of the most important wheat diseases worldwide, including in Morocco. This study aimed to evaluate the health status of five no-till soils compared to a conventionally tilled soil in terms of the dry root rot severity, microbial biodiversity, and potential inoculum level of Fusarium culmorum. To assess the disease severity, a root rot-susceptible variety, “Ourgh”, was grown under greenhouse conditions in six natural soils collected from three regions (Abda, Chaouia, and Ourdigha), each with different previous crops (lentils, fallow, wheat, barley, and forage). The disease severity was assessed at the flowering on the roots and stem internodes, and the microbial biodiversity was estimated using microbial counting techniques. These evaluations were also performed after artificial inoculation with F. culmorum. Root rot symptoms, confirmed through pathogen isolation from infected roots and stems, were observed in all six soils at varying levels. Three pathogenic genera were identified—Fusarium spp., Alternaria spp., and Bipolaris (B. sorokiniana)—with Fusarium spp. being present in all the soils. The no-till soils showed higher microbial diversity than the conventionally tilled soil, which was dominated by bacteria, except the soil from Ourdigha with barley as the previous crop, in which the fungal and bacterial levels were similar. Inoculation increased the microbial diversity and disease severity and reduced the plant height without significantly affecting the dry biomass. Except for in this latter soil, the microbial profiles shifted post-inoculation, with soils becoming either bacteria-dominant or balanced. The soil type, texture, and crop history (except a crop history of barley) had no significant impact on the microbial biodiversity. These findings highlight potential natural resistance mechanisms against F. culmorum for exploitation in future biological control strategies.