The Sudan covers an area of more than 2.5 million km2 and is as big as India. The total cultivable area, however, is approximately 80 million ha, and only 10 percent, i.e. 8 million ha, is under cultivation at present. The climate is mostly arid in the northern part, extending to subtropical or tropical in the south. Accordingly, rainfall varies from a few millimetres per annum in the extreme north, to more than 800 mm in the extreme south; it averages 400 to 600 mm in the central plains where most of the cultivable area exists. In the north, the temperature is typical of an arid climate, ranging from 10° to 15°C (mean minimum) and 25° to 30°C (mean maximum) during the winter period, November to February, and from 20° to 25°C (mean minimum) and 40° to 45°C (mean maximum) during the summer period, March to June. During the rainy period, July to September, temperatures are less extreme than in summer. In the less arid southern parts of the country, however, the difference between minimum and maximum temperatures is much smaller. The relative humidity is about 5 percent or less in the extreme north, with almost no rainfall, and around 20 to 30 percent and 60 to 80 percent in the central and southern parts, respectively. The soil is either riverain or volcanic. While riverain soil can either be sandy or silty, volcanic soil usually varies from pure sand in the western region, to alluvium in the south and heavy vertisol clays in the east. The soil pH is mostly neutral or alkaline, around pH 7 to 8. According to the climatic zones the vegetation varies from desert to desert-scrub in the north, merging to savannah in the centre, and hence to subtropical-tropical forests in the south. Among the most important plants grown throughout the Sudan are fibre crops (mainly cotton), oil crops (groundnut and sesame), cereals (sorghum and wheat), vegetable crops (e.g. tomato, onion, eggplant, hot and sweet peppers, okra and cucurbits) and orchard crops (mango, citrus, guava and date-palm).

Nematological investigations undertaken during three decades have covered most of climatic zones as well as crop plants, timber trees and some weed flora in the country, as detailed below.

Status of nematology in relation to other aspects of crop protection

Since such investigations started in the early 1960s, few nematologists have been actively involved in nematological investigations throughout the country (see Bibliography). Although of limited number, however, Sudanese nematologists have established a set of wider scientific links with other nematologists and/or institutions worldwide (Table 20).

However, nationally much less attention has been given to nematology compared with other aspects of crop protection, e.g. entomology or pathology. This is partly because of the fact that nematode problems can often be easily overlooked or else mistaken for other soil factors, such as mineral deficiency. Another reason for such a lack of attention is associated with a lack of appreciation of problems arising from nematodes and their economic magnitude, especially in field crops.