Nematodes as suitable indicators for soil health

During the Greenresilient project, nematode communities will be characterized at the beginning, in the middle and at the end of the field trials to identify shifts in their community. These shifts will be analysed to determine whether the chosen ‘innovative’ methods tested in the project are beneficial for soil health, causing an increased resilience to pests and diseases and a more balanced nutrient supply, for more sustainable and high-quality crop production. This leaflet explains why nematodes can be excellent indicators for soil health

Nematodes as indicators of soil biodiversity in Greenresilient

Soil biodiversity is reflected in the composition of its nematode fauna. In Greenresilient, we are analyzing nematode communities (genera, numbers, feeding types), which provides important information about the soil health status

Morphological and molecular characterisation of Scutellonema species from yam (Dioscorea spp.) and a key to the species of the genus

The yam nematode, Scutellonema bradys, is a major threat to yam (Dioscorea spp.) production across yam-growing regions. In West Africa, this species cohabits with many morphologically similar congeners and, consequently, its accurate diagnosis is essential for control and for monitoring its movement. In the present study, 46 Scutellonema populations collected from yam rhizosphere and yam tubers in different agro-ecological zones in Ghana and Nigeria were characterised by their morphological features and by sequencing of the D2-D3 region of the 28S rDNA gene and the mitochondrial COI genes. Molecular phylogeny, molecular species delimitation and morphology revealed S. bradys, S. cavenessi, S. clathricaudatum and three undescribed species from yam rhizosphere. Only S. bradys was identified from yam tuber tissue, however. For barcoding and identifying Scutellonema spp., the most suitable marker used was the COI gene. Additionally, 99 new Scutellonema sequences were generated using populations obtained also from banana, carrot, maize and tomato, including the first for S. paralabiatum and S. clathricaudatum, enabling the development of a dichotomous key for identification of Scutellonema spp. The implications of these results are discussed

Heat tolerance among different strains of the entomopathogenic nematode Heterorhabditis bacteriophora

Quality of biological control products based on entomopathogenic nematodes can be severely damaged due to exposure to high temperature surpassing 40A degrees C. The study screened 36 natural populations and 18 hybrid or inbred strains of Heterorhabditis bacteriophora for their response to high temperature. Nematodes were tested with or without prior adaptation to heat at 35A degrees C for 3 h. Five strains of H. indica and one of H. megidis were also included. Molecular identification using nuclear ribosomal DNA sequences confirmed the designation to the three Heterorhabditis spp. The mean tolerated temperature ranged from 33.3A degrees C to 40.1A degrees C for non-adapted and from 34.8A degrees C to 39.2A degrees C for adapted strain populations. H. indica was the most tolerant, followed by H. bacteriophora and H. megidis. No correlation was recorded between tolerance assessed with and without adaptation to heat, implying that different genes are involved. Correlation between heat tolerance and mean annual temperature at place of origin of the strains was weak. A high variability in tolerance among strains and the relatively high heritability (hA(2)A = 0.68) for the adapted heat tolerance recorded for H. bacteriophora provide an excellent foundation for future selective breeding with the objective to enhance heat tolerance of H. bacteriophora

Distribution, prevalence, and severity of damages caused by nematodes on yam (Dioscorea rotundata) in NIssathme30igeria

