The Sudan

A.M. Yassin

Introduction
Status of nematology in relation to other aspects of crop protection
Major nematode problems and possible control measures
Major achievements
Future priorities
Bibliography
Pioneer nematologists in the Sudan

Introduction

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.

Major nematode problems and possible control measures

Since serious nematological investigations started, some 70 species of plant-parasitic nematodes have been detected in and around the roots of many cultivated and weed plants in various localities throughout the country (El-Amin and Siddiqi, 1970; Decker, Yassin and El-Amin, 1975a). The following are some of the most important problems arising from plant nematodes throughout the country.

Root-lesion nematodes in cotton

Species and distribution. At least two species were isolated from within and around the roots of cotton with stunted growth in widely scattered foci throughout the main cotton-growing areas, e.g. the Gezira, Khashm El-Girba and Guneid. These are, Pratylenchus sudanensis n.p. Loof and Yassin and P. delattrei Luc. The commonest, however, is P. sudanensis. It occurred in densities of ten or less, or up to 100 to 200 nematodes per 200 g rhizosphere soil. Investigations were therefore undertaken into certain aspects of its biology and control.

TABLE 20
Principal scientific staff involved in nematological investigations in the Sudan

Local staff	Institute	Leading international staff in cooperation	Location	Joint activities
Siddiqi, M.R.	UKh	Conink	Belgium	Visit
Yassin, A.M.	ARC	Coomans, M.	Belgium	Visits, species identity
Zeida, A.B.	AHAC	Decker, H.	Germany	Surveys, species identity
El-Amin, E.M.*	ARC	Hooper, D.J.	United Kingdom	Species identity
El-Amin, E.M.*	UKh	Lamberti, F.	Italy	Visit
Khalifa, O.*	ARC	Loof, P.A.A.	Netherlands	Visits, species identity
Fattah, M.A.*	ARC	Oostenbrink, I.M.	Netherlands	Visit, species identity
Mohammed, Z.E.*
Nasr, I.A.*	ARC	Oteifa, B.A.	Egypt	Visits
Saadabi, A.M.*	ARC	Sasser, J.N.	United States	Visits, conferences, workshops, projects (IMP, CNRCP)
USAID-funded:
El-Badri, G.A.	ARC	Seinhorst, J.E.	Netherlands	Visits
		Siddiqi, M.R.	United Kingdom	Visits
		Taylor, C.E.	United Kingdom	Soil-borne virus investigation

* no longer involved; UKh = University of Khartoum; ARC = Agricultural Research Corporation; AHAC = Abu Haraz Agricultural College.

Mode of parasitism. P. sudanensis was found to be highly pathogenic to cotton, cv. Barakat under laboratory conditions at the Gezira Research Station (GRS) (Yassin, 1973). Destructive lesions developed in the root within two to three days of infestation, using a relatively small number of 30 or fewer nematodes per test. The migratory behaviour of the nematode during parasitism was clearly observed in this test and was in accordance with the large amount of damage to the root despite a relatively small number of invading nematodes.

TABLE 21
Effect of cropping on population levels of Pratylenchus sudanensis at the GRS, during three seasons, 1969/70 to 1970/71 to 1971/72

		Pigeon pea	Lubia	Cotton	Sorghum	Groundnut	Wheat
6 weeks after sowing
	a	20	25	10	6	10	1
	b	154	83	14	2	0	0
	a+b	174	108	24	8	10	1
12 weeks after sowing
	a	463	218	122	85	3	9
	b	26	74	4	14	1	1
	a+b	489	292	126	99	4	10
Before harvest
	a	19	54	22	8	6	8
	b	32	2	2	0	1	0
	a+b	51	56	24	8	7	8
Mean total
	a+b	245	152	58	54	7	6
Degree of root necrosis		+++	+++	++	++	+	+

Notes: a = number of P. sudanensis per 200 g soil; b = denotes number of P. sudanensis per g root; + = mild; ++ = medium; +++ = severe.

