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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.

Treatment of seeds with an aqueous extract of yucca (YE), Yucca schidigera, was evaluated for antifungal activity against seedborne pathogens as well as its effect on seed germination and seedling growth of sorghum (Sorghum bicolor). The antifungal effect of YE was observed against Leptosphaeria sacchari (syn. Phoma sorghina) when the extract was applied at 2AE5 and 10% concentrations. At 10% concentration, YE significantly reduced not only the incidence of L. sacchari, but also that of Fusarium spp., Cochliobolus lunatus (syn. Curvularia lunata) and Cladosporium spp. The effect of 10% YE on seedborne fungi was broader than the fungicide fludioxonil, particularly with regard to Fusarium. Furthermore, the number of normal, healthy-looking seedlings increased in a dose-responsive manner with YE treatment. Seedling vigour was also stimulated by YE but no correlation was observed with the concentrations tested. Under glasshouse conditions, the treatment of seeds with 10% YE increased the emergence of seedlings and plant height and reduced the number of seedlings with crown rot compared to negative controls and saponin. The positive effect was similar to the effect obtained with fungicide-treated seeds. Treatment of seeds with synthetic saponin inhibited seedborne fungi less effectively and also negatively affected germination and vigour of the seedlings, compared to the treatment with YE. The results demonstrate an agronomic potential for the use of YE as a biofungicide for seed treatment of sorghum. The difference between the antifungal and the vigour-stimulating effects of YE warrants further investigation.

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Le niébé (Vigna unguiculata) est la principale légumineuse produite en Afrique. Sa production est confrontée à une contrainte majeure qui est la maladie de la mosaïque du niébé transmise par pucerons. Cette maladie peut entraîner des pertes de rendement de 87%. Les objectifs de cette étude étaient d'étudier les caractères sérologiques, moléculaires et la virulence du virus (CABMV) responsable de cette maladie au Burkina Faso, au Cameroun et en Centrafrique. Pour cela, la détection du virus par le test ACP-ELISA, l'inoculation mécanique, l'extraction de l'ARN viral total au TRizol et la RT-PCR ont été les méthodes utilisées pour caractériser le CABMV. Les caractérisations sérologique et moléculaire ont permis de détecter le CABMV sur 5 isolats et ont permis de confirmer l'existence du virus dans les trois pays. Plusieurs infections mixtes CABMV-CPMoV ont aussi été détectées. En outre, le criblage de dix variétés du Burkina Faso avec les cinq isolats a permis de distinguer quatre pathogroupes et un délai d'apparition de symptômes variant entre 6 et 20 JAI. Les variétés TZ1 Gourgou, KVx404-8-1x 693-2 BC4F9 et KVx 396-4-5-2Dx 693-2BC4F9 ont été résistantes à l'isolat RCA1. Les isolats BF et CAM2 ont été les plus virulents, suivis de RCA7, puis RCA4 et enfin RCA1.