Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2016
Publication Date: 5/31/2016
Citation: Carta, L.K., Li, S., Skantar, A.M., Newcombe, G. 2016. Morphological and molecular characterization of two Aphelenchoides from poplar leaves. Journal of Nematology. 48(1):28-33.
Interpretive Summary: There are a wide variety of microscopic roundworms called nematodes which inhabit agricultural fields. Although many cause global crop losses exceeding $100 billion annually, others are found in above-ground plant parts where they may feed on fungi that may be good or bad for crops. A major problem with determining the role of these fungal-feeding nematodes is that the anatomical descriptions and keys used for their identification are outdated and unreliable. In this study, ARS scientists from Beltsville, Maryland, and an ecologist from the University of Idaho in Moscow, identified and described from poplar tree leaves two nematodes that feed on fungi, some of which cause plant disease. They compiled information on anatomical features for new populations of two previously described nematode species, and they also characterized the DNA of the nematode to build a family tree for this group of nematodes. These results are significant because they provide the details necessary for identifiers and ecologists to confidently name these species wherever they may occur in the world. This information will be used by scientists, extension agents and pest managers engaged in nematode and fungi research and control.
Technical Abstract: During a long-term, large network study of the ecology of plant endophytes in native habitats, various nematodes were found. Two poplar species, Populus angustifolia (narrowleaf cottonwood) and P. trichocarpa (black poplar) represent important ecological and genomic models now used in ongoing plant-pathogen-endophyte interaction studies. Two different aphelenchid nematodes from the northwestern U.S. were identified and molecularly characterized from within surface- sterilized healthy leaves of P. angustifolia and P. trichocarpa. From P. angustifolia, Aphelenchoides pinusi was identified and was cultured on a Trichoderma sp. living endophytically within the leaves. These nematodes are identified and characterized microscopically, and with three molecular markers, 28S rDNA, 18S rDNA and cytochrome oxidase 1. The 28S sequence of this L. heidelbergi population has only one base pair difference compared to a Portuguese population, and one from the original Australian population. Both 28S and 18S rDNA trees of Aphelenchoides and Laimaphelenchus species indicates laimaphelenchus heidelbergi fails to cluster with three other Laimaphelenchus species, including the type species of the genus. Therefore, we agree with a more conservative definition of the genus Laimaphelenchus, and consider these populations to belong to Aphelenchoides. Aphelenchoides pinusi came closest to A. saprophilus among sequenced taxa in the 18S tree. This is the first report of these nematodes from within leaves. The presence of these fungal-feeding nematodes can affect the balance of endophytic fungi which are important determinants of plant health.