Distribution Of Plant-parasitic Nematodes Research Articles

Meloidogyne hapla dominates plant‐parasitic nematode communities associated with kiwifruit orchards in Portugal

AbstractKiwifruit, Actinidia spp., is an important crop worldwide and its cultivation has been increasing in Portugal. Kiwifruit plants are susceptible to plant‐parasitic nematodes (PPNs), including Meloidogyne spp. M. hapla and M. incognita have been reported to affect kiwifruit in major production regions worldwide, although information is lacking on the distribution and identity of PPNs associated with kiwifruit orchards in Portugal. Moreover, research is scarce on the drivers of PPN communities in this crop. Our primary objective was to investigate the diversity, density and distribution of PPNs within kiwifruit orchards of Portugal and to elucidate the influence of environmental factors on their community composition. Additionally, we aimed to evaluate population densities and identity of Meloidogyne spp. Nematodes were extracted from composite soil and root samples collected from orchards. Analysis of soil nematode communities suggested bacterial‐driven decomposition and high nutrient enrichment in these soils. Sixteen different genera of PPNs were detected, with Meloidogyne spp. as the dominant genus, mostly represented by a single species, M. hapla. PPN communities exhibited low richness, and β‐diversity analysis indicated a high degree of similarity among them. Additionally, their composition was significantly influenced by soil and climatic parameters. We found that 37 out of 40 kiwifruit orchards in Portugal were infested by root‐knot nematodes. The unexpectedly low species diversity, dominated by M. hapla, merits further research to establish underlying factors for its high incidence in this crop and to assess the impact of these nematodes on kiwifruit performance and productivity.

Occurrence and Distribution of Plant Parasitic Nematodes in Mungbean in Jaipur District, Rajasthan, India

Aim: Mungbean (Vigna radiata (L.) R. Wilczek) is one of the important pulse crops grown in India. Considering the economic importance of nematodes as disease causing organism of mungbean the present investigation was carried out to know the distribution of plant parasitic nematodes in mungbean crops in Jaipur district of Rajasthan. Methodology: A total 139 soil samples were collected from mungbean fields of 12 different localities in Jaipur district. The samples were processed using Cobb's sieving and decanting technique followed by Baermann's funnel technique and nematode population was counted in suspension and identified on the basis of their morphological characters. Results: The samples were infected with mainly four genera of plant parasitic nematodes i.e., Meloidogyne spp., Helicotylenchus spp., Pratylenchus spp. and Tylenchorhynchus spp. etc. Out of 139 soil samples, 120 samples showed the presence of Meloidogyne javanica with 86.33 % occurrence, 18.82 % absolute density, 83.81 % relative density and 15.85 % prominence value and found most predominant in different surveyed localities in Jaipur district.

Molecular Characterization of Sweet Potato Plant Parasitic Nematodes in Different Agroecological Zones of Kirinyaga County, Kenya

Plant parasitic nematodes (PPNs) are widely distributed in all agroecological zones (AEZs) within Kenya. Plant parasitic nematodes are important pests of many cultivated crops and they exert a detrimental influence on a wide range of vascular plants, leading to significant crop losses by reducing both quantity and quality of the yield. However, due to inadequate taxonomic descriptions and a low number of diagnostic features, the morphological diagnosis of many species remains a challenge. The objective of this study was to characterize PPNs associated with sweet potatoes in different agroecological zones of Kirinyaga County, Kenya, using 18S rRNA gene sequencing. Seventy-seven soil samples from sweet potato tubers rhizosphere were collected from different agroecological zones and nematodes were extracted using Baermann’s technique. Thirteen nematode isolates were obtained and only seven could be identified morphologically to their genus level based on their distinct phenotypes. Seven isolates that could not be identified through the microscope were advanced to molecular sequencing. The nematode DNA were extracted and the PCR amplification and sequencing of 18S rRNA gene carried out. The study identified six PPN species, including Mylonchulus hawaiiensis, Aporcelaimellus nigeriensis, Rotylenchulus reniformis, Rotylenchulus borealis, Aporcella femina, Heterodera dunensis, and a predatory nematode (Dorylaimus aff. stagnalis) as part of the soil biota. This study showed significant distribution of plant parasitic nematodes across the agroecological zones. Thus, the occurrence of a nematode species complex in sweet potato farms requires the development of specific and appropriate sustainable control strategies.

