Nordiska jordbruksforskares frening (NJF)

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1 Bibliografiska uppgifter för Importance of Nematodes in Organic farming Tidskrift/serie NJF Report Utgivare Utgivningsår 2005 Nr/avsnitt 1 Nordiska jordbruksforskares frening (NJF) Författare Holgado R., Magnusson C. Adress The Norwegian Crop Research Institute Ingår i... NJF-Seminar 369. Organic farming for a new millenium - status and future challenges Huvudspråk ngelska Målgrupp Forskare Nummer (ISBN, ISSN) ISSN

2 Importance of Nematodes in Organic farming R. Holgado 1 and C. Magnusson 1 1 The Norwegian Crop Research Institute, Plant Protection Centre, Dep. of ntomology and Nematology, Høgskoleveien 7, 1432 Ås, Norway. ricardo.holgado@planteforsk.no Abstract Soil nematodes are important components of soil ecosystems, but have so far received little attention in organic farming. Many free-living nematodes are important for decomposition and mineralization processes, and it is estimated that the nematode grassing of bacteria would mobilise up to 124 kg N ha -1 yr 1. Furthermore, their feeding activities on the rhizoplane may reduce microbiological immobilisation of nitrogen. In organic farming the use of clover and other nitrogen fixating legumes is important for securing appropriate nitrogen levels. Clover is an excellent host for a wide range of plant parasitic nematodes. In organic farming damage has so far been reported for root lesion nematodes (Pratylenchus spp,), clover cyst nematode (Heterodera trifolii) and the northern root knot nematode (Meloidogyne hapla). Nematode monitoring is a prerequisite for management. ffective control measures of plant parasitic nematodes and good management systems for beneficial nematodes would allow for increasing yields and improved quality. Organic farming puts new challenges to the science of nematology, and would profit from a close interaction between nematology and soil science. Keywords: free-living, plant parasitic, nematodes, ecosystem processes Introduction Organic farming seeks to build up the reserves of nutrients in the soil while at the same time reducing inputs. Soil microorganisms are the essential link between the mineral nutrient reserves and the plants. Soil nematodes are important components of the soil ecosystem. Microbivorous and predatory nematodes may enhance the rate of mineralisation, while plant parasitic nematodes seriously affect plant health and reduce the yield and quality of crops. In this paper we want to draw the attention to the roles of nematodes in organic farming. Nematodes in general Nematodes are worm-like animals, which inhabit almost every niche available in nature, and are the most numerous multicellular animals on earth. Soil nematodes are microscopic and their population densities may reach millions of individuals per m 2. The morphology of the nematode stoma often indicates the food preferences and makes it possible to distinguish between different ecological groups like bacterial-, fungal- and plant feeders, omnivores and predators. Beneficial nematodes Bacterial feeding nematodes have a higher carbon:nitrogen (C:N) ratio than bacteria (Ferris et al. 1997), and consume therefore more N than is required for the maintenance of their body structure (assimilation). The excess nitrogen is excreted as ammonia/ammonium, urea, peptides and amminoacids (Thompson & Geary 2002). The assimilation of bacterial feeding nematodes is between % of the consumption (Sohlenius, 1979), and it is estimated that the nematode grassing of bacteria would mobilise kg N ha -1 yr -1 (Anderson et al. 1981) 177