Nigeria is the main yam-growing country of the world. In the country, various plant-parasitic nematodes have been reported constraining yam production and the storability of tubers. This study established the damage level of nematodes on white yam tubers (Dioscorea rotundata) across the major production areas in the country for management purposes. Incidence and severity of symptoms (cracking, dry rot, and galling) associated with nematodes were assessed on 1,114 yam heaps (181 vendors) from 23 markets and on 2,502 tubers from 26 farmer storage areas (yam barns) in the Humid Forest (HF), Derived Savanna (DS) and Southern Guinea Savanna (SGS) agro-ecological zones (AEZ). On yam heaps, the symptom incidence averaged 55%, 35%, and 6% for galls, dry rot, and for cracks, respectively. Only the incidence of dry rot was significantly different (P<0.0001) across the AEZ. On yam tubers, the incidence averaged 24%, 8%, and 2% for galls, dry rot, and for cracks, respectively. The incidence for galls was higher in the SGS than in the DS (P=0.0018) whereas the incidence of cracks was higher in the DS than in the SGS (P=0.0080). The actual values of symptom severity were, in general, low in the AEZ compared with the predicted values except for dry rot. A significant positive correlation was found between galls and Meloidogyne and between dry rot and Scutellonema. Pratylenchus was also recovered from a few yam tubers; however, no link with symptoms on yam tubers could be established. Vendors and farmers, based on the answers from a questionnaire, were very familiar with nematode symptoms on yam tubers, but awareness of nematodes was low. This study shows that Meloidogyne and Scutellonema are the major nematode constraints to yam production in the three AEZ of Nigeria and calls for effective yam nematode management in Nigeria and in other yam-producing countries

Effects of synthetic fertilizer and farm compost on soil nematode community in long-term crop rotation plots : a morphological and metabarcoding approach

Soil biodiversity plays a key regulation role in the ecosystem services that underpin regenerative sustainable agriculture. It can be impacted by agricultural management techniques, both positively (through measures such as compost application) and negatively (through, for example, application of synthetic nitrogen). As one of the most numerous members of the soil biota, nematodes are well established as indicators for the soil food web. However, compost application also includes the addition of nematodes present in compost and their subsequent survival in soil is unknown. Nematode communities within the compost applied to soil, and nematode communities in the soil of a multi-year rotational cropping field trial in Melle (Belgium) were studied using morphological and metabarcoding techniques. Compost (C) and nitrogen fertilizer (NF) treated plots were compared. Three replicate plots were investigated for each of the following treatments: C application only; C and NF application; NF only; no C and no NF (control). Plots were sampled six times between 2015-2017, before and after C or NF were added each spring and after crop harvest (except for 2017). NF treatment resulted in a significant decrease of fungal feeding and predatory nematodes, while herbivorous nematodes were positively affected. Remarkably, we did not find compost addition to exert any noticeable effects on the soil nematode community. The morphological and metabarcoding data resulted in different results of the nematode community composition. However, trends and patterns in the two data sets were congruent when observed with NMDS plots and using the nematode maturity index. Metabarcoding of individual compost nematode taxa demonstrated that nematodes originating from compost did not persist in soil

Morphological and molecular characterization of Pratylenchus species from Yam (Dioscorea spp.) in West Africa

The root-lesion nematodes (RLN), Pratylenchus spp., are among the major plant-parasitic nematodes affecting yam (Dioscorea spp.) production in West Africa. The distribution and diversity of RLN species associated with yam was investigated through a soil and tuber survey of the main producing areas in Nigeria and Ghana. Pratylenchus spp. were detected in the yam rhizosphere in 59% of 81 soil samples from Ghana and 39% of 114 soil samples from Nigeria. Pratylenchus spp. were detected in 24 of 400 tubers examined, in combination with root-knot nematodes (Meloidogyne spp.) and their associated damage of galls and crazy roots (79%), and with yam nematode (Scutellonema bradys) and their associated damage of dry rot (17%), although no specific additional symptoms were observed for Pratylenchus spp. Species of Pratylenchus were identified by their morphological features and by sequences of the D2-D3 region of the 28 S rDNA gene and the mitochondrial cytochrome oxidase I gene (COI). Pratylenchus brachyurus was the most frequent RLN species in both the rhizosphere and tubers of yam. Pratylenchus hexincisus was recovered from one tuber collected in Nigeria. While further investigations are required to establish the host status of yam for this nematode, this appears to be the first record of P. hexincisus on yam. The present taxonomical status of P. scribneri and P. hexincisus is discussed