Identification of Plant Parasitic Nematodes Associated with Citrus in Dibrugarh District

The present investigation was carried out to determine the occurrence and distribution of plant parasitic nematodes associated with citrus plants of different citrus orchards in Dibrugarh district. A total of 149 soil and root samples were collected randomly from the rhizosphere of citrus plants from the twenty four different citrus orchards of seven blocks from Dibrugarh district. Eight genera of plant parasitic nematodes were found to be associated with citrus plants of Dibrugarh district. Genera of plant parasitic nematodes recorded were namely Tylenchulus, Hoplolaimus, Helicotylenchus, Tylenchorhynchus, Meloidogyne, Xiphinema, Paratylenchus and also nematodes genera found under criconematids. Among them Hoplolaimus sp., Helicotylenchus sp., Tylenchorhynchus sp. and T. semipenetrans were found to be present in most of the samples. Community analysis of plant parasitic nematodes revealed that the genus Hoplolaimus ranked first in relative frequency, absolute frequency, absolute density, relative density and prominence value. Genus Helicotylenchus ranked second in absolute density, relative density and prominence value and genus Tylenchorhynchus ranked third in case of absolute density absolute frequency and prominence value. Results shown that Tylenchulus semipenetrans ranked second in absolute frequency and relative frequency and fourth in prominence value.

Plant parasitic nematodes associated with oil palm trees in three regions of Ghana

Field surveys were conducted in three oil palm producing regions of Ghana to determine the frequency, population density and geographical distribution of plant parasitic nematodes associated with oil palm. Palms ranging from 4 to 12 years were surveyed during the peak periods of two successive cropping seasons of 2019 and 2020. A total of 64 soil and root samples were collected and plant parasitic nematodes extracted and identified from them. 716 mixed populations of 11 economically important plant-parasitic nematode genera were recovered and identified from both roots and soils during the period. These were Aphelenchus, Criconemoides, Helicotylenchus, Hemicriconemoides, Meloidogyne, Pratylenchus, Radopholus, Rotylenchus, Tylenchorynchus, Tylenchus and Xiphinema. Meloidogyne and Pratylenchus were the most frequently isolated and widely distributed geographically. Meloidogyne recovered from both soil and roots were 220 whilst Pratylenchus recovered were 129. These nematodes are very important pests of several crops, therefore, if not managed properly, could pose a threat to oil palm production in Ghana.

Occurrence and Distribution of Root-Knot Nematodes in Kiwifruit Orchard

The study was conducted to investigate the infestation and distribution of plant-parasitic nematodes on kiwi orchards in Korea. Plant parasitic nematodes genus and densities were investigated at a total of 102 sites in Jeollanam-do, Gyeongsangnam-do, and Jeju-do, which are the main production areas of domestic kiwi orchards. Plant parasitic nematodes detected were of 9 genera, including root-knot nematodes (Meloidogyne spp.), spiral nematodes (Helicotylenchus spp.), and needle nematodes (Paratylenchus spp.), and 56% of the 102 plantations were infected with root-knot nematodes. Root-knot nematodes were found to be the most important plant parasitic nematode in domestic kiwi orchards. The average density of root-knot nematodes is 97 per 300 cm<sup>3</sup> soil, and there is concern about the kiwi yield reduction. As a result of identifying the root-knot nematode species: M. arenaria, M. hapla, M. incognita, and M. javanica. Among them, M. arenaria is the most dominant. As the plant parasitic nematode infection route in fruit trees is often spread through the transplantation of infected seedlings, attention should be paid to the production of nematode-free plants during the production and supply of kiwifruit plants.

Prevalence and ecological factors affecting the distribution of plant-parasitic nematodes in Prunus groves in Spain

A wide survey was conducted to study plant-parasitic nematodes (PPNs) associated with Prunus groves in Spain. This research aimed to determine the prevalence and distribution of PPNs in Prunus groves, as well as the influence of explanatory variables describing soil, climate and agricultural management in structuring the variation of PPNs community composition. A total of 218 sampling sites were surveyed and 84 PPN species belonging to 32 genera were identified based of an integrative taxonomic approach. PPN species considered as potential limiting factors in Prunus production, such as Meloidogyne arenaria, M. incognita, M. javanica, Pratylenchus penetrans and P. vulnus, were identified in this survey. Seven soil physico-chemical (C, Mg, N, Na, OM, P, pH and clay, loamy sand and sandy loam texture classes), four climate (Bio04, Bio05, Bio13 and Bio14) and four agricultural management variables (grove-use history less than 10 years, irrigation, apricot seedling rootstock, and Montclar rootstock) were identified as the most influential variables driving spatial patterns of PPNs communities. In particular, younger plantations showed higher values for species richness and diversity indices than groves cultivated for more than 20 years with Prunus spp. Our study increases the knowledge of the distribution and prevalence of PPNs associated with Prunus rhizosphere, as well as on the influence of explanatory variables driving the spatial structure PPNs communities, which has important implications for the successful design of sustainable management strategies in the future in this agricultural system.