3 for uptake by plants and by microbes. In the presence of a suitable carbon source bacteria may out-compete plant roots for N, resulting in a microbiological immobilisation of N on the surface of growing root tips. By grassing on rhizoplane bacteria, nematodes may liberate N of bacterial cells and again make it available to plant roots. Fungal-feeding nematodes have a C:N ratio closer to that of their food source. However, for nematodes of both feeding habits the grazing activity stimulates the growth and metabolic activity of the microflora (Trofymow & Coleman, 1982, Griffiths, 1994, Wasilewska et al. 1975). Predatory nematodes contribute to nitrogen mineralization by feeding on other nematodes. Under field conditions bacterial feeding nematodes and predatory nematodes are estimated to contribute to 8% and19% of the nitrogen mineralization in conventional and integrated farming systems respectively (Beare, 1977). Nematodes respond rapidly to changes in their environment. Increased microbial activity first leads to an increased proportion of opportunistic bacterial feeders, which later are followed by general opportunists, which include fungal feeders and slower growing species of bacterial feeders (Bongers & Ferris, 1999). This succession is important for the decomposition of soil organic matter and mineralization of plant nutrients (Ingham et al. 1985, Hunt et al. 1987). The faunal composition may mirror the activity of decomposition pathways and give indications of nutrient status and fertility of soil (Bongers & Ferris, 1999). Harmful nematodes Out of the nematodes described today some 4000 species are parasites of plants. The major characteristic of plant parasitic nematodes is the presence of a mouth spear (stylet), which is used to puncture plant cell walls, and inject nematode secretion, which changes plant physiology and facilitates food up-take by the nematode. Some species feed only on the outer tissue of the root (ectoparasites), others penetrate more deeply (migratory endoparasites), and some completely enter the host inducing the formation of a permanent feeding site (sedentary endoparasites) (Table 1). Above-ground symptoms Symptoms are similar to those resulting from many kinds of root injury, lack of nutrients or inadequate plant nutrition. Growth is stunted and weak and attacked plants wilt readily in dry weather. Symptoms usually appear in patches, which increase over time. Below-ground symptoms Root symptoms include stunting of roots, root lesions, reduced or excessive proliferation of lateral roots, forked or fanged roots and root galls, Damaged roots are often dark in colour. Fungi and bacteria which cause root rots, wilts, and other plant diseases often infect nematode-damaged roots earlier and more severely than uninjured roots (Back et al. 2002, Khan, 1993). Important plant parasitic nematodes In organic farming the use of clover and other nitrogen fixating legumes is important for securing appropriate nitrogen levels. Some plant parasitic nematodes of potential importance on crops in the Nordic area are presented in table 1, together with some crops, which are relevant to organic farming. Clover is an excellent host plant for many plant parasitic nematodes. The stem nematode (Ditylenchus dipsaci), the root lesion nematodes (Pratylenchus spp.) and the clover cyst nematode (Heterodera trifolii) are a few examples of potentially damaging species which could reach high populations in cropping systems with clover (Holgado & Magnusson, 2000). Plant parasitic nematodes also have been reported to interfere with the formation of Rhizobium nodules in various leguminous plants (Khan 1993). So far, few studies have been made on the importance of plant parasitic nematodes in organic farming. Observations in Germany, however, demonstrate that problems with plant parasitic 178

4 nematodes may arise after a 5 years period (Hallmann et al. 2004). specially nematodes with broad host spectra, such as Meloidogyne hapla and Pratylenchus spp., can cause severe damage occasionally leading to almost a total loss of the crop. In Denmark, Møller & Søegaard (2004) have demonstrated the involvement of clover cyst nematode (Heterodera trifolii), in the clover-tired soil syndrome. Table 1. xamples of some crops and some plant parasitic nematodes likely to cause economic damage in organic farming in the Nordic area. = ectoparasite; M = migratory endoparasite; S = sedentary endoparasite. Cereals Clover Potato Sugar beet Carrot Strawberry Nematode control Stunt nematodes Tylenchorhynchus spp. Merlinius spp. Cereal cyst nematode Heterodera avenae S Rye cyst nematode H. filipjevi S Stem nematode Ditylenchus dipsaci M Clover cyst nematode H. trifolii S Potato rot nematode Ditylenchus destructor M Potato cyst nematode Globodera rostochiensis S G. pallida S Stubby root nematodes Trichodorus spp. Paratrichodorus spp. Beet cyst nematode H. schachtii S Pin nematode Paratylenchus bukowinensis Stubby root nematodes Trichodorus spp. Paratrichodorus spp. Carrot cyst nematode H. carotae S Northern root knot Meloidogyne hapla S nematode Leaf nematodes Aphelenchoides fragariae M A. blastophthorus M Root lesion nematodes Pratylenchus spp. M Needle nematode Longidorus elongatus The aim of control measures should be to keep plant parasitic nematode at densities below their economic threshold for damage. Nematodes need to be monitored on a regular basis. Control measures include hygiene, black fallow, crop rotation (with poor host plants between main crops), trap crops, resistant cultivars, weed control, soil conditioning (soil amendment), soil steaming and biological control. It is likely that good management strategies for nematodes would allow for increased yields and better sustainability of organic cropping systems. Conclusion The occurrence of plant parasitic nematodes in organic farming systems needs to be investigated further, and the reaction of these nematodes on cultural practices would provide valuable information for management routines. Organic farming obviously puts new and 179

