Patrick P.J. Haydock

Potential enhancement of degradation of the nematicides aldicarb, oxamyl and fosthiazate in UK agricultural soils through repeated applications.

BACKGROUND The potential for enhanced degradation of the carbamoyloxime nematicides aldicarb and oxamyl and the organophosphate fosthiazate was investigated in 35 UK agricultural soils. Under laboratory conditions, soil samples received three successive applications of nematicide at 25 day intervals. RESULTS The second and third applications of aldicarb were degraded at a faster rate than the first application in six of the 15 aldicarb-treated soils, and a further three soils demonstrated rapid degradation of all three applications. High organic matter content and low pH had an inhibitory effect on the rate of aldicarb degradation. Rapid degradation was observed in nine out of the ten soils treated with oxamyl. In contrast, none of the fosthiazate-treated soils demonstrated enhanced degradation. CONCLUSION The potential for enhanced degradation of aldicarb and oxamyl was demonstrated in nine out of 15 and nine out of ten soils respectively that had previously been treated with these active substances. Degradation of fosthiazate occurred at a much slower rate, with no evidence of enhanced degradation. Fosthiazate may provide a useful alternative in cases where the efficacy of aldicarb and oxamyl has been reduced as a result of enhanced degradation.

Isolation and localisation of an annexin gene ( gp-nex ) from the potato cyst nematode, Globodera pallida

A full length cDNA clone was isolated by screening a mixed stage Globodera pallida expression library using the monospecific polyclonal antibody IACR-PC320. Sequence comparison indicated that the predicted 332 amino acid protein encoded by the cDNA was a member of the annexin gene family named gp-nex and very similar to annexins found in other nematode species. Annexins are calcium-dependent phospholipid binding proteins characterised by four repeated domains approximately 70 amino acids in length. The predicted amino acid sequence of the protein did not contain an N-terminal secretion signal peptide; however, the protein was shown to be present in excretory/secretory products from G. pallida second stage juveniles treated with the neurotransmitter 5 methoxy-N, N dimethyl tryptamine. Gp-nex encodes a protein of 35 kDa and was immunolocalised in the amphids, genital primordium and in the constraining muscles above and below the metacorpus pump chamber of G. pallida second stage juveniles. It is also present in eggs and adult females of the two species of the potato cyst nematodes.

Biofumigation with brassica juncea, raphanus sativus and eruca sativa for the management of field populations of the potato cyst nematode globodera pallida

BACKGROUND The viability of potato cyst nematode (PCN) populations (Globodera pallida) was evaluated in three field experiments using Brassica juncea, Raphanus sativus and Eruca sativa amendments. These species were summer cultivated and autumn incorporated in experiment 1; in experiment 2, overwintered brassicaceous cover crops were spring incorporated. Experiment 3 involved determination of effects of metconazole application on biomass/glucosinolate production by B. juncea and R. sativus and on PCN pre- and post-incorporation. Glucosinolate contents were determined before incorporation. Following cover crop incorporation, field plots were planted with susceptible potatoes to evaluate the biofumigation effects on PCN reproduction. RESULTS In experiment 1, PCN population post-potato harvest was reduced (P = 0.03) in B. juncea-treated plots, while R. sativus prevented further multiplication, but in experiment 2 there were no significant effects on PCN reproduction. In experiment 3, B. juncea or R. sativus either untreated or treated with metconazole reduced PCN populations. Glucosinolate concentrations varied significantly between different plant regions and cultivation seasons. Metconazole application increased the sinigrin concentration in B. juncea tissues. Glucosinolate concentrations correlated positively with PCN mortality for summer-cultivated brassicaceous plants. CONCLUSION The results demonstrated that B. juncea and R. sativus green manures can play an important role in PCN management, particularly if included in an integrated pest management scheme.

