Hazelnut (Corylus avellana L.) is one of the most important nut crops of Turkey, and Turkey is ranked the first place worldwide for hazelnut production and export value. Annual hazelnut production of Turkey is 660 000 tons with shell. Turkey supplies 70% of the world’s hazelnut exportation as 146 322 tons with shell among top 20 exporter countries (FAO, 2013). The hazelnut is considered one of the most ancient plants with naturally occuring cultured varieties and wild types in the Black Sea region. The ecological conditions of Black Sea Region of Turkey overlap best with the requirements of hazelnut by moderate climate and high relative humidity throughout year. Although hazelnuts have been grown in more than 35 cities around Turkey, production is primarily concentrated along Turkey’s Black Sea coast (Güney, 2014). The provinces Ordu, Giresun, Sakarya, Samsun, Trabzon and Bolu are the main places for hazelnut production in Turkey, but Ordu can be named as the leading province of hazelnut production for Turkey. The growth practices are traditional and generally syntethic fertilizers are used. The irigation method is also ancient and the source of water is rainfall. The pest manage-ment approach is conventional with pesticides based on mites and insects. There is no concern of farmers for nematode management by the lack of information for nematodes, high slope of the agriculture orchards and the difficulties of training system. The training system of hazelnut trees in Turkey is multi-stem system for C. avellana. Multi-stem form is named as “Ocak” in Turkey and that contains 8 or 10 stems of the plant. Harvest is carried out by hand. Another training system is single-trunk form for Coryllus colurna which can be grafted with shrub form, C. avellana and suituble for mechanical harvest. In addition to that, single-trunk form is a modern training system for Ordu province and Turkey and still in trails of Hazelnut Research Institute (Giresun, Turkey).

Hazelnut has some pests and diseases. Therefore com-mercial hazelnut production is difficult without manage-ment. Considering the pests of hazelnut, the pest status of hazelnut have been investigated by many of the scientists so far and the main focus was on the insect and mite pests of hazelnut. For instance, insects can reduce the yield of hazelnut between 15-60% and the level of this loss is dependent on the year, growing conditions and control measures (Milenkovic and Mitrovic, 2001). This explains the reason of intensive focus on insect pests. Insects and mite species as the pests of hazelnut for Turkey and other countries were reported by many authors (AliNiazee, 1983; Hill, 1987; Ioachim and Bobarnac, 1997; Ak et al., 2005; Özman-Sullivan, 2006; Saruhan and Tuncer, 2010; Saruhan and ?en, 2012). General control strategies against the pests on crops may include application of insecticides, classical and augmen-tative biological control, utilization of resistant varieties, and use of bio-based preparations (AliNiazee, 1998). Until the discovery of the management or control techniques of the pests mentioned above, the first step to carry out is to identify the pests species or determine the fauna of the cultivar. In addition to these perspectives, nematode fauna for hazelnut is also a subject in the limited numbers of researches and management. Only a few authors pointed out the nematode pest status of hazelnut in some countries: Greece (Kyrou, 1976), Spain (Pinochet et al., 1992) and California, US (Norton et al., 1984). When considering Turkey for the nematode pest status of hazelnut; only Kepenekci (2002) studied on nematodes associated with hazelnut and pointed out several nematodes occuring in hazelnut orchards and reported the nematodes, Filenchus afghanicus Hemicycliophora punensis, Pratylenchoides hispaniensis, Pratylenchus pratensisobrinus, Helicotylenchus crenacauda, Hemicycliophora sturhani, Merlinius (=Scutylenchus) lenorus, Tylenchorhynchus cylindricus as plant parasitic species and Ditylenchus anchilosposomus as fungivorous species in the west part of Blacksea region of Turkey. In this context, it is difficult to say that there are investigations adequately about nematodes of hazelnut in Turkey and worldwide. Therefore, the requirement to detailed investigation of nematodes in the hazelnut rhizosphere was obvious and it was determined with this investigation on province scale where the hazelnut production is ancient and commercial. We hope to elucidate the hazelnut producers clearly about the presence and importance of nematodes on hazelnut with this study.

Our objectives were to make an investigation for more detailed nematode faunal assemblages including the free living and plant parasitic trophic groups in hazelnut orchards of Ordu province. This survey will provide a backround for further research about nematode fauna of hazelnut.

This study examined the frequency of occurence and abundance of particular nematode trophic groups in hazelnut growing areas in Ordu province, Turkey. The totals of 110 hazelnut orchards from 18 districts (Figure 1) were surveyed for investigation.

Nematode faunal analysis of 110 hazelnut orchads showed that the plant parasitic nematodes were the most abundant (95.7 ind./100 cm³ soil) trophic group (Figure 2). As plant parasitic group; the genera, Tylenchus, Gracilacus, Helicotylenchus has been found in the all investigated districts (Table 3). The nematodes of the genus Tylenchus were the most abundant (45.8 ind./100 cm³ soil) with frequency of occurrence of 94.5% followed by genus Gracilacus (25.4; 79.1%), Helicotylenchus (8.4; 56.4%), Pratylenchus (2.3; 22.7 %), Meloidogyne (5.9; 14.5%) and Criconemella (1.6; 24.5 %) (Table 2). The mean abundance of plant parasitic nematode species were the highest in Kabata? district (277 ind./ 100 cm³ soil) followed by Gölköy (196.6) and Çama? (170.8) districts (Figure 3).

