Grass-Endophyte Interactions and Their Associated Alkaloids as a Potential Management Strategy for Plant Parasitic Nematodes.

Claviceptaceous endophytic fungi in the genus Epichloë mostly form a symbiotic relationship with cool-season grasses. Epichloë spp. are capable of producing bioactive alkaloids such as peramines, lolines, ergot alkaloids, and indole-diterpenes, which protect the host plant from herbivory by animals, insects, and nematodes. The host also benefits from enhanced tolerance to abiotic stresses, such as salt, drought, waterlogging, cold, heavy metals, and low nitrogen stress. The bioactive alkaloids produced can have both direct and indirect effects towards plant parasitic nematodes. Direct interaction with nematodes' motile stages can cause paralysis (nematostatic effect) or death (nematicidal effect). Indirectly, the metabolites may induce host immunity which inhibits feeding and subsequent nematode development. This review highlights the different mechanisms through which this interaction and the metabolites produced have been explored in the suppression of plant parasitic nematodes and also how the specific interactions between different grass genotypes and endophyte strains result in variable suppression of different nematode species. An understanding of the different grass-endophyte interactions and their successes and failures in suppressing various nematode species is essential to enable the proper selection of grass-endophyte combinations to identify the alkaloids produced, concentrations required, and determine which nematodes are sensitive to which specific alkaloids.

A new method to validate and compare varietal resistance and yield tolerance of sugar beet (Beta vulgaris) against the beet cyst nematode, Heterodera schachtii Schmidt.

BACKGROUND: Beet cyst nematode, Heterodera schachtii Schmidt is a global threat to sugar beet crops, and is found in every major sugar beet growing region. Annual losses due to this nematode can be severe, being estimated at €90 m in Europe alone in the 1990s. Fortunately tolerant, resistant and partially resistant varieties have since been introduced which help to limit yield loss and are now widely being deployed in infested fields. However, understanding yield performance of these varieties has been difficult, especially when variety testing programmes usually require uninfested fields. RESULTS: For the first time, and in a standardised manner, we can now assess simultaneously the resistance of different varieties to BCN and their actual yield tolerance, by comparing them to varieties grown in uninfested micro-plots alongside those which are infested. This method provides new insights on variety yield performance and nematode reproduction over an entire growing season. In addition, the investigations are also been able to detect significant physiological differences in the development and growth of the tolerant varieties' canopies and leaf chlorophyll levels. CONCLUSIONS: Our findings are of direct benefit to sugar beet growers challenged by BCN. The standardised testing provides new information on predicted variety performance. We found that these tests are justified, as not all tolerant varieties respond in the same manner to nematode infestation. Therefore, these assessments will become a vital part of variety testing for sugar beet growers, allowing for tailored deployment of variety types and more informed decision making on-farm, helping to maximise yields whilst minimising nematode damage. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Locomotor behaviour promotes stability of the patchy distribution of slugs in arable fields: Tracking the movement of individual Deroceras reticulatum.

BACKGROUND: The distribution of the grey field slug (Deroceras reticulatum Müller) in arable fields is characterised by patches containing higher slug densities dispersed within areas of lower densities. Behavioural responses that lead to the spatial/temporal stability of these patches are poorly understood, thus this study investigated behavioural mechanisms underpinning slug distribution using a new method for long-term tracking of individual slug movement in the field. RESULTS: A technique for implanting radio frequency identification (RFID) tags (each with a unique identification code) beneath the body wall of slugs was developed. Laboratory tests indicated no consistent detrimental effect on survival, feeding, egg laying or locomotor behaviour (velocity, distance travelled). Movement of individual slugs above and below the soil surface was recorded for >5 weeks (in spring and autumn) in winter wheat fields. Most (~80%) foraged within a limited area; and at the end of the observation period were located at a mean distance of 78.7 ± 33.7 cm (spring) or 101.9 ± 24.1 cm (autumn) from their release point. The maximum detected distance from the release point was 408.8 cm. The remaining slugs (~20%) moved further away and ultimately were lost. CONCLUSIONS: RFID tagging allowed continuous tracking of individual slugs, even below the soil surface. Localised movement of 80% of tracked slugs over 5 weeks offers a mechanism promoting stable slug patches in arable crops. Rapid dispersal of the remaining slugs facilitates exchange of individuals between patches. Precision targeting of pesticides at such stable slug patches may facilitate reduced usage. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evaluating resistant brassica trap crops to manage Heterodera schachtii (Schmidt) infestations in eastern England.

BACKGROUND: The beet cyst nematode (BCN), Heterodera schachtii Schmidt, is a plant parasitic nematode that causes severe yield losses in sugar beet. Resistant brassicas (radish and mustard) have been bred to be planted after harvest of the main crop, for example a cereal, and encourage BCN juvenile hatching. The resistant plants stimulate juvenile hatching but are not suitable hosts. Juveniles are unable to complete their lifecycle and thus populations are lowered. This research aimed to investigate the effectiveness of a range of brassicas in terms of BCN control when grown in infested fields in eastern England. RESULTS: Experiments used four different radish cultivars, which differed in their resistance to BCN, and one resistant mustard variety. Field experiments were sown in early September in 2016 and 2017. Significant reductions in BCN populations were found only following resistant mustard and the radish with the greatest resistance level. CONCLUSIONS: Further research is needed to understand how best to utilize brassicas and whether they are economically viable when alternative management options for BCN are available. Time of planting may be crucial to fully achieve their BCN-reducing potential. © 2018 Society of Chemical Industry.

Field evaluation of the nematicide fluensulfone for control of the potato cyst nematode Globodera pallida.

BACKGROUND: Three field experiments evaluated the performance of the nematicide fluensulfone against the potato cyst nematode Globodera pallida in Shropshire, England. RESULTS: Experiments 1 and 2 showed reduced root infection and lowered multiplication of G. pallida following fluensulfone (Nimitz 15G(®) ) soil treatments at five rates (1.95, 3.00, 4.05 (full rate), 5.05 and 6.00 kg AI ha(-1) ) and Nimitz 480EC(®) at the full rate. Experiment 3 demonstrated a positive interaction between the full rate of Nimitz 15G and the potato variety Santé in the reduction of G. pallida. The fluensulfone treatments at the full rate had more consistent effects than the lower rates, and there were no greater effects for the treatments higher than this full rate. Generally, fluensulfone was less efficacious than oxamyl or fosthiazate, which suggests that the treatment may not be reliably integrated within shorter potato rotations. CONCLUSION: The data suggest that fluensulfone soil application could make a useful addition to the few available nematicide treatments for the control of G. pallida rather than be a substitute for these treatments.© 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.