Bakir A. Oteifa
Nematode problems encountered in the region
Impact on productivity and plant protection resources
Present-day agricultural development relies on the generation of new technologies through research and their adoption by farmers. In the Near East region agricultural scientists are attempting to provide more food in sustainable systems to meet the needs of growing populations. This situation poses tremendous challenges and opportunities for those involved in plant protection research.
Plant-parasitic nematodes are a severe constraint on agricultural production. They cause considerable annual losses among the broad range of crops grown in the Near East region. Major inputs are needed to reduce the damage caused by these pests, and increase the world's food supplies.
Progress in agricultural nematology research in the Near East region has been notable in the last 30 years. Nematology, as a new science within the framework of plant protection disciplines, was established in the region around the mid-1950s. Since then gradual progress has been achieved through extensive teaching programmes and research projects. At present, the number of nematologists in the region, whether they are affiliated to universities, academies, and/or ministries of agriculture, is quite adequate for the advancement of nematology education, research and technology in the respective countries. Few research projects related to nematode problems have been sponsored by foreign donors for promoting knowledge about these pests and protecting crops from their damaging effects. Information on nematode diagnosis, biology, population dynamics, and host-parasite relationships has been acquired as a valuable prerequisite for the future establishment of management control practices. The fact that countries in this region have different ecological zones with various cropping patterns that influence the nature and magnitude of nematode problems emphasizes the need to strengthen their national research and extension capacities.
Nematode problems are aggravated by prevailing environmental conditions that favour rapid reproduction of certain species. Infestation appears to be widespread where cultivated lands in the region are concentrated in specific ecological zones:
· In temperate zones at intermediate to high altitude, with high rainfall, snow and cold winters, and dry cool summers, the cyst nematodes, Globodera rostochiensis, Heterodera schachtii, H. trifolii and H. avenae infecting potato, sugar beet, clover and wheat, respectively, are quite prevalent.
· In moderately warm zones at intermediate altitude, with cool rainy winters and hot dry summers, especially in the coastal belts, the root-knot nematodes, Meloidogyne incognita, M. javanica, M. arenaria, M. hapla, M. thamesi, M. naasi and M. artiellia commonly occur in many field and horticultural crops; certain cyst-forming nematodes e.g. Heterodera latipons on wheat and barley, H. ciceri on chickpeas, H. goettingiana on broad beans and peas, H. cajani on cowpeas, and H. zeae on maize, are frequently found; the stem nematode race of Ditylenchus dipsaci attacks broad beans and various species of the root-lesion nematodes, especially Pratylenchus penetrans, P. thornei, P. neglectus and P. vulnus, are widespread in many orchard, field and vegetable crops; and the citrus nematode, Tylenchulus semipenetrans is a common pest in citrus, olive and vineyard plantations.
· In warmer and subtropical zones at low altitude, with cool winters, little rainfall and very hot humid summers, the root-knot nematodes, M. javanica, M. incognita and the root-lesion nematode, P. brachyurus are frequently found in date-palms, olives, mangoes, groundnuts, alfalfa, melons, tomatoes, okra and beans; the root-rot nematodes, Radopholus similis and Helicotylenchus multicinctus are commonly associated with the decline of banana and sugar-cane plantations; the reniform nematode, Rotylenchulus reniformis is widespread in the barbadense cotton belts, banana plantations and many vegetable-growing areas; and the rice nematode, Hirschmanniella oryzae is common in the paddy rice-growing belts.
These comments only summarize the extent of the distribution of the known economically important nematodes in the region. There are other nematode species that have been reported in countries of the region that have specific hosts as well as wide host ranges. Species of the genera Longidorus, Xiphinema and Trichodorus that are capable of transmitting viruses from one plant to another are also common.
Although many of the nematodes identified are capable of inflicting direct severe damage to growing plants, the degree of injury depends on the level of soil infestation by the dominating pathogenic species, new races, or pathotypes, and the prevailing environmental stress conditions such as drought, waterlogging, salinity, and inadequate plant nutrition. Many nematodes are involved in the expression of disease complexes, syndrome problems and in the reduction of benefits from nitrogen-fixing bacteria.