Bacteriovorouss were the second widespread and diverse group with ten genera after plant parasitic nematodes. The bacterivorous genera, Acrobeloides and Plectus were recorded in all districts and the mean abundance and frequency values were 20.6 (61.8%) and 2.3 (49.1%) respectively (Table 2). The abundance of this group was the highest in Aybast? (104.8 ind./ 100 cm³ soil) followed by Per?embe (83.5) and Çama? (74.6) (Figure 3). The fungivorous group had the highest values in Akku? (92 inds./ 100 cm³ soil) followed by Kabata? (39.7) and Per?embe (31.5) (Figure 3). The genera, Aphelenchoides and Aphelenchus in this group were recorded in all districts and the abundance and frequency values were 13.5 (68.2%) and 5.0 (53.6%) respectively. Ditylenchus and Tylencholaimus were also recorded fungivorous genera: (2.6; 22.7%) and (3.5; 37.3%) respect-tively (Table 2).

Amoung the omnivorous group, the most abundant and frequent genera were Aporcelaimus (2.5; 50.9%), Prodorylaimus (1.0; 20.9%), Eudorylaimus (0.7; 16.4%) (Table 2) for this trophic group. Omnivorous reached the highest abundance in the Fatsa and Ünye districts (12.2 ind./100 cm³ soil) (Figure 3). The highest abundance of predators was in Gülyal? (8.3 ind./ 100 ml soil) followed by Ulubey (5.4) and Mesudiye (4.3) districts (Figure 3) and the first three genera were represented by Clarkus (1.0, 28.2%), Tripyla (0.7; 22.7%) and Mononchus (0.5; 18.2%) nematodes (Table 2).

2.1 ind./ 100 cm³ soil) (Figure 2). Omnivorous and predatory could be more sensitive in defining the soil ecosystem status (Xiang et al., 2006), but they undoubtedly play an important role by feeding all types of organisms. Predator nematodes eat all types of nematodes or protozoa while omnivorous consume a variety of organisms inclu-ding bacteria, fungus, protozoa, other nematodes and roots and may have a different diet at each life stage (Hoorman, 2011).

The soil properties on nematode communities cannot be overlooked as well. The texture might effect the density and distribution of nematodes in soil profile (Mcsorley and Frederick, 2002) and when the percentage of clay increased, the root penetrating ability of plant parasitic nematodes might decrease (Prot and Van Gundgy, 1981). The soil reaction factors can also have some effect on nematode groups. In general, pH is inhibitory to most nematode activities below 5.0 and above 8.0 (Ravichandra, 2008). For instance, the number of nematodes was negatively affected in acid soil reaction at pH 4.0 with lowest nutrient application rate. In additon to combinations of higher nutrient rates, low pH significantly reduced the number of bacterial-feeding nematodes, whereas it increased the number of hyphal-feeding nematodes. Indirect effect of nutrient and pH via other components of the soil food web is also in question (Korthals et al, 1996). Organic content is another important fraction of the soils and it can be considered as a positive source on nematode communities. Shabeg et al. (2007) reported that during period of 4 years in field plots of different crops transitioning from conventional to organic farming practice, nematode faunal profile estimates showed that the food webs were highly enriched and moderately to highly struc-tured and the decomposition channels were bacterial in both systems. Bacterivore nematodes were more abundant in the organic soil compared to conventional system.

By the lights of these, the nematode com-munities vary in different sites and are effected by agronomic applications. In case of any nematode management attempts on hazelnut, as for other crops, site, land or country-spesific management pratices must be considered and applied because nematode groups are dependent on the effects of spesific conditions.

As a concequence, this survey pointed out the general nematode status of hazelnut for an intensive production area. Many factors such as fertilization, climate, soil texture, cultivation and cultivar are expected to affect the abundance and frequency. Therefore, the results would change from region to region. When considering the levels of free living trophic groups (bacterivorous, fungi-vorous), the values were in desirable levels for eco-system. On the other hand, plant parasitic group was the highest in abundance and frequency of occurrence. This suggested that it has potential for damage or yield loss in case of any increasing levels especially for Pratylenchus and Gracilacus genera which need to be studied on. The nematode problems might seem as unimportant on hazelnut for classical Ocak training system because of the lack of any management practice on hazelnut, but will undoubtly be very important for any further application with modern training systems like single trunk tree form grafted with cultivar. Because the growth decline on single trunk form can be observed easily when compared with the multistem shrub form (Ocak), the modern systems are in progress for hazelnut in Black Sea region. In these perspectives, any study on yield loss caused by nematodes on hazelnut would provide more information for management of the crop, especially for modern systems in world scale and Turkey. This faunistic investigation is expected to be beneficial for researchers and growers in the future.

The author(s) have not declared any conflict of interests.