Important Nematode Pests Research Articles

Nematicidal effects of silver nanoparticles (AG-NPs) on the root-knot nematode, Meloidogyne javanica associated with Swiss chard (Beta vulgaris L.).

Root-knot nematodes (RKNs) are important nematode pests, causing huge economic losses on vegetable crops worldwide. A decline in the yield of Swiss chard (Beta vulgaris L.) which was associated with RKNs was observed on an organic vegetable farm in the Western Cape Province of South Africa. Nematodes were extracted from galled plant roots and identified using molecular tools. PCR-based Sequence Characterised Amplified Region (SCAR) primers was used to confirm the specie of the RKN associated with the infected plants. Thereafter, a pot assay was conducted to determine the response of artificially infected Swiss chard plants to varying concentrations of bio-synthesized silver nanoparticle Ag-NP (1 μg/mL, 2 μg/mL, and 3 μg/mL) under controlled conditions. The results of the study showed that Swiss chard is highly susceptible to M. javanica with an egg-laying-female index of >5 in all infected plants. Significantly lower values (at P=0.05) in egg masses (EM), juveniles (J2s), and reproduction factor (RF) of nematodes were recorded on plants treated with 3 μg/mL, indicating a potential for nematode control. A negative correlation was also observed in the number of egg masses, J2s, and RF of the nematodes with increasing concentrations of the Ag-NP. This study confirms that Swiss chard is highly susceptible to M. javanica and demonstrates the potential nematicidal property of Ag-NP in controlling the nematode pest of Swiss chard.

First detection of the potato cyst nematode (Globodera rostochiensis) in a major potato production region of China.

The potato cyst nematodes (PCN) Globodera rostochiensis and Globodera pallida are the very important quarantine nematode pests of potato [Stone 1973]. Both species cause serious potato tuber yield losses. These species are subjected to strict quarantine regulations in many countries (EPPO 2017). G. rostochiensis was detected in Sichuan and Yunnan province, China in 2022 (Jiang et al. 2022). A survey for cyst nematodes in potato fields was conducted in Guizhou Province from 2018 to 2020. A total of 200 samples, including roots and soil, were collected from 40 potato fields in Hezhang (N27 06.145, E104 39.153) and Weining (N26 50.541, E104 09.885) counties in Guizhou Province, China. The Cobb decanting and sieving method was used to isolate cysts and J2s from the soil samples (Southey 1986). The potato roots were stained with acid fusion to observe cyst development. Morphological and molecular analyses indicated that 27 (13.5%) of the samples contained G. rostochiensis. The cyst density ranged between 1-85 cysts per 100 cm3 of soil and a mean density was 15 cysts per 100 cm3 soil. The smoothly rounded cysts were in brown and golden color, and the terminal cone was absent and circumfenestrate. The