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Problems and perspectives in nematology in the Near East

D.L. Trudgill

In discussing the above I am starting from a highly personal perspective. Progress in any area of human endeavour is dependent on the talents of those who work in that area. People function most effectively when they have a clear view of their role and purpose, and I think this is what we are trying to establish here. They need also to possess the necessary skills and knowledge.

When asked what do I do, I variously reply that I am a nematologist or a research scientist or a biologist, depending on who is asking. Even after 28 years of doing what I do, I am still a little unsure.

I work with nematodes, but am I a nematologist? I have not had in-depth formal training in them, and I am certainly not a nematologist in the mould of some of the greats such as Cobb, Christie, Goodey or Thorne.

Am I a research scientist? Research is defined as the endeavour to discover new facts by careful, critical investigation. I certainly try to fulfil this definition, but in common with many, I frequently fail to be sufficiently critical of my own work and ideas.

Am I a scientist? Science in the natural and physical world is the pursuit of knowledge based on observation, experimentation and induction. Progress in science is stepwise, each person building on the achievements of others. Underpinning that process is the establishment of techniques, of observational information, of basic principles, and of mechanisms.

Central to the process of scientific investigation is the hypothesis. Beyond the purely observational phase, the objective of experimentation should be either to provide the information to formulate a hypothesis or, at a later stage, to test the hypothesis. Either way, the hypothesis is the starting point around which experiments are formulated. From the hypothesis come the objectives, and it is these which define the requirements of the work.

I may be a kind of nematologist and a research scientist, but I am also a biologist. I work with a complex of nematodes, plants and the soil. I also have a particular interest in environmental interactions that, in nematological research, can rarely be avoided. For example, nematode population dynamics and the degree of damage caused are subject to large environmental influences.

To interpret many of my results I have to understand the dynamics of plant growth. Also, I have to collaborate with other specialists, picking their brains, using their techniques, borrowing their equipment and ideas, etc. This is for me one of the advantages of nematology; it allows one to do plant physiology, or molecular biology, or mathematical modelling. Another big advantage is that nematodes are relatively immobile, have relatively low rates of multiplication and few generations per year. This makes studies on their population dynamics and damage relationships easier than with many other crop pests/pathogens.

Returning to my title, what are the current problems? I suggest that there is too much observational information being generated that is not related to the development of hypotheses, establishment of mechanisms or principles, or the solving of field problems. The application of thermal time (°C days) relationships to nematodes provides a good example of the application in the laboratory of certain basic principles to nematodes. In a series of studies on root-knot nematodes (Meloidogyne spp.) the base temperatures for development of M. hapla and M. javanica were shown to be about 8.25°C and 12.8°C, respectively. Above these base temperatures the minimum time for one generation (i.e. from J2 to first J2 of the next generation under optimum conditions), measured as rate of development, was shown to be directly related to temperature up to 28°C. Consequently, between the base temperature and 28°C there was a constant heat requirement (above base) for this development. For M. hapla this thermal constant was calculated as 554°C days and for M. javanica as 355°C days.

This information has considerable practical value. Together with soil temperature records it can be used to calculate the likely range of species, their generation times, and to compare likely competition advantages, e.g. from these results it can be calculated that M. hapla has a shorter generation time than M. javanica at all temperatures below 21°C.

Perhaps more pressing still is the dearth of good, field-based information on the extent of nematode density-dependent yield losses in the major field crops grown throughout much of the Near East. That we still have no agreed basis for measuring population densities of Meloidogyne spp., the most widespread and serious nematode problem in the region, points to the lack of relevant applied research. If we do not know and cannot demonstrate how much nematodes are reducing yields, how can we expect to convince administrators and farmers?

The perspective for the future is of an increasing world population resulting in further intensification of agriculture. In the longer term continued unchecked population increase will completely outstrip the capacity of even sophisticated agriculture to satisfy world needs and mass starvation is inevitable. In the shorter term we know intensification of agriculture will increase the damage and problems caused by nematodes. Nematicides will remain expensive and the synthetic ones are likely to become progressively less available. Genetic engineering offers the prospect of novel control, but it would be unwise to rely on it to solve most of the problems. Biological control will probably be made to work only in a limited range of special situations.

Therefore the bulk of farmers will continue to rely on rotation, diversity and a degree of crop tolerance/crop loss. For them, the way forward is in a series of small, interacting steps involving better husbandry and improved rotations with an integration of all that is best for their situation. This will include the introduction of new crops and more resistant varieties, better hygiene and better integration of all the available nematode control measures, including peripheral techniques such as solarization, fallowing, soil drying, and possibly natural nematicides. In seeking to develop such integrated techniques nematologists will have to collaborate with many other disciplines including plant breeders and agronomists. The paramount need is to establish and apply the basic principles to field situations. This means working in the field. Also, the role of extension workers, and especially of leading farmers, in demonstrating and persuading their colleagues to adopt new ideas should not be underestimated.

Training and education at all levels are vital. Nematologists are often naive about agriculture and need to collaborate with agriculturally trained extension workers. In such an integrated approach even the trained nematologist will find, as I have, that the process of education is continuous.

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