Field Application of Entomopathogenic Nematodes for Control of Delia radicum in Collards

Control of Delia radicum (cabbage maggot) in field collards (Brassica oleracea) was compared after one or two applications of entomopathogenic nematodes, Steinernema carpocapsae (All strain) and Heterorhabditis bacterophora (HP88 strain), a single application of granular chlorpyrifos, and a water-only treatment. Nematodes were applied with a sprayer during the egg stage of first-generation D. radicum, and chlorpyrifos was hand placed around collard stems during the same period. A second nematode application was made 10 days later. Chlorpyrifos treatment resulted in fewer puparia per plant, less root damage and higher yield than all other treatments, including the control. Collard yield from nematode-treated beds did not differ from controls. These data indicate that, under these field conditions, the species or strains of entomopathogenic nematodes tested did not reduce the number of active cabbage maggots, nor did they prevent collard root damage.     

The making of a pest: the evolution of a fruit-penetrating ovipositor in Drosophila suzukii and related species

Evolutionary innovation can allow a species access to a new ecological niche, potentially reducing competition with closely related species. While the vast majority of Drosophila flies feed on rotting fruit and other decaying matter, and are harmless to human activity, Drosophila suzukii, which has a morphologically modified ovipositor, is capable of colonizing live fruit that is still in the process of ripening, causing massive agricultural damage. Here, we conducted the first comparative analysis of this species and its close relatives, analysing both ovipositor structure and fruit susceptibility. We found that the ovipositor of the species most closely related to D. suzukii, Drosophila subpulchrella, has a similar number of enlarged, evolutionarily derived bristles, but a notably different overall shape. Like D. suzukii, D. subpulchrella flies are capable of puncturing the skin of raspberries and cherries, but we found no evidence that they could penetrate the thicker skin of two varieties of grapes. More distantly related species, one of which has previously been mistaken for D. suzukii, have blunt ovipositors with small bristles. While they did not penetrate fruit skin in any of the assays, they readily colonized fruit interiors where the skin was broken. Our results suggest that considering evolutionary context may be beneficial to the management of invasive species.     

Morphological Comparisons Between Xiphinema rivesi Daimasso and X. americanum Cobb Populations from the Eastern United States

Though in the past Xiphinema americanum has been the most commonly reported dagger nematode in the eastern United States, our studies revealed the presence in Pennsvlvania of a previously unrecognized and unreported species related to X. americanum, Morphometric data and photomicrographs establish the identity of this form as X. rivesi and show expected variations in populations of this species from various locations. Similar data and illustrations are given for X. americanum populations from Pennsylvania and other areas, showing variations and relationships. Xiphinema rivesi is widely distributed in the fruit producing area of south-central Pennsylvania and is also reported herein from raspberry in Vermont and apple in Maryland and New York. This species is frequently found in fruit growing areas of Pennsylvania associated with tomato ringspot virus-induced diseases and is also found associated with corn, bluegrass sod, and alfalfa.     

Distribution of Xiphinema americanum and Related Species in North America

All species of the Xiphinema americanum-group and their synonyms are listed. The North American species reported are listed by state or province. Among these species, X. rivesi has the most widely reported distribution. Six species (X. diffusum, X. floridae, X. laevistriatum, X. luci, X. shell, and X. tarjanense) have been reported from only Florida. The reports of X. pachtaicum, X. sheri, and X. luci did not include morphometrics and need to be confirmed; X. brevicolle from California was identified before Lamberti and Bleve-Zacheo described 15 new species in 1979 and similarly needs to be confirmed. Because of the proliferation of species in this group, reports of X. americanum (sensu stricto) before 1979 are questionable. Extraction techniques for longidorids are discussed.     

Resistance of Auto- and Allotetraploid Triticeae Species and Accessions to Meloidogyne chitwoodi based on Genome Composition

The Columbia root-knot nematode Meloidogyne chitwoodi parasitizes several plant species, including grasses that have been developed for semiarid environments, and substantially reduces the productivity of cereals and the longevity of perennial grasses growing under semiarid conditions throughout the intermountain region. Thirty-two auto- and allotetraploid (2n = 28) taxa in the perennial Triticeae were evaluated as possible sources of resistance to M. chitwoodi. Low levels of root galling were observed on roots of all accessions; root-gall indices ranged from 0 (no galls) to 1.95 in the grasses compared to 4.67 for the susceptible ''Ranger'' alfalfa check on a scale of 1 to 6. Even though the gall ratings were low, significant (P < 0.01) differences among accessions of the same species, among species, and among genera with different genomes were observed. Within the reproductive indices, which ranged from 0.01 to 1.20 in the grasses compared to 65.38 for the alfalfa check, there was no difference among genera with different genomes and accessions within the same species and genome; however, there was a significant (P < 0.05) difference among species with the same genomes. This variation can be traced to Thinopyrum nodosum (Jaaska-19), which was the only accession with a reproductive factor greater than 1.00. Based on the data, all auto- and allotetraploids are considered resistant to M. chitwoodi.     