key morphometrics of cysts (n=20) were 695 ± 26 (685-757) μm in length excluding neck and 690 ± 30 (668 to769) μm in width; the number of cuticular ridges between anus and vulval fenestra was 16.3 ±2.1 (14 to 18); fenestral length was 15.1 ± 2.1 μm (13.18 to 19.27); distance from anus to the edge of fenestra was 61.12 ± 8.9 (49.22 to76.27) μm; and Granek's ratio was 4.54 ± 0.8 (3.97-5.26). The key morphometrics of J2 (n = 20): 468.0 ± 20.1 (427 to - 521) μm in body length, 20.58 ± 0.7 (20.2 to 21.8) μm in stylet length, 43.9 ± 5.6 (40.3 to 53.9) μm in tail length, and 23.1 ± 1.8 (21.77 to 25.32) μm in hyaline region length. The cyst and J2 morphologies were consistent with those of G. rostochiensis (Subbotin et al. 2010, EPPO 2017). Genomic DNA was isolated from cysts (n=20). DNA extraction was performed in a volume of 20 μl containing 3 μl 10× PCR buffer, 3 μl Proteinase K (600 μg μl-1), 14 μl distilled water and a single cyst was added and ground in an ice bath as described by Ou et al. (2008). The internal transcribed spacer (ITS) regions were amplified using the universal primers: rDNA1 (5'-TTGATTACGTCCCTGCCCTTT-3') and rDNA2 (5'-TTTCACTCGCCGTTACTAAGG-3') (Fleming 1998 ), and the 28S rDNA-D2/D3 regions were amplified using the primers: D2A (5´-ACAAGTACCGTGAGGGAAAGTTG-3´) and D3B (5´-TCGGAAGGAACCAGCTACTA-3´) (Subbotin et al. 2006). After the brackets at the beginning and end of the sequences were closed-up, the ITS rDNA sequences (GenBank Accession No. MZ042367 and MZ042368) showed 99.66% - 99.92% identity to G. rostochiensis sequences available in GenBank (FJ212166.1, GQ294513, FJ212164.1 and KJ409617.1). Sequences from the 28S region (GenBank Accession No. MZ057597 and MZ057598) were 99.23% - 99.74% similar to those of G. rostochiensis isolate from Slovakia (KJ409625.1), Italy (KJ409631.1) and United Kingdom (KJ409633.1). We used species specific primers ITS5（5'-GGAAGTAAAAGTCGTAACAAGG-3'）and PITSr3 (5'AGCGCAGACATGCCGCAA-3') to amplify the product (Bulman & Marshall 1997; EPPO 2017). A single 434bp fragment was obtained from Hezhang and Weining populations. A host test for the Hezhang and Weining populations were performed by inoculating 1,000 eggs per plant of varieties Qingshu 9, Huize 2 and Hezuo 88 grown in the pots containing 800 cm3 of sterilized soil (soil: sand ratio was 3:1), and four replications were tested in greenhouse under 16 h light, 22°C in the day and 8 h dark in the night. At 90 days post inoculation, 32.6 ± 7, 31.2 ± 8, and 29.5 ± 8 females and cysts were extracted from the infected roots and soils of the varieties Qingshu 9, Huize 2 and Hezuo 88, respectively. No females and cysts were observed on the control plants. The trial indicated that potato cultivars Qingshu 9, Huize 2 and Hezuo 88 are hosts for the Hezhang and Weining populations of Globodera rostochiensis. To the best of our knowledge, this is the first detection of potato cyst nematode Globodera rostochiensis in Guizhou Province, China.

