Nematode Population Densities Research Articles

Response of selected nutrient elements in leaf tissues of sweet potato cv. 'Bophelo' to Nemafric-BL phytonematicide

Nemafric-BL phytonematicide is a potent plant-based nematicide which consistently suppress nematode population densities of root-knot (Meloidogyne species) nematodes on various crops, but with limited information on its effects on foliar nutrient elements in sweet potato. The objective of this study, therefore, was to investigate the effects of Nemafric-BL phytonematicide on accumulation of nutrient elements in leaf tissues of sweet potato cv. 'Bophelo' under greenhouse conditions in Limpopo Province, South Africa, during autumn (February-April) in 2021 and validated in 2022. The product was applied weekly at geometric concentrations, with mature leaves collected and prepared for analysis of nutrient elements at eight weeks. Seasonal interactions were not significant and therefore data were pooled (n = 70) and then subjected to the Curve-fitting Allelochemical Response Dose (CARD) algorithm computer model. Iron (R2 = 0.86), K (0.91) and Na (0.82) versus Nemafric-BL phytonematicide each exhibited negative quadratic relations, whereas Zn (0.83) versus the product exhibited positive quadratic relations. In all test elements, the CARD-generated biological indices illustrated that the accumulation of elements was highly sensitive to the concentration of Nemafric-BL phytonematicide. In conclusion, in sweet potato production, the application of Nemafric-BL phytonematicide can inhibit (Fe, K) and stimulate (Zn) the accumulation of certain elements in leaf tissues of sweet potato cv. ′Bophelo‵.

Caracterización de Meloidogyne spp. y densidad poblacional de nematodos fitoparásitos asociados a cultivos de aliáceas en la región Arequipa, Perú

Alliaceae crops includes several species of agricultural importance for the Arequipa region, among them the onion is the most produced in the country, however, these crops are affected by phytoparasitic nematodes, including Meloidogyne spp. which causes significant losses in the yield. The aim of the present study was to characterise the root-knot nematode (Meloidogyne spp) and determine the population density of phytoparasitic nematodes in alliaceae crops in the main producing localities of the Arequipa region. Samples of roots and soil were collected in onion, chinese onion, leek and chives crops in the provinces of Arequipa, Castilla, Caylloma and Islay. The identification of nematode genus was found by morphological characteristics and the characterization of Meloidogyne were performed by perineal patterns and electrophoretic pattern of esterase (Est). In the 38 soil samples, different genus of plant-parasitic nematodes was found: Aphelenchus, Dorylaimus, Helicotylenchus, Hemicycliophora, Meloidogyne, Mesocriconema, Mononchus, OGMA, Pratylenchus, Rotylenchus, Tylenchus, Xiphinema and free-living nematodes, in root samples, eight populations of Meloidogyne spp. were found. distributed among three species: (1) M. incognita phenotype Est I1, Rm: 1.0 with 33.33% of frequency and Est I2, Rm: 1.03, 1.07 (50%); (2) M. javanica Est J3, Rm: 1.03, 1.24, 1.37 (16.67%) and an atypical species named Meloidogyne sp. Rm: 0.85 (33.33%). The identification of genus and species phytoparasitic nematodes in alliaceae will allow the adoption of more efficient integrated management measures, because have a distinct parasitism behavior.

Diversity of plant-parasitic nematodes associated with chickpea (Cicer arietinum L.) in the main growing areas of Ethiopia

Summary Chickpea is one of the most important legume crops in Ethiopia; however, its production is far below the mean international chickpea production due to biotic and abiotic stressors. Plant-parasitic nematode infestation is extensive in chickpea-growing areas worldwide. The distribution and population density of plant-parasitic nematodes in chickpea were determined during the September-December 2021 growing season. Ten plant-parasitic nematode taxa were identified from 27 localities across ten districts in the main chickpea-growing areas in Ethiopia. Pratylenchus had the highest prominence values, followed by Rotylenchulus and Meloidogyne spp. Helicotylenchus, Hoplolaimus, Scutellonema and Quinisulcius were more prevalent than Criconemoides and Ditylenchus. Sequences of different molecular markers, including D2-D3 of 28S rDNA, ITS of rDNA, and COI and Nad5 of mtDNA, revealed the presence of Meloidogyne javanica, Rotylenchulus parvus, Scutellonema clathricaudatum and Helicotylenchus caudatus. Helicotylenchus caudatus and R. parvus are the first reports from Ethiopia and chickpea, while S. clathricaudatum is the first report for chickpea. This study provides essential baseline information of nematode pest occurrence on chickpea in Ethiopia. This information will raise awareness among growers, agricultural officers, and extension advisors, enabling them to develop effective nematode management strategies for the chickpea production system in Ethiopia.

