Nematode Population Densities Research Articles

Capacidad hospedera de la Chía (Salvia hispanica) a los nematodos Meloidogyne incognita, Meloidogyne graminicola y Pratylenchus sp”, bajo condiciones controladas

Los nematodos Meloidogyne incognita, Meloidogyne graminicola y Pratylenchus sp, son de mucha importancia económica para el Ecuador y en especial para la provincia de Los Ríos donde con frecuencia en el mismo campo se siembra arroz- soya- maíz, difícil de incluir otros cultivos en rotación con fines de manejo de estas tres especies de nematodos. Esta investigación se realizó en la Facultad de Ciencias Agropecuarias de la Universidad Técnica de Babahoyo, ubicada en el kilómetro 7 ½ de la vía Babahoyo-Montalvo. El objetivo fue evaluar la capacidad hospedera de la Chía a los nematodos Meloidogyne incognita, M. graminicola y Pratylenchus sp en condiciones controladas. Para cada especie de nematodos se utilizó 10 macetas llenas con suelo solarizado, en cada una se sembró una planta de chía y se inocularon individualmente con 2500 especímenes de los nematodos mencionados. Las 30 macetas se distribuyeron en un diseño Completamente al Azar. A los 60 días de inoculación se evaluó peso de raíces por planta, número de agallas por planta (Meloidogyne spp.), densidad poblacional de nematodos en suelo y raíces e índice de reproducción de las especies de nematodos investigados. Según los resultados obtenidos, el cultivo de chía silvestre variedad “semilla negra” es altamente susceptible al nematodo agallador de raíces, Meloidogyne incognita, e inmune a M. graminicola. Este cultivo se comportó como hospedero pobre de Pratylenchus sp (población maíz). El índice de reproducción de Meloidogyne incognita en 60 días fue cinco veces superior a la población inicial, y en Pratylenchus sp. fue de 0.3.

Resistance of Wheat Genotypes to Root-Lesion Nematode (Pratylenchus thornei) Can be Used to Predict Final Nematode Population Densities, Crop Greenness, and Grain Yield in the Field.

The root-lesion nematode Pratylenchus thornei is a major pathogen of wheat (Triticum aestivum) in many regions globally. Resistance of wheat genotypes to P. thornei can be determined from final nematode population densities in glasshouse experiments but combining results across multiple experiments presents challenges. Here, we use a factor analytic method for multiexperiment analysis of final population densities of P. thornei for 1,096 unique wheat genotypes in 22 glasshouse experiments. The resistance to P. thornei of the genotypes was effectively represented by a two-factor model with rotation of the axes to a principal components solution. Principal axes 1 and 2 (PA1 and PA2) accounted for 79 and 11% of the genetic variance, respectively, over all experiments. Final population densities of P. thornei as empirical best linear unbiased predictors (PA[1+2]-eBLUPs) from the combined glasshouse experiments were highly predictive (P < 0.001) of final nematode population densities in the soil profile, crop canopy greenness (normalized difference vegetation index), and grain yield of wheat genotypes in P. thornei-infested fields in the Australian subtropical grain region. Nine categories of resistance ratings for wheat genotypes from resistant to very susceptible were based on subdivision of the range of PA(1+2)-eBLUPs for use in growers' sowing guides. Nine genotypes were nominated as references for future resistance experiments. Most (62%) Australian wheat genotypes were in the most susceptible three categories (susceptible, susceptible to very susceptible, and very susceptible). However, resistant germplasm characterized in this study could be used in plant breeding to considerably improve the overall resistance of Australian wheat crops.

