Aspergillus spp. eliminate Sclerotinia sclerotiorum by imbalancing the ambient oxalic acid concentration and parasitizing its sclerotia

Abstract

Sclerotinia sclerotiorum, a pathogen of more than 600 host plants, secretes oxalic acid to regulate the ambient acidity and provide conducive environment for pathogenicity and reproduction. Few Aspergillus spp. were previously proposed as potential biocontrol agents for S. sclerotiorum as they deteriorate sclerotia and prevent pathogen's overwintering and initial infections. We studied the nature of physical and biochemical interactions between Aspergillus and Sclerotinia. Aspergillus species inhibited sclerotial germination as they colonized its rind layer. However, Aspergillus-infested sclerotia remain solid and viable for vegetative and carpogenic germination, indicating that Aspergillus infestation is superficial. Aspergillus spp. of section Nigri (Aspergillus japonicus and Aspergillus niger) were also capable of suppressing sclerotial formation by S. sclerotiorum on agar plates. Their culture filtrate contained high levels of oxalic, citric and glutaric acids comparing to the other Aspergillus spp. tested. Exogenous supplementation of oxalic acid altered growth and reproduction of S. sclerotiorum at low concentrations. Inhibitory concentrations of oxalic acid displayed lower pH values comparing to their parallel concentrations of other organic acids. Thus, S. sclerotiorum growth and reproduction are sensitive to the ambient oxalic acid fluctuations and the environmental acidity. Together, Aspergillus species parasitize colonies of Sclerotinia and prevent sclerotial formation through their acidic secretions.

Use of transcriptomic profiling to identify candidate genes involved in Polyporus umbellatus sclerotial formation affected by oxalic acid

“…It was found that oxalic acid accumulation led to lowering ambient pH and promoted Sclerotinia sclerotiorum sclerotial development 13 . Recently, it has also been reported that S. sclerotiorum sclerotial formation was inhibited by exogenous oxalic acid at 25 mM and higher 14 . In this study, oxalic acid also had a dual effect on the sclerotia formation of P. umbellatus : a low concentration of OA (ranging from 0.05 to 0.10 mg/mL) promoted sclerotia differentiation from mycelia, while a high concentration of OA (1.10 mg/mL and higher) inhibited the formation of sclerotia (Fig.…”

Polyphasic Characterization of Four Aspergillus Species as Potential Biocontrol Agents for White Mold Disease of Bean

“…showed efficient suppression against a broad range of plant pathogenic fungi, bacteria, and nematodes [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. The suppressive effect of Aspergillus was explained by several mechanisms including direct mycoparasitism [ 31 , 32 ], indirect inhibitory secretome such as hydrolytic chitinase and β-glucanase enzymes [ 22 , 33 ], and organic acids [ 34 , 35 , 36 , 37 ].…”

“…This work was established to evaluate the biocontrol potential for diverse species of Aspergillus on white mold disease of legumes caused by S. sclerotiorum under lab and greenhouse conditions. The examined species were genetically identified, and their organic acid profile was characterized in our previous work [ 37 ]. As a continuation, the morphological, microscopic, mycotoxigenic, and pathological attributes were characterized as well to demonstrate variability among tested species.…”

Transcriptomic Profiling Identifies Candidate Genes Involved in Polyporus Umbellatus Sclerotial Formation Affected by Oxalic Acid

“…It was found that oxalic acid accumulation led to lowering ambient pH and favored Sclerotinia sclerotiorum sclerotial development 13 . Recently, it has also been reported that S. sclerotiorum sclerotial formation was inhibited by exogenous oxalic acid of 25mM and higher 14 . Thus, oxalic acid played dual roles in sclerotial differentiation.…”