5 exciting challenges to the science of nematology in that the management systems also need to maintain and improve the environment for the important beneficial nematodes. Organic farming would profit from a close interaction between nematology and soil science. References Anderson, R. V., D. C. Coleman and C. V. Cole (1981). ffects of saprotrophic grazing on net mineralization. In: Clark, F.. and T. Rossvall (eds.) Terrestrial Nitrogen Cycles. cological Bulletins. (Stockholm) 33, Back, M. A., P. P. J. Haydock and P. Jenkinson (2002). Diseases complexes involving plant parasitic nematodes and soil borne pathogens. Plant pathology, 51, Beare, M. H. (1997). Fungal and bacterial pathways of organic matter decomposition and nitrogen mineralization in arable soil. In: L. Brussaard and R. Ferrera Cerrato (eds.) Soil ecology in sustainable agricultural systems Boca Raton, FL.: CRC/Lewis Press pp Bongers, T and H. Ferris (1999). Nematode community structure as a bioindicator in environmental monitoring. Trends in cology and volution, 14, Ferris, H., R. C. Venette and S. S. Lau (1997). Population energetics of bacterial-feeding nematodes: carbon and nitrogen budgets. Soil Biology & Biochemistry 29, Griffiths, B. S. (1994). Microbial-feeding nematodes and protozoa in soil: Their effects on microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere. Plant and Soil 164, Hallmann, J., A. Frankenberg, A. Pattrath and F. Rau (2004). Occurrence of plant parasitic nematodes in organic farming in Germany. (Abstract). Proc. XXVII SN Intern. Symp June 2004, Roma, Italy. p.59. Holgado, R. and C. Magnusson (2000). Nematoder i belgvekster. Grønn Forskning, 2, Hunt, H. W., D. C. Coleman, R.. Ingham,. R., Ingham,. T. lliott, J. C. Moore, S. L. Rose, C. P. C. Reid and C. R. Morley (1987). The detrital food web in a shortgrass prairie. Biology and Fertility of Soils, 3, Ingham, R.., J. A. Trofymow,. R. Ingham and D. C. Coleman (1985). Interactions of bacteria, fungi and their nematode grazers: ffects on nutrient cycling and plant growth. cological Monographs 55, Møller, K. and K. Søegaard (2004). Kløvertræthet er koblet til tidlig nematodeangrep. Nyhedsbrev fra Forskningscenter for Økologisk Jordbrug 6/ Sohlenius, B. (1979). A carbon budget for nematodes, rotifers and tardigrades in a Swedish coniferous forest soil. Holarctic cology 2, Thompson, D. P. and T. G. Geary (2002). xcretion/secretion, Ionic and Osmotic Regulation. In: Lee, D. L. (ed.). The Biology of Nematodes. Taylor and Francis, London and New York: Trofymow, J. A. and D. C. Coleman (1982). The role of bacterivorous and fungivorous nematodes in cellulose and chitin decomposition in the context of a root/rhizosphere/soil conceptual model. In:.D. Freckman (ed.) Nematodes in soil ecosystems. Univ. Texas Press, Austin, U.S.A. pp Wajid Khan, M Nematode Interactions. Chapman & Hall, London. 377pp. Wasilewska, L., H. Jakubczk and. Paplinska. (1975). Production of Aphelenchus avenae Bastian (Nematoda) and reduction of mycelium of saprophytic fungi by them. Polish cological Studies, I,