Plant health evaluations of Belonolaimus longicaudatus and Meloidogyne incognita colonized bermudagrass using remote sensing

The objective of this study was to evaluate the ability of an unmanned aerial system (UAS) equipped with a multispectral sensor to track plant health in the presence of plant-parasitic nematodes in conjunction with nematicide applications. Four nematicides were evaluated for their ability to suppress Belonolaimus longicaudatus and Meloidogyne incognita in microplots, and three nematicides were evaluated on a golf course for their ability to suppress multiple plant-parasitic nematode genera. Visual ratings, Normalized Difference Vegetation Index (NDVI), and Normalized Difference RedEdge Index (NDRE) were reported throughout the trial to assess plant health. B. longicaudatus and M. incognita population density was significantly lowered by nematicide treatments in microplots and correlated with visual ratings, NDVI, and NDRE plant health ratings. On the golf course, all nematicides reduced total plant-parasitic nematode population density at 28, 56, and 84 days after treatment (DAT). Visual turf quality ratings, NDVI, and NDRE were positively correlated with lower nematode population density in the majority of evaluation dates. In the microplot and golf course settings, the parameters evaluated for plant health were correlated with plant-parasitic nematode population density: visual ratings, NDVI, and NDRE improved as nematode population density declined. These results show that remote sensing has the potential to be a beneficial tool for assessing plant-parasitic nematode infected bermudagrass.

Nematicide influence on cotton yield and plant-parasitic nematodes in conventional and sod-based crop rotation.

Plant-parasitic nematodes (Rotylenchulus reniformis (reniform, RN), Helicotylenchus dihystera (spiral), and Mesocriconema ornatum (ring)) and yield were investigated in cotton phases of conventional (peanut–cotton–cotton) and sod-based (bahiagrass–bahiagrass–peanut–cotton) rotations with or without irrigation and fluopyram nematicide at a long-term research site, established in 2000, in Quincy, Florida, USA. Objectives were to determine impacts of nematicide application on cotton yield and evaluate effects of nematicide on plant-parasitic nematodes in these rotations in 2017 and 2018. Reniform nematode population densities were greater in conventional cotton than sod-based cotton. Ring and spiral nematode population densities were greater in sod-based cotton than conventional cotton. Plots receiving nematicide had increased RN population densities in preplant 2018 soil samples and spiral nematode population densities in preplant 2017, harvest 2017, preplant 2018, and harvest 2018 soil samples compared to untreated plots. Cotton seed yield in conventional rotation was increased by 18% following nematicide application in 2017 but decreased by 10% in sod-based rotation in 2018, relative to the untreated control. Sod-based rotation had greater cotton yield than conventional rotation in 2017 and 2018. Nematicide application did not improve cotton yield in sod-based rotation and was inconsistent in conventional rotation.

First report of the root-knot nematode, Meloidogyne morocciensis infecting peach in Southern Brazil.

The peach tree (Prunus persica) is the third most cultivated temperate fruit species in Brazil. In August 2017, peach seedling plants showing symptoms of stunting and multiple galls in the roots were detected in the municipality of Pelotas, state of Rio Grande do Sul, Brazil. Samples of peach roots were collected and they were subsequently processed to obtain eggs and second-stage juveniles (J2), to determine the number of nematodes per gram of roots and to proceed with morphological studies. Additionally, individual females were extracted from the peach roots and submitted to Meloidogyne species identification by electrophoresis using α-esterase (Est) and malate dehydrogenase (Mdh) phenotypes and perineal pattern. The nematode population density in the samples was 283 eggs + J2s per gram of fresh roots. The polymorphism analysis revealed the A3N1 phenotype, typical to Meloidogyne morocciensis. Perineal patterns of females showed oval squared shapes, with moderately high to high dorsal arches, streaks widely separated, generally continuous, sometimes broken; the phasmids were separate by 29.3 μm (25.43-31.94 μm), similar to M. arenaria and M. incognita, as observed by Hammah and Hirschmann (1990). The second-stage juveniles had the following morphometric characters: L = 389.3 ± 3.8 (377.5-425.1) μm, stylet = 13.9 ± 0.2 (12.7-14.9) μm, DGO = 3.6 ± 0.1 (3.3-4.2) μm, tail length 47.5 ± 0.6 (45.3-48.9) μm, hyaline tail terminus = 14.1 ± 0.3 (12.5-17.0) μm, a = 25.6 ± 0.4 (23.8-28.8) μm and c = 8.6 ± 0.1 (8.0-9.3). The known SCAR marker obtained for M. arenaria is the same as that amplified for M. morocciensis. Under greenhouse conditions, peach plants seedlings inoculated with 1,000 eggs (Pi) with M. morocciensis were evaluated 28 days after inoculation compared to non-inoculated plants. The inoculated peach plants showed a mean of 338 galls per root system, and a nematode reproduction factor of 10.3. Besides this plants exhibited a reduction in fresh weight of shoots and roots compared to the non-inoculated plants. These results confirm M. morocciensis pathogenicity on P. persica.

