Inoculation of Medicago sativa cover crop with Rhizophagus irregularis and Trichoderma harzianum increases the yield of subsequently-grown potato under low nutrient conditions

Arbuscular mycorrhizal fungi (AMF) and Trichoderma spp. are soil microorganisms that increase growth and improve a/biotic stress resistance of numerous crop plants. So far, most studies on potato were conducted under greenhouse or in vitro conditions and few reported on results within the field. Therefore, the objective was to investigate the impact on potato yield of the co-inoculation of R. irregularis MUCL 41833 and T. harzianum MUCL 29707 applied to a cover crop (i.e. Medicago sativa) preceding potato planting or to potato at planting. Two macroplot trials were set up over two growing seasons with the cultivars Sarpo Mira and Bionta, respectively. In both trials, individual subplots were arranged in a randomized complete block design replicated four times. Microbial inoculants were entrapped in alginate beads. Four treatments were considered: inoculum applied to the cover crop preceding potato planting (I+CC+), inoculum applied on potato at planting and absence of a preceding cover crop - i.e. bare soil - (I+CC−), no inoculum applied either at cover crop preceding potato planting or on potato at planting (I−CC+), no inoculum applied on potato at planting and absence of a preceding cover crop - i.e. bare soil - (I−CC−). Potato yield (i.e. tuber weight, size and number) was evaluated in both trials. Potato root colonization by arbuscular mycorrhizal fungi and abundance of Trichoderma harzianum in soil were evaluated in trial 2. In both trials, the most advantageous strategy to increase potato tuber weight was by inoculating the cover crop. For cultivar Sarpo Mira (trial 1) inoculation increased significantly (P < 0.001) potato yield and the number of tubers only if inoculum was applied to the cover crop. For cultivar Bionta (trial 2), inoculation and cover crop had an additive effect on potato yield. Inoculation increased significantly (P < 0.01) the percentage of potatoes >30 mm long. Total root colonization by AMF and% arbuscules in potato roots was increased significantly (P < 0.001) following inoculation but seemed not influenced by cover crop alone (i.e. without inoculation). Our results suggested that the application of beneficial microorganisms at cover crop sowing prior to potato planting is an adequate, easy-to-apply cropping practice to increase potato production.