Comprehensive periodic evaluation of Oryza sativa germplasms for resistance against rice root-knot nematode, Meloidogyne graminicola

Rice root knot nematode, Meloidogyne graminicola is an important nematode pest with a devastating potential that causes serious damage to rice crop. There is an intensive search for eco-friendly, sustainable alternative to the existing nematode management practices. Host plant resistance offers propitious results in managing this minuscule crop enemy. Preliminary screening of 1731 Oryza sativa germplasms followed by periodic evaluation of nine resistant / tolerant germplasms shed new insights on nematode resistance. We observed seasonal inconsistency in the resistance in previously reported germplasms 'Ramakrishna', 'TKM6', 'Abhisek', 'Laxman sal', 'Ratna', and 'TKM1'. Hence, we strongly recommend repeated screening of identified resistant/tolerant rice germplasm lines against M. graminicola in both winter and summer season to confirm the consistency in resistance scale. Further investigation is needed to nullify other chance factors like nematode pathotypes.

Occurrence, Diversity and Abundance of Nematode Pests of Pineapple (Ananas comosus) in Two Local Government Areas of Rivers State, Nigeria

Plant-parasitic nematodes (PPNs) contribute to yield losses in pineapple production. Limited studies have been conducted on plant-parasitic nematodes on pineapple despite reports of PPNs infecting it. A survey was conducted in Obio-Akpor and Ikwerre Local Government Areas (LGAs) of Rivers State to determine the occurrence, abundance and diversity of PPNs associated with pineapple. A total of 60 composite samples were collected from the two LGAs. Nematodes were extracted from soil and root samples using the modified Baermann technique and identified using standard procedures. Data were processed using relative frequency of occurrence (RFOC), relative importance values (RIVs), diversity indices, nematode population was calculated and analysis of variance. The most occurring plant-parasitic nematodes were Pratylenchus, Helicotylenchus, Meloidogyne, Scutellonema and Tylenchulus. In Obio Akpor LGA, Helicotylenchus with RFOC 33.3% was the most occurring nematode pests, while Pratylenchus was the most important plant-parasitic nematode (RIV 33.8%). In Ikwerre LGA, both Helicotylenchus and Pratylenchus have the same occurrence (RFOC 33.3%) with Pratylenchus being the most important nematode pest. Pratylenchus species with RIV of 52.4% were the most important PPNs associated with pineapple in both Obio-Akpor and Ikwerre LGAs. Dominance and Shannon- Weiner indices among the PPNs are 0.58 and 0.86, respectively. In Ikwerre and Obio-Akpor LGAs, Aluu (1530) and Rumuekini (630) pineapple farms have the highest population of PPNs, respectively. Ikwerre LGA (2,150) pineapple farms had more PPNs than Obio-Akpor LGA (660). Nematode pests are associated with pineapple in the two LGAs and could be contributing to yield losses.

Molecular diagnostics of the pigeon pea cyst nematode, Heterodera cajani Koshy, 1967, using real-time PCR

Summary The pigeon pea cyst nematode, Heterodera cajani, is an important nematode pest of pigeon pea that is present in all major growing regions of this crop in India and reported from Pakistan, Egypt and Myanmar. In this study, a new real-time PCR assay for detection of H. cajani using a species-specific primer and a TaqMan probe was developed. The primers and a probe were designed to amplify the COI gene fragment. The specificity of the primer-probe set was tested in singleplex or multiplex reactions against target and non-target nematodes. In multiplex real-time PCR experiments with the specific and universal primer-probe sets, the signals were simultaneously observed for COI and D3 of 28S rRNA target genes. The results showed that the real-time PCR assay with species-specific primer and probe was sensitive enough to detect H. cajani DNA extracted from 0.003 egg or second-stage juvenile.

NEMATODE PARASITES OF WATERLEAF (Talinum triangulare) IN OBIO-AKPOR AND IKWERRE LOCAL GOVERNMENT AREAS OF RIVERS STATE, NIGERIA

Waterleaf, Talinum triangulare is cultivated in home gardens and fields to improve nutritional quality for the family and a source of livelihood for farmers. However, the role of T. triangulare is often counteracted by plant-parasitic nematodes (PPNs). Effective management of PPNs will depend on the identification and determination of their population and distribution. A survey was conducted in two Local Government Areas (LGAs), Ikwerre and Obio-Akpor of Rivers State to identify plant-parasitic nematodes associated with waterleaf. Multistage random sampling technique was employed in the collection of 60 bulked soil and root samples across six waterleaf monoculture farming communities. The nematodes were extracted, identified and their population determined using standard procedures. Occurrences, relative importance values (RIV) and diversity indices were determined. Other data were analysed using descriptive statistics and analysis of variance. Six plant-parasitic nematodes genera were encountered in this study, Helicotylenchus, Pratylenchus, Paratylenchus, Meloidogyne, Scutellonema and Tylenchulus. Pratylenchus and Helicotylenchus were the most frequently occurring nematode pest genera with equal relative frequency of occurrence of 38.89%. Pratylenchus species with RIV of 61.34% was the most important nematode pest associated with waterleaf across the six farm communities. The dominance index of 0.71 for the nematode genera showed that some nematode species dominated others. Alakahia farms had the highest population of plant-parasitic nematodes (2,780) across the six farm communities, whereas Omagwa farms had the lowest (250). The study showed that nematode pests are associated with waterleaf and could be contributing to yield losses in this crop

Selection and characterization of two Bacillus thuringiensis strains showing nematicidal activity against Caenorhabditis elegans and Meloidogyne incognita.