Crotalaria species in succession to soybean for the management of Pratylenchus brachyurus

ABSTRACT: Soybean is the main agricultural crop in the State of Mato Grosso do Sul, Brazil. It is primarily cultivated in a crop succession system, in wich soybean is grown in spring/summer, followed by corn or graminaceous pastures in autumn/winter as a second crop. Due to the intensive cultivation, new phytosanitary problems have arisen, among them the root-lesion nematode, Pratylenchus brachyurus, which besides causing damage to plant roots, can be important gateway for other soil pathogens. The recent occurrence of high nematode population densities has brought great concern due to the limited resistant soybean genotypes available. Besides, the use of nematicides only reduces nematodes populations temporarily. A viable alternative for the control of soil nematodes could be the use of Crotalaria spp. in succession or rotation with soybean. Crotalaria is immune or a bad host to the nematode, besides having high capacity of biological nitrogen fixation. Thus, the objective of the present research was to define the best way of insertion of this legume as a second crop in soybean production systems to reduce the population density of the root-lesion nematode. Two experiments were carried out: one in the field, in an infested area, and other in a greenhouse. In both experiments, the treatments were: 1) Zea mays, 2) Brachiaria brizantha cv. Xaraés,, 3) Z. mays + Crotalaria spectabilis, 4) Z. mays + C. ochroleuca, 5) B. brizantha cv. Xaraés + C. spectabilis, 6) B. brizantha cv. Xaraés + C. ochroleuca, 7) C. spectabilis, and 8) C. ochroleuca. The effect of the treatments was evaluated by estimating the number of nematodes in the roots of autumn/winter crops, as well as in the roots of the soybean cultivated in the sequence. The cultivation of both Crotalaria species provided suppression of the nematode population. However, when intercropped with corn or Xaraés palisade grass, the suppressive effect of Crotalaria was supplanted by corn and Xaraés palisadegrass susceptibility to the root-lesion nematode.

Difference in lesion formation by male and female Pratylenchus penetrans.

Pratylenchus penetrans induce necrotic lesions, the hallmark symptom for the genus, soon after infection. The objective of our study was to characterize and quantify gender differences in lesion development. Independent experiments were conducted in vitro for three hosts; pea (Pisum sativum L. cv. Early Alaskan), dill (Anethum graveolens cv. Long Island Mammoth), and alfalfa (Medicago sativa cv. Vernal). Each experimental unit was an excised radical placed on water agar in a Petri dish and inoculated with either 40 adult males or 40 fourth-stage juvenile females. Length, size, and number of lesions were recorded during the experiment and the radicals were harvested 14 days after introducing nematodes. Lesions were first observed on pea after two days for female-inoculated roots, and 24 hr after introducing both genders to dill and alfalfa. Lesions expanded either by multiple lesions coalescing or individual lesions expanding over time. Males made fewer, smaller lesions with less discoloration for all three hosts. There was no difference among genders for the total number of nematodes recovered per Petri dish or the number of endoparasitic nematodes after 14 days. The survival rate of males and females at harvest was not different, indicating that the difference in lesion formation was not related to nematode population densities. This study verified and quantified the observation that lesions induced by males are less extensive and in smaller numbers than lesions by females.

The effects of Meloidogyne incognita and Heterodera glycines on the yield and quality of edamame (Glycine max l.) in Arkansas.