Distribution of Plant-Parasitic Nematodes in Michigan Corn Fields.

Plant-parasitic nematodes (PPNs) can cause substantial economic yield losses to many agronomic crops in the United States. A regional-scale survey was completed across 20 counties to determine PPNs prevalence in Michigan corn and how factors such as soil type, tillage, irrigation, and cropping systems influence their distribution. Ten different major genera of PPNs were identified in Michigan corn fields: Longidorus (needle), Helicotylenchus (spiral), Pratylenchus (lesion), Meloidogyne (root-knot), Heterodera (cyst), Hoplolaimus (lance), Tylenchorhynchus or Merlinius (stunt), Paratylenchus (pin), Criconemella (ring), and Xiphinema (dagger). No significant differences among different categories of tillage for lesion, stunt, or needle nematode prevalence was detected. Lesion nematodes were most prevalent in muck soil, while stunt nematode prevalence was significantly affected by the soil type. Needle nematodes were least abundant in irrigated soils and in contrast, stunt nematodes were higher in non-irrigated soils. Spiral nematodes were the most common PPNs in Michigan corn in all cropping systems. These findings will be helpful in planning future nematode studies in Michigan and in developing and evaluating corn nematode management strategies.

Survey and Distribution of Plant Parasitic Nematodes on Tomato at Baruasagar in Jhansi (India)

Survey and Distribution of Plant Parasitic Nematodes on Tomato at Baruasagar in Jhansi (India)

Enset (Ensete ventricosum) landraces associated parasitic nematodes and their relationship with Xanthomonas wilt disease in Gurage, Ethiopia

Enset production in Ethiopia is constrainted by nematode disease. This study has examined the type, abundance and distribution of plant parasitic nematodes (PPNs) and their relationship with Xanthomonas wilt of enset. Stratified random sampling technique was used to collect soil and root samples, and nematodes were extracted from the soil and fresh root samples. Eight nematode genera including. Pratylenchus, Meloidogyne, Helicotylenchus, Tylenchorhynchus, Meloidodera, Machroposthonia, Scutellonema and Xiphinema were recovered from the soil samples as well as Pratylenchus and Meloidogyne from the root samples. All roots and 87.7% of the soil samples possessed one or more nematode genus. Pratylenchus was the most abundant and frequently occurring nematode, accounting for 99.9% and 51.6 % of the total nematode density recovered from the root and soil samples, respectively. The studied enset landraces significantly differed in the nematode they harbored, of which Ageremremat, Shertye, Kibnar and Guarye were the top for Pratylenchu but was lowest on Lemat, Yiregiye, Beshute, Woka, Derewetye, Gufenwe, Charkma and Emirye landraces. Nematode density was significantly higher in samples collected from agro-ecologies at higher altitudes. Moroever, the density of Pratylenchus, Meloidogyne and Helicotylenchus, was remarkably higher on acidic compared with alkaline soils. Enset plants infected by Xanthomonas wilt showed significantly higher densities of Pratylenchus, Helicotylenchus and Tylenchorhynchus. This study provided additional evidence on the distribution and level of damage caused by nematodes on enset crops that is important to all the relevant stakeholders across the crop's value chain in designing and implementing feasible integrated pest management approaches.

