Antoine Affokpon

Mitochondrial haplotype-based identification of ethanol-preserved root-knot nematodes from Africa.

The asexual root-knot nematodes (RKNs) (Meloidogyne spp.) exemplified by Meloidogyne incognita are widespread and damaging pests in tropical and subtropical regions worldwide. Comparison of amplification products of two adjacent polymorphic regions of the mitochondrial genome using DNA extracts of characterized RKN strains, including 15 different species, indicate that several species are derived from the same or closely related female lineages. Nevertheless, M. javanica, M. enterolobii, M. incognita, and other key species could each be assigned unique mitochondrial haplotypes based on polymerase chain reaction fragment size and restriction cleavage patterns. M. arenaria isolates did not group as a single haplotype, consistent with other reports of diversity within this species. To test the utility of this assay, we characterized ethanol-preserved samples from 103 single-species isolates from four countries in sub-Saharan Africa (Benin, Nigeria, Kenya, and Tanzania). Mitochondrial haplotypes corresponding to M. javanica and M. incognita were the most prevalent. Samples from western Africa included several instances of M. enterolobii but this species was not detected in samples from East Africa. This protocol provides progress toward a standardized strategy for identification of RKN species from small, preserved samples and a rational starting point for classifying species present in regions where previous knowledge has been limited.

In vitro growth characterization and biocontrol potential of naturally occurring nematophagous fungi recovered from root-knot nematode infested vegetable fields in Benin

Naturally occurring fungal antagonists of root-knot nematodes (Meloidogyne spp., RKNs) were collected from 88 root and corresponding rhizosphere soil samples from 50 intensively cultivated fields used for peri-urban vegetable production in Benin, West Africa. Five species of Trichoderma viz.: T. asperellum, T. harzianum, T. brevicompactum, T. hamatum and T. erinaceum and four isolates of Pochonia chlamydosporia were isolated from RKN egg masses on root systems of crops and/or infested soil. During temperature-tolerance assessment studies, most isolates had maximum growth rates in Petri dishes at 28 °C. Chlamydospore production by P. chlamydosporia was high in 2:1 v/v sand-milled corn medium. In pots, P. chlamydosporia isolates showed high ability to colonize and persist in tomato rhizosphere over 10 weeks. Pre-planting application with some P. chlamydosporia isolates led to up to 50% infected eggs and 25% reduction of RKN multiplication and root galling damage. This study provides valuable information for the mass rearing of the respective fungal inoculum and the first information on the potential of West African P. chlamydosporia isolates for use against RKN in vegetable production systems.

Molecular diversity of Scutellonema bradys populations from Benin, based on ITS1 rDNA and COI mtDNA

In Benin, yam production continues to face numerous production constraints, including yield and quality reduction by Scutellonema bradys. Implementation of efficient management techniques against this pest requires an improved understanding, including at the molecular level, of the pest. The current study aimed at identifying the Scutellonema spp. associated with yam in Benin and investigating the phylogenetic relationships between populations. Nematodes of the genus Scutellonema were obtained from tubers exhibiting external dry rot symptoms. DNA was extracted from nematodes belonging to 138 populations collected from 49 fields from 29 villages. For 51 of these populations, both the ITS1 and COI regions could be amplified via PCR, sequenced, compared with available sequences in the NCBI database and were identified as S. bradys. Maximum likelihood was used to construct 60% consensus phylogenetic trees based on 51 sequences. This phylogenetic analysis did not reveal any genetic separation between populations by cultivar, village, cropping system nor by agroecological zone. Neither could any subgroups within S. bradys be separated, indicating that no subspecies were present. An earlier published species-specific primer set was verified with the DNA of the 51 sequences and was considered a reliable and rapid method for S. bradys identification.