Host status. The effect of cropping on P. sudanensis populations was studied in some detail in a field plot at a site at the GRS, containing ten or fewer P. sudanensis per 200 g soil prior to the tests. Important crop plants in the Gezira (Yassin, 1973), were rotated in this experimental plot for three consecutive seasons and the results of nematode counts are summarized in Table 21. Both Cajanus cajan L. (pigeon pea) and Lablab vulgaris L. (lubia bean) were among the best hosts, supporting increases in the number of P. sudanensis of over 20-fold. By comparison, both cotton and Sorghum vulgare (dura, cv. Dwarf Milo) behaved as moderate hosts on which populations increased about fivefold. Conversely, others, such as Hibiscus esculantus (okra), Solanum melongena (eggplant), groundnuts, wheat, cucumber and tomato, were poor or non-hosts, with no increase over the original numbers.

Life cycle and persistence. According to investigations in the laboratory by the author, the life cycle of P. sudanensis in its best hosts took 28 to 30 days to complete from first stage to mature, gravid, female (Yassin, 1973). Evidently, this will allow for several generations of the nematode per cropping season. In another test, the nematode persisted in a completely flooded field soil for some two weeks. Both these trials might help to explain its wide and common occurrence in the Gezira and other localities.

Association with other organisms. Pratylenchus sudanensis resulted in accentuated wilt of Barakat cotton plants when coupled with the vascular wilt fungus, Fusarium oxysporum f. sp. asinectum, in greenhouse tests at the GRS (Yassin, 1974a). Under field conditions both this fungus and the nematode were commonly associated with wilted cotton plants in certain localities in the Gezira, e.g. Newaila, and also in Khashm El-Girba and Um Gerr in the White Nile schemes. Probably P. sudanensis plays a synergistic role in the disease, fusarium wilt, in these localities.

Economic importance. At present there is no estimate of the effect of P. sudanensis on the yield of cotton in any one locality. However, there is substantial evidence that the impact of the nematode upon the yield is underestimated, at least in the Gezira. This is by virtue of its highly pathogenic nature, its persistent manner and common occurrence in widely scattered foci, coupled with a relatively fast rate of reproduction, and also because of its possible interaction in fusarium wilt. Even more striking is the significant response in the yield of cotton, over 70 percent increase, following nematicidal applications against the nematode (Table 22).

TABLE 22
The effect of three different nematicides, applied at standard dosage rates, on mean seed yield of cotton, and final Pratylenchus sudanensis nematode numbers, per 200 g soil and 1 g root sample, for two consecutive seasons (percentage decrease of nematodes in parentheses)

	1973/74		1974/75
Nematicide	Mean1 grain yield (kg/0.405 ha)	Yield increase over control (%)	Final1 nematode number	Mean1 grain yield (kg/0.405 ha)	Yield increase over control (%)	Final1 nematode number
Fenamiphos	4993	88	6 (68)3	2872	90	49 (36)3
Aldicarb	4242	60	5 (74)3	2752	82	36 (53)3
Nemagon	4152	57	6 (68)3	2592	72	9 (88)4
Control	265	0	19 (0)	151	0	76 (0)
SE ±	24.62			36.66

¹ Mean of three replicates.
² Significant at 0.05 probability level.
³ Significant at 0.01 probability level.
⁴ Significant at 0.001 probability level.

Possible control measures

Crop sequence, among the important crop plants rotated with cotton in the Gezira at present are dura, lubia, groundnuts and wheat; the first two of which are favourable, and the second two are poor or non-hosts of P. sudanensis (see above). The effect of dura and lubia in increasing nematode densities under the conditions in the Gezira might therefore be mitigated by that of both wheat and groundnuts. Work is in progress to test other pioneer crops or crop cultivars, e.g. soybean, Giza 155 or Mexicani wheat, Dabar dura and rice.

Nematicide applications. A number of nematicides, including fenamiphos, aldicarb and Nemagon, were all tested by the author in soil under cotton cv. Barakat, at a site at the GRS containing relatively high densities of P. sudanensis. All three nematicides resulted in up to 72 to 90 percent increase in the yield of seed cotton and up to 36 to 88 percent reduction in nematode densities over the control (Table 22). Although very effective, at present there are still many technical and economic difficulties in their application on a large scale. In the presence of less toxic, cheaper nematicides and the future mechanization of cotton cultivation, e.g. placement of seed and fertilizer, these difficulties might be largely surmounted.