Many plant-parasitic nematodes are widely distributed in this part of the world. Their association with other soil pathogens in disease complexes, as well as with abiotic stress conditions in crop physiological syndromes, ranks them in the list of major economic pests affecting the yield and quality of our major food and fibre crops.
Unfortunately, the majority of growers in this region, being unaware of the nature and harmfulness of nematode infestations in their fields, do not seriously consider the destructive effect of these noxious pests on their crops. These pests are a severe constraint to agricultural production in several countries of this region. There are no reliable estimates of the magnitude of the annual losses to crops, but diagnostic surveys have shown, however, that many economic nematode species are widespread and the damage they cause to crops is more evident than was anticipated. Nematode damage in this region may well come up to the estimate of 10 percent of total production, and if these pests are not controlled, losses in the production of principal crops may be more serious.
Currently, many agricultural chemicals used for nematode control are no longer available because of health and environmental hazards associated with their use. Those nematicides that remain on the market are less effective and continue to increase in cost while farm revenues decrease. These realities demand that nematode management should become an integrated programme of practices that includes alternative measures to the use of chemicals and provides sustainable nematode control systems. There is no standard formula for a plant protection programme, and such programmes must be designed to fit the requirements and options available within a specific growing region.
Each farming situation requires a different set of production and protection management inputs for greatest profitability, and the requirements may change from year to year. Climate, soil type, cropping system, nematode pest history, cultural practice, cultivar and the nature of the surrounding environment all affect nematode problems on a given site. In some areas, where resistant cultivars have been deployed, their effectiveness has been rapidly reduced by the emergence of new host races of the target nematode species, or by emergence of new infestations of different nematode species on the resistant hosts.
These are but a few of the biological and environmental factors that illustrate the complexities of the nature of these pests in the region. It is a situation that calls for appropriate nematode management approaches. Modified cultural practices, non-host rotation crops, host-crop resistance and/or tolerance, biorational nematicidal compounds, nematode antagonists, cover crops and better nematode identification and enumeration are all tools that call for improvement as components of nematode management programmes. Various plant protection resources are available in this region and their potential is beginning to be explored. The following are examples of existing resources:
· Human resources. The region has a number of highly qualified, university graduate specialists in plant protection and pesticide management disciplines. Those involved in nematology have acquired the necessary basic and applied studies in nematode taxonomy and biology that allow them to perform diagnostic surveys and research on nematode control strategies.
· Energy resources. The region is particularly rich in fossil deposits that are exploited as petroleum and coal. New classes of chemical materials and by-products have been introduced and utilized as soil conditioners and mulches for crop production and protection.
· Natural botanical resources. Many areas in the region are endowed with native lines of wild plants that could be utilized as sources of genetic material in breeding for nematode resistance or as sources of biologically active chemicals that may be inhibitors or have nematostatic or plant-growth regulatory properties.
· Natural microbial resources. Sites with soil suppressive to certain nematodes have been identified. Isolates of bacteria and fungi antagonistic to nematodes have been discovered. Technologies to stimulate the effectiveness of such indigenous nematode antagonists are being explored through the employment of various soil amendments and organic additives or supplements.
In a meeting like this, we should be concerned about the future effectiveness of research programmes in reducing losses caused by nematodes and in developing and advocating appropriate agricultural systems that are sustainable, environmentally friendly and more productive within existing resources. Donor agencies should place strong emphasis on increasing nematology research capacity in this region, both through funding of projects by institutional grants and support of advanced training programmes. Institutional mechanisms, for example, such as those already established in some countries of the region as national nematology research centres, need to be improved and strengthened to act as centres of excellence for the advancement of agricultural nematology in the region. These centres of excellence should be adequately supported financially and technically to:
· collaborate with national programmes and national agencies in the design of projects related to basic mechanisms of nematode interactions in the agro-ecosystem, as well as biochemical relationships that may be of an allelopathic nature;
· facilitate research development and implementation of national nematode pest management programmes through technical support and distribution of materials for nematological research;
· engage in training and delivery of information in order to ensure more efficient use of resources;
· develop databases that quantify the relationship between nematode populations and crop-yield losses under the prevailing biotic and abiotic factors.
There is no doubt that there are many critical issues, specific projects and opportunities for which, during our discussions and consultations, we can develop adequate programmes with the aim of promoting nematological research and technology in this region of the world.