Integrative taxonomy, distribution, and host associations of Geocenamus brevidens and Quinisulcius capitatus from southern Alberta, Canada

The Impact of Winter Cover Crops on Soil Nematode Communities and Food Web Stability in Corn and Soybean Cultivation

There is increasing adoption of winter cover crops (WCCs) in corn and soybean production in Canada, primarily to reduce erosion and increase soil organic matter content. WCCs have the potential to influence nematode communities by increasing free-living nematodes and decreasing plant-parasitic nematodes or vice versa. However, the mechanism by which WCCs change nematode community assemblages still remains a key question in soil food web ecology. We tested the hypothesis that the long-term use of rye (Secale cereale), barley (Hordeum vulgare) and oat (Avena sativa) as monocultures or mixtures promotes nematode communities and improves overall soil health conditions compared to winter fallow. The results from this study revealed that the use of WCCs generally promoted a higher abundance and diversity of nematode communities, whereas plant parasitic nematodes were the most abundant in winter fallow. Moreover, the mixtures of WCCs had more similar nematode communities compared to rye alone and winter fallow. The structure and enrichment indices were higher with WCCs, indicating higher nutrient cycling and soil suppressiveness, which are signs of healthy soil conditions. Furthermore, WCCs significantly reduced the populations of root lesion nematode Pratylenchus, although their numbers recovered and increased during the main crop stages. Additionally, mixtures of WCCs promoted the highest abundance of the stunt nematode Tylenchorhynchus, whereas winter fallow had a higher abundance of the spiral nematode Helicotylenchus during the fallow period and the main crop stages. The results show that the long-term use of cover crops can have a positive impact on nematode communities and the soil food web, but these changes depend on the type of WCCs and how they are used.

Integrative taxonomy and phylogenetic relationships between representatives of genera within Merliniinae (Nematoda: Merliniidae), with new data on fourteen known and one unknown species

The application of integrative taxonomic approaches is useful to species delineation based on a combination of distinct types of characters, here morphological features and ribosomal DNA sequences. In this study, we surveyed ectoparasitic nematodes of the subfamily Merliniinae in cultivated and natural environments in Iran. Results of morphological and morphometrical studies, light and scanning electron microscopic observations, and molecular analyses allowed us the identification of fourteen known and one unknown species including representatives of the genera Amplimerlinius (five species), Geocenamus (one species), Merlinius (three species), Nagelus (two species), Paramerlinius (one species), Scutylenchus (two species), and Telomerlinius (one species). The unknown species, Scutylenchus sp., characterized by having 35-50 incisures at mid-body; lateral field with 6 longitudinal incisures; lip region slightly offset by a constriction, flattened at front end; bearing 5-7 annuli; cephalic framework not refractive; stylet robust, 18.3-27 μm long; post anal intestinal sac absent; tail elongate conical, dorsally convex, with 24 (19-28) annuli in ventral side, ending to a smooth terminus and males common; spicules 24.5-31 μm long. The phylogenetic analyses were carried out using molecular data from nuclear ribosomal DNA (rDNA) genes viz. D2-D3 expansion segments of the large ribosomal subunit (28S rRNA), partial small ribosomal subunit (18S rRNA), and internal transcribed spacer (ITS). The molecular variability of D2-D3 expansion segments of the 28S rRNA and partial 18S rRNA was low in this family in comparison to the ITS region, which could be a more helpful molecular marker in species and genus identification.

New Records of Ditylenchus Species from Southern Alberta, Canada

The presence of plant-parasitic nematodes (PPNs) in cultivated areas is a limiting factor in achieving marketable crop yield. To control and alleviate the effects of these nematodes and determine appropriate management strategies, species-level identification is crucial. Therefore, we conducted a nematode diversity survey, which resulted in the detection of four Ditylenchus species in cultivated areas of southern Alberta, Canada. The recovered species had six lines in the lateral field, delicate stylets (>10 µm long), distinct postvulval uterine sacs, and pointed to rounded tail tips. The morphological and molecular characterization of these nematodes revealed their identity as D. anchilisposomus, D. clarus, D. tenuidens and D. valveus, all of which are members of the D. triformis group. All of the identified species were found to be new records in Canada except for D. valveus. Accurate Ditylenchus species identification is crucial because false-positive identification can result in the implementation of quarantine measures over the detected area. Our current study not only documented the presence of Ditylenchus species from southern Alberta, but also described their morpho-molecular characteristics and subsequent phylogenetic relationships with related species. The results of our study will aid in the decision on whether these species should become a part of nematode management programs since nontarget species can become pests due to changes in cropping patterns or climate.