Certification. Many plant-parasitic nematodes are known to break the resistance of crop varieties to other invading organisms, especially fungi and bacteria. This has to be be taken into consideration in breeding cotton varieties for resistance against Fusarium, at least by frequent testing of such varieties in the presence of the nematode P. sudanensis. Such a scheme is already under way (Yassin, 1974a).

Root-knot nematodes in tomato

Species and distribution. Root-knot nematodes are among the most important tropical parasites. These are widely occurring in river silt along the Nile bank and also in light alluvial soils, such as in western and southern Sudan, but not under the Gezira heavy clay. They can infest many crop and weed plants but those severely affected are vegetables and tobacco. A total of five species have been identified thus far (Decker, Yassin and El-Amin, 1979) but the most common are Meloidogyne arenaria, M. incognita and M. javanica. The most economically important are, however, the last two (Yassin, 1974b). While M. javanica can inflict heavy damage, especially in tomato and tobacco, in the northern sector, M. incognita is more prevalent in the south, both on tomato and eggplant (Yassin, 1986).

Symptoms. The first indication of infested plants above ground level is a manifestation of generalized stunting, poor growth and yellow foliage. When such affected plants are pulled out, diagnostic symptoms of galled growth along the roots can easily be detected. This typically occurs in the form of conspicuous large knots, and hence their name, the root-knot nematodes. Furthermore, by tearing open the knots, typical pear-shaped females of the nematode can be easily seen either with the bare eye or with a hand lens. They occur in the form of tiny round structures similar to white sand particles.

Economic importance. It is difficult to assess damage resulting from root-knot invasion under the existing system of peasant farming along the Nile bank. On the other hand, up to 70 to 100 percent of the tobacco and tomato plants in pilot farms around Zalingel could be completely devastated by M. javanica. Likewise, in southern Sudan, e.g. around the canning factory in Wau district, M. incognita is a limiting factor in the production of vegetables to supply the factory. In fact it was responsible for the failure of pilot experiments in the locality.

Pathogenic capabilities. All species are polyphagous. Each infective female can produce an average of 500 eggs. These can persist in the soil for years before hatching and the liberated juveniles invade host-plant roots. Furthermore, farm animals fed on infested plants often excrete eggs in a viable form. Species of Meloidogyne are known to exist in many pathogenic forms or biotypes. There is a strong indication of the presence of such biotypes under Sudan conditions, at least as regards M. incognita in tomato (Table 23): both races 1 and 2 of this species have been identified recently.

Possible control. The majority of investigations were undertaken on M. javanica in tomato as it is the most important pest in this very popular and widely grown vegetable crop. The main methods for control are:

· cultivation of tomato on heavy clay: this is the most practicable means of control whenever possible;

· use of resistant tomato lines: extensive breeding work has been undertaken in tomato against root-knot nematodes in many countries throughout the world, e.g. United States, France, Italy and the Netherlands. All of the 11 imported cultivars tested by the author at the GRS were found to be highly resistant to the local race of M. javanica, but resistance of many of them broke down after two to three seasons (Table 23); perhaps due to the occurrence of more than one species in the locality, or else due to the presence of physiological races or biotypes (Yassin, 1978). Work is in progress to screen other cultivars, e.g. from India and the United States;

TABLE 23
Performance of various tomato varieties towards the local race of Meloidogyne javanica (Wad Medani)

Root-knot index
VFN-8 (United States)	0	0	0
VFN-Bush (United States)	0	1	2
Motabo (France)	0	0	3
Rossol (France)	0	0	4
Piersol (France)	0	0	5
MON-144 (United States)	-	-	5
Romano NR (Netherlands)	-	-	5
Ronita (Italy)	0	0	6
Marsol (France)	0	0	6
68N-144 (United States)	-	0	71
Anahu (United States)	0	-	-
Local (Gezira)	91	71	-

Note: The figures refer to mean root-knot index: 0 = no infestation; 1-3, 4-6 and 7-9, mild, moderate and severe infestations, respectively.
- = not tested.
¹ Root function largely impaired, often wilted plants.