In 2012, the first domestic commercial edamame processing plant was established in Arkansas and edamame production was contracted out to local growers. Although the state is a major soybean producer, studies of nematode effects on edamame are limited. A survey of nematode genera and density in 64 contracted edamame production fields was conducted in 2013 and 2014. In both years, Meloidogyne and Heterodera were present in less than half of the surveyed fields while Pratylenchus was the most prevalent in 2013 and Helicotylenchus in 2014. A microplot study was conducted in 2014 in two locations to evaluate the effects of root-knot nematode (Meloidogyne incognita, race 3) and soybean cyst nematode (Heterodera glycines, HG type 2.5.7) on plant growth, yield and food quality components of edamame. Yield was the most consistent factor influenced by nematode pressure with increasing nematode population densities resulting in suppressed pod and seed weight. Additionally, seed protein content was reduced in the highest tested population density of H. glycines. In greenhouse studies, 22 advanced edamame breeding lines from the University of Arkansas soybean breeding program were compared with two susceptible commercial cultivars for suitability as hosts for both M. incognita and H. glycines independently. Four lines showed consistent reductions in M. incognita reproduction relative to the commercial cultivars and could represent sources of moderate resistance for development of future root-knot nematode resistant edamame cultivars.

Utjecaj pripravka na bazi fluopirama i tekućega pilećeg stajnjaka na nematode korijenovih kvržica (Meloidogyne spp.) u nasadu mrkve

The aim of this study was to investigate the nematocidal effect of the preparations based on fluopyram (pesticide) and liquid chicken manure (natural amendment) on the population density of the root-knot nematodes, Meloidogyne spp. in carrot crops. The field experiment was set up in four treatments: control (C), fluopyram (FLU), fluopyram and liquid chicken manure (FLU+LCM) and liquid chicken manure (LCM) by a random block design in four replicates. Population density of Meloidogyne spp. juveniles varied between the treatments, and the number of Meloidogyne spp. was significantly decreased in all treatments with fluopyram (FLU and FLU+LCM). All amended treatments (FLU, FLU+LCM, LCM) decreased galling of the roots and had a positive effect on carrot yield. The population of Meloidogyne spp. juveniles increased with the plant growth, regardless of the treatments applied. Fluopyram negatively affected the biodiversity indicating greater disturbance for the nematode community structure in the soil. It can be concluded that fluopyram and liquid chicken manure have nematicidal potential, while liquid chicken manure maintained or enhanced nematode biodiversity.

Evaluation of Nematicidal Activity of Fluensulfone against Non-Target Free-Living Nematodes under Field Conditions

The use of nematicides with reduced toxic side-effects against non-target free-living nematodes is a favorable option for farmers to control plant-parasitic nematodes. The nematicide fluensulfone was registered in several countries for the control of the root-knot nematodes, Meloidogyne spp. among other plant-parasitic nematodes. This study aimed to evaluate the nematicidal activity of fluensulfone against non-target nematode fauna in four field experiments, each under different conditions (soils types and plant hosts). Nematodes extracted from soil samples were classified and counted based on their morphological characters. Fluensulfone significantly reduced damage caused by root-knot nematodes to tomato and sweet potato plants, while overall non-target free-living nematode population densities were maintained at the same level as those in control. Different diversity indices (e.g., Shannon-Wiener H’, Simpson’s D, species richness, evenness J’, maturity indices) and principal component analyses in the four experiments showed that fluensulfone treatment kept a similar diversity level of non-target free-living nematode fauna to that of the non-treated control. The results suggested that fluensulfone may have minimal impact to free-living nematode fauna in both population density and diversity when the nematicide was applied to control Meloidogyne spp.

Abundant and diverse fungal microbiota inhabit the white females and brown cysts of the cereal cyst nematode