First Reports and Morphological and Molecular Characterization of Pratylenchus delattrei and Quinisulcius capitatus Associated with Chickpea in Ethiopia

Chickpea (Cicer arietinum L.) is classed among the most important leguminous crops of high economic value in Ethiopia. Two plant-parasitic nematode species, Pratylenchus delattrei and Quinisulcius capitatus, were recovered from chickpea-growing areas in Ethiopia and characterized using molecular and morphological data, including the first scanning electron microscopy data for P. delattrei. New sequences of D2-D3 of 28S, ITS rDNA and mtDNA COI genes have been obtained from these species, providing the first COI sequences for P. delattrei and Q. capitatus, with both species being found for the first time on chickpea in Ethiopia. Furthermore, Pratylenchus delattrei was recovered in Ethiopia for the first time. The information obtained about these nematodes will be crucial to developing effective nematode management plans for future chickpea production.

Pea Breeding for Resistance to Rhizospheric Pathogens

Pea (Pisum sativum L.) is a grain legume widely cultivated in temperate climates. It is important in the race for food security owing to its multipurpose low-input requirement and environmental promoting traits. Pea is key in nitrogen fixation, biodiversity preservation, and nutritional functions as food and feed. Unfortunately, like most crops, pea production is constrained by several pests and diseases, of which rhizosphere disease dwellers are the most critical due to their long-term persistence in the soil and difficulty to manage. Understanding the rhizosphere environment can improve host plant root microbial association to increase yield stability and facilitate improved crop performance through breeding. Thus, the use of various germplasm and genomic resources combined with scientific collaborative efforts has contributed to improving pea resistance/cultivation against rhizospheric diseases. This improvement has been achieved through robust phenotyping, genotyping, agronomic practices, and resistance breeding. Nonetheless, resistance to rhizospheric diseases is still limited, while biological and chemical-based control strategies are unrealistic and unfavourable to the environment, respectively. Hence, there is a need to consistently scout for host plant resistance to resolve these bottlenecks. Herein, in view of these challenges, we reflect on pea breeding for resistance to diseases caused by rhizospheric pathogens, including fusarium wilt, root rots, nematode complex, and parasitic broomrape. Here, we will attempt to appraise and harmonise historical and contemporary knowledge that contributes to pea resistance breeding for soilborne disease management and discuss the way forward.

Morphological and Molecular Characterization of Nothotylenchus medians and N. similis (Nematoda: Anguinidae) from Southern Alberta, Canada

The nematode family, Anguinidae, is a diverse group of polyphagous nematodes, generally known as fungal feeders or parasites of aerial plant parts. Here, we present the morphological and molecular characterization of adult females of two Nothotylenchus species, N. medians and N. similis, along with host association and geographical distribution data of the genus. Both species are recorded as new reports from Canada and designated as reference populations for future studies. Morphological or morphometrical variation was not observed in the Canadian population of N. medians and N. similis, in comparison with the original description. Phylogenetic analyses based on 18S and D2–D3 of 28S genes placed both species within Anguinidae. Since the biology of the genus Nothotylenchus has not been rigorously characterized, the habitat and distribution information presented in this study will shed some light on the ecology of these nematodes. Notably, the detection of N. medians and N. similis in our nematode inventory survey indicates that considerable Nothotylenchus diversity is hidden in these soils. Consequently, increased surveys and more in-depth research are needed to explore the full diversity of anguinids inhabiting these cultivated areas.

Prevalence and Molecular Diversity of Plant-Parasitic Nematodes of Yam (Dioscorea spp.) in China, with Focus on Merlinius spp

Simple Summary

Plant nematodes (PPNs) have been documented as economically important pests of yam in different parts of the world with Pratylenchus spp. and Meloidogyne spp. being the most widespread and destructive pests in Asia, causing significant yield losses. The primary inspiration for this study is the scarcity of information about nematode pests of yam in China and the fact that no previous study has looked into the prevalence, diversity, and integrative taxonomy of PPNs species in China cropping systems, as well as their consequences on yam cultivation. Therefore, the objectives of this study were to conduct a nematode study in south-eastern China to (i) record the prevalence and diversity of PPNs of cultivated yam with emphasis on the five prominent genera identified, and (ii) characterized morphologically, morphometrically, and molecularly Merlinius spp. The high prevalence of the Merlinius spp. revealed that the species may be more important to yam than previously thought. Conclusively, this study provided useful baseline PPNs data for yam in China. Hence, future study should focus on; developing innovative, environmentally friendly, and cost-effective nematode management strategies to control this pest that damage farmers’ yam fields in China, and constantly updating information of PPNs species found to allow proactive measures in terms of their spread and management.