Slit Injection of 1,3-Dichloropropene for Management of Belonolaimus longicaudatus on Established Bermudagrass

Belonolaimus longicaudatus is a serious problem on bermudagrass, a common warm-season turfgrass, in Florida. The cancellation of organophosphate nematicides necessitates that new management tools be identified for use on sports turf. Postplant application of 1,3-dichloropropene (1,3-D) on bermudagrass was evaluated for management of B. longicaudatus on golf course fairways and driving ranges. A series of 10 experiments were conducted to evaluate the effectiveness of 1,3-D in reducing population densities of B. longicaudatus and enhancing bermudagrass recovery from nematode damage. In 5 of 10 experiments, 1,3-D injected at 46.8 liters/ha was effective in reducing population densities of B. longicaudatus (P < 0.05) compared to untreated plots 2 to 4 weeks after treatment. One month after treatment, population densities of B. longicaudatus ranged from 59% to 97% of those in untreated plots. Nematode suppression generally lasted 2 months or less. Turf visual performance was improved following injection with 1,3-D (P < 0.05) over untreated plots when other factors were not limiting. Turf root development also was enhanced following injection with 1,3-D. Postplant injection of 1,3-D could be a useful nematode management tool for certain sports turf applications.     

Comparison of Reproduction by Meloidogyne graminicola and M. incognita on Trifolium Species

The reproductive potential of Meloidogyne graminicola was compared with that of M. incognita on Trifolium species in greenhouse studies. Twenty-five Trifolium plant introductions, cultivars, or populations representing 23 species were evaluated for nematode reproduction and root galling 45 days after inoculation with 3,000 eggs of M. graminicola or M. incognita. Root galling and egg production by the two root-knot nematode species was similar on most of the Trifolium species. In a separate study, the effect of initial population densities (Pi) of M. graminicola and M. incognita on the growth of white clover (T. repens) was determined. Reproductive and pathogenic capabilities of M. graminicola and M. incognita on Trifolium spp. were similar. Pi levels of both root-knot nematode species as low as 125 eggs per 10-cm-d pots severely galled white clover plants after 90 days. Meloidogyne graminicola has the potential to be a major pest of Trifolium species in the southeastern United States.     

Influence of Temperature and Host Plant on the Interaction Between Pratylenchus neglectus and Meloidogyne chitwoodi

The interaction between Pratylenchus neglectus (Pn) and Meloidogyne chitwoodi (Mc) was investigated at soil temperatures of 15, 20, and 25 C on barley and potato. Maximum numbers of Pn and Mc penetrated barley roots at 20 C, whereas a minimum number penetrated at 15 C. Pratylenchus neglectus restricted root penetration by Mc over time and vice-versa. Population densities of each species increased with increasing temperature. Concomitant inoculation of the two species resulted in lower numbers of Pn at 15 and 25 C in both barley and potato, whereas the numbers of Mc were lower at 15 C in barley and at 25 C in potato. Root weights of potato and barley at 15 and 20 C, respectively, were lowered by the presence of both nematodes singly or concomitantly. At 25 C, barley plants inoculated with Mc alone had lower shoot weight than uninoculated controls, but the damage was restricted when Pn also was present. The two species interact competitively, and the outcome varies with soil temperature and host plant. Pn has the potential to suppress Mc population levels and reduce the damage it causes to potato and barley.     

Pathogenicity of Pratylenchus penetrans,Heterodera glycines,and Meloidogyne incognita on Soybean Genotypes

