The goal of agricultural nematologists is usually considered to be the prevention of harmful nematode populations from reaching levels that cause noticeable yield losses in field crops. Usually, it is the plant-parasitic nematodes that are attributed with constraining plant growth and development. Not nearly as well understood is the impact on crop plants of the non-plant-parasitic and bacteria-feeding nematodes. This latter group can interact with plant-growth-promoting bacteria to improve soil fertility and improve crop productivity. The challenge has become finding methods to develop and maintain those systems that build-up beneficial nematode populations while simultaneously suppressing plant-parasitic nematodes and associated plant pathogens. Beneficial soil nematodes are usually more abundant in crop management systems subjected to sophisticated crop sequences, cultivation practices and organic amendments. Models to predict the population dynamics of a nematode species have been developed. However, the inadequacies of nematode identification, compounded by the irregular distribution of nematodes in soil, have made it difficult to obtain reliable data on nematode distribution and abundance with which to refine these simulation models. Since many different nematode extraction methods are in use today it also becomes extremely difficult to meaningfully compare quantitative data from different laboratories. As the number of factor variables affecting soil nematode populations is large and monitoring seasonal populations awkward, nematode influence on crop health and yield determination is seldom fully recognized. Thus, it is usually only those catastrophic nematode outbreaks that are recognized, while systematic benefits are rarely recognized or appreciated. Perhaps, with the utilization of molecular biotechnology it will become possible to better elucidate nematode plant-host interactions. Clearly, these root zone relationships will increasingly become a key component in understanding soil ecosystem function and lead to better cropping system design. Crown Copyright © 2003 Published by Elsevier Science B.V. All rights reserved.
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