Cysts of plant-parasitic nematodes containing eggs with secondary-stage juveniles represent entities for long-term survival in soils and serve as an inoculum source for the next cropping season. Fungi are considered to be one of the major factors regulating population densities of cyst nematodes in natural and agricultural ecosystems. However, our understanding regarding the structure of fungal communities colonizing white females and cysts of the cereal cyst nematode (CCN, Heterodera avenae) and information on microbial succession from female to cyst is still limited. Herein, CCN white females attached to wheat roots and mature brown cysts in soil were collected from wheat grown fields at four different locations in central China, and their associated fungal communities were investigated using high-throughput sequencing. The results showed that there were no significant differences in the observed OTUs and Shannon diversity of fungal communities in the white females and cysts across the four locations. However, the mycobiota composition was different between white females and cysts. The phylum Mortierellomycota was more abundant in the white females than in cysts, while Ascomycota had higher relative abundance in the cysts than in white females. An operational taxonomic unit (OTU) enrichment analysis using combined samples for the white females as well as for the cysts from four locations revealed that only a small subset of OTUs were significantly enriched in white females (15 OTUs) and cysts (12 OTUs). These OTUs belonged to genera such as Mortierella, Fusarium, Alternaria, Aphroditeola, Cladosporium, Cryptococcus, Olpidium, Penicillium, Periconia, Volvariella, Phaeosphaeria and Moleospora, and most of them were assigned to functional traits such as endophyte, plant pathogen, animal pathogen, fungal parasite and saprophyte. However, the relative abundances of previously well-documented nematode egg-parasites such as Pochonia chlamydosporia, Purpureocillium lilacinum and other potent taxa were not significantly different between white females and cysts. Our results indicated that white females and cysts harbor diverse mycobiota, and the majority of fungal taxa maintain a steady-state composition from the white females to mature brown cysts.

Fitness cost but no selection for virulence in Meloidogyne incognita after two consecutive crops of eggplant grafted onto Solanum torvum

The eggplant Solanum melongena cv. Cristal, either ungrafted or grafted onto the Solanum torvum rootstock cv. Brutus, was cultivated for two consecutive years in the same plots in a plastic greenhouse to assess the level of resistance to Meloidogyne incognita and crop yield. At the end of the second crop, the putative selection for virulence of the nematode subpopulations coming from infected ungrafted and grafted eggplant was assessed in the eggplant and in S. torvum in a pot experiment. Nematode population densities at transplantation in 2017 ranged from 2 to 378 per 100 cm3 of soil and did not differ between ungrafted and grafted eggplant. At the end of each crop, a higher galling index and number of nematodes in soil and in roots was registered in ungrafted compared to grafted eggplant. The grafted eggplant was categorized as resistant in 2017 and as highly resistant in 2018. Eggplant yield did not differ irrespective of grafting in 2017 after being cultivated for 135 days, but it differed after 251 days of cultivation in 2018. In the pot experiment, S. torvum was categorized as resistant to both M. incognita subpopulations. However, the M. incognita subpopulation obtained from roots of S. torvum produced 49.4% fewer egg masses and 56% fewer eggs per plant in the eggplant than the nematode subpopulation obtained from roots of the eggplant cv. Cristal. The results of this study revealed that the infective and reproductive fitness of the nematode decreased without having been selected for virulence.

Meloidogyne hapla development on growing legume plants - Short Communication

The legume genus lupine, pea, faba bean and common vetch were cultivated under natural conditions in pots filled with soil naturally infected with Meloidogyne hapla Chitwood, 1949. The nematode population density increased relevantly in the soil planted with the faba bean (cultivars (cvs.) Bobas, Amulet, Albus) and the pea cv. Lasso, in which numerous root galls and egg masses appeared. The narrow-leaved lupine (cvs. Karo, Zeus), yellow lupine (cvs. Parys, Lord) and white lupine (cv. Boros) cultivation decreased the nematode population density and these were not statistically significant when compared with the nematode density in a fallow soil.

Distribution and Population Density of Cereal Cyst Nematode in Ardabil Province

Distribution and Population Density of Cereal Cyst Nematode in Ardabil Province

Identification of Chili Pepper Genotypes (Capsicum spp.) Resistant to Meloidogyne enterolobii

