Influence of different biological control agents and compost on total and nitrification-driven microbial communities at rhizosphere and soil level in a lettuce -Fusarium oxysporumf. sp.lactucaepathosystem

Abstract

Aims The response of rhizosphere and bulk soil indigenous microbial communities focusing on nitrifiers was evaluated after the application of different biological control agents (BCAs; Bacillus, Trichoderma, Pseudomonas) and compost in controlling lettuce Fusarium wilt. Methods and Results Experiments were conducted ‘in situ’ over two lettuce cropping seasons. Total fungal, bacterial and archaeal populations and the nitrifiers were analysed using quantitative polymerase chain reaction method. The pathogen, Fusarium oxysporum forma specialis lactucae (FOL), Bacillus, Trichoderma and Pseudomonas and three antifungal genes (chiA, 2,4‐diacetylphloroglucinol ‐ phlD and HCN synthase ‐ hcnAB genes) were also assessed. Quantitative data were corroborated with disease severity (DS), potential nitrification activity and soil chemical parameters. The application of BCAs and compost resulted in the disease reduction by as much as 69%, confirmed by significant negative correlations between Bacillus subtilis, Trichoderma and Pseudomonas sp. abundances and DS. The FOL presence in the untreated control resulted in the nitrifiers niche differentiation. Conclusions The used treatments were efficient against Fusarium wilt and did not influence negatively the nontarget microbial communities. Significance and Impact of the Study The use of BCAs and compost appears as an effective and safe strategy to implement sustainable agricultural practices.

A Compost Treatment Acts as a Suppressive Agent in Phytophthora capsici – Cucurbita pepo Pathosystem by Modifying the Rhizosphere Microbiota

“…Bacteria and fungi had almost similar gene copy number. This is in agreement with previous studies (Cucu et al, 2019), where the fungal and bacterial abundance in rhizosphere were found to be at the same level compared to bulk soil.…”

“…Above 12 compostpeat mixtures, only CM -10% was able to suppress PHC, due to its microbial composition that can play a major role in its suppressiveness (Reuveni et al, 2002;Tilston et al, 2002;Papasotiriou et al, 2013;De Corato et al, 2019). The mycobiota composition of the CM -10% treated pots clustered separately if compared to CC and UC, confirming that beneficial microorganisms present in CM -10% treatment can protect the plant root system by microbiota modulation (Antoniou et al, 2017;Mwaheb et al, 2017;Cucu et al, 2019;Topalović et al, 2020;Zhang et al, 2020). Further investigations should be necessary to obtain a deeper understanding of how this protection is conferred because the complex interaction between rhizosphere, microbiota and pathogens is less explored.…”

“…Compost microbiota plays a major role in the suppressive activity of composts, and in an attempt to prove this, many studies have compared sterilized composts with their non-sterilized counterparts and have found that the inactivation of microbiota is connected to the loss of suppressive activity (Reuveni et al, 2002;Tilston et al, 2002;Papasotiriou et al, 2013;De Corato et al, 2019). The microorganisms present in a compost are also selected by root exudates, according to the need and the genotype of the plant, resulting in the shaping of the rhizosphere composition and accomplishing the suppressive activity against several biotic stresses such as fungi and nematodes (Antoniou et al, 2017;Mwaheb et al, 2017;Cucu et al, 2019;Zhang et al, 2020). Thus, in order to prevent soil-borne diseases when pathogens are present in field, it is very important to know which microorganisms confer compost suppressiveness according to the type of pathosystem.…”

Effects of Bacillus subtilis and Pseudomonas fluorescens Inoculation on Attributes of the Lettuce (Lactuca sativa L.) Soil Rhizosphere Microbial Community: The Role of the Management System

“…This increase could be attributed to the increased B. subtilis biomass. However, the low temperatures prevailing during the experiment, compared to the optimum temperature for this species (30)(31)(32)(33)(34)(35) • C, makes this explanation less possible. Alternatively, B. subtilis could act synergistically with the other Gram-positive bacteria supporting their growth.…”

“…Bacillus and Pseudomonas-based inoculants have presented promising results for lettuce crop yield [32,33]. Nevertheless, only a few studies have focused on the effect of PGPR inoculants' application on the indigenous soil microbial communities [33,34]. The incorporation of PGPR inoculants into the soil could have a significant impact on indigenous soil microbial community because these exogenous microbes are involved in a wide range of interactions with the autochthonous microbes such as competition, synergy, or prey-predator interactions.…”