MANAGING FREE-LIVING PLANT-PARASITIC NEMATODES IN POTATO, VEGETABLES, STRAWBERRY AND CEREALS USING PATCH DYNAMICS IN NORWAY

Nematodes (roundworms) are microscopic worms living in the water films surrounding the soil particles. Nematodes are the most common multicellular animals on planet Earth. Free-living plant-parasitic nematodes move freely in soil attacking roots externally and internally. Crops attacked by nematodes may develop patches of poor growth and low yield due to root damage and malfunction in the up-take of water and nutrients. The aim of the project is to study the involvement of nematodes in growth disturbances of different crops using, among others, aerial photography from a drone. Growth disturbances will be correlated with nematode densities through soil sampling in different crops. Data from Norway will be included in the already-exisiting EU project Best4Soil (https://www.best4soil.eu) that will be licenced and adjusted for Norwegian conditions. Best4Soil is a database with information on plant-parasitic nematodes, their hosts and their reproduction rates on different host plants. The data will be used by Norwegian growers to decide which crops to grow to eliminate unwanted nematodes. Soil samples have been collected in several fields and crops at different locations for the past three years. Samples have been collected in the beginning of the growing season and from potato, onions and wheat. Soil samples have also been collected at the end of the growing season with emphasis on the important crops like potato and carrot. Drone images from all fields were collected in the beginning of the season (April/May), and in June and July, with two different cameras, giving rise to images showing plant health status. Several genera of plant-parasitic nematodes were detected in the samples, namely lesion nematodes, stubby-root nematodes, root-knot nematodes, potato cyst nematode and stunt nematodes. Preliminary results indicate that root lesion nematodes do little damage to potato. Further information on nematode status has been obtained through isolation and analysis of gene material (DNA) from nematodes, bacteria, fungi and oomycetes isolated directly from soil. In collaboration with Norwegian Agricultural Extension Service (Norsk Landbruksrådgiving), soil samples were taken from carrot fields in the counties: Vestfold and Telemark in the east, Rogaland in the west and Finnmark and Troms in the north, at planting and at harvest. The samples were analysed for plant-parasitic nematodes. The aim of this study is to determine the nematode densities (and species) under carrot production. Results are in progress. In a carrot field in Karmøy (west Norway) the spiral nematode species Rotylenchus robustus was detected for the first time in Norway. Severe damage was observed in this field. Results from pot experiements have not shown that this nematode can cause damage in carrot when being the only plant-parasitic nematode present. Reproduction factors have been calculated for the different groups of plant-parasitic nematodes in the four fields. The root-lesion nematode Pratylenchus crenatus was associated with damage in several carrot fields. Results from pot experiments indicate that P. crenatus reduce both germination and yield in carrot, and the nematode has been detected in both the lateral roots and taproot. Use of soil treatment combined with crop rotation has been performed to study the effect of different types of fertilizers in different types of plant parasitic nematodes. Field trials have been conducted in cooporation with the Norwegian Agricultural Extension Service (Norsk Landbruksrådgiving). The following treatments were included in the trials: cow manure, pig manure (wet fraction), pig manure (dry fraction), chicken manure (pellets) and a chitin based product from mussels, in addition to a control treatment without manure, but with synthetic fertilizer. The aim of the trials was to investigate the effect of different types of manure that may indirectly have an effect on the population densities of key plant-parasitic nematodes, among others, in crops of barley. Preliminary results suggest that there are only small differences in effect of the different treatments. However, the results may be masked by high densities of nematodes. The data are being further processed and experiments in greenhouse will be performed in the last phase of the project to better control the amounts of nematodes in the samples. In a greenhouse experiment, several growth promoting products were tested on strawberry plants to determine if such amendments would increase the plants tolerance to needle nematode. Strawberry seedlings (plugs) were planted in pots containing soil naturally infested with needle nematode. There was an overall decline in nematode population. Pots with chitin rich amendments had a significant higher dry weight compared with plants grown in infested soil with no treatment. No significant differences were observed in plant tolerance.

The spiral nematode Rotylenchus robustus was detected for the first time in Norway, in a carrot field with severe damage. Results from field work and controlled experiments in the greenhouse suggests that Pratylenchus crenatus is pathogenic in carrot, but not in potato. Damage has also been observed in an onion field with high numbers of P. crenatus, but this has not been investigated in controlled experiments. These results form the basis for further work on free-living plant-parasitic nematodes in vegetables. Molecular analysis of nematodes, fungi, bacteria and oomycetes have been performed, with environmental DNA isolated directly from soil, known as metabarcoding. Results from traditional morphological analysis of nematodes have been correlated to results from the metabarcoding analysis, both in regards to the detection of nematodes in DNA isolated directly from soil, and to the abundance of different plant-parasitic genera. The results from the metabarcoding analysis showed that we were able to detect all four plant-parasitic nematodes present in the field, when combining two nematode-specific primers. The abundance of all organisms detected in the metabarcoding analysis were correlated with an index for plant health (Normalized Difference Vegetation Index, NDVI). The index (NDVI) was calculated based on images obtained with a multispectral camera mounted on a drone. These correlations can be used as a tool for detecting the probable cause of poor growth in a field, in less labour-intensive way than sampling and analysing the soil with traditional methods. Furthermore, the results of the project will have a positive impact on the environment by the development of sustainable approaches, and environmental-friendly methods for the control of plant-parasitic nematodes, e.g. the Best4Soil database that will be available in Norwegian. Good management of plant-parasitic nematodes means that the use of nematicides in Norway still can be avoided. The knowledge and experience gained will be useful also to farmers in other regions.

Free-living plant parasitic nematodes are microscopic round worms that move freely in soil feeding on roots. Soil samples indicate an increasing damage from free-living nematodes in Norway. Yield losses of up to 50 % have been noted in local fields, and indeed some farmers have considered abandoning crop production on nematode infested land. Because of this, methods of efficient nematode management have been sought for both in the extension service and among farmers. The main objective of this project is to increase and improve the current knowledge on the occurrence and management of free-living nematodes in potato, vegetables, strawberry and cereals in Norway. Nematode damage shows as patches of poor plant growth and this project will combine nematode patch dynamics and remote sensing with drone technology, and image analysis to estimate damaging thresholds and reproductive factors of free-living plant parasitic nematodes on selected plants in the field. The effect of soil amendments with organic waste, compost and silicone in nematode management will also be investigated. An important aim is also to strengthen, develop and maintain the national competence in Norwegian nematology by training a PhD student. Collaborators in this project are a) The Norwegian Agricultural Extension Service (NLR); b) University of Hertfordshire School of Life and Medical Sciences; Chinese Academy of Agricultural Sciences; and The Julius Kühn-Institut Germany. Dissemination will be conducted via open days with field demonstrations, publications in (technical) journals in cooperation with NLR and on their website and in meetings with farmers. Results from the project will increase the competence on free-living plant-parasitic nematodes in NIBIO, the extension service and among farmers. Successful nematode control will decrease the current loss in yield and quality of Norwegian produce and be to the economic benefit of both wholesalers and retailers.