Interactions between the potato cyst nematodes, Globodera pallida , G. rostochiensis , and soil-borne fungus, Rhizoctonia solani (AG3), diseases of potatoes in the glasshouse and the field

This is the first report of a positive interaction between the nematode Globodera pallida and Rhizoctonia solani diseases of potato, and is an important step in the general understanding of interactions between nematodes and fungal diseases. One glasshouse and two field experiments were performed to investigate interactions between G. pallida or G. rostochiensis and R. solani diseases of potatoes. The glasshouse experiment investigated the independent and combined effects of G. pallida or G. rostochiensis and R. solani on the growth of plants and R. solani disease severity. In the glasshouse experiment the combined effects of G. pallida with R. solani or G. rostochiensis with R. solani showed greater R. solani diseases of potatoes compared with only R. solani. The field experiments examined the development of R. solani diseases on potatoes grown in soil with potato cyst nematode population densities ranging from eight to 140 and four to 50 eggs (g soil)–1 in the years 2006 and 2007, respectively. The 2006 field experiment revealed a clear positive relationship between initial population densities of G. pallida and the incidence of stolons infected by R. solani, subsequent stolon pruning and stem canker. In both field experiments a clear positive relationship was found between densities of nematodes within the potato roots and the incidence of infected stolons, stolon pruning and stem canker. Nematicide applied together with R. solani in the 2007 field experiment reduced the effect of G. pallida on the incidence and severity of diseases caused by R. solani.

Studies on the effect of mycorrhization of potato roots on the hatching activity of potato root leachate towards the potato cyst nematodes, Globodera pallida and G. rostochiensis

Successful mycorrhization of potato plants cv. Golden Wonder was achieved with three commercial preparations of arbuscular mycorrhizal fungi (AMF): Vaminoc (mixed-isolate inoculum) and two of its components, Glomus intraradices and Glomus mosseae. Potato cyst nematode hatching assays were conducted on the potato root leachate (PRL) produced by inoculated and non-inoculated potato plants to examine the effect of AMF inoculation on the hatching response of the two PCN species, Globodera rostochiensis and G. pallida. The overall hatch response of G. rostochiensis to the potato root leachate was greater than G. pallida. Root leachates from Vaminoc- and G. mosseae-inoculated plants were found to stimulate the hatch of G. pallida in the first 3 weeks after shoot emergence. Fractionation of root leachates with standardised carbon content by Sephadex G-10 chromatography revealed multiple AMF effects on hatching factor (HF) production. Root leachates from Vaminoc-inoculated plants contained markedly more G. pallida-active HF than all other treatments; by contrast, PRL from the three AMF treatments exhibited little variation in the quantity of G. rostochiensis-active HF produced. Several HF were PCN species-specific or species-selective, with those resolved from the G. intraradices and G. mosseae PRL profiles exhibiting an apparent preference for G. rostochiensis rather than G. pallida. Mycorrhization also significantly increased the root dry weight of plants.

Degradation of the nematicide oxamyl under field and laboratory conditions

The persistence of nematicides such as oxamyl can vary greatly in field conditions. The objectives of the present studies were: i) to compare oxamyl degradation in soils with different properties; ii) to quantify and examine the influence of various abiotic factors on oxamyl degradation; iii) to establish the validity of using simulated models to predict the degradation in the field; and iv) to examine if a second application of oxamyl to the same soil 13 or 26 weeks after the first application enhances degradation. The first two studies included field measurements of oxamyl concentration and parallel laboratory incubations. For the field measurements, soils were collected from each of ten potato (Solanum tuberosum) fields in Shropshire, UK, immediately after application of oxamyl on the day of planting and then at weekly intervals for the duration of the two experiments. After each collection, oxamyl was extracted and its concentration determined. For the laboratory incubations, soils were collected from the same ten sites immediately prior to field application and received one application of oxamyl in the laboratory at the same day (day 0). The PERSIST model was then used to predict oxamyl degradation in the field (modelled degradation). Modelled degradation was then compared with the measured degradation up to 91 days (study 1) or 56 days (study 2) after application. In study 3, an extra application of oxamyl to that in the field at day 0 was made in the laboratory at 13 or 26 weeks after application. There were wide variations in the persistence of oxamyl between the ten sites, with the field half-life ranging from 10 to 24 days. Degradation in the field was significantly greater at site 4, where it could not be detected 28 days after application. At other sites, the chemical persisted for 42-63 days and was still detectable at two sites 91 days following application. Soil temperatures had a greater impact on oxamyl degradation than rainfall accounting for up to a maximum of 79% of the variation. The short persistence at site 4 was attributed to the combination of warm and moist conditions in a higher pH soil. The PERSIST model predicted the same rate of decline of oxamyl as actually occurred in the field at only four (sites 5, 6, 7 and 8) sites. At the other sites, degradation in the field occurred at more rapid rates than predicted. This could be as a result of the model not allowing for the movement of nematicide by leaching, or because enhanced degradation of nematicides occurred at these latter sites, or due to a combination of these factors. The wide variation in half-lives and the behaviour of soils after subsequent additions of oxamyl in study 3 were suggestive of complex microbial dynamics even under controlled conditions. Further studies would be required to establish the influence of soil microflora together with that of abiotic parameters on oxamyl degradation.