Plant Parasitic Nematodes Associated with Okra in the Forest Savanna Transition and Semi-Deciduous Forest Agro-Ecologies of Ghana

Okra is an important vegetable crop in Ghana. Plant-parasitic nematodes infect okra, reducing the quality and quantity of fresh immature and dry fruits. This study was carried out to determine diversity, density and distribution of plant parasitic nematodes attacking okra in the Forest savanna transition and Semi-deciduous forest agro-ecologies of Ghana. In each agro-ecology, soils from okra rhizosphere were sampled from 15 farms for plant-parasitic nematodes assessment. Nematodes were extracted using the modified Baermann nematodes extraction method. Six nematode genera were identified; Meloidogyne, Pratylenchus, Xiphinema, Helicotylenchus, Rotylenchulus and Scutellonema. Meloidogyne occurred with 64.9% relative abundance and 100% frequency. Rotylenchulus, Pratylenchus, and Helicotylencus nematodes also occurred with 100% frequency. Xiphinema were the least abundant (0.05%) and the least frequent (15%). The findings have shown that a large number of nematodes exist on okra plants and therefore there is the need for educational campaigns to be stepped up by Agricultural Extension Services of the Ministry of Food and Agriculture on plant parasitic nematode infections in okra production.

Abundance and distribution of plant-parasitic nematodes in tomatoes grown in a semi-arid agro-ecological zone in Tanzania

The abundance and distribution of plant-parasitic nematodes (PPN) on tomato plants grown in nine villages in the semi-arid zones of Singida and Dodoma in Tanzania were assessed in December 2020. Samples from soil and plant roots were evaluated for abundance, genera and distribution of PPN. Nematodes were extracted, counted and identified based on morphological descriptors. Ten genera of PPN were identified in both root and soil samples, with root-knot nematodes (RKN) being the most common PPN in all nine villages surveyed. The results showed that the abundance of RKN was significantly higher (p = 0.002) in soil than in tomato roots. Tutu and Chamkoroma villages had a significantly (p = 0.001) higher population density of RKN compared to other villages. In addition, RKN was associated with Penicillium and Aspergillus fungi, while the nematode genera Helicotylenchus, Aphelenchus, Scutellonema and Pratylenchus exhibited relationships with Alternaria and Fusarium fungi. The results also indicated that the abundance of RKN was significantly higher (p = 0.001) in sandy soil as compared to other types of soils. Inappropriate agronomical practices (e.g., no fallow, rotation of tomato plant with related crops) and poor phytosanitary measures were the major factors associated with high levels of abundance and distribution of RKN in soil.

Abundance, diversity, and distribution of plant-parasitic nematodes in horticultural soils under different management systems in a tomato-producing area in Argentina

Summary Monitoring the diversity and structure of plant-parasitic nematode (PPN) communities together with developing appropriate control strategies can reduce the occurrence of these pathogens and other plant pests in horticultural crops. In this context a study of the abundance, frequency, diversity and distribution of PPN in horticultural soils under glasshouse conditions from the Green Belt of La Plata, Buenos Aires, Argentina, under different management systems was undertaken. Soil samples were collected from three horticultural areas with different tomato crop managements: agroecological crop (AC); organic crop with Brassicaceae soil amendments (OC); intensive conventional crop treated with methyl bromide (MeBr) (IC). The parameters evaluated were: nematode genera richness (G); Shannon-Wiener diversity index () (Hutcheson’s t-test was applied for this index); equitability index (E); abundance; and frequency of genera. ANOSIM and SIMPER statistical analyses were performed to find significant differences between the nematode assemblages from the different sites. A total of 14 genera of PPN were identified among the three crop sites. Members of the feeding habits categories ectoparasites, semi-endoparasites, migratory endoparasites and sedentary endoparasites were observed. Statistical analysis enabled us to characterise each site based on the composition of the nematode assemblages. Helicotylenchus, Tylenchus and Nacobbus were the most frequent and abundant genera. AC and OC showed similar values of richness and diversity; the crop treated with MeBr (IC) showed the lowest diversity of PPN.

Diversity and distribution of plant-parasitic nematodes associated with watermelon, in northwest Morocco

Watermelon (Citrullus lanatus) fields in northwest Morocco’s Molay Bousselham region were surveyed to study the distribution and occurrence of plant-parasitic nematodes. Eighteen nematode taxa were identified in soil and root samples collected from 24 watermelon plots. The most common plant-parasitic nematodes (PPN) identified were Meloidogyne (M. javanica, M. incognita, M. arenaria and M. hapla), Pratylenchus (P. penetrans, P. thornei, and P. fallax), Tylenchus, Helicotylenchus, Xiphinema and Ditylenchus genera. The diversity patterns of PPN were thoroughly assessed via calculating diversity indices. High species richness was recorded while significant differences were observed between the main locations based on the Shannon–Wiener index (H’) and the Evenness (J). This description of PPN assemblages associated with watermelon fields in northwest Morocco provides fundamental information to design suitable nematode management strategies to reduce yield loss and benefit our food security.