Parasitic nematode populations associated with developmental stages of mango in production regions of Ghana

Nematode (Phylum nematoda) infestation is a major set back in mango (Mangifera indica) production world-wide. Control of nematodes requires understanding of their diversity, distribution and population densities. The objective of this study was to identify plant-parasitic nematodes associated with mangoes and their population densities at seedling and maturity stages in production regions of Ghana. The study was conducted in Greater Accra (Manya and Klagon) and the Eastern region (Somanya) during December 2016 to January 2018. Mango farmlands were surveyed for soil and root samples, from which nematodes were extracted, identified and quantified. Twenty-four nematode genera were identified in mango seedlings and matured trees from Somanya; and 14 genera dentified in seedlings and 22 in matured trees from Manya; while at Klagon, 15 nematode genera were identified in matured trees. Helicotylenchus spp. were the most populated in seedlings obtained from Somanya and Manya, with relative abundance of 23.29%. Tylenchus spp. had the highest population in mature trees, with relative abundance of 24.49% at Somanya and 38.86% at Manya; while Helicotylenchus spp. had the highest relative abundance of 43.96% at Klagon. Mature trees had higher nematode population densities, compared to seedlings. There were significant variation in nematode populations between seedlings and matured stages of mango.

A 2‐year, multi‐county survey of plant‐parasitic nematodes in North Carolina flue‐cured tobacco

AbstractNorth Carolina is the leading producer of flue‐cured tobacco (Nicotiana tabacum L.) in the United States. Production in the state is threatened by numerous plant‐parasitic nematodes, including Meloidogyne spp. (root‐knot), Globodera tabacum (tobacco cyst), Pratylenchus spp. (lesion), Rotylenchulus reniformis (reniform), and Tylenchorhynchus spp. (stunt) nematodes. The invasive Meloidogyne enterolobii is also a major threat as it can infect tobacco varieties carrying the Rk gene, which conditions resistance to other Meloidogyne species. To gain an updated understanding of which nematode taxa are present in tobacco production and investigate distribution of M. enterolobii in North Carolina, a 2‐year survey was conducted. From 2021 to 2022, 188 fields were sampled across 24 tobacco‐growing counties. Samples were assayed for identification and quantification of nematodes at the genus level; where Meloidogyne spp. was identified, molecular testing was used to determine the species. Data were also collected on the previous crop and tobacco variety grown. In both years, lesion, root‐knot, dagger, and stunt nematodes were found in the highest incidence among samples. In 2022, M. enterolobii was identified in a single sample each from Granville and Pitt counties; this is the first report of M. enterolobii from Granville County. Tobacco variety NC 196 and soybean were the most common variety and previous crop grown, respectively, in both years of the survey. Tobacco variety did not have an effect on nematode population density. The previous crop had a significant effect on root‐knot and spiral nematodes in 2021, and lesion and stubby root nematodes in 2022.

Host-status of sixteen crops used in potato-based crop rotation systems against Meloidogyne javanica in South Africa