Chili pepper has economic importance and is the dominant Solanaceae in the market of spicy spices. Among the pathogens that affect this crop, Meloidogyne enterolobii is one of the most important because it presents a wide range of hosts and there are no resistance genes identified that are efficient against this species. The present study aimed to evaluate the reaction of chili pepper genotypes (Capsicum spp.) to M. enterolobii in order to identifify genetic resistance. Three experiments were conducted in a completely randomized design under greenhouse conditions: Experiment I, with 53 genotypes with ten replications; Experiment II, with twenty genotypes with ten replications; Experiment III in a 16 &amp;times; 4 factorial scheme, with sixteen Capsicum spp. genotypes and four inoculum concentrations of M. enterolobii and eight replications. Inoculation was performed seven days after transplanting the Capsicum spp. seedlings into 2L plastic bags filled with sterilized soil and sand (2:1), using 4,000 eggs + J2/plant. Ninety days after inoculation (DAI) (Experiments I and II) and 60 DAI (Experiment III) nematode population density, reproduction factor (RF), fresh root mass, egg mass index (EMI) and gall index (GI) were evaluated. Genotypes with RF &amp;lt; 1.0 were considered resistant according to Oostenbrink (1966). Thirty one genotypes of Capsicum spp. showed resistance to M. enterolobii with RF ranging from 0.87 to 0.08. Seventeen resistant genotypes of C. chinensis presented RF lower than 0.85, ten genotypes of C. annuum had the RF lower than 0.75, three genotypes of C. frutescens had the RF lower than 0.87 and only one genotype of C. baccatum was resistant to M. enterolobii, presenting RF = 0.6. EMI and GI weren&amp;rsquo;t considered reliable variables to determine resistance and susceptibility. Fourteen genotypes rated as resistant in Experiments I and II were submitted to increasing concentrations of inoculum and, nevertheless, remained resistant.

Research advances on resource and biological control of endoparasitic fungi.

Endoparasitic fungi are a group of nematophagous fungi which produce a variety of special spores to infect free nematodes. They play a key role in maintaining the population density of nematodes in the natural systems. Moreover, they are important materials for the study of species diversity. Therefore, they have special research significance and economic values. At present, many studies mainly focus on the infectivity of trapping fungi to nematodes, and mainly directed at the second instars larvae. However, the endoparasitic fungi have infectivity to nematodes at all stages. Here, we reviewed the resource status, diversity of spore morphology, infection modes, life history and host of endoparasitic fungi, and the biocontrol fungi with development potential and their commercialized application. Finally, we proposed some suggestions for future researches.

Control of root-knot nematodes by a mixture of maleic acid and copper sulfate

Organic acids released during the decomposition of organic soil amendments have been used in crop fields as benign chemicals to control phytopathogens. However, the use of organic acids against root-knot nematodes (RKNs, Meloidogyne spp.) has not been recommended in practice, owing to their short retention time in the soil. In this study, we tested the nematicidal activity of organic acids including maleic, fumaric, acetic, acrylic, caprylic, oxalic, and formic acids, as well as copper sulfate against Meloidogyne incognita. Maleic acid showed the strongest nematicidal activity with induction of 100% second-stage juvenile (J2) mortality and 70.47% hatching inhibition at a concentration of 0.37 mmol/L. In addition, the combination of maleic acid and copper sulfate was revealed to have an additive effect in J2 mortality. Application of a wettable powder-type formulation of a mixture of maleic acid and copper sulfate (MIX-WP30) reduced RKN disease on tomato by 51.72% in a pot experiment, suppressed gall formation on melon and decreased nematode population density in the soil. Under field conditions, the efficacy of MIX-WP30 (46.73%) was comparable with that of the commercial nematicide fosthiazate (48.38%). This study identified the effectiveness of MIX-WP30 against RKNs, and demonstrated that there was an in vivo synergistic effect of MIX-WP30. Based on its nematicidal activity, MIX-WP30 could be used as an effective nematicide for RKN management.