Abstract

There is little information about nematode pests associated with yam in China. Between 2020 and 2021, surveys of yam fields were conducted to investigate the abundance and prevalence of plant-parasitic nematodes in major yam growing areas. A total of 110 bulk soil samples from the yam rhizosphere and 48 yam tubers were collected from seven counties in Jiangxi and Shandong provinces. Standard protocols were used to extract nematodes from soil and tubers and identified at the genus level. In this study, 16 species and 13 nematode genera were recorded. The five most prominent species on the yam rhizosphere according to mean population densities were Pratylenchus coffeae (291/individuals), Meloidogyne (262/individuals), Rotylenchulus reniformis (225/individuals), Merlinius (224/individuals), and Helicotylenchus dihystera (171/individuals). In the tubers, the three most prominent species were Pratylenchus coffeae (415/individuals), Meloidogyne (331/individuals), and Rotylenchulus reniformis (115/individuals). These species were verified with appropriate molecular analysis. The high prevalence of the ectoparasite (Merlinius spp.) on the rhizosphere of yam also revealed that Merlinius spp. May be more important to yam than previously thought. Morphological and molecular analyses further confirmed the identity of the species as Merlinius brevidens and were characterized for the first time on yam in China. Minor morphometrical differences (slightly longer body and stylet) were observed in Chinese populations of M. brevidens compared to the original description. Additionally, this study reveals that M. brevidens isolated from China showed a higher nucleotide sequence in the ITS region compared to M. brevidens populations from India. This finding provides baseline information on the nematode pest occurrence on yam in China and calls for effective management.

Morphological and Molecular Characterization of Quinisulcius curvus from China

A stunt nematode species, Quinisulcius curvus, recovered from the rhizosphere of sea randa (Guettarda speciosa), is described and characterized herein based on integrative taxonomy. Morphometrics and distribution of all reported populations of Q. curvus are also discussed. The Chinese population of Q. curvus displayed slight variation in stylet length; however, the rest of the characters matches well with the original description. This is the first record of Q. curvus from Hainan, China, and the first molecular characterization for this species. Phylogenetic analysis based on partial 18S, 28S and ITS sequences placed Q. curvus with related stunt nematodes species, but clearly separated from them. The present study expanded the geographic record and provided molecular data on Q. curvus from China.

First Report of Three Tylenchidae Taxa from Southern Alberta, Canada

Members of the family Tylenchidae are highly abundant in soil habitats, including agricultural settings, where they play key ecological roles. In the present study, we identified three Tylenchidae species, namely Basiria bhabi, Coslenchus acceptus, and Filenchus vulgaris, using integrative taxonomy. The detailed morphological and morphometric characteristics, distribution, and host associations of each species were also discussed. Phylogenetic analyses of these populations with other Tylenchidae nematodes indicated the presence of divergent lineages in Filenchus and Basiria, whereas Coslenchus appeared to be a monophyletic genus. Herein, we aim to grow awareness about this common but least studied group of nematodes. The species reported in this study are new records for Canada, revealing that the identified nematode diversity in our cultivated areas is relatively underrepresented. Our analyses also provided greater taxonomic resolution and captured rare taxa that might have been missed or misidentified in prior nematode inventory surveys. These findings will add to our understanding of the nematofauna of southern Alberta, thereby providing a more complete picture of existing nematode diversity present in the fields of this highly cultivated region.

Overview of the Genus Boleodorus and First Reports of Boleodorus thylactus and B. volutus from Southern Alberta, Canada

Simple Summary

Two Boleodorus species were detected in cultivated areas of southern Alberta. The aim of the present work was to characterize the discovered populations of Boleodorus using morphological and molecular methods. Boleodorus is the least studied genus in family Tylenchidae, with very few species reported after formal descriptions and outside their type locality. To date, Boleodorus species are not considered nematode pest species, rather they can serve as environmental indicators. Therefore, it is important to quantify and monitor the population densities of these species for soil health management studies. The current study encompasses the distribution and host association of all described Boleodorus species. In addition, morphometrical characters of all valid species are listed for their prompt identification.

Abstract

The present study provides the morphological and molecular characterization of Boleodorus thylactus and B. volutus populations, recovered from agricultural fields of southern Alberta. Despite a significant abundance of this group of nematodes, none of the Boleodorus species were previously reported in Canada. Therefore, representative adult specimens of each population were photographed and examined morphometrically. Phylogenetic trees were reconstructed using partial D2–D3 expansion segments of the 28S and 18S rDNA sequences to understand the relationships of Boleodorus species with Tylenchidae-related genera. Boleodorus species are relevant to soil ecological studies and therefore we summarized the important morphological and morphometric characters in tabular form for easy and efficient species identification. Moreover, we discuss the associated hosts and the distribution of all described Boleodorus species. This study will serve as a guide and basic framework for species diagnostics in the genus Boleodorus and will aid in filling the gaps in our knowledge of the species present in our cultivated lands.