Combined Field Inoculations of Pseudomonas Bacteria, Arbuscular Mycorrhizal Fungi, and Entomopathogenic Nematodes and their Effects on Wheat Performance

Abstract

In agricultural ecosystems, pest insects, pathogens, and reduced soil fertility pose major challenges to crop productivity and are responsible for significant yield losses worldwide. Management of belowground pests and diseases remains particularly challenging due to the complex nature of the soil and the limited reach of conventional agrochemicals. Boosting the presence of beneficial rhizosphere organisms is a potentially sustainable alternative and may help to optimize crop health and productivity. Field application of single beneficial soil organisms has shown satisfactory results under optimal conditions. This might be further enhanced by combining multiple beneficial soil organisms, but this remains poorly investigated. Here, we inoculated wheat plots with combinations of three beneficial soil organisms that have different rhizosphere functions and studied their effects on crop performance. Plant beneficial Pseudomonas bacteria, arbuscular mycorrhizal fungi (AMF), and entomopathogenic nematodes (EPN), were inoculated individually or in combinations at seeding, and their effects on plant performance were evaluated throughout the season. We used traditional and molecular identification tools to monitor their persistence over the cropping season in augmented and control treatments, and to estimate the possible displacement of native populations. In three separate trials, beneficial soil organisms were successfully introduced into the native populations and readily survived the field conditions. Various Pseudomonas, mycorrhiza, and nematode treatments improved plant health and productivity, while their combinations provided no significant additive or synergistic benefits compared to when applied alone. EPN application temporarily displaced some of the native EPN, but had no significant long-term effect on the associated food web. The strongest positive effect on wheat survival was observed for Pseudomonas and AMF during a season with heavy natural infestation by the frit fly, Oscinella frit, a major pest of cereals. Hence, beneficial impacts differed between the beneficial soil organisms and were most evident for plants under biotic stress. Overall, our findings indicate that in wheat production under the test conditions the three beneficial soil organisms can establish nicely and are compatible, but their combined application provides no additional benefits. Further studies are required, also in other cropping systems, to fine-tune the functional interactions among beneficial soil organisms, crops, and the environment.

Belowground Microbiota and the Health of Tree Crops

“…The combined application of wide-spectrum BCA with efficient plant growth promoting microorganisms has the potential to reach the increased consistency of performance over a wider range of soil conditions. A recent example was presented by Imperiali et al ( 2017 ), who applied Pseudomonas bacteria, AM fungi and EPN to improve wheat performance. Moreover, the application of entire, well-characterized, complex microbiota may further improve the efficiency of soil-borne pathogen management and other biotic constraints (Gopal et al, 2013 ; Berg et al, 2014 ; Kowalski et al, 2015 ).…”

Respuesta morfo-productiva de plantas de pimiento morrón biofertilizadas con Pseudomonas putida y dosis reducida de fertilizantes sintéticos en invernadero

“…On the other hand, rhizobacteria have been described as having the ability to improve the mineral nutrition process in plants, facilitating its availability, and increasing nutriment absorption, such as N, P and chelating ions, as Fe (Kumar-Solanki et al, 2014;Singh et al, 2018). In that respect, several authors have pointed out the importance of using rhizobacterial strains of the genus Pseudomonas as biofertilizer agents because of their capacity to stimulate growth and/or productivity in plants of economic interest, such as tomato (Hernández-Montiel et al, 2017), habanero pepper (Chiquito-Contreras et al, 2017), bell pepper (Bacilio et al, 2016), potato (Arseneault et al, 2015), soybean (Rubina et al, 2018, wheat (Imperiali et al, 2017), maize (Di Salvo et al, 2018), among others.…”

The symbiotic bacteria Alcaligenes faecalis of the entomopathogenic nematodes Oscheius spp. exhibit potential biocontrol of plant‐ and entomopathogenic fungi

“…Different combinations of EPNs and commercial EPF for increasing plant growth and protection have already been attempted in several greenhouse and field trials. Generally, however, they did not show clear additive or synergistic effect of both biocontrol agents and even find negative interactive effects (Wu et al ., ; Imperiali et al ., ; Wakil et al ., ). EPNs were detected in larvae only in a few cases (11%) in the EPF and EPNs combination treatments (Tarasco et al ., ).…”