· crop rotation: this is very difficult to devise because the nematodes are polyphagous. However, both Barakat cotton and Ashford groundnut were found to exhibit absolute immunity towards a population of M. javanica from central Sudan (Table 24);

· chemical control: several nematicides were found very effective in increasing tomato fruit yield and reducing M. javanica infestation. This was according to tests undertaken by the author at a site at Wad Medani river bank during several seasons (Table 25) using a small fumigun for liquid formulations. Nevertheless, such chemicals are expensive and rather hazardous to use under the country's existing peasant farming system;

· cultural practices: deep ploughing, dry fallow, flooding of soil and organic amendments can be useful.

TABLE 24
Greenhouse experiment: host range of Meloidogyne javanica¹ from Region No. 1, central Sudan, using crops of economic importance and major weed species, in the Gezira locality, 1979/80

Plant species	Infestation level (R.I.)
Crop plant
Arachis hypogaea L. (peanut, cv. M.H. 383)
Gossypium barbadense L. (cotton, cv. Barakat)	0 (immune)
Allium cepa L. (onion, cv. Nasie)
Capsicum annuum L. (green pepper, cv. cal. wonder)
Cajanus cajan L. (pigeon pea)
Glycine max L. (soybean, cv. Semes)
Glycine max L. (soybean, cv. Williams)
Oryza sativa L. (rice, cv. IR 2053-206-1-3-5)
Pennisetum typhoideum Strap (finger millet)	1-3 (moderately susceptible)
Cucurbita maxima Duch. (vegetable marrow)
Cucurbita pepo L. (squash)
Cucumus sativus L. (cucumber)
Corchillus vulgaris Schral (watermelon)
Corchorus olitorius L. (Jew's mallow)
Lablab vulgaris L. (lubia bean)
Lycopersicon esculentum Mill. (tomato, cv. Pearson)
Lycopersicon esculentum Mill. (tomato, money maker)
Lycopersicon esculentum Mill. (tomato, strain B)
Nicotiana tabacum L. (tobacco NC-95)
Phaseolus vulgaris L. (haricot bean)
Portulaca oleraceae L. (purslane)
Hibiscus esculentus L. (okra)
Solanum melongena L. (eggplant)
Sorghum vulgare Pers. (sorghum millet, cv. Dabar)
Sorghum vulgare (sorghum millet, cv. Feterita)
Triticum vulgare H.C. (wheat, cv. Giza 155)
Triticum vulgare H.C. (wheat, cv. Mexicani)	4-5 (highly susceptible)
Weed
Acalypha indica L.
Datura metal L.
Phyllanthus niruri L.
Abutilon gluacum Webb.
Sida alba L.
Cynodon dactylon L. (Bermuda grass)
Cyperus rotundus L. (sedge grass)
Brachiaria sp. (Trin) Griseb.
Dicanthium annulatum Forsk.
Ischaemum afrum Jameel.
Eragrostis sp. (Jacq.) Nees.
Echinochloa cotounm L.
Sorghum sudanense Piper (Sudan grass)
Heliotropium sudanicum Andr.
Corchorus trilocularis L. (wild Jew's mallow)	1-3 (moderately susceptible)
Solarium dubium Fresen.
Ipomoea kordofana Choisy.
Merremia emarginata Burm.
Ocimum basilicum L.
Rhynchosia memnonia (Del) D.C.
Hibiscus sp. L. (wild okra)
Phaseolus trilobus L. (phillipesara)
Sonchus cornutus Hochst.
Calotropis procera Ait.	4-5 (highly susceptible)

Notes: The figures refer to mean and range of root-knot rating as 0-5; where 0 = no infestation, 1-3 = mild to moderate, and 4-5 = heavy infestation. Unless otherwise stated, the plant cultivar is of local source.

¹ Meloidogyne javanica was originally isolated from a mixture of M. javanica and M. incognita from root samples at a site at Region No. 1, central Sudan, during the season 1978/79.