Root-knot nematodes (Meloidogyne species) are the most important group of plant nematodes in potato-producing regions of South Africa. Prior to the withdrawal of synthetic chemical fumigant nematicides from the agrochemical markets, Meloidogyne species were viewed as a minor pest in potato-producing regions. Currently, it has been established that all potato cultivars are host to Meloidogyne species, with the preferred management option of the genus being the use of resistant crops. However, the host status of most crops used in potato-based crop rotations intended to manage nematode population densities of the genus had not been established. Globally, M. incognita is viewed as being more aggressive than M. javanica, whereas in South Africa the opposite is true. Therefore, the objective of the study was to determine whether the reproduction potential (RP) values of M. javanica on 16 crops used in potato crop rotation systems would be below unity. The experiment was conducted under greenhouse conditions at the University of Limpopo during autumn (February-April) 2022 and validated in spring (September-November) of the same year in South Africa. Treatments (16 crops) were laid out in a randomized complete block design, with six replications. The crops were inoculated with 250 eggs + second-stage juveniles (J2). At 56 days after inoculation, nematodes variables were collected and expressed as RP, which demonstrated that there were similarities and differences in RP of the 16 crops to infection by M. javanica, but with the values being below one in white maluti oats, tillage radish, forage sorghum, and jap radish. In conclusion, the four crops with RP values below one could be used in a potato-crop rotation system intended to manage the population densities of M. javanica.

Eksplorasi Populasi dan Kepadatan Genus Nematoda Parasit pada Rizosfir Tanaman Kopi di Kota Solok, Sumatera Barat

Coffee is a plantation crop that has high economic value among other plantation crops and plays an important role as a source of foreign exchange for the country. The decline and low productivity of coffee plants in coffee production centers in Solok City, West Sumatra is one of the causes of plant parasitic nematode attacks. This nematode attack causes disrupted plant growth and reduces the value of crop production both in quantity and quality. This study aims to determine the diversity and population density of parasitic nematodes in the rhizosphere of coffee plants in Solok City, West Sumatra. This research was conducted from March to July 2023 at the Laboratory of Biological Control, Department of Plant Protection, Faculty of Agriculture, Andalas University. Soil samples were taken in two central areas of coffee plantations in Solok City, West Sumatra. In the rhizosphere of coffee plants in Solok City, four genera of parasitic nematodes were found, namely: the genera Pratylenchus, Helicotylenchus, Meloidogyne, Rotylenchulus, Paratylenchus, and Tylenchorhynchus. The highest frequency of presence of nematodes, namely the genus Rotylenchulus, was 50.99 belonging to the medium category in Jorong Kayu Aro, and 44.80 in the rare category in Jorong Kayu Jao.

Comparative analysis of soil nematode biodiversity from five different fruit orchards in Osmaneli district, Bilecik, Türkiye.

Nematode population densities were determined in 60 soil and root samples collected from 6 fruit orchards in the Bilecik province (western Turkey), between April 2022 and June 2022. The total number of identified nematodes have reached up to 2418 individuals (number of female: 1036; male: 154; and juvenile: 1228). They belong to 54 species, 54 genera, 33 families and 11 orders. Plant parasitic nematodes that were detected mostly are listed as follows: Helicotylenchus (6,12 %), Pratylenchus (5,74 %), Paratylenchus (4.83 %), Xiphinema (3,06 %), Tylenchorhynchus (2,19 %), Malenchus (1.94 %) and Tylenchus (1.19 %). According to the maturity index analysis, mean values showed the highest maturity level at peach trees (MI value: 3,52), followed by; walnut trees (MI value: 2.49), cherry trees (MI value: 2.15), nectarine trees (MI value: 1.86), plum trees (MI value: 1.57), and olive trees (MI value: 1.42). Mostly the diverse group in terms of species richness was within the order Dorylaimida. The nematodes associated with peach and walnut trees here showed the most stable environments in terms of soil nematode community structure.

Abundance, diversity and distribution of soil nematodes in Kangaita and Weru tea catchments of Kirinyaga and Tharaka Nithi counties, Kenya

