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United States Department of Agriculture

Agricultural Research Service

Title: Specific Gravity As a New Physical Character of Nematodes

Authors
item Carta, Lynn
item Carta, David - VOLUNTEER

Submitted to: Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 1999
Publication Date: N/A

Interpretive Summary: Plant parasitic nematodes are microscopic worms that cause an $8 billion annual agricultural loss in the U. S. An important aspect of assessing nematode damage requires distinguishing species after extraction from soil. One problem with distinguishing species is that the cleanest, most efficient separation procedure currently used employs a concentrated sugar solution which extracts all nematodes in an often dehydrated and distorted condition, thereby reducing their shelf-life before identification and counting may be completed. This "one-size-fits-all" solution has obscured real density differences that can be used to separate different groups of nematodes. In this paper, we outline a new procedure for extracting nematodes from soils or tissue culture. The new procedure includes sugar solutions of different concentrations and a dye; it allows a researcher to determine the density profile of any nematode group. The results indicate that measurable differences exist among species of different nematodes and even life stages of the same nematode. This is a significant discovery because the effect may be used to design gentle extraction methods for nematodes from mixed soil populations to allow efficient counting with computerized systems. It will also allow researchers to cleanly separate certain nematode species or stages from mashed plant tissue for more accurate nematode invasion counts. It will allow researchers to enrich nematode inoculum for certain stages to better understand nematode development and, depending on density profiles, can physically separate species or aid in the identification of species.

Technical Abstract: A technique is developed that refines the standard sugar flotation procedure used to isolate nematodes from their surroundings. This allows the extraction of information about nematode density which can be used as a physical character. By centrifuging nematodes in a number of increasing specific gravity solutions and plotting the fraction floating, the cumulative probability distribution of the population's specific gravity is generated. By assuming normality, the mean and the standard deviation can be found by a nonlinear least squares procedures. Problems arising in the development of the flotation technique are discussed. Mean and standard deviation pairs were found for the specific gravities of the adult stage of the plant parasites Pratylenchus agilis (1.068, 0.017), P. scribneri (1.074, 0.027) P. penetrans (1.060, 0.015), and the bacterial-feeder Caenorhabditis elegans (1.091, 0.016).

Last Modified: 4/17/2014