The pathogenicity of Heterodera glycines, Meloidogyne incognita, and Pratylenchus penetrans on H. glycines-resistant ''Bryan,'' tolerant-susceptible ''G88-20092,'' and intolerant-susceptible ''Tracy M'' soybean cultivars was tested using plants grown in 800 cm³ of soil in 15-cm-diam. clay pots in three greenhouse experiments. Plants were inoculated with 0, 1,000, 3,000, or 9,000 H. glycines race 3 or M. incognita eggs, or vermiform stages of P. penetrans/pot. Forty days after inoculation, nmnbers of all three nematodes, except H. glycines on Bryan, generally increased with increasing inoculum levels in Experiment I. Heterodera glycines and M. incognita significantly decreased growth only of Tracy M. At 45 and 57 days after inoculation with 6,000 individuals/pot in experiments II and III, respectively, significantly more P. penetrans and M. incognita than H. glycines were found on Bryan. However, H. glycines and M. incognita population densities were greater than P. penetrans on G88-20092 and Tracy M. Growth of Tracy M infected by H. glycines and M. incognita and growth of G88-20092 infected by M. incognita decreased in Experiment III. Pratylenchus penetrans did not affect plant growth. Reduction in plant growth differed according to the particular nematode species and cultivar, indicating that nematodes other than the species for which resistance is targeted can have different effects on cultivars of the same crop species.     

Endogenous cytokinin in developing kiwifruit is implicated in maintaining fruit flesh chlorophyll levels

Background and Aims

Green kiwifruit (Actinidia deliciosa) retain high concentrations of chlorophyll in the fruit flesh, whereas in gold-fleshed kiwifruit (A. chinensis) chlorophyll is degraded to colourless catabolites during fruit development, leaving yellow carotenoids visible. The plant hormone group the cytokinins has been implicated in the delay of senescence, and so the aim of this work was to investigate the link between cytokinin levels in ripening fruit and chlorophyll de-greening.

Methods

The expression of genes related to cytokinin metabolism and signal transduction and the concentration of cytokinin metabolites were measured. The regulation of gene expression was assayed using transient activation of the promoter of STAY-GREEN2 (SGR2) by cytokinin response regulators.

Key Results

While the total amount of cytokinin increased in fruit of both species during maturation and ripening, a high level of expression of two cytokinin biosynthetic gene family members, adenylate isopentenyltransferases, was only detected in green kiwifruit fruit during ripening. Additionally, high levels of O-glucosylated cytokinins were detected only in green kiwifruit, as was the expression of the gene for zeatin O-glucosyltransferase, the enzyme responsible for glucosylating cytokinin into a storage form. Season to season variation in gene expression was seen, and some de-greening of the green kiwifruit fruit occurred in the second season, suggesting environmental effects on the chlorophyll degradation pathway. Two cytokinin-related response regulators, RRA17 and RRB120, showed activity against the promoter of kiwifruit SGR2.

Conclusions

The results show that in kiwifruit, levels of cytokinin increase markedly during fruit ripening, and that cytokinin metabolism is differentially regulated in the fruit of the green and gold species. However, the causal factor(s) associated with the maintenance or loss of chlorophyll in kiwifruit during ripening remains obscure.     

Agistemus aimogastaensis sp. n. (Acari,Actinedida, Stigmaeidae), a recently discovered predator of eriophyid mites Aceria oleae and Oxycenus maxwelli,in?olive orchards in Argentina

A new species, Agistemus aimogastaensis, is described with the aid of optical and Scanning Electron Microscopy. This mite is an important predator of two eriophyid mites (Aceria oleae and Oxycenus maxwelli) in olive orchards (Olea europaea, variety Arauco) in La Rioja Province. The problems related to eriophyids in olive orchards in Argentina are highlighted and photos of the damage on leaves and fruit are included.     

Review of Pasteuria penetrans: Biology,Ecology, and Biological Control Potential

Pasteuria penetrans is a mycelial, endospore-forming, bacterial parasite that has shown great potential as a biological control agent of root-knot nematodes. Considerable progress has been made during the last 10 years in understanding its biology and importance as an agent capable of effectively suppressing root-knot nematodes in field soil. The objective of this review is to summarize the current knowledge of the biology, ecology, and biological control potential of P. penetrans and other Pasteuria members. Pasteuria spp. are distributed worldwide and have been reported from 323 nematode species belonging to 116 genera of free-living, predatory, plant-parasitic, and entomopathogenic nematodes. Artificial cultivation of P. penetrans has met with limited success; large-scale production of endospores depends on in vivo cultivation. Temperature affects endospore attachment, germination, pathogenesis, and completion of the life cycle in the nematode pseudocoelom. The biological control potential of Pasteuria spp. have been demonstrated on 20 crops; host nematodes include Belonolaimus longicaudatus, Heterodera spp., Meloidogyne spp., and Xiphinema diversicaudatum. Pasteuria penetrans plays an important role in some suppressive soils. The efficacy of the bacterium as a biological control agent has been examined. Approximately 100,000 endospores/g of soil provided immediate control of the peanut root-knot nematode, whereas 1,000 and 5,000 endospores/g of soil each amplified in the host nematode and became suppressive after 3 years.     