Nematodes are the most abundant animals on earth and play essential roles in ecosystem functioning hence their abundance and diversity affect soil health. Nematodes have been reported in tea fields in some parts of Kenya and previous studies indicate that they may be a cause for the decline of tea population in some tea fields in Kenya. Nematodes of Moloidogyne spp have also been reported to be responsible for death of tea plants in nursery conditions. A survey was carried out in Weru and Kangaita tea factories catchment areas in Tharaka Nithi and Kirinyaga counties respectively. The survey aimed to determine the abundance and diversity of nematodes in small holder tea farms. Kangaita represented the high elevation site while Weru represented the low elevation site. Soil samples were collected from smallholder tea farms from which nematodes were extracted, identified based on their morphological characteristics, and classified according to their feeding habits then quantified using standard protocols. Nematodes from 23 genera were recovered in the two study sites representing all the five feeding groups: plant feeders, fungal feeders, bacterial feeders, omnivores, and predatory nematodes. Of the 23 genera, 11 were plant feeders, 6 bacterial feeders, 3 fungal feeders 2 omnivores and 1 predatory nematode. Kangaita, being a high elevation site reported higher population density in most genera reported than Weru which is a low elevation site. This is a departure from most studies that have reported higher nematode population densities in low altitudes. This can be attributed to differences in climatic and soil conditions in the two study sites in the same season. Kangaita was cooler with deep, well-ventilated, and loose soils while Weru was hotter with mostly compacted, shallow, and poorer soils in the tea farms. There is need for further research on the effect of elevation and farming practices on the distribution, abundance, and diversity of nematodes in tea fields. Key words: Nematodes, abundance, soil health, tea fields, elevation, diversity, feeding group

Plant-parasitic nematodes associated with Panicum maximum and Mimosa hirsutissima in a pasture field

Pastures and weed plants can host plant-parasitic nematodes of economic importance, with the limited yield of pastures representing a continuous challenge for agriculture, especially in the lower Jequitinhonha Valley in southeastern Brazil, where dairy and beef cattle play a crucial role in the local economy. From this perspective, this study aimed to provide information on the population density of plant-parasitic nematodes associated with Panicum maximum cv. Mombaça and Mimosa hirsutissima, weed species commonly found in pasture areas cropped with this grass in the municipality of Almenara, MG, in the Jequitinhonha Valley region of southeastern Brazil. Soil and root samples were collected from the field and placed in plastic bags, which were labeled and taken to the laboratory for nematode extraction. Nematode population densities were estimated in a Peters counting slide under a light microscope, and genera identification was based on morphological traits. In rhizosphere soil (100 g) of P. maximum cv. Mombaça, the highest population densities were observed for Helicotylenchus sp. (3,999), followed by Tylenchus sp. (1,191), Meloidogyne spp. (939), and Pratylenchus sp. (544). In roots (1 g), on the other hand, the highest values corresponded to Pratylenchus sp. (19.6) and Meloidogyne spp. (15.5). However, in rhizosphere soil of M. hirsutissima, the highest population densities were recorded for Tylenchus sp. (2,072), Helicotylenchus sp. (1,883), Pratylenchus sp. (751), and Meloidogyne spp. (307). In contrast, in the roots, the highest values were observed for Meloidogyne spp. (6.9), Tylenchus sp. (4.4), and Pratylenchus sp. (2.7). These findings are essential to take decisions on the management of plant-parasitic nematodes.

Effect of Fluopyram on Pratylenchus penetrans on Corn in the Field and In Vitro.

The effects of a fluopyram seed treatment on lesion nematodes (Pratylenchus spp.) and other plant-parasitic nematodes (PPNs) were evaluated on corn in multiple field locations in 2020 and 2021. The highest rate of fluopyram seed treatment (0.15 mg seed-1) reduced early season population density of lesion nematodes compared with the base treatment control in 2020 only. However, fluopyram did not affect late season lesion nematode population density and corn yields. Fluopyram seed treatment also had minimal or nonsignificant effects on other PPN species. Based on these results, the effects of fluopyram were tested in vitro on Pratylenchus penetrans. Results demonstrated that fluopyram severely affected motility in P. penetrans. The sensitivity of P. penetrans second-stage juveniles (J2s) to fluopyram was significantly higher than at J4 and adult, suggesting that sensitivity to fluopyram is dependent on developmental stage. In addition, the effects of fluopyram were reversible at an EC50 but were irreversible at the maximum concentration (25 μg/ml). Overall, our results indicate that fluopyram has potential for controlling P. penetrans, but its efficacy is variable depending on nematode developmental stage and chemical concentration. Further research is needed to determine if these impacts can translate to field scenarios.