TABLE 25
Effect of selected nematicides at standard dosage rates against the local race of Meloidogyne javanica from the Gezira on the local variety of tomato

	Treatments	Mean plant weight (kg)	Mean plant growth size (rad × ht) (cm)	Root-galling index
1970-71	Terracur	0.663	25×75	4.42
	Methomyl 5% G	0.412	27×75	2.52
	DBCP	0.512	21×68	6.31
	Dazomet	0.392	23×66	5.61
	Thionazin	0.22	24×69	6.9
	Methomyl 90% wp	0.1	25×66	7.5
	Control	0.23	21×62	7.9
	SE	0.089
1970-71 (average of two plots)	Metam-sodium	0.692	21×25	3.02
	DD	0.601	19×44	2.52
	Terracur	0.601	21×53	3.02
	DBCP	0.571	18×47	4.02
	Oxamyl	0.672	18×48	5.6
	Methomyl 5% G	0.652	19×51	5.01
	Prophos	0.60	18×45	5.01
	Control	0.32	18×47	6.0
	SE	0.074
1972-73	Metam-sodium	0.333	22×562	1.02
	Prophos	0.112	15×382	1.52
	DBCP	0.152	11×31	2.51
	DD	0.091	13×352	2.51
	Methomyl 5% G	0.082	8×25	2.01
	Oxamyl	0.09	14×341	2.8
	Terracur	0.06	12×32	2.8
	Control	0.04	9×27	2.8
	SE	0.028

¹ Probability at 0.05.
² Probability at 0.01.
³ Probability at 0.001.

Dagger nematodes in citrus and mango

The most important of these is Xiphinema basin, with a distinct long needle-like stylet. It was isolated from around the roots of diseased citrus and mango trees grown at a site at Wad Medani and at the GRS in numbers of up to 200 or more nematodes per 200 g soil. Distinctly stunted roots were associated with high densities of the nematode in the rhizosphere of such diseased plants. The stunted root systems could also be reproduced in potted seedlings grown in sterilized soil infested with X. basin (Yassin, 1974c). The majority of other species were associated with the roots of orchard trees. An exception was X. simillimum n. sp. Loof and Yassin, 1970, which was associated with the roots of cotton plants at a site at the GRS (Plot 4).

Needle nematodes in cotton and other field crops

Needle nematodes in the genus Longidorus are closely related to dagger nematodes. Ecologically, however, they are different from dagger nematodes in that they often occur in association with the roots of field crops, e.g. cotton, mint, Jew's mallow (Decker et al., 1979). The damage they can inflict on the roots is also very similar to that resulting from dagger nematode attack (Yassin, 1974c).

The citrus nematode

The citrus nematode, Tylenchulus semipenetrans, is a well-known universal pest of citrus orchards often resulting in slow decline and gummosis. Because there is no organized citrus cultivation throughout the Sudan as yet, the exact status of this nematode as a pest of citrus is difficult to determine. However, it has been isolated from within the roots of many diseased citrus trees with distinct symptoms of dieback and gummosis in many localities throughout the Sudan. Distinct symptoms of necrotic and irregular roots were often associated with infestations. At the GRS, for example, up to over 400 infective larvae of the nematode per gram of soil were recovered from the rhizosphere of infested roots.

Other nematode species

Among these are the lance, the stunt and the helical nematodes.

Lance nematodes. Several species of these, including Hoplolaimus columbus, H. pararobustus and H. seinhorsti, were found associated with the rhizosphere regions of many crop plants with decline symptoms; e.g. various citrus species, sugar cane and banana. They occurred in numbers of up to 100 or more nematodes per 200 g soil, especially in association with citrus and banana roots.

Stunt nematodes. Species within the genus Tylenchorhynchus, e.g. T. brevilineatus, T. martini and T. mashhoodi, were found especially in association with roots of stunted sugar cane at sites at Sennar, Guneid and the GRS. They often occur in numbers of up to 100 or more nematodes per 200 g rhizosphere soil.

Helical nematodes. Helicotylenchus spp. occurred in association with roots of diseased onion plants at El Ban Gedid in western Sudan, showing yellow foliage, poor bulb development and general stunted growth. They were isolated from the rhizosphere of such diseased plants in numbers of more than 200 nematodes per 200 g soil. Furthermore, typical symptoms of such diseased plants could be reproduced in potted onion seedlings infested with the nematode under greenhouse conditions at the GRS.

Major achievements

These might be summarized as follows:

· Isolation of over 70 species of plant-parasitic nematodes in association with the roots or rhizosphere of major crop plants throughout the country. Among the most important of these were: root-knot nematodes, Meloidogyne javanica, M. incognita, M. arenaria, M. africana and M. megadora; root-lesion nematodes Pratylenchus sudanensis, P. delattre, P. neglectus and P. zeae; burrowing nematode Radopholus similis; citrus nematode, Tylenchulus semipenetrans; lance, helical, kidney, needle and dagger nematodes, Helicotylenchus, Rotylenchulus, Longidorus and Xiphinema species, respectively.