Distribution of plant-parasitic nematodes and comparative effects of fadama (hydromorphic) fields and upland fields on plant-parasitic nematodes and free-living nematodes on three indigenous vegetables commonly grown in Osun State Nigeria

Surveys were conducted in 2016 and 2017 to investigate the distribution of plant-parasitic nematodes and the effects of fadama fields and upland fields on plant-parasitic and free-living nematodes. A total of 84 soil samples were collected from seven Local Government Areas visited in Osun State. Soil samples were collected from two fadama fields and two upland fields in all the LGAs visited. Nematodes were extracted, counted and identified under a compound microscope according to the morphological characteristics of the nematodes. The results showed that sixteen genera of plant-parasitic nematodes were found associated with Solanum macrocarpon, Amaranthus cruentus and Telfairia occidentalis. Meloidogyne\\ Helicotylenchus and Rotylenchulus were the most abundant nematodes associated with the vegetables. Fadama fields significantly had lower populations of plant-parasitic nematodes and higher populations of free-living nematodes in comparison with upland fields in fields sown to the vegetables. Farmers are advised to take full advantage of fadama fields in vegetable production.

Occurrence of plant-parasitic nematodes in sugarbeet fields of North Dakota and Minnesota

Plant-parasitic nematodes (PPNs) are an important group of pathogens on sugarbeet. Surveys were conducted in the Red River Valley (RRV) area of North Dakota (ND) and Minnesota (MN) to determine the incidence, abundance, and distribution of PPNs in sugarbeet fields. A total of 217 soil samples were collected in 2016 and 2017 from fields with sugarbeet or a history of sugarbeet production. In addition, 48 samples were collected in 2016 from tare soils in sugarbeet piling stations, and two samples were collected in 2017 from sugarbeet production fields in eastern Montana (MT) and western ND border area. The incidence and abundance of major genera of PPNs identified from sugarbeet production fields in 2016 and 2017 were: Heterodera (incidence = 15%, abundance = 1,351/200 gm of soil); Helicotylenchus (38%, 157); Tylenchorhynchus (37%, 121); Paratylenchus (28%, 108); Pratylenchus (6%, 38); Paratrichodorus (7%, 37); Xiphinema (3%, 32); and Hoplolaimus (0.4%, 20). Helicotylenchus, Tylenchorhynchus, Paratylenchus, and Heterodera were the most frequent and widely distributed nematode genera whereas, Paratrichodorus and Pratylenchus were found less frequently and at low densities. Xiphinema and Hoplolaimus were rarely detected at lower densities. Paratylenchus and Tylenchorhynchus were widely distributed in most of the sampled counties (n = 11), followed by Helicotylenchus (10), Heterodera (8), Pratylenchus (8), Xiphinema (4), Paratrichodorus (3), and Hoplolaimus (1). Species-specific PCR assays and direct sequencing of ribosomal DNA were conducted to identify species. Species identification revealed that the cyst nematodes from one of the counties in eastern MT were Heterodera schachtii and the cyst nematodes analyzed from 31 samples in 12 counties in ND and MN were H. glycines. We have not identified any H. schachtii thus far from surveyed samples in eastern ND and western MN. Other nematode species identified include Paratrichodorus allius, Pratylenchus neglectus, Tylenchorhynchus sp., Paratylenchus nanus, Helicotylenchus microlobus, and H. pseudorobustus. Accurate identification of these nematodes and awareness of their occurrence across the region is essential for developing effective pest management strategies for improved sugarbeet production.

Trends in Occurrence, Distribution, and Population Densities of Plant-Parasitic Nematodes in the Pacific Northwest of the United States from 2012 to 2016

The Pacific Northwest (PNW) of the United States (Idaho, Oregon, and Washington) is a diverse agricultural production area with over 400 different commodities grown in the region. Plant-parasitic nematodes are a constraint to the production of many of these commodities. Soil sample data from 2012 to 2016 were obtained from nematode diagnostic laboratories in the region to assess trends in occurrence, population densities, and distribution of plant-parasitic nematodes in the PNW. A total of 38,022 unique data points were analyzed. The number of plant-parasitic nematode samples processed in the PNW by diagnostic laboratories has significantly increased from 2012 to 2016. Fifteen genera of plant-parasitic nematodes were identified by diagnostic laboratories, with 86% of the samples in the PNW containing at least one plant-parasitic nematode genus. These laboratories provide a valuable service to agriculture in the PNW. Additionally, they serve as a rich source of information on plant-parasitic nematode distribution, occurrence, and abundance that, when analyzed, provides an empirical basis upon which to interpret individual grower reports and make management recommendations.