Bacillus thuringiensis has been widely used as a biological control agent against insect pests. Additionally, nematicidal strains have been under investigation. In this report, 310 native strains of B. thuringiensis against Caenorhabditis elegans were tested. Only the LBIT-596 and LBIT-107 strains showed significant mortality. LC50s of spore-crystal complexes were estimated at 37.18 and 31.89μg/mL for LBIT-596 and LBIT-107 strains, respectively, while LC50s of partially purified crystals was estimated at 23.76 and 20.25μg/mL for LBIT-596 and LBIT-107, respectively. The flagellin gene sequence and plasmid patterns indicated that LBIT-596 and LBIT-107 are not related to each other. Sequences from internal regions of a cry5B and a cyt1A genes were found in the LBIT-596 strain, while a cry21A, a cry14A and a cyt1A genes were found in the LBIT-107 strain. Genome sequence of the LBIT-107 strain showed new cry genes, along with other virulence factors, hence, total nematicidal activity of the LBIT-107 strain may be the result of a multifactorial effect. The highlight of this contribution is that translocation of spore-crystal suspensions of LBIT-107 into tomato plants inoculated at their rhizosphere decreased up to 90% the number of galls of Meloidogyne incognita, perhaps the most important nematode pest in the world.

Morphological and Molecular Characterization of Pratylenchus dakotaensis n. sp. (Nematoda: Pratylenchidae), a New Root-Lesion Nematode Species on Soybean in North Dakota, USA.

Root-lesion nematodes (Pratylenchus spp.) of the genus Pratylenchus Filipjev, 1936, are among the most important nematode pests on soybean (Glycine max (L.) Merr.), along with soybean cyst and root-knot nematodes. In May 2015 and 2016, a total of six soil samples were collected from a soybean field in Walcott, Richland County, ND and submitted to the Mycology and Nematology Genetic Diversity and Biology Laboratory (MNGDBL), USDA, ARS, MD for analysis. Later, in 2019, additional nematodes recovered from a greenhouse culture on soybean originally from the same field were submitted for further analysis. Males, females, and juveniles of Pratylenchus sp. were recovered from soil and root samples and were examined morphologically and molecularly. DNA from single nematodes were extracted, and the nucleotides feature of three genomic regions targeting on the D2–D3 region of 28S rDNA and ITS rDNA and mitochondrial cytochrome oxidase subunit I (COX1) gene were characterized. Phylogeny trees were constructed to ascertain the relationships with other Pratylenchus spp., and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was performed to provide a rapid and reliable differentiation from other common Pratylenchus spp. Molecular features indicated that it is a new, unnamed Pratylenchus sp. that is different from morphologically closely related Pratylenchus spp., including P. convallariae, P. pratensis, P. fallax, and P. flakkensis. In conclusion, both morphological and molecular observations indicate that the North Dakota isolate on soybean represents a new root-lesion nematode species which is named and described herein as Pratylenchus dakotaensis n. sp.

Identification and Abundance of Plant-parasitic Nematodes Associated with Amenity Trees in the University of Port Harcourt, Rivers State, Nigeria

Plant-parasitic nematodes contribute to unnoticeable damages which lead to gradual decline in the values and eventually death of amenity trees. Identification of these nematode pests is vital for their effective management. Reconnaissance survey was carried out to identify amenity tree species present in the University of Port Harcourt (UNIPORT). Composite bulked soil and root samples (126) were collected from amenity trees in UNIPORT and nematode pests were extracted from samples using modified Baerman method. The nematode pests were identified and their populations determined using standard procedures. Relative importance value (RIV) and diversity indices were calculated with appropriate software. Data were processed using descriptive statistics and with analysis of variance. 38 tree species were identified in UNIPORT belonging to 20 families. Terminalia mantaly, Cocos nucifera and Terminalia catappa with RIVs of 15.1, 9.35, and 9.12 respectively were the three most important amenity trees in UNIPORT. Fifteen nematode pest genera; Helicotylenchus, Aporcelaimus, Tylenchulus, Meloidogyne, Scutelonema, Pratylenchus, Tylenchus, Rotylenchoides, Criconema, Hemicyliophora, Trichodorus, Mesodorylaimus, Heterodera, Paratylenchus and Longidorus were associated with 21 of the amenity trees. The three most important nematode pest genera were Helicotylenchus, Tylenchulus and Aporcelaimus with RIVs of 42%, 16% and 5.34%, respectively. Helicotylenchus (RIV 45.41%) and Tylenchulus (RIV 30%) were the most important plant-parasitic nematode genera in the soil and roots of amenity trees, respectively. Helicotylenchus, Tylenchulus and Aporcelaimus were the three most important plant-parasitic nematode genera associated with amenity trees in UNIPORT.
 Keywords: Amenity trees, Diversity indices, Identification, Nematode pests, Survey

