Intercropping with maize (Zea mays L.) enhanced the suppression of pepper (Capsicum annuum L.) Phytophthora blight by arbuscular mycorrhizal fungi

Purpose The biocontrol of pepper ( Capsicum annum L.) Phytophthora blight by either exploitation of arbuscular mycorrhizal (AM) fungus or intercropping with maize ( Zea mays L.) has been well documented, while the potential contribution of AM fungal hyphal networks is poorly understood. The purpose of this work was to resolve the abundance, colonization, and role of AM fungi in the pepper/maize combinations with different row distances, focusing on pepper Phytophthora blight suppression and interspecific nutrient competitive relations. Materials and methods A 14-week pot experiment was firstly carried out on a sterilized soil inoculated with Phytophthora capsici and with (+ M) or without (-M) AM fungus Funneliformis caledonium . Pepper and maize roots were absolutely separated (Sep) by polyvinyl chloride layer or semi-separated (Semi-Sep) by nylon mesh (30 μm) screen. Blight severity, fruit yield, plant biomass, and P and K acquisitions were all measured. Another 158-day field experiment included three treatments: pepper monocropping (control) and intercropping with maize under same ridge width (SRW) or same row distance (SRD). The disease categories of ten pepper plants per ridge and the economic yields of both plants per plot were recorded, and five pepper and three maize plants per plot were collected to test tissue biomass, and P and K acquisitions. Results and discussion Sep + M resulted in lower pepper Phytophthora blight severity relative to Sep-M, while Semi-Sep + M induced lower blight severity and higher mycorrhizal colonization, K acquisition, and fruit biomass of pepper compared to Sep + M. Both SRW and SRD increased AM fungal abundance, mycorrhizal colonization, and plant total P and K acquisition per plot, and decreased blight incidence and severity and fruit biomass of individual pepper due to interspecific competition. Compared with SRD, SRW induced higher mycorrhizal colonization of both plants, and lower blight incidence and severity and higher maize yield per plot. There were no significant differences in interspecific nutrient distributions between SRW and SRD, but SRW had higher P acquisition per plot of both plants, as well as K acquisition per plot of maize compared to SRD. Conclusions Intercropping with maize could further suppress pepper Phytophthora blight and increase the fruit biomass via elevating root mycorrhization. Compared with SRD, intercropping at a relatively narrow row distance (e.g., SRW) did not change the interspecif