The better suppression of pepper Phytophthora blight by arbuscular mycorrhizal (AM) fungus than Purpureocillium lilacinum alone or combined with AM fungus

Abstract

Phytophthora blight caused by Phytophthora capsici (Pc) is one of the most economically destructive soilborne diseases of pepper (Capsicum annum L.) on a global scale. Biocontrol using antagonistic microbes, such as Purpureocillium lilacinum (Pl) and arbuscular mycorrhizal (AM) fungus Funneliformis caledonium (Fc), is one of the significant strategies for ecologically sound plant disease management. The purpose of this work was to investigate the sole and combined suppression of pepper Phytophthora blight by Fc and Pl. The 14-week pot experiment with three pepper plants per pot included five treatments: control (non-inoculation), inoculation with Pc, inoculation with Pc and Pl (Pc + Pl), inoculation with Pc and Fc (Pc + Fc), and inoculation with Pc, Pl, and Fc (Pc + Pl + Fc). Pots were randomly arranged with eight replicates per treatment. The incidence and severity of Phytophthora blight at plant full productive stage were recorded. The biomasses and N, P, and K concentrations of pepper shoots, roots, and fruits were all measured. In addition, root mycorrhizal colonization rate and soil pH, phosphatase activity, and available P concentration were also tested. The inoculation of Pc induced both high incidence (92%) and severity (33%) of pepper Phytophthora blight, and the alleviating effects of Pl, Fc, and Pl + Fc were 46%, 79%, and 59%, respectively. The Fc significantly increased (P < 0.05) root mycorrhizal colonization, nutrient (N, P, and K) acquisition, plant biomass, and fruit yield of pepper, while Pl only significantly increased (P < 0.05) plant nutrient (N and P) acquisition and tended to increase the fruit yield. The Pc, Pl, and Fc all had additive effects on decreasing soil pH, but only Fc significantly increased (P < 0.05) soil phosphatase activity and available P concentration, contributing partly to the elevated P acquisition as well as the increased P concentrations in both shoot and root. Compared with the sole inoculation of Fc, the extra inoculation of Pl had negative effects on mycorrhizal colonization, soil P mobilization, and plant growth and nutrient acquisition. It suggests that AM fungus (Fc) has the superiority of formatting symbioses with plant roots and enhancing soil P mobilization for the suppression of pepper Phytophthora blight compared with Pl, and the joint application of different fungal agents to improve plant health needs careful consideration.