First report of northern root-knot nematode, Meloidogyne hapla (Chitwood, 1949) on strawberry in Turkey.

Strawberry is one of the most economically important crops worldwide. Several species of plant-parasitic nematodes have been reported to be pathogenic on strawberries, among them the northern root-knot nematode (Meloidogyne hapla), which considered to be strawberry most important nematode pest worldwide. In August 2019, strawberry growers at Silifke (Mersin, Turkey) identified nematode-like symptoms on strawberry roots and infected seedlings were brought to the nematology laboratory at of Mersin University for diagnostics. Roots were separated into small pieces and nematode extraction was performed by a modified Baermann funnel method and identified under the microscope. DNA was extracted from individual nematodes using Worm Lysis Buffer(WLB (+)). The species-specific SCAR markers (JMV1, JMV2, and JMVhapla) yielded a 440 bp band specific to M. hapla. The 28S rRNA gene region, obtained using the general primers D2\\D3, sequence was analysed from. The analyzed sequence was 100% identicle to M. hapla. The gene sequences were deposited into GenBank database with accession numbers MN897751 and MN895037. Both morphological and molecular diagnostic methods confirmed that the strawberry plants collected in Silifke were infested with M. hapla. To our best knowledge this is the first report of plant-parasitic nematode species M. hapla infecting strawberry in Turkey. Currently, the adverse effect of RKN on strawberry production in the region is unknown to strawberry growers.

Molecular and morphological characterization of the amaryllis lesion nematode, Pratylenchus hippeastri (Inserra et al., 2007), from California.

Root-lesion nematodes (Pratylenchus spp.) are among the most important nematode pests on grapevine along with root-knot, dagger, and ring nematodes. In 2019, two samples of both soil and roots were collected from a vineyard in Delano, Kern County, California and submitted to the United States Department of Agriculture, ARS, Mycology and Nematology Genetic Diversity and Biology Laboratory, Beltsville, MD, for identification purposes. Females and juveniles of Pratylenchus sp. were recovered from the root and soil samples using the sugar centrifugal flotation and Baermann funnel extraction methods. Both morphological observations and molecular analysis of internal transcribed spacer (ITS), 28S large subunit ribosomal DNA, and mitochondrial cytochrome oxidase (COI) sequences indicated that the specimens recovered from the soil and roots were Pratylenchus hippeastri. To the best of the authors’ knowledge, this is the first report of P. hippeastri from California including the first record of this species on grapevine and the second state record in North America. Damages caused by nematodes cannot be over-emphasized, although economic importance of P. hippeastri has never been established. Hence, there is an urgent need to investigate the economic impact of this nematode in vineyards in California State in order to develop sustainable management strategies.

