Interactions of free-living amoebae with the rice fungal pathogen, Rhizoctonia solani

Abstract

ObjectiveRhizoctonia solani is a soil-borne fungal pathogen of many important crop plants. In rice, R. solani causes sheath blight disease, which results in devastating grain yield and quality losses. Few methods are available to control this pathogen and classic single gene resistance mechanisms in rice plants have not been identified. We hypothesize that alternate means of control are available in the environment including free-living amoebae. Amoebae are soil-, water- and air-borne microorganisms that are predominantly heterotrophic. Many amoeba species are mycophagous, and several harm their prey using mechanisms other than phagocytosis. Here, we used light and scanning electron microscopy to survey the interactions of R. solani with four amoeba species, with the goal of identifying amoebae species with potential for biocontrol.ResultsWe observed a wide range of responses during interactions of R. solani with four different free-living amoebae. Two Acanthamoeba species encyst in co-cultures with R. solani at higher rates than medium without R. solani. Vermamoeba vermiformis (formerly Hartmanella vermiformis) attach to R. solani mycelium and are associated with mycelial shriveling and perforations of fungal cell walls, indicating an antagonistic interaction. No phenotypic changes were observed in co-cultures of Dictyostelium discoideum and R. solani.

A Review of Methods to Determine Viability, Vitality, and Metabolic Rates in Microbiology

“…However, unlike tetrazolium salt or resazurin reduction, FDA hydrolysis is not expected to be directly linked to O 2 consumption, although many studies have shown that the two are often correlated ( Fontvieille et al, 1992 ). Still, the assay can be widely used in many setups as FDA hydrolysis capacity is widespread ( Schnurer and Rosswall, 1982 ; Gaspar et al, 2001 ; Prosser et al, 2011 ; Liang et al, 2019 ; Long et al, 2019 ; Braun et al, 2020 ). Intracellular hydrolysis of FDA results in the accumulation of fluorescein (which is unable to pass cell membranes) in metabolically active cells.…”

Plant Growth-Promoting Activity of Pseudomonas aeruginosa FG106 and Its Ability to Act as a Biocontrol Agent against Potato, Tomato and Taro Pathogens

“…The development of reliable microbial treatments to promote plant growth requires, however, the identification of new beneficial bacterial strains with high antagonistic activity towards phytopathogens. Several mechanisms have been suggested to explain the antagonistic effects of beneficial microorganisms on phytopathogens, including competition for nutrients, minerals, and colonization sites [ 8 ], inhibition of the pathogens via secreted toxins, antibiotics and biosurfactants [ 9 ], and parasitism based on the production of hydrolytic enzymes that degrade pathogens’ cell walls [ 10 ].…”

No rest for resting spores: Can predators mitigate clubroot disease?

“…Microbiome predators—protists, nematodes and microarthropods—are the main consumers of soil bacteria and fungi (Gao et al, 2019; Geisen et al, 2016; Neher, 2010; Xue et al, 2023). Predation by nematodes (Meyer‐Wolfarth et al, 2017; Zhang et al, 2023), collembola (Meyer‐Wolfarth et al, 2017; Neher & Barbercheck, 2019; Zhang et al, 2023) and protists (Guo et al, 2022; Long et al, 2019; Xiong et al, 2020) on fungal and oomycetes soilborne pathogens has been shown to reduce infections in other plant‐pathogen systems. However, other soilborne pathogens often differ profoundly in terms of size (oomycetes, nematodes, and fungi), mobility (nematodes), or filamentous growth pattern (oomycetes and fungi) compared to P. brassicae .…”

“…What remains unconsidered to date is the potential of microbiome predators to act as BCAs and reduce infections by soilborne pathogens (Chandarana & Amaresan, 2022;Martins et al, 2022;Nguyen et al, 2023). These abundant microbiome predator groups, such as protists, nematodes, collembola, and microarthropods, mediate soil microbiome structures (Afridi et al, 2022;Dumack et al, 2016Dumack et al, , 2019Friberg et al, 2005;Guo et al, 2022;Innocenti & Sabatini, 2018;Long et al, 2019;McGrann, 2022;Meyer-Wolfarth et al, 2017) potentially in a clubroot suppressive manner (Afridi et al, 2022;Friberg et al, 2005;McGrann, 2022) and might directly prey on P. brassicae. In fact, the diet of many soil-dwelling organisms includes bacterial, fungal, or oomycete pathogens, leading to a reduction of pathogen loads (Dumack et al, 2016(Dumack et al, , 2019Guo et al, 2022;Innocenti & Sabatini, 2018;Long et al, 2019;Martins et al, 2022;Meyer-Wolfarth et al, 2017;Old & Darbyshire, 1978;Potapov et al, 2022;Xiong et al, 2019;Zhang et al, 2023).…”