Nematode Management in the Strawberry Fields of Southern Spain

(1) Background: Spain is the sixth strawberry producer in the world, with about 6500 ha producing more than 350,000 tons, and an annual commercial value about 390 million €. Stunted and dead strawberry plants are frequently associated with plant-parasitic nematodes, but nematode diseases have not been characterized to date in the country. (2) Methods: A poll on the perception of the impact of nematodes on strawberry production was carried out by face-to-face interviews with farm advisors. In addition, nematological field surveys were carried out at the end of the growing season in 2017 and 2018 to determine prevalence and abundance of plant-parasitic nematodes in strawberry crops. The host suitability to Meloidogyne hapla of seventeen strawberry cultivars and the tolerance limit to M. hapla at progressively higher initial population densities (Pi) were assessed in pot experiments in a growth chamber. Comparison of the relative efficacies of several soil disinfestation methods in controlling nematode populations (M. hapla and Pratylenchus penetrans) was carried out in experimental field trials for twelve consecutive years. (3) Results: Meloidogyne spp., Pratylenchus penetrans, and Hemicycliophora spp. were the main plant-parasitic nematodes in the strawberry fields in South Spain. Root-knot nematodes were found in 90% of the fields, being M. hapla the most prevalent species (71% of the fields). A tolerance limit of 0.2 M. hapla juveniles per g of soil was estimated for strawberry, and currently cropped strawberry cultivars did not show resistance to M. hapla. Nematode population densities were reduced by more than 70% by soil fumigation with 1,3-dichloropropene, dazomet, dimethyl-disulfide, and methyl iodide. The efficacy of metam-sodium in reducing nematode populations was about 50% and that of chloropicrin, furfural, and sodium-azide, less than 40%. Combination of solarization with organic manures (biosolarization) reduced soil nematode populations by 68–73%. (4) Conclusions: Plant-parasitic nematodes (Meloidogyne, Pratylenchus, and Hemicycliophora) are widely distributed in the strawberry fields of Southern Spain. Strawberry is a poor host for M. hapla with a tolerance limit of 0.2 J2 per g of soil, and low population increases in cropping cycles of 7–8 months. Strawberry cultivars show a range of susceptibility and tolerance to M. hapla, but no resistance is found. Nematodes are effectively controlled by chemical fumigation of soils, but soil biosolarization is equally effective, and therefore, can be proposed as a sustainable alternative for pathogen control in strawberry cultivation.

Integrated management of plant-parasitic nematodes on guava and fig trees under tropical field conditions

Two field experiments were carried out to study the efficacy of different biological control agents in controlling certain plant-parasitic nematode species including Meloidogyne javanica, Tylenchorhynchus mediterraneus, Hoplolaimus seinhorsti, Longidorus latocephalus, and Xiphinema elongatum on guava and fig trees under the tropical field conditions of Jazan region, south-west Saudi Arabia during two successive seasons from Feb. 15, 2016 to Jan. 15, 2017. The evaluated bio-agents were used in different integrated management combinations of certain fungal species (Trichoderma harzianum, Verticillium chlamydosporium, and Purpureocillium lilacinum), the bacterium Pasteuria penetrans, some organic amendments (cow manure, compost, and chicken manure), urea 46% as a nitrogenous fertilizer, and the nematicide carbofuran 10G for comparison. Results showed that all the tested treatments gradually decreased (P ≤ 0.05) the population densities of plant-parasitic nematodes on guava and fig trees over the study period. The highest reduction of nematode densities occurred at the end of the experiment. Carbofuran 10G was the most effective treatment in suppressing the nematode densities on guava and fig trees. The most effective management combinations, next to carbofuran 10G, in suppressing the nematode densities in the rhizosphere of guava trees were P. lilacinum + P. penetrans + urea 46%, P. lilacinum + P. penetrans + chicken manure, and T. harzianum + P. penetrans + chicken manure (66.54–69.22% nematode reductions). Correspondent combinations in the rhizosphere of fig trees were P. lilacinum + P. penetrans + cow manure, T. harzianum + P. penetrans + cow manure, P. lilacinum + P. penetrans + urea 46%, and V. chlamydosporium + P. penetrans + urea 46% (54.68–57.17% nematode reductions). On the other hand, nematode population densities continued to increase (P ≤ 0.05) in the rhizosphere of guava and fig trees in the absence of nematode management combinations. All the tested treatments significantly increased (P ≤ 0.05) the number of fruits/tree on guava and fig trees. Treatments which included the combinations of fungal and bacterial parasites along with chicken manure gave the highest numbers of fruits/tree, followed by the treatment with the nematicide carbofuran 10G. Regression analysis showed a significant negative linear relationship between the number of nematodes/kg soil and the number of guava and fig fruits/tree.