DISTRIBUTION OF PCN PATHOTYPES IN POLAND

Both Globodera rostochiensis (Wollenweber, 1923) Behrens, 1975 and Globodera pallida (Stone, 1973) are considered the most economically important nematode pest. Annual regional survey conduct in Poland have revealed high infestation of pathotype Ro1 to the northwest of the country and presence of new pathotype Ro5 of G. rostochiensis. In 2009-2013 fifty eight soil samples were tested. parasitic root organisms cause significant losses in quantity and quality of potato crops. In many European countries PCN have become a major problem in potato production mainly in starch potato cultivars. The pathotype Ro1 was detected mostly in central and northern Poland and pathotype Ro5 in four separated provinces: malopolskie, lubuskie, lubelskie and pomorskie. The abundance of cysts in location where the new pathotype was detected suggests that is a thread of further spread of pathotype Ro5 of G. rostochiensis in the country. Consequently, producers and farmers need to grow resistant potato cultivars to keep nematode population below damaging level. These results indicate the urgent need to prevent the spread of PCN to non-infested areas. This report focused on identification of nematode pathotypes in soil samples from infested polish fields and presentation of G. rostochiensis distribution on territory of Poland.

Resistance to Cereal Cyst Nematodes in Wheat and Barley: An Emphasis on Classical and Modern Approaches.

Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals like wheat and barley. These nematodes alone are estimated to reduce production of crops by 10% globally. This necessitates a huge enhancement of nematode resistance in cereal crops against CCNs. Nematode resistance in wheat and barley in combination with higher grain yields has been a preferential research area for cereal nematologists. This usually involved the targeted genetic exploitations through natural means of classical selection breeding of resistant genotypes and finding quantitative trait luci (QTLs) associated with resistance genes. These improvements were based on available genetic diversity among the crop plants. Recently, genome-wide association studies have widely been exploited to associate nematode resistance or susceptibility with particular regions of the genome. Use of biotechnological tools through the application of various transgenic strategies for enhancement of nematode resistance in various crop plants including wheat and barley had also been an important area of research. These modern approaches primarily include the use of gene silencing, exploitation of nematode effector genes, proteinase inhibitors, chemodisruptive peptides and a combination of one or more of these approaches. Furthermore, the perspective genome editing technologies including CRISPR-Cas9 could also be helpful for improving CCN resistance in wheat and barley. The information provided in this review will be helpful to enhance resistance against CCNs and will attract the attention of the scientific community towards this neglected area.

Root-lesion nematodes in cereal fields: importance, distribution, identification, and management strategies

Root-lesion nematodes of the genus Pratylenchus are among the most important nematode pests that limit production of small-grain cereals. Four Pratylenchus species, viz. P. thornei, P. neglectus, P. penetrans, and P. crenatus, are considered of major economic significance in cereals of which P. thornei and P. neglectus are the most important and widely distributed species in cereal crops worldwide. However, P. thornei is more destructive causing estimated yield losses of up to 50% in the USA and 85% in Australia. This paper provides information regarding the global distribution of Pratylenchus species, yield loss due to their attack, their biology and pathogenic relation to plants, the research cutting edges in nematode identification of different Pratylenchus species, and their control through cultural practices and resistant varieties as correct identification of root-lesion nematodes can be difficult to achieve, particularly if a quick diagnosis is needed. In this context, in recent years, several molecular techniques for these Pratylenchus species have been developed such as quantitative PCR assays which are able to produce precise and rapid identification of several root-lesion nematodes species. So far, many global attempts have been made to control root-lesion nematodes in cereals, including cultural practices and development of resistant varieties. The use of resistant accessions is considered the most economically feasible and environmentally sustainable method. Resistance genes in several lines have been identified and are being used in numerous breeding programmes against root-lesion nematodes species.

Cereal Cyst Nematodes: A Complex and Destructive Group of Heterodera Species.

