Improved nutrient status and Fusarium root rot mitigation with an inoculant of two biocontrol fungi in the common bean (Phaseolus vulgaris L.)

Among beneficial microbial inoculants, consortia have been advocated for application in modern agriculture as they may easily overcome the rhizospheric constraints, in addition to enhancing biocontrol efficacy through partners' reinforcement in an additive or synergistic manner. Unfortunately, the historical antagonistic potential of Trichoderma spp. has compromised its co-operation with Arbuscular mycorrhizal Fungi (AMF), misleading several attempts in building up artificial consortium between these undefeated biocontrol agents (BCA's). The present study unveils a strategy of exploiting the beneficial traits of a Common bean endophytic Trichoderma (Trichoderma harzianum T8) and a recently described AMF formulation (AMF2) with individual biocontrol traits for better nutrients uptake and resistance induction against Fusarium root rot (FRR) in common bean. Standard plate-based approaches, as well as sequential inoculation of BCA's followed by colorimetric, Flame Photometry (FP) and Atomic Absorption Spectrometry (AAS) analyses revealed that co-inoculation of the BCA's mobilised more zinc (Zn) and phosphorus (P) from the soil substrate to the plant than the BCA's tested alone. Moreover, enhanced shoot growth (123% increase) and chlorophyll pigment synthesis (137% increase) were recorded compared to Trichoderma-treated plants. Most importantly, a substantial suppression of both disease incidence (92% protection) and severity (42.2% protection) was achieved upon combining the BCA's, leading to 140% protective effect relative to Dithane M-45 (Mancozeb) fungicide. The Pearson correlation test depicted a negative correlation between protection rate and total phenols, total soluble flavonoids, total tannins and Phenylalanine Ammonia Lyase activity (r > −0.5; P = 0.05). Meanwhile, a positive correlation was recorded with Polyphenol Oxydase activity (r > 0.5; P = 0.05). The results achieved unveil a substantial enhancement in bean plant growth and resistance against FRR mediated by a consortium of AMF2 and T. harzianum T8. This consortium might represent a cheaper and environmental friendly alternative to agrochemicals if further developed.