Prevalence, Spatial Distribution, and Population Density of Plant-Parasitic Nematodes in Vegetable Fields of North Carolina, South Carolina, and Tennessee Counties

Plant-parasitic nematodes are a diverse group of soilborne plant pathogens that limit the yield of numerous vegetable crops globally. Few studies have investigated nematode populations affecting vegetable crops in Tennessee and North and South Carolina. Between December 2020 and October 2022, vegetable fields in selected counties of these states were sampled for plant-parasitic nematodes. Data on the prevalence, spatial distribution, and population density of seven genera of plant-parasitic nematodes, identified via morphology, were collected. Root-knot nematodes were identified in 60% of the fields sampled, with population densities ranging from 10 to 10,400 nematodes per 500 cm3 of soil. Detection rates of other genera as percentages of total fields sampled were: spiral (42%), stubby root (32%), stunt (21%), ring (13%), and lesion (8%) nematodes. Out of eight crops sampled, fields either currently or formerly planted to tomato or pepper were the most frequently sampled in the survey (77% of total fields). This is the first survey to collect data on populations of plant-parasitic nematodes in this region, and the results highlight the need for continued surveillance and study of their impact in vegetable production.

The Biofumigation Potential of Wild Radish (Raphanus Raphanustrum) and Field Mustard (Sinapis Arvensis) in Controlling Some Phytoparisitic Nematodes

Biofumigation is the process of introducing plants and their residues into the soil to release volatile compounds. Among these plants, those belonging to the Brassicaceae family are the most commonly used ones for biofumigation purposes. These plants are rich in glucosinolates, which upon enzymatic hydrolysis produce compounds such as isothiocyanates, which are approved as nematicides. Raphanus, Sinapis, and Eruca species genera are the most frequently used plants in the Brassicaceae family for biofumigation. This technique is becoming increasingly popular as a sustainable alternative to restricting fumigants in agriculture production. Dry plants (at vegetative and flowering stages) of Raphanus raphanustrum and Sinapis arvensis are incorporated into the soil and evaluated for their biofumigation effects on some phytoparasitic nematodes in comparison to a synthetic nematicide (tefluthrin 1.5%) and untreated control. Thirty days post-incorporation, soil samples were collected for nematode extraction and counting, and subsequently identified at the genus level. We identified four phytoparasitic nematodes that are most harmful to cultivated plants (Tylenchorhynchus, Pratylenchus, Paratylenchus, and Tylenchus). Each treatment decreased nematode population densities from 67% to 92%. Sinapis arvensis biofumigation was the most effective, reducing nematode densities by up to 92%. Conversely, Raphanus raphanustrum and Tefluthrin 1.5% treatments generally resulted in increased nematode densities (up to 74% and 67% respectively). The results of this study have given valuable information and suggest that Sinapis arvensis could be used to manage plant-parasitic nematodes, particularly the Tylenchorhynchus population. Biofumigation is a promising strategy that can be used especially by subsistence farmers for the sustainable production of crops in the presence of lower nematode pest densities.

Vineyard soil texture and pH effects on Meloidogyne hapla and Mesocriconema xenoplax

AbstractNorthern root‐knot nematode (Meloidogyne hapla) and ring nematode (Mesocriconema xenoplax) are the most prevalent plant‐parasitic nematodes of wine grapes in the Pacific Northwest, but M. hapla is most important in eastern Washington and M. xenoplax in western Oregon. These regions differ edaphically where Washington soils are minimally weathered and alkaline while Oregon soils are highly weathered and acidic. To examine the effect of soil texture and pH on nematode reproduction, an alkaline, sandy loam soil (pH 7.9) from Washington and an acidic loam soil from Oregon (pH 5.4) were modified to the other pH extreme, and to a middle pH of 6.9. Tomatoes were planted into each soil/pH combination, and either 500 M. hapla second‐stage juveniles or M. xenoplax individuals were added to each pot. After 7 weeks, plants were harvested, three roots collected for analysis, remaining roots and leaves dried and weighed, and nematode population densities determined as eggs on roots (M. hapla) and nematodes in soil (M. xenoplax). Soil texture (sandy loam or loam) had no effect on either nematode, but M. hapla reproduction was greater in the lowest pH soil while M. xenoplax was unaffected by soil pH. Mesocriconema xenoplax parasitism reduced root length and root tip number, whereas M. hapla increased root mass in the highest pH Washington soil. Under these experimental conditions, it appears vineyard soil texture in the Pacific Northwest is not a determining factor in population growth of these nematodes, but M. hapla performed better at low pH.