Occurrence and distribution of plant parasitic nematodes in Cabbage growing regions of Tamil Nadu

A total of 60 samples were collected from cabbage viz., Quisto, Priyadharshini, Golden Acre and Maha Rani at a depth of 10–15 cm. The soil samples were analyzed by using modified Baermann's funnel technique and the root samples were analyzed by using Acid fuschin lactophenol solution for identification of females. The survey revealed that, the root knot nematode, Meloidogyne incognita, lesion nematode, Pratylenchus penetrans, spiral nematode, Helicotylenchus dihystera, lance nematode, Hoplolaimus indicus, dagger nematode, Xiphinema americanum and Tylenchus filiformis were encountered in the samples. Among the districts, the highest incidence of damage by M. incognita was observed in Krishnagiri followed by The Nilgiris and Coimbatore districts. The maximum population (262.48/250cc soil) and minimum population (72.93/250cc soil) was observed in Krishnagiri and Theni districts, respectively.

Occurrence and Distribution of Plant-Parasitic Nematodes on Muscadine Grapes in Georgia and North Carolina

Muscadine grape, Vitis rotundifolia, is native to the southeastern United States, but Georgia (GA) and North Carolina (NC) are the largest North American producers. Plant-parasitic nematodes (PPNs) have become a significant factor affecting the health, quality, production, and maintenance of bunch grapes (V. labrusca, V. vinifera), but little is known about muscadine PPNs. A systematic survey was conducted of PPNs infesting eight and 11 muscadine grape vineyards in GA and NC in August and October 2018, respectively. The most frequently detected PPNs across all samples from both states were Helicotylenchus (90%), Mesocriconema (72%), and Xiphinema (58%). However, 5 Hemicycliophora and 710 Scutellonema nematodes/100 cm3 of soil were found only in GA, whereas only 1 Belonolaimus nematode/100 cm3 of soil was found only in NC. Ordination of the nematode communities from the samples collected in GA and NC yielded groupings that aligned with the state of origin. Multivariate tests for group membership indicated that several genera were statistically associated with either NC or GA muscadines, and the PPN communities distinctly differed between states. Because muscadine grapes do not have established nematode thresholds, it is not known whether these nematode species are negatively impacting mature grapes.

Occurrence and population distribution of plant parasitic nematodes associated with roselle (<i>Hibiscus sabdariffa</i> L.) in northern Nigeria

Pests including nematodes have been reported as a limiting factor to the production of roselle worldwide. A survey of rosellefarmsinsix Northern Sates of Nigeria was conductedin 2013 to identify the diverse nematode species associated with the soils and roots of the plant and determine their population densities on farmers’ fields. Eightsoil and ten plant samples were randomly collected from each of twenty farms from which nematodes were extracted and identified. Four genera of plantparasitic nematodes ( Meloidogyne spp., Helicotylenchus spp., Rotylenchulus spp.and Tylenchus spp.) were found in association with roots and rhizosphere of roselle plants. Meloidogyne were most populous (62.29%) on the roots while Tylenchuswas least (1.68%). Helicotylenchus spp appeared in highest density (50.05%) in plant rhizosphere, but not identified from the roots. The highest percentage of nematode population (22.7 %) wasfrom Katsina, followed by Sokoto (21.6%), Jigawa (17.4%), Zamfara (16.5%), Kano (15.1%) and Kaduna states (6.7%).The generally low nematode density observed might be due to low precipitation and high soil temperature of the six states. Occurrence of varied species of nematodes demands effective control measures for improved roselle productivity. Kano, Zamfara and Jigawawith low nematode population densities can be considered for further research towards the establishment of pest-free areas or area of low pest prevalence for roselle nematodes in Nigeria, useful in the agricultural export trade. Further studies are required on the determination of density economic threshold and the definitive roles of nematodes in causing low productivity of roselle. Keywords: Export value, Hibiscus sabdariffa , nematodes, population densities, pest-free area