Diversity of Root-knot Nematodes Associated with Tubers of Yam (Dioscorea spp.) Established Using Isozyme Analysis and Mitochondrial DNA-based Identification.

The root-knot nematodes (RKN), Meloidogyne spp., represent an important threat to yam (Dioscorea spp.) production in West Africa. With the aim to establish the diversity of RKN species affecting yam tubers, for control and resistance screening purposes, surveys were conducted in the main yam producing areas of Nigeria. Galled tubers (N = 48) were collected from farmers' stores and markets in nine states in Nigeria and in one district in Ghana. RKN isolated from yam tubers were identified using enzyme phenotyping (esterase and malate dehydrogenase) and mitochondrial DNA (mtDNA) NADH dehydrogenase subunit 5 (Nad5) barcoding. Examination of 48 populations revealed that yam tubers were infested by Meloidogyne incognita (69%), followed by M. javanica (13%), M. enterolobii (2%), and M. arenaria (2%). Most of the tubers sampled (86%) were infected by a single species, and multiple species of RKN were detected in 14% of the samples. Results of both identification methods revealed the same species, confirming their accuracy for the identification of these tropical RKN species. In addition to M. incognita, M. javanica, and M. enterolobii, we report for the first time M. arenaria infecting yam tubers in Nigeria. This finding extends the list of yam pests and calls for caution when developing practices for yam pest management.

Species of Heterodera cysts in cereal fields in Flanders.

Heterodera is a genus of cyst-forming nematodes, including the cereal cysts which can provoke yield reductions in grain crops. As little is known about the occurrence of these cysts in Belgian grain fields, a survey was organized, starting in Flanders. Soil samples were taken from 50 fields where cereals are grown in rotation with mainly beet, potato and vegetables. Cysts were extracted from the 112 samples and 10 individuals per sample were identified up to species level by morphometrical and morphological observations. The beet cyst nematode, Heterodera schachtii, was found in 34 fields (56%) at infestation levels varying from 0.6 to 1322 cysts/kg soil. Other Heterodera species (e.g. H. trifolii, H. mani) were found in low numbers and sometimes in mixtures with H. schachtii, but no cereal cysts were detected. This survey confirms that beet cyst nematodes are a problem in Flanders. The few cereal cysts that might be present were perhaps not detected due to the few individuals that were identified. For this reason, molecular identification tools which allow fast and accurate identification of Heterodera species would be very useful. It could be interesting to find out why cereal cysts are suppressed in our regions and to expand the survey to the Walloon region where more cereals are grown.

Effect of several centrifugal pump passages on the viability and activity of Steinernema carpocapsae, a biopesticide.

The effect of several passages through a centrifugal pump on the viability and activity of Steinernema corpocapsoe was investigated. A tendency of reduced viability was detected after 10 passages through the centrifugal pump, but the difference was not statistically significant. Activity decreased significantly from 91.9% to 83.6%. The experimental set-up was chosen to eliminate temperature increase. Therefore, the results prove that mechanical pump damage cannot be excluded as the cause of EPN damage during spray application.

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.