Relative Damage Functions and Reproductive Potentials of Meloidogyne arenaria and M. hapla on Peanut

The reproductive potential and damage functions for Meloidogyne hapla and M. arenaria race 1 on Virginia-type peanuts (Arachis hypogaea cv. Florigiant) were determined over 2 years in microplot experiments in North Carolina. Peanut yield suppression and damage to pods as a result of galling were greatest in response to M. arenaria (P = 0.01). Damage functions for the two species were adequately described by the quadratic models: yield (g/plot) = 398 - 17.1 (log₁₀[Pi + 1]) - 17.0(log₁₀[Pi + 1])²; (R² = 0.83, P = 0.0001) for M. arenaria; and yield = 388 - 10.2(log₁₀[Pi + 1]) - 7.5(log₁₀[Pi + 1])², (R² = 0.30, P = 0.0001) for M. hapla. Both species caused galling on pods, but this was more severe in response to M. arenaria. Reproduction of M. arenaria race 1 was greater than M. hapla on peanut, which accounts in part for the more severe pod galling. Peanut was an excellent host for both M. arenaria race 1 and for M. hapla, but reproduction by M. hapla was more variable.     

Nematodes in Dryland Field Crops in the Semiarid Pacific Northwest United States

Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plantparasitic and non-plant-parasitic nematodes. Lesion nematodes (Pratylenchus species) were recovered from 123 of 130 non-irrigated and 18 of 18 irrigated fields. Pratylenchus neglectus was more prevalent than P. thornei, but mixed populations were common. Population densities in soil were affected by crop frequency and rotation but not by tillage or soil type (P < 0.05). Many fields (25%) cropped more frequently than 2 of 4 years had potentially damaging populations of lesion nematodes. Pratylenchus neglectus density in winter wheat roots was inversely correlated with grain yield (r² = 0.64, P = 0.002), providing the first field-derived evidence that Pratylenchus is economically important in Pacific Northwest dryland field crops. Stunt nematodes (Tylenchorhynchus clarus and Geocenamus brevidens) were detected in 35% of fields and were occasionally present in high numbers. Few fields were infested with pin (Paratylenchus species) and root-knot (Meloidogyne naasi and M. chitwoodi) nematodes. Nematodes detected previously but not during this survey included cereal cyst (Heterodera avenae), dagger (Xiphinema species), and root-gall (Subanguina radicicola) nematodes.     

The application of multiplex fluorimetric sensor for the analysis of flavonoids content in the medicinal herbs family Asteraceae,Lamiaceae, Rosaceae

Background

The aim of our research work was to quantify total flavonoid contents in the leaves of 13 plant species family Asteraceae, 8 representatives of family Lamiaceae and 9 plant species belonging to family Rosaceae, using the multiplex fluorimetric sensor. Fluorescence was measured using optical fluorescence apparatus Multiplex(R) 3 (Force-A, France) for non-destructive flavonoids estimation. The content of total flavonoids was estimated by FLAV index (expressed in relative units), that is deduced from flavonoids UV absorbing properties.

Results

Among observed plant species, the highest amount of total flavonoids has been found in leaves of Helianthus multiflorus (1.65 RU) and Echinops ritro (1.27 RU), Rudbeckia fulgida (1.13 RU) belonging to the family Asteraceae. Lowest flavonoid content has been observed in the leaves of marigold (Calendula officinalis) (0.14 RU) also belonging to family Asteraceae. The highest content of flavonoids among experimental plants of family Rosaceae has been estimated in the leaves of Rosa canina (1.18 RU) and among plant species of family Lamiaceae in the leaves of Coleus blumei (0.90 RU).

Conclusions

This research work was done as pre-screening of flavonoids content in the leaves of plant species belonging to family Asteraceae, Lamiaceae and Rosaceae. Results indicated that statistically significant differences (P > 0.05) in flavonoids content were observed not only between families, but also among individual plant species within one family.     

Comparison of Three Methods for Estimating the Number of Entomopathogenic Nematodes Present in Soil Samples

Numbers of Steinernema sp. (CB2B) and S. carpocapsae (Agriotos) exponentially declined after application into a clay loam soil. Over a 35-day sampling period, Steinernema sp. (CB2B) was more persistent than S. carpocapsae (Agriotos). The presence or absence of the second-stage cuticle on the third-stage juveniles (J3) at the time of application did not alter the rate of population decline of Steinernema sp. (CB2B). Nearly all J3 of Steinernema sp. (CB2B) and S. carpocapsae (Agriotos) lost their cuticle within 24 hours of being in soil. Centrifugal flotation recovered the greatest number of nematodes, with a lower variance than either the live bait or Baermann funnel techniques. A strong positive linear relationship was evident between numbers of nematodes present in the soil and the numbers that established in a bait insect. Approximately 40% of Steinernema sp. (CB2B) and 30% of the S. carpocapsae (Agriotos) present in the soil established in Galleria mellonella larvae. The extraction techniques had different efficiencies and gave different relative estimates of persistence for the two species. Persistence and infectivity was best measured using a combination of live bait and flotation techniques.     

