Plant parasitic nematodes are a main pest to crops. For ex am pie, the root-knot nematodes belonging to the genus Meloidogyne are worldwide in their distribution and attack almost every type of crop, causing considerable losses of yield and affecting quality of produce. The cyst nematodes within the genera Globodera and Heterodera constitute a major group of plant pathogens in many countries throughout the world, suppressing yields of potato, sugar beet, soybean and cereals. Several nematodes such as longidorids and trichodorids are implicated in the transmission of numerous plant viruses. Many others cause constraints to agricultural production either locally or on large areas. However, despite their economic importance (they account for worldwide crop reduction in excess of 10%), plant parasitic nematodes are still poorly understood, because most of them are obligate parasites of roots. Environmental concerns over the agricultural use of pesticides demand the development of alternative measures to control them. To achieve environmentally sound control, knowledge of the basic biology of nematodes must be expanded. Important research areas include understanding the molecular bases for pathogenicity, the molecular mechanisms of the host parasite interactions and the genetic bases for population fluctuations. The workshop has, for the first time, brought together an international group of researchers using molecular approaches to study plant parasitic nematodes and their host responses."

Plant parasitic nematodes are a main pest to crops. For ex am pie, the root-knot nematodes belonging to the genus Meloidogyne are worldwide in their distribution and attack almost every type of crop, causing considerable losses of yield and affecting quality of produce. The cyst nematodes within the genera Globodera and Heterodera constitute a major group of plant pathogens in many countries throughout the world, suppressing yields of potato, sugar beet, soybean and cereals. Several nematodes such as longidorids and trichodorids are implicated in the transmission of numerous plant viruses. Many others cause constraints to agricultural production either locally or on large areas. However, despite their economic importance (they account for worldwide crop reduction in excess of 10%), plant parasitic nematodes are still poorly understood, because most of them are obligate parasites of roots. Environmental concerns over the agricultural use of pesticides demand the development of alternative measures to control them. To achieve environmentally sound control, knowledge of the basic biology of nematodes must be expanded. Important research areas include understanding the molecular bases for pathogenicity, the molecular mechanisms of the host parasite interactions and the genetic bases for population fluctuations. The workshop has, for the first time, brought together an international group of researchers using molecular approaches to study plant parasitic nematodes and their host responses."

Although nematodes had long been suspected as vectors of soil borne plant diseases, unequivocal proof of their implication was not forthcoming until 1958 when Professor William Hewitt and his colleagues in California demonstrated experimentally that Xiphinema ~ was the vector of grapevine fanleaf virus. This opened up a new and exciting field in plant pathology and discoveries quickly followed of other nematode species associated with soil-borne diseases of many different crops and in several countries. After the initial enthusiasm of discovering new vectors and new viruses there followed a period of consolidation in which research workers sought answers to tantalising questions about the location of the virus within the nematode, the factors governing the close speci ficity between virus and vector; and more mundane but equally important and compelling questions about life cycles, geographical distribution, host relations, morphology and taxonomy. No other group of nematodes has attracted such a concentrated effort involv ing many different scientific specialisations and yielding so much progress in a relatively short time. The NATO Advanced Study Institute held at Riva dei Tessali, Italy, during 19 May to 2 June, 1974, provided the forum for a critical discussion of all aspects of biology of virus vector nema todes.

Plant diseases and pests are a major constraint to agricultural production despite the various measures used to control them. Chemical control, although often e~~ective, may pose environmental hazards and is relatively expensive, especially in developing countries where it may be completely uneconomic. Control through genetically mediated resistance to diseases and pests, is both cheap and environmentally sa~e and at present most diseases and pests o~ staple ~ood crops are controlled through some form of resistance. One of the basic problems in the use of resistance is its ~re quent lack of durability; very often a type of resistance is used that 'breaks down' after a certain period. The temporary nature of this resistance, due to the development of new strains of pest or pathogen able to overcome it, has seriously hindered the improvement o~ the yield potential of many crops as a continuing effort is needed to replace old cultivars who resistance has failed, with new ones. Following Vanderplank's now classical publications (1963, 1968) which differentiated horizontal and vertical resistance, studies on several host-parasite systems have shown that di~ferent types of resistance can be distinguished genetically and epidemiologically, and on the ability o~ the pests or pathogens to adapt to them. A knowledge of how resistance operates at the population level has also opened up possibilities of 'managing' relatively simple resistance types in such a way that a stable host-pathogen system can be pro duced with a minimum of crop loss.

The cyst nematodes are a major group of plant pathogens of economic importance in many countries throughout the world. Considerable yield losses have been attributed to cyst nematodes attacking potatoes, sugar beet, soybean and cereals. Because of the protective cyst that is formed, which encloses the eggs, they pose special problems in their control and also in preventing their distribution in soil from infested areas. There has been much research on many aspects of the biology of cyst nematodes and the large number of publications are testimony to their importance as crop pests and of the interest of nematologists in the group. Nevertheless, they continue to pose problems because of the complexity of their phylogeny and taxonomy and there is still much to be investigated on their biology, particularly with those aspects which relate to improving the effectiveness of control. In many respects the biology of the various cyst nematode species is similar, although with variations due to different interactions with hosts and geographical location. Thus, research on any one species has general applicability and this is particularly so with regard to evaluation of control measures, or to the methodology of soil sampling for the assessment of populations prior to growing crops.