Nematode community structures in different deciduous tree fruits and grape in Colorado, USA and impact of organic peach and apple production practices

Although free-living nematodes improve soil health and crop production, plant-parasitic nematodes (PPNs) damage crop plants and reduce crop yield. In this investigation, surveys were conducted to determine the PPNs associated with Colorado tree fruit orchards, and research blocks were evaluated to study the effects of crops and production practices on nematode community structure, a soil health indicator. During the surveys, a total of 16 PPN genera were observed: eight in grape, eight each in pear, cherry and peach, seven in apple and 11 each in prune, plum and apricot soils. Xiphinema sp. (dagger nematode), Pratylenchus sp. (root lesion nematode) and Meloidogyne sp. (root-knot nematode) were the predominant nematodes. Based on the results, Xiphinema sp. can be considered an important and other two potentially important PPNs. In the research blocks, nematode diversity, abundance, and structural indices were compared in organic and conventional peach and apple production systems as well as the apple cultivars 'Honeycrisp' and 'Cameo'. Both peach and apple organic production systems had higher nematode diversity and significantly higher total nematodes than their conventional counterparts. A significant interaction of variety and production system in apple was observed for Ditylenchus and total fungivores, Helicotylenchus, Paratylenchus, and Discolaimium populations. In peach, nematode indices such as percentage of fungivores, fungivore/bacterivore and fungivore/(fungivore + bacterivore) ratios, richness, diversity, and Maturity Index were significantly higher in organic soils. In apple, the Enrichment Index and Structure Index were significantly higher in the organic production systems, whereas the Basal Index was significantly lower in organic production systems as compared to the conventional ones. Subsets of other parameters studied were not significantly different between the organic and conventional production system in both apple and peach crops. These results indicate that crop type as well as management practices influence nematode communities and that organic apple and peach production may be better than conventional apple and peach production with respect to improved nematode community structure. However, soil improvement such as addition of organic matter, especially in conventional production systems and in apple orchards, might improve soil health and productivity.