Occurrence of Meloidogyne javanica as a Pathogen of Cockscomb (Celosia cristata) in Brazil

Cockscomb (Celosia cristata L., family Amaranthaceae) is an ornamental plant species cultivated in pots or used as cut flowers in floral arrangements. In April 2018, cockscomb ‘Comum’ exhibiting many galls on the roots was detected and sampled from several areas (27°21′34″S, 53°23′37″W) of Frederico Westphalen county, Rio Grande do Sul State, Brazil. Identification of Meloidogyne sp. (Nematoda: Meloidogynidae) was carried out by observations of perineal patterns (n = 30) and esterase phenotypes (n = 30), morphological measurements of second-stage juveniles (J2) (n = 50), and amplification and sequencing of the ITS1-5.8S-ITS2 rRNA region (primer set: forward 5′-TTGATTACGTCCCTGCCCTTT-3′ and reverse 5′-TCCTCCGCTAAATGATATG-3′) and the D2 to D3 fragment of the 28S rRNA gene (primer set: forward 5′-ACAAGTACCGTGAGGGAAAGTTG-3′ and reverse 5′-TCGGAAGGAACCAGCTACTA-3′). In addition, cockscomb roots were processed to determine the number of J2 and eggs of Meloidogyne sp. Nematode population density observed in the sample was 2,100 J2 per gram of cockscomb roots. The J2 had the following morphometric characteristics: length (L) = 405.5 ± 61.0 (368.5 to 415.6) µm, a = 29.6 ± 2.5 (26.8 to 33.4), c = 8.00 ± 0.5 (6.0 to 9.6), stylet = 13.5 ± 0.5 (11.3 to 15.9) µm, dorsal esophageal gland orifice (DGO) = 3.20 ± 0.4 (2.9 to 3.9) µm, tail length = 55.5.5 ± 4.0 (54.1 to 59.5) µm, and hyaline tail terminus = 10.3 ± 0.8 (9.0 to 11.5) µm. Female perineal patterns included a low trapezoidal dorsal arch and smooth striae interrupted by a pair of incisions on both sides. These lateral ridges that divide the dorsal and ventral striae are unique to Meloidogyne javanica (Treub, 1885) Chitwood, 1949 (Rammah and Hirschmann 1990). The polymorphisms in the esterase bands observed during electrophoresis revealed the typical phenotype of J3 (Rm = 1.00,1.25, 1.40) M. javanica populations (Carneiro et al. 2000). Sequence homologies were determined by comparing sequences of polymerase chain reaction (PCR) amplicons of D2 to D3 of 28S and ITS1-5.8S-ITS2 rRNA region that were noted to be 516 bp (GenBank MK072827) and 554 bp (MK072828) in length, respectively. The sequences of both markers exhibited 99 and 100% identity, respectively, with sequences being more similar to those of M. javanica isolates from Brazil, Vietnam, and China. The confirmation of nematode species identity was performed by PCR species-specific sequence characterized amplified region (SCAR) using a primer set composed of Fjav (5′-GGTGCGCGATTGAACTGAGC-3′) and Rjav (5′-CAGGCCCTTCAGTGGAACTATAC-3′). The PCR amplification using SCAR produced a specific fragment of expected size (∼670 bp) for M. javanica (Donkers-Venne et al. 2000). In greenhouse tests, cockscomb Comum plants being maintained in pots containing sterilized soil were inoculated with 5,000 eggs and J2 of the original M. javanica population; a noninoculated control was included, and treatments were replicated 10 times. After 60 days, all inoculated plants showed reduced growth compared with the control. Galling symptoms on the roots were similar to those observed in field-grown plants, and the nematode reproduction factor (final population/initial population) was 20.5. The noninoculated plants did not present gall formation in the roots, and their development was not affected either. The morphological and molecular characteristics of reisolated root-knot nematodes were identical to those of M. javanica. These results confirmed the nematode’s pathogenicity to cockscomb. To our knowledge, this is the first report on M. javanica parasitizing cockscomb in Brazil; therefore, our findings are of great importance to Brazilian flower growers to help them establish management measures M. javanica.