A Revised Classification Scheme for Genetically Diverse Populations of Heterodera glycines

Heterodera glycines, the soybean cyst nematode, is a major yield-limiting pathogen in most soybean production areas worldwide. Field populations of H. glycines exhibit diversity in their ability to develop on resistant soybean cultivars. Since 1970, this diversity has been characterized by a bioassay used to assign a race classification to a population. The value of the race scheme is reflected in the number and quality of resistant soybean cultivars that have been developed and released by soybean breeders and nematologists working in concert. However, the race scheme also has been misapplied as a means of studying H. glycines genotypes, in part due to the use of the term "race." For fungal and bacterial pathogen species, "race" can theoretically be applied to individuals of a population, thus allowing inference of individual genotypes. Application of a race designation to an individual egg or second-stage juvenile (J2) of H. glycines is not possible because a single J2 cannot be tested on multiple hosts. For other nematode species, "race" is defined by host ranges involving different plant species, whereas the H. glycines race test involves a set of lines of the same plant species. Nonetheless, because H. glycines populations vary in genetic diversity, and this variation has implications for management strategies, a mechanism is needed for documenting and discussing population differences. The HG Type scheme described herein avoids the implication of genetic uniformity or predictability in contrast to the way the race scheme has been used.     

Competition Between Tylenchorhynchus annulatus and Mesocriconema xenoplax on Grain Sorghum as Influenced by Macrophomina phaseolina

Greenhouse experiments were conducted to examine competition between Tylenchorhynchus annulatus and Mesocriconema xenoplax on grain sorghum roots that were colonized by the fungus Macrophomina phaseolina or free from fungus colonization. An incomplete factorial treatment design consisted of two levels of M. phaseolina (0 or 10 colony-forming units/g soil) and 12 T. annulatus:M. xenoplax ratios: 1,000:0; 750:0; 500:0; 250:0; 0:0; 0:250; 0:500; 0:750; 0:1,000; 750:250; 500:500; and 250:750. Plants were harvested after 105 days. Despite similar feeding habits, competition between these ectoparasitic nematode species was limited. Tylenchorhynchus annulatus was more susceptible to antagonism by M. xenoplax than the reverse, but susceptibility depended on initial inoculum ratio. Root colonization by M. phaseolina reduced competitive effects of T. annulatus on M. xenoplax but not the reverse. Both nematode species reduced shoot dry weight but only T. annulatus reduced root dry weight. Both plant weight parameters were reduced by M. phaseolina.     

Competition between Heterodera glycines and Meloidogyne incognita or Pratylenchus penetrans: Independent Infection Rate Measurements

Competition on soybean between Heterodera glycines (race 3) and Meloidogyne incognita or H. glycines and Pratylenchus penetrans were investigated in greenhouse experiments. Each pair of nematode species was mixed in 3-ml suspensions at ratios of 1,000:0, 750:250, 500:500, 250:750, and 0:1,000 second-stage juveniles or mixed stages for P. penetrans. Nematodes from a whole root system were counted and infection rates standardized per 1,000 nematodes (per replication) prior to testing the null hypothesis through a lack-of-fit F-test. Although the effect of increasing H. glycines proportions on the infection rate of M. incognita was generally adverse, the rate deviated significantly from a trend of linear decline at the 75% H. glycines level in one of two experiments. All lack-of-fit F-tests for the H. glycines and P. penetrans mix were significant, indicating that infection rates for both nematodes varied considerably across inocula. The infection rate of H. glycines decreased with increasing P. penetrans proportions. The rate of P. penetrans infection increased with increasing H. glycines proportions up to the 50% level, but declined at the 75% level. Competition had no effect on nematode development. The general adverse relationships between M. incognita and H. glycines and those between P. penetrans and H. glycines showed a linear trend. The relationship between H. glycines and P. penetrans indicates that the former may be competitive when present at higher proportions than the latter. In this study we have evaluated nematode competition under controlled conditions and provide results that can form a basis for understanding the physical and physiological trends of multiple nematode interactions. Methods critical to data analyses also are outlined.