Effect of temperature on the life cycle of Heterodera schachtii infecting oilseed rape (Brassica napus L.).

Oilseed rape (OSR; Brassica napus L.) is a crop of increasing world importance and suffers yield loss when infected with Heterodera schachtii. The in vitro hatch, in planta root invasion and development of a field population of H. schachtii were investigated in six thermostatically-controlled water baths at temperatures of 5.0, 10.1, 20.5, 27.8, 32.2 and 37.5°C in a glasshouse. The UK winter OSR cvs Flash and Castille were used. Temperature was shown to have a major influence on the development of H. schachtii in OSR. The highest cumulative percentage hatch of second-stage juveniles (J2) observed over an 8-week incubation period occurred between 20.5 and 27.8°C in leachates of both OSR cultivars, indicating that this is the optimum temperature range for hatching of this population. Cumulative hatch was lowest at 37.5 and 5.0°C. Root invasion was inhibited at 5.0 and 37.5°C, whilst the highest number of J2 invaded the roots between 20.5 and 32.2°C, indicating that this is the optimum temperature range for root invasion. The life cycle took between 21 days at 20.5°C and 42 days at 5.0°C from the inoculated J2 to the J2 of the second generation, with the associated accumulated heat units (AHU) of 424 and 203 degree-days with a base temperature (Tb) of 5.0°C. The optimum temperature range (To) for development was between 20.5 and 27.8°C and the maximum (Tm) was 37.5°C. As temperature increased, the AHU required to complete the life cycle increased from 203 degree-days at 5.0°C to 1406 at 37.5°C. Leachates from both OSR cultivars stimulated more J2 to hatch than the distilled water controls. No significant cultivar differences were observed for J2 hatching, root invasion and duration of the life cycle at the different temperatures but significantly more cysts of the second generation (g root)−1 were observed in cv. Flash than cv. Castille at 27.8 and 32.2°C, suggesting that the latter cultivar is a poorer host of H. schachtii than cv. Flash. This is the first report of the effect of temperature on H. schachtii development on current winter OSR cultivars in the UK and provides insight into the potential effects of climate change on the nematode-host interaction.

Interactions between field populations of the potato cyst nematode Globodera pallida and Rhizoctonia solani diseases of potatoes under controlled environment and glasshouse conditions.

This research elucidates interactions between Globodera pallida and Rhizoctonia solani (AG3) by comparing disease development in potato plants inoculated with G. pallida and R. solani. The effects of juvenile population density and time of infestation on R. solani disease were investigated in controlled environments. Plants were inoculated with a range of densities of second-stage juveniles (J2) of G. pallida (800, 4000, 10 000, 20 000 and 40 000 J2/plant) and R. solani at 2, 4 and 6 weeks after planting and a single treatment of G. pallida density and R. solani alone. The experiment demonstrated that greatest disease incidence and severity occurred when high population densities of G. pallida were applied at an early stage of plant development. To determine if this effect could explain differences in R. solani disease incidence and severity following interactions with individual field populations of G. pallida, a glasshouse experiment was conducted using two populations of G. pallida with known hatching characteristics (fast and slow hatching). The experiment revealed that a combination of a fast-hatching population with R. solani caused significantly more R. solani disease incidence and severity than a population of G. pallida with slower hatching characteristics.

