Antifungal and Antiaflatoxinogenic Effects of Cymbopogon citratus, Cymbopogon nardus, and Cymbopogon schoenanthus Essential Oils Alone and in Combination.

The antifungal and antiaflatoxinogenic activities of the essential oils (EOs) from the leaves of Cymbopogon schoenanthus, Cymbopogon citratus, Cymbopogon nardus, and their pair combinations were investigated. Antifungal susceptibility and the efficacy of paired combinations of EOs were assessed using agar microdilution and checkerboard methods, respectively. Identification and quantification of chemical components of the EOs were carried out by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector (GC-MS and GC-FID), respectively. Aflatoxins were separated and identified by High-Performance Liquid Chromatography (HPLC) and then quantified by spectrofluorescence. The EO of C. nardus exhibited the highest inhibitory activity against Aspergillus flavus and Aspergillus parasiticus. The combination of C. citratus and C. nardus and that of C. nardus and C. schoenanthus exhibited a synergistic effect against Aspergillus flavus and Aspergillus, respectively. Both C. citratus and C. schoenanthus EOs totally inhibited the synthesis of aflatoxin B1 at 1 µL/mL. C. citratus blocked the production of aflatoxins B2 and G2 at 0.5 µL/mL. Both C. citratus and C. schoenanthus totally hampered the production of the aflatoxin G1 at 0.75 µL/mL. The combination of C. citratus and C. schoenanthus completely inhibited the production of the four aflatoxins. The study shows that the combinations can be used to improve their antifungal and antiaflatoxinogenic activities.

DNA barcoding and isolation of vertically transmitted ascomycetes in sorghum from Burkina Faso: Epicoccum sorghinum is dominant in seedlings and appears as a common root pathogen.

Molecular identification of fungal taxa commonly transmitted through seeds of sorghum in Western Africa is lacking. In the present study, farm-saved seeds, collected from four villages in Northern Burkina Faso, were surface sterilized and the distribution of fungal DNA in seeds and seven-day-old seedlings was analyzed by 18S ribosomal DNA (rDNA) amplicon sequencing. More than 99% of the fungal rDNA was found to originate from ascomycetes. The distribution of ascomycetes at species level was subsequently analyzed by barcoding of ITS2 rDNA. Eighteen Operational Taxonomic Units (OTUs) were identified from seedlings, compared to 29 OTUs from seeds. The top-eight most abundant ascomycete OTUs from seedlings were annotated as: Epicoccum sorghinum, Fusarium thapsinum, four different Curvularia spp., Exserohilum rostratum and Alternaria longissima. These OTUs were also present in amplicons from seed samples collected in Central Burkina Faso confirming a common occurrence. E. sorghinum was highly predominant in seedlings both measured by DNA analysis and by isolation. The dominance of E. sorghinum was particularly strong in roots from poorly growing seedlings. Pathogenicity of E. sorghinum isolates was compared to F. thapsinum by inoculation to seeds in vitro. Both fungal species caused significant inhibition of seedling growth (P<0.001) and Koch's postulates were fulfilled. Extensive, dark necrosis in roots was a typical symptom of E. sorghinum, whereas wilting of leaves was caused primarily by F. thapsinum. This study provides the first molecular approach to characterize the seedling mycoflora of sorghum in Western Africa and suggests E. sorghinum as a common root pathogen.