Evaluation of Wheat Cultivars and Germplasm Lines for Resistance to Pratylenchus neglectus Populations Collected in North Dakota.

Root-lesion nematode (RLN; Pratylenchus neglectus) is a migratory endoparasite and a major soilborne pathogen that affects wheat (Triticum spp.) production worldwide. Genetic resistance is one of the most economical and effective ways to manage P. neglectus in wheat. This study evaluated 37 local cultivars and germplasm lines in seven greenhouse experiments, including 26 hexaploid wheat, six durum wheat, two synthetic hexaploid wheat, one emmer wheat, and two triticale for P. neglectus resistance from 2016 to 2020. North Dakota field soils infested with two RLN populations (350 to 1,125 nematodes per kilogram of soil) were used for resistance screening under controlled greenhouse conditions. The final nematode population density for each cultivar and line was counted under the microscope to categorize the resistance ranking of these entries as resistant, moderately resistant, moderately susceptible, and susceptible. Out of the 37 cultivars and lines, one was classified as resistant (Brennan); 18 were moderately resistant (Divide, Carpio, Prosper, Advance, Alkabo, SY Soren, Barlow, Bolles, Select, Faller, Briggs, WB Mayville, SY Ingmar, W7984, PI 626573, Ben, Grandin, and Villax St. Jose); 11 were moderately susceptible; and seven were susceptible to P. neglectus. The resistant to moderately resistant lines identified in this study could be used in breeding programs after the resistance genes or loci are further elucidated. This research provides valuable information about P. neglectus resistance among wheat and triticale cultivars used in the Upper Midwest region of the United States.

First Report of Meloidogyne enterolobii Infecting Solanum nigrum in China.

Black nightshade (Solanum nigrum) typically grows as a weed species, but it is also widely used as an herb to treat stomach ulcers and dermal infections in many countries (Jabamalairaj et al. 2019). In April 2023, extensive root galls similar to those associated with by root-knot nematodes (RKNs), Meloidogyne spp., were observed on the roots of black nightshade in several commercial fields in Lufeng county (22°55'57.44″N, 115°33'10.31″E), Guangdong Province, China. Upon inspection, there were one to several female RKN in each gall, and egg masses protruding through the root surface. The disease incidence rate was more than 90% in each field using the random sampling method. The nematode population densities in the samples ranged from 279 to 656 eggs and second-stage juveniles (J2s) per gram of fresh roots. Females and egg masses were collected from the roots, and egg masses were incubated in sterile water at 25°C to obtain J2s. Males were not collected in root galling or soil samples. The J2 tail is thin with a broad, bluntly pointed tip, and a clearly defined hyaline tail terminus. Measurements of J2 (n = 20) included: L= 440 ± 30.5 (384 to 500) µm, stylet = 12.3 ± 0.7 (11.3 to 13.7) µm, tail = 51.6 ± 2.4 (47.9 to 57.0) µm. For females (n = 15), vulval slit length = 25.5 ±1.9 (23.6 to 29.1) µm, vulval slit to anus distance = 22.1 ± 3.0 (18.2 to 27.0) µm. Stylet knobs in females are divided longitudinally by a groove so that each knob appears as two. The perineal patterns are round to ovoid, with coarse and smooth striae, moderate to high dorsal arch and mostly lacking distinct lateral lines. Morphological characteristics from J2s and perineal patterns from adult females fit the original description of M. enterolobii (Yang and Eisenback 1983). Furthermore, species identity was explored by sequencing the D2-D3 region of the 28S rRNA gene using primers D2A/D3B (Vrain et al. 1992), and the mtDNA cytochrome c oxidase I (COI) genes using primers JB3/JB5 (Derycke et al. 2005). The sequences for the target genes were 759 bp (GenBank Accession No. OR046056) and 447 bp (GenBank Accession No. OR042802), respectively. The BLAST analysis suggested 98.17~99.78% similarities to other available M. enterolobii sequences in GenBank. Species identity was further confirmed with the species-specific primer pair Me-F/Me-R (Long et al. 2006). An approximately 240 bp PCR product was produced, which was previously reported only for M. enterolobii, whereas no product was obtained from control populations of M. incognita or M. javanica. The pathogenicity test was conducted in a greenhouse at 28°C using seedlings of S. nigrum maintained in pots containing 500 cm3 sterilized soil. Ten replicates were inoculated with 800 eggs and J2s of the original population of M. enterolobii, while another 10 replicates of control plants were not inoculated. After 7 weeks, the inoculated plants exhibited galling symptoms similar to plants observed in the field, and females and egg masses were obtained by dissecting galls. No galling symptoms were observed on control plants. These results confirmed the nematode's pathogenicity. To our knowledge, this is the first record of M. enterolobii parasitizing black nightshade. M. enterolobii stands out as a highly deleterious variant among the species of RKNs owing to its extensive repertoire of host plants, pathogenicity, and proficiency in thriving and multiplying even on crops possessing resistance genes (Sikandar, 2022). In addition to being a medicinal plant, S. nigrum is a widespread weed found in fields throughout China. This report also showed that S. nigrum could play an important role as a reservoir host of M. enterolobii aiding its survival, reproduction, spread, and increasing the potential damage for host crops.

