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

Authors: POKHAREL, RAMESH - Maryland Department Of Agriculture; MARAHATTA, SHARADCHANDRA - University Of Hawaii; Handoo, Zafar; Chitwood, David

Submitted to: European Journal of Soil Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2015
Publication Date: 3/11/2015
Publication URL: http://handle.nal.usda.gov/10113/60517
Citation: Pokharel, R., Marahatta, S.P., Handoo, Z.A., Chitwood, D.J. 2015. Nematode community structures in different deciduous tree fruits and grape in Colorado, USA and impact of organic peach and apple production practices. European Journal of Soil Biology. 67(1):59-68.

Interpretive Summary: Nematodes are microscopic worms that live in the soil. Some cause crop diseases of $100 billion annually; others feeding on fungi or other microorganisms are beneficial to agriculture. One major agricultural problem is that the species of nematodes in a particular field are often unknown to science, such as in the case of Colorado tree fruit orchards. In this study, ARS, Maryland Department of Agriculture, and University of Hawaii scientists report the results of surveys conducted to determine the plant-parasitic nematodes associated with Colorado tree fruit orchards managed conventionally or with organic management practices. During the surveys, a total of 16 plant-parasitic nematode genera, eight in grape, eight each in pear, cherry and peach, seven in apple and 11 each in prune, plum and apricot soils were observed. Dagger, lesion and root-knot nematodes were the predominant types of plant-parasitic nematodes. Based on the results, dagger nematode can be considered an important and the other two (root lesion and root-knot) potentially important nematodes. The results are significant because they provide the first indication that dagger and possibly lesion and root-knot nematodes may be problematic in Colorado orchards, as well as the first evidence that management practices influence beneficial nematode communities there. This research will be used by scientists designing strategies for reducing the damage caused by plant-parasitic nematodes as well as enhancing the numbers of beneficial nematodes in fruit production systems in agricultural soils.

Technical Abstract: 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 as a soil health indicator. During the surveys, a total of 16 PPN genera, eight in grape, eight each in pear, cherry and peach, seven in apple and 11 each in prune, plum and apricot soils were observed. 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, fungivore/ (fungivore+bacterivore) ratio, 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. This result indicated that crop type as well as management practices influences 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.