The world potato is facing major economic losses due to disease pressure and environmental concerns regarding pesticides use. This work aims at addressing these two issues by isolating indigenous bacteria that can be integrated into pest management strategies. More than 2,800 strains of Bacillus-like and Pseudomonas-like were isolated from several soils and substrates associated with potato agro-systems in Belgium. Screenings for antagonistic activities against the potato pathogens Alternaria solani, Fusarium solani (BCCM-MUCL 5492), Pectobacterium carotovorum (ATCC 15713), Phytophthora infestans (CRA-W10022) and Rhizoctonia solani (BCCM-MUCL 51929) were performed, allowing the selection of 52 Bacillus spp. and eight Pseudomonas spp. displaying growth inhibition of at least 50% under in vitro conditions, particularly against P. infestans. All 60 bacterial isolates were identified based on 16S rRNA gene sequencing and further characterized for the production of potential bio-active secondary metabolites. The antagonistic activities displayed by the selected strains indicated that versatile metabolites can be produced by the strains. For instance, the detection of genes involved bacilysin biosynthesis was correlated with the strong antagonism of Bacillus pumilus strains toward P. infestans, whereas the production of both bio-surfactants and siderophores might explain the high antagonistic activities against late blight. Greenhouse assays with potato plants were performed with the most effective strains (seven Bacillus spp. and four Pseudomonas spp.) in order to evaluate their in vivo antagonistic effect against P. infestans. Based on these results, four strains (Bacillus amyloliquefaciens 17A-B3, Bacillus subtilis 30B-B6, Pseudomonas brenneri 43R-P1 and Pseudomonas protegens 44R-P8) were retained for further evaluation of their protection index against P. infestans in a pilot field trial. Interestingly, B. subtilis 30B-B6 was shown to significantly decrease late blight severity throughout the crop season. Overall, this study showed that antagonistic indigenous soil bacteria can offer an alternative to the indiscriminate use of pesticide in potato agro-systems.

SummaryFungi, nematodes and oomycetes belong to the most prominent eukaryotic plant pathogenic organisms. Unicellular organisms from other eukaryotic lineages, commonly addressed as protists, also infect plants. This review provides an introduction to plant pathogenic protists, including algae infecting oomycetes, and their current state of research.

The control of rhizomania, one of the most important diseases of sugar beet caused by the Beet necrotic yellow vein virus, remains limited to varietal resistance. In this study, we investigated the putative action of Bacillus amylolequifaciens lipopeptides in achieving rhizomania biocontrol through the control of the virus vector Polymyxa betae. Some lipopeptides that are produced by bacteria, especially by plant growth-promoting rhizobacteria, have been found to induce systemic resistance in plants. We tested the impact of the elicitation of systemic resistance in sugar beet through lipopeptides on infection by P. betae. Lipopeptides were shown to effectively induce systemic resistance in both the roots and leaves of sugar beet, resulting in a significant reduction in P. betae infection. This article provides the first evidence that induced systemic resistance can reduce infection of sugar beet by P. betae.

Plants have always grown and evolved surrounded by numerous microorganisms that inhabit their environment, later termed microbiota. To enhance food production, humankind has relied on various farming practices such as irrigation, tilling, fertilization, and pest and disease management. Over the past few years, studies have highlighted the impacts of such practices, not only in terms of plant health or yields but also on the microbial communities associated with plants, which have been investigated through microbiome studies. Because some microorganisms exert beneficial traits that improve plant growth and health, understanding how to modulate microbial communities will help in developing smart farming and favor plant growth-promoting (PGP) microorganisms. With tremendous cost cuts in NGS technologies, metagenomic approaches are now affordable and have been widely used to investigate crop-associated microbiomes. Being able to engineer microbial communities in ways that benefit crop health and growth will help decrease the number of chemical inputs required. Against this background, this review explores the impacts of agricultural practices on soil- and plant-associated microbiomes, focusing on plant growth-promoting microorganisms from a metagenomic perspective.

This study aimed to verify the potential of three Aspergillus and Bacillus species as growth promoters in cotton plants under greenhouse conditions. The experiment was conducted with a completely randomized design with seven treatments (six microorganisms plus one control) and five replicates until the flowering stage at 70 days after emergence. The inoculation of cotton plants with Bacillus velezensis (Bv188) and Bacillus subtilis (Bs248 and Bs290) had a positive effect on total nitrogen extraction (899.31, 962.18, and 755.41 mg N/kg dry matter, respectively) compared to the control (459.31 mg N/kg dry weight), total phosphorus extraction (121.94, 124.31, and 99.27 mg P/kg dry matter, respectively) compared to the control (65.10 mg P/kg dry matter), and total dry matter (41.08, 43.59, and 49.86 g/plant, respectively) compared to the control (26.70 g/plant), as well as biomass carbon (72.26, 35.18, and 14.7 mg/kg soil, respectively). Cotton plants inoculated with Aspergillus brasiliensis (F111), Aspergillus sydowii (F112), and Aspergillus sp. (versicolor section) (F113) had higher total nitrogen extraction (953.33, 812.59, and 891.62 mg N/kg dry matter, respectively) compared to the control (459.31 mg N/kg dry matter), a higher total phosphorus (122.30, 104.86, and 118.45 mg P/kg dry matter, respectively) compared to the control (65.10 mg P/kg dry matter), a higher total dry matter (37.52, 37.41, and 53.02 g/plant) compared to the control (26.70 g/plant), and greater respiratory activity (14.98, 10.43, and 7.11 mg CO2/100 g soil, respectively) compared to the control (3.5 mg CO2/100 g soil). The fungi A. brasiliensis (F111) and A. sydowii (F112) promoted higher phosphorus absorption by cotton plants, which was reflected by the lower amount of nutrients in the soil (7.10 and 16.96 g P/dm3 soil) than in the control (26.91 g P/dm3 soil). The results suggest that B. subtilis 248 promoted an increase in phosphorus extracted from the roots and total and phosphorous compounds from the root dry matter and increased the value of soil respiratory activity, and this bacterium could be used as an inoculant in cotton crops.