Effects of Soil Solarization and Grafting on Tomato Yield and Southern Root-knot Nematode Population Densities

High tunnel production has increased in the past 10 years in Kentucky with more than 1500 high tunnels constructed across the state. Tomato is the most popular and most valuable high tunnel crop per square foot. This has contributed to a lack of rotation and increased pressure from root-knot nematodes (RKN; Meloidogyne spp.). Infection by RKN leads to root galling and reduces the host plant’s ability to take up water and nutrients. Sustainable strategies are needed to manage increasing RKN populations for long-term health of high tunnel soils. Soil solarization is a nonchemical management strategy that has shown promise in other regions and in open field systems. Because tunnels are primarily used to produce high-value crops and are often used for season extension, solarizing during the off-season would be the most beneficial for growers because solarizing would require taking the tunnel out of production. The primary objective of this study was to determine whether springtime soil solarization in Kentucky high tunnels followed by use of resistant tomato cultivars is a viable and effective management strategy for RKN populations. Soil solarization was performed in two commercial high tunnels naturally infested with southern RKN (Meloidogyne incognita) for 2, 4, and 6 weeks and compared with a nonsolarized control. Soil temperatures reached during solarization were assessed at 7.6-, 15.2-, and 22.8-cm soil depth. After solarization, tomato was transplanted, including ‘Cherokee Carbon’ grafted onto RKN-resistant rootstocks ‘Fortamino’ and ‘Estamino’, RKN-resistant nongrafted ‘Caimon’, and susceptible ‘Cherokee Carbon’ as the control. The highest soil temperature achieved was 50 °C during 6 weeks of solarization at 7.6-cm soil depth compared with 38 °C reached in nonsolarized soil. Soil population densities of RKN increased each month after solarization and were generally lower after solarization with resistant tomato cultivars. The interaction of soil solarization and tomato cultivars was significant with respect to RKN densities in soil and roots. The mean RKN soil and root population densities in the nonsolarized, nonresistant treatment combination was significantly greater compared with all other treatments (P < 0.0001). Population densities of RKN were significantly higher in the nonsolarized control compared with solarized treatments (P = 0.0002). Nongrafted ‘Cherokee Carbon’ had significantly more RKN in surrounding soil compared with all other tomato treatments. Tomato yield was unaffected by soil solarization, but there were significant differences based on tomato cultivars alone; nongrafted ‘Cherokee Carbon’ yielded less than the resistant ‘Caimon’. Together, solarization and resistant cultivars reduced RKN population densities in soil and roots, which can provide growers with a nonchemical approach for long-term RKN management and high tunnel resiliency.