In vitro nematicidal activity of a garlic extract and salicylaldehyde on the potato cyst nematode, Globodera pallida.

The in vitro nematicidal effects of an aqueous garlic extract, salicylaldehyde, a nonylphenol ethoxylate surfactant and a formulation containing these constituents were evaluated against the potato cyst nematode, Globodera pallida. Newly hatched, infective second-stage juveniles (J2) were placed for 24, 48 and 72 h in solutions containing concentrations of the formulation from 30.080.0 μl l–1 with 20% (v/v) potato root leachate and sterile distilled water controls. The garlic extract, salicylaldehyde and surfactant treatments were assessed at concentrations proportional to their occurrence in the formulation. Hatching assays involved a series of experiments in which G. pallida cysts were incubated for 8 weeks in potato root leachate solution containing different concentrations of the test substances. A second set of experiments involved incubating cysts in different concentrations of the test substances for 2, 4 and 8 weeks prior to hatching in potato root leachate solution to determine how prior exposure to these substances influences hatching and in-egg viability. The formulation caused 100% mortality at 75.0 μl l–1 with an LC50 of 43.6 μl l–1 after 24 h exposure. Salicylaldehyde was the most toxic constituent of the formulation with an LC50 of 6.5 μl l–1 after 24 h, while the garlic extract achieved 50% J2 mortality at 983.0 μl l–1, demonstrating that the formulation and salicylaldehyde are more toxic to G. pallida in vitro than oxamyl but less toxic when compared with aldicarb. The surfactant showed no dose-dependent toxic effects on J2 when compared with the controls. Emergence of J2 from the cysts was significantly reduced by concentrations of the formulation above 688.0 μl l–1 and its equivalent concentration of salicylaldehyde, while concentrations of the formulation above 2752.0 μl l–1 and the corresponding salicylaldehyde concentrations resulted in complete irreversible hatch inhibition. Concentrations of the garlic extract below 137.6 μl l–1 caused 26% more J2 hatch in comparison to the potato root leachate solution. This study has shown that salicylaldehyde is more toxic to nematodes than the garlic extract, and is the first report of a hatch stimulatory effect of a garlic extract on G. pallida under in vitro conditions.

Interaction between arbuscular mycorrhizal fungi and the nematicide aldicarb on hatch and development of the potato cyst nematode, Globodera pallida , and yield of potatoes

The effects of inoculation of roots of the potato (Solanum tuberosum) cv. Golden Wonder with the mixed-isolate arbuscular mycorrhizal fungus (AMF) inoculum Vaminoc, or with three single-isolates AMF inocula (Glomus intraradices, G. mosseae and G. dussii; components of Vaminoc), on the potato cyst nematode (PCN) Globodera pallida were assessed in a pot experiment in the presence or absence of the nematicide aldicarb (Temik 10G). Mycorrhization of potato roots stimulated an 11% overall mean increase in the hatch of G. pallida within the first 2-4 weeks from planting. In the presence of aldicarb, AMF-inoculated plants exhibited only 57% of the PCN population size (viable eggs (g soil)−1) of the non-inoculated plants; in the absence of aldicarb the respective value was 42%. Root length colonisation by AMF was unaffected by the application of aldicarb. Roots of PCN-infested plants exhibited reduced levels of mycorrhizal colonisation (41%) compared to non-PCN-infested plants (45%). The AMF isolates used differed in their ability to produce a plant growth response (expressed as root dry weight, shoot dry weight or total dry biomass) and to affect tuber yield. In this regard, the single Glomus isolates enhanced plant growth (36% increase in total dry biomass) and improved fresh tuber yield by 22% on average, while Vaminoc had, in most cases, no effect. It was concluded that AMF have potential to reduce G. pallida multiplication via a dual mechanism involving stimulation of nematode hatch and inhibition of root invasion. Field experimentation will be required to take this research forward and assess the feasibility of including AMF in G. pallida integrated management strategies.