Small grain cereals have served as the basis for staple foods, beverages, and animal feed for thousands of years. Wheat, barley, oats, rye, triticale, rice, and others are rich in calories, proteins, carbohydrates, vitamins, and minerals. These cereals supply 20% of the calories consumed by people worldwide and are therefore a primary source of energy for humans and play a vital role in global food and nutrition security. Global production of small grains increased linearly from 1960 to 2005, and then began to decline. Further decline in production is projected to continue through 2050 while global demand for these grains is projected to increase by 1% per annum. Currently, wheat, barley, and oat production exceeds consumption in developed countries, while in developing countries the consumption rate is higher than production. An increasing demand for meat and livestock products is likely to compound the demand for cereals in developing countries. Current production levels and trends will not be sufficient to fulfill the projected global demand generated by increased populations. For wheat, global production will need to be increased by 60% to fulfill the estimated demand in 2050. Until recently, global wheat production increased mostly in response to development of improved cultivars and farming practices and technologies. Production is now limited by biotic and abiotic constraints, including diseases, nematodes, insect pests, weeds, and climate. Among these constraints, plant-parasitic nematodes alone are estimated to reduce production of all world crops by 10%. Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals. Heavily invaded young plants are stunted and their lower leaves are often chlorotic, forming pale green patches in the field. Mature plants are also stunted, have a reduced number of tillers, and the roots are shallow and have a "bushy-knotted" appearance. CCNs comprise a number of closely-related species and are found in most regions where cereals are produced.

First Report of the New Root-Lesion Nematode Pratylenchus sp. on Soybean in North Dakota

Root-lesion nematodes (RLN; Pratylenchus spp.) are important nematode pests on soybean (Glycine max (L.) Merr.). In May 2015 and 2016, sixtwo soil samples were collected from a soybean field in Walcott, Richland County, ND. Nematodes were extracted from soil using a sugar centrifugal flotation method., revealing these two All the samples contained RLN from 125 to 2, 000and 350 root-lesion nematodes per kg soil, respectively. In 2016, four soil samples were collected from the same field and all the samples had root-lesion nematodes ranging from 300 to 2,000. One soil sample with 350 RLN lesion nematodes per kg soil was planted withto soybean cultivar Barnes in four replicates each in a pot (6.4-cm × 25.4-cm) with 500 g soil(n = 4). After 15 weeks of growth at 22°C in a greenhouse room at 22°C, the root-lesion nematode RLN population was found to have increased greatly. The final population density in soil was 1,518 ± 541 lesion nematodesRLN per kg soil. Soybean roots were rinsed with water and brown lesion...

Negative phototaxis in M. incognita

Phototaxis is a well-known behavior in many animals. However, little is known whether nematodes living in soil recognize light. Meloidogyne incognita is one of the most important root-knot nematode pests in the world. It has a very wide host range and can infect almost all plant species. Here, we examined the phototactic response in M. incognita. Negative phototactic behavior was observed in M. incognita on an agar plate. Nematodes responded by avoiding white light and blue light more than red light on agar plates. Light avoidance behavior of the nematodes was examined by microscopic analysis, and the nematodes escaped from near ultraviolet light (365 nm) in only approximately 3.2 seconds. They also avoided blue (470 nm), blue-green (500 nm), and green (550 nm) light in approximately 4.1, 7.4, and 10.0 seconds, respectively. These results suggest that M. incognita exhibits negative phototaxis, in particular, responding efficiently to shorter wavelength of light.

Use of GFP-tagged Trichoderma harzianum as a tool to study the biological control of the potato cyst nematode Globodera pallida

The fungus Trichoderma harzianum strain ThzID1-M3 isolated in the Palouse region of the state of Idaho and transformed to express green fluorescent protein (GFP) was used as a biomarker to study the biological control processes of the potato cyst nematode Globodera pallida. Experiments were conducted to evaluate the effect of T. harzianum ThzID1-M3 on G. pallida infection and reproduction at 45 and 75days after inoculation respectively; and to observe, through microscopy rhizosphere chamber, the colonization of G. pallida second-stage juveniles and potato rhizoplane by T. harzianum ThzID1-M3 10days after inoculation. Significant reduction of G. pallida infection in potato roots was observed when soil was amended with T. harzianum ThzID1-M3. Globodera pallida cysts recovered from soil and G. pallida reproduction rate were significantly reduced by 49% and 60% respectively, when soil was amended with T. harzianum ThzID1-M3 compared to the non-amended soil. Microscopic observations showed that T. harzianum ThzID1-M3 colonized G. pallida second-stage juveniles and cysts, and proliferated in the rhizoplane and rhizosphere of potato. To our knowledge, this is the first report on the study of Trichoderma spp. marked with GFP against a potato cyst nematode. The use of GFP-tagged T. harzianum has the potential to monitor the biological control processes of G. pallida and the tools advanced in this study should facilitate the design of novel strategies to control this economically important nematode pest of potato.