· Defining the most important nematode species attacking the major crop plants, e.g. cotton, 12 species, most important of which is P. sudanensis; sorghum millet, 25 species; wheat, 12 species; groundnut, 11 species; pigeon pea, 10 species; horticultural, orchard and field crops, 55 species; and sugar cane, more than 10 species.

· Investigations into biological and ecological aspects of the major nematode species, e.g. root-lesion, dagger and needle nematodes.

· Discovery of at least six new species, e.g. Merlinius brevidens Siddiqi, 1970, Pratylenchus lobatus, P. sudanensis and Xiphinema simillimum Loof & Yassin, 1970, Pratylenchus sudanensis Decker, Yassin & El-Amin, 1975, P. kenanae Decker & El-Amin, 1978.

· Discovery of two races of M. incognita; races 1 and 2.

· Association of P. sudanensis with vascular wilt of cotton.

· Executing nematology consultancy, e.g. in the United Arab Emirates.

· Defining effective control measures against major species, e.g. M. javanica in vegetables (REF) and P. sudanensis in cotton.

Future priorities

General

· Qualified scientific and technical staff: to recruit at least three more qualified nematologists and two well-trained technicians.

· Nematology laboratory: to establish a well-equipped nematology laboratory.

· Association with local and international institutions: such association needs to be consolidated with local universities and centres (Gezira and Khartoum), as well as international institutions, e.g. in Egypt (Gezira, Alexandria), Europe and the United States. In fact, the association between the United States (University of North Carolina) and Sudanese nematologists can hardly be overlooked (see also Bibliography); mainly via the International Meloidogyne Project (IMP) and the Crop Nematode Research and Control Project (CNRCP). Close association with FAO is also strongly advocated.

Specific

· Continued investigations with pathogenic races, e.g. of M. incognita.

· Investigations of the possibility of the presence of more than one race of the new root-lesion nematode species, P. sudanensis, on the basis of variations of male/female ratios within different localities at the GRS.

· More investigations into pathogenic capabilities and economic threshold infestation levels.

· Extended nematology consultancies, both international and local.

· Control practices based on integrated crop management already initiated (see above).

Bibliography

Decker, H. & El-Amin, E.M. 1960. Observations on nematodes in the roots of plants in the Sudan. FAO Plant Prot. Bull., 8: 110-112.

Decker, H. & El-Amin, E.M. 1971. Weitere Untersuchungen über das Vorkommen pflanzenparasitärer Nematoden in der Demokratischen Republik Sudan. Wiss. Z. Univ. Rostock, 20, Math.-Nat. Reihe, H., 5/6: 245-253.

Decker, H. & El-Amin, E.M. 1978. Paratrophurus kenanae n. sp., (Nematoda:Trophurinae) from the Democratic Republic of Sudan. Aktuelle Probleme der Phytonematologie Rostock, p. 89-95.

Decker, H. & El-Amin, E.M. 1979a. Einige Beobanchtungen über den Einfluss ökologischer Faktoren auf das Vorkommen pflanzenparasitärer Nematoden. Trop. u. Subtrop. Landw. (Leipzig).

Decker, H. & El-Amin, E.M. 1979b. Observations on the occurrence of plant parasitic nematodes in the Tokar Delta.

Decker, H., El-Amin, E.M. & Yassin, A.M. 1978. Neue Ergebnisse zur Phytonematodenfauna der zentralen und östlichen Provinzen der D.R. Sudan. Wiss. Z. Wilh. Pieck Univ. Rostock.

Decker, H., Yassin, A.M. & El-Amin, E.M. 1975 a. Neue Untersuchungen über das Vorkommen pflanzenparasitärer Nematoden in der Demokratischen Republik Sudan. Wiss. Z. Univ. Rostock, 24: 875-884.

Decker, H., Yassin, A.M. & El-Amin, E.M. 1975b. Zur Gattung Paratrophurus arias, 1970 (Nematoda: Dolichodoridas). Der 1. Vortragstag, Aktuelle Probleme der Phytonematologie Rostock, 29: 89-102.