Population dynamics and damage threshold of Pratylenchus n. sp. and Meloidogyne javanica on finger millet

Summary Finger millet (Eleusine coracana) is a staple crop for subsistence farmers and is primarily cultivated in arid and semi-arid regions. Nevertheless, there are limited data available on the occurrence of plant-parasitic nematodes that specifically target finger millet, and the damage arising from such infections. In this study, we investigated the population dynamics, damage threshold and tolerance of the lesion nematode, Pratylenchus n. sp., and the root-knot nematode, Meloidogyne javanica, on finger millet ‘P-224’. We used 11 initial population densities (Pi) of second-stage juveniles (J2): 0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32 and 64 J2 (g soil)−1 for M. javanica and the same densities of mixed life-stages for Pratylenchus n. sp. The logistic growth model, Seinhorst yield loss and population dynamic models were fitted to the shoot height, plant biomass and final nematode population density. Based on the population dynamics model parameters, maximum multiplication rates and maximum population densities for each nematode species were estimated. The maximum multiplication rates (a) were 32.39 and 17.46, whilst the maximum population densities (M) were 18.83 nematodes (g soil)−1 and 19.78 J2 (g soil)−1 for Pratylenchus n. sp. and M. javanica respectively. The maximum height reached (C) was negatively affected by increasing Pi for both nematode genera, while the rate of growth (B) and the time to reach was not affected based on the logistic model. A tolerance limit (T) of 1.70 nematodes (g soil)−1 and 0.65 J2 (g soil)−1; relative minimum grain yield (m) of 0.23 and 0.40 for Pratylenchus n. sp. and M. javanica was found, respectively. The results indicate that ‘P-224’ is a good host for both Pratylenchus n. sp. and M. javanica, which significantly reduce yield. These findings can be used as a base to develop effective nematode management strategies for finger millet.

Metarhizium carneum Formulations: A Promising New Biological Control to Be Incorporated in the Integrated Management of Meloidogyne enterolobii on Tomato Plants.

The increase in the populations of root-knot nematode Meloidogyne enterolobii in various vegetables such as tomatoes grown under greenhouse conditions as well as increasing restrictions on the use of certain chemical nematicides have led to the search for new, effective management strategies, preferably ones that are sustainable biological alternatives. In this work, two formulations of the nematophagous fungus Metarhizium carneum, one concentrated suspension and one wettable powder, were evaluated under greenhouse conditions to reduce the M. enterolobii infestation in tomato plants. In addition, the effectiveness of the liquid formulation of M. carneum was compared with two biological and three chemical commercial nematicides. The results show that the two M. carneum formulations reduced the M. enterolobii population density by 78 and 66% in relation to the control treatment. In comparison, the liquid formulation of M. carneum and Purpureocillium lilacinum treatments reduced nematode population density by 72 and 43%, respectively, while for metam sodium preplanting applications followed by M. carneum applications during the tomato growth stage, the reduction was 96%. The alternate use of some chemical compounds plus the application of M. carneum as a biocontrol is a good starting strategy for managing M. enterolobii populations. These results confirm that M. carneum is a serious candidate for the short-term commercialization of an environmentally friendly biological nematicide.

Abscisic Acid Is Involved in the Resistance Response of Arabidopsis thaliana Against Meloidogyne paranaensis.

Abscisic acid (ABA) is a classical hormone involved in the plant defense against abiotic stresses, especially drought. However, its role in the defense response against biotic stresses is controversial: it can induce resistance to some pathogens but can also increase the susceptibility to other pathogens. Information regarding the effect of ABA on the relationship between plants and sedentary phytonematodes, such as Meloidogyne paranaensis, is scarce. In this study, we found that ABA changed the susceptibility level of Arabidopsis thaliana against M. paranaensis. The population of M. paranaensis was reduced by 58.3% with the exogenous application of ABA 24 h before the nematode inoculation, which demonstrated that ABA plays an important role in the preinfectional defense of A. thaliana against M. paranaensis. The increase in the nematode population density in the ABA biosynthesis mutant, aba2-1, corroborated the results observed with the exogenous application of ABA. The phytohormone did not show nematicide or nematostatic effects on M. paranaensis juveniles in in vitro tests, indicating that the response is linked to intrinsic plant factors, which was corroborated by the decrease in the number of nematodes in the abi4-1 mutant. This reduction indicates that the gene expression regulation by transcript factors is possibly related to regulatory cascades mediated by ABA in the response of A. thaliana against M. paranaensis.