First report of the root-knot nematode (Meloidogyne graminicola) in Madagascar rice fields

Rice is the major crop produced in Madagascar and is infested by numerous plant-parasitic nematodes. An extensive list of plant-parasitic nematodes found in association with rice roots during a survey of 14 sites is presented. This is the first time that Meloidogyne graminicola has been detected in Madagascar, which is relevant information for future management of this economically important nematode pest of rice.

First Report of the Root-lesion Nematode Pratylenchus neglectus on Wheat (Triticum aestivum) in North Dakota

Root-lesion nematodes (Pratylenchus spp.) are important nematode pests that invade roots of plants and restrict productivity of wheat (Smiley et al. 2005). In August 2015, a soil sample was collected from a harvested wheat field in Walsh County, ND, and was found to contain 1,044 root-lesion nematodes per kg of soil using the sugar centrifugal flotation method. In October 2015, four soil samples were collected from the same field and had root-lesion nematodes ranging from 125 to 1,000/kg soil. One soil sample with 500 lesion nematodes/kg soil was used to inoculate hard red spring wheat cvs. Glenn and Faller. After 10 weeks of growth in a greenhouse room maintained at 22°C, wheat roots were harvested and washed, and light brown lesions were observed on lateral roots. The washed roots were cut into 1-cm segments for nematode extraction using the Whitehead tray method. After 48 h, lesion nematodes were recovered from the root tissues. Averages of 24 and 20 root-lesion nematodes per gram were found in the roots of Glenn and Faller, respectively. Nematodes from soil and wheat roots were examined morphologically and molecularly for species identification. Morphological measurements of adult females (n = 10) included body length (range = 402.0 to 495.0 μm, mean = 446.0 μm), stylet (15.0 to 17.5, 16.4), tail length (16.0 to 22.0, 18.8), body width (17.0 to 22.0, 19.6), anterior end to basal bulb (90.0 to 115.0, 101.6), a = (21.2 to 24.7, 23.1), b = (3.7 to 4.8, 4.4), c = (19.6 to 27.1, 23.8), and V (81.0 to 85.0%, 82.8%). The lip region had two annules, and was not set off, with anterior margins of apical lip annule convex, second annule was slightly wider than the first; lateral field had four lines with central zone of lateral field having oblique striae; tail terminus was smooth, rounded, or slightly oblique. The nematode species was identified as Pratylenchus neglectus (Rensch, 1924) Filipjev & Schuurmans Stekhoven, 1941 based on morphological and morphometric characteristics (Castillo and Vovlas 2007). DNA was extracted from single nematodes (n = 11) isolated from soil and wheat roots, and ITS region of rDNA was amplified (Tanha Maafi et al. 2003). PCR products from three nematodes were cloned using pGEM-T easy vector and sequenced, and the resulting ITS sequences were identical. The consensus sequence (GenBank Accession No. KU705392, 684 bp) was 99% homologous with one population of P. neglectus from China (JX046941) and 83% or less identical to other Pratylenchus spp. including P. thornei, a species closely related to P. neglectus. The specific primers from D3 28S rRNA and ITS rDNA were used to amplify DNA of eight nematodes and produced single bands specific for P. neglectus (Yan et al. 2008, 2013). The combination of the molecular tests confirmed the target species as P. neglectus. Two species of root-lesion nematodes, P. neglectus and P. thornei, were reported as damaging pathogens affecting wheat production in the Pacific Northwest (Smiley et al. 2005). To our knowledge, this is the first report of P. neglectus on wheat in North Dakota. The resistance levels of various wheat cultivars to this lesion nematode are being identified.