Decker, H., Yassin, A.M. & El-Amin, E.M. 1979. Plant nematology in the Sudan, a review article. An. Zool., 1/80: 1-20.

Decker, H., Yassin, A.M., El-Amin, E. M. & Nasr, I.A. 1977. Untersuchungsergebnisse über die Phytonematodenfauna der Demokratischen Republik Sudan. Wiss. Z. Wilh. Pieck-Univ. 26, Math. Nat. Reihe, H.E. 315-320.

Decker, H., Yassin, A.M. & El-Amin, E.M. 1984. Incidence of plant-parasitic nematodes on horticultural crops in the Sudan. Acta Hort., 143: 397-906.

El-Amin, E.M. & Siddiqi, M.R. 1970. Incidence of plant-parasitic nematodes in the northern Fung area, Sudan. FAO Plant Prot. Bull., 18:102-106.

Loof, P.A.A. & Yassin, A.M. 1970. Three species of plant-parasitic nematodes from the Sudan with a note on Xiphinema basin Siddiqi, 1959. Nematologica, 16:537-546.

Yassin, A.M. 1967a. Record of two Longidorus spp. from the Sudan. Plant Dis. Rep., 51.

Yassin, A.M. 1967b. A study of some factors influencing extraction of the needle nematode, Longidorus elongatus, from soil. Plant Dis. Rep., 51:1028-1030.

Yassin, A.M. 1968. Transmission of viruses by Longidorus elongatus. Nematologica, 14:419-428.

Yassin, A.M. 1969. Glasshouse and laboratory studies on the biology of the needle nematode, Longidorus elongatus. Nematologica, 15:169-178.

Yassin, A.M. 1972. A perspective of plant-parasitic nematodes in the Sudan. Sudan Agric. J., 7: 61-66.

Yassin, A.M. 1973. A root-lesion nematode parasitic to cotton in the Gezira. Cotton Grow. Rev., 50: 161-168.

Yassin, A.M. 1974a. Role of Pratylenchus sudanensis in the syndrome of cotton wilt with reference to its vertical distribution. Sudan Agric. J., 2: 48-52.

Yassin, A.M. 1974b. Root-knot nematodes in the Sudan and their chemical control. Nematol. Medit., 1: 103-112.

Yassin, A.M. 1974c. A note on Longidorus and Xiphinema species from the Sudan. Nematol. Medit., 2: 141-147.

Yassin, A.M. 1978a. Root-knot nematodes. Paper presented at the International Meloidogyne Project Symposium, 4 February, Cairo.

Yassin, A.M. 1978b. Problems of plant-parasitic nematodes in the Sudan. Paper presented at the Plant Protection Symposium, 6-8 February, Khartoum.

Yassin, A.M. 1978c. A perspective of crop protection problems of vegetable production in the Sudan. Paper presented at the Ibadan Conference, April 1978.

Yassin, A.M. 1979. Root-knot nematodes in the Sudan. Proc. 2nd Res. Plan. Conf., Athens.

Yassin, A.M. 1986. Nematode parasites of crop plants in the Sudan. Tech. Bull., 4 (New Series), ARC.

Yassin, A.M. 1988a. Nematode pests of cereal legumes and fodder crops in the Sudan. Proc. Symposium, Cyprus.

Yassin, A.M. 1988b. Diseases of tomato and pepper in the Sudan and their control. Proc. Conf. on Tomato and Pepper Production, Taiwan, Province of China.

Yassin, A.M. 1988c. Nematode problems of cotton. Proc. IMP Symposium, Wad Medani, the Sudan.

Yassin, A.M. &Ahmed, M.S. 1970. Guneid Annual Report for growing, season 1969/70.

Yassin, A.M. & Mohammad, Z.E. 1980. Biology and chemical control of root-lesion nematode, Pratylenchus. Z. Ange. Zool, 15: 225-231.

Yassin, A.M., Loof, P.A.A. & Oostenbrink, H. 1970. Plant-parasitic nematodes in the Sudan. Nematologica, 16: 567-571.

Pioneer nematologists in the Sudan

E.M. El-Amin

B.Sc. in Agriculture, Cairo, 1956
Ph.D. in Crop Protection, Rostock, 1961
Career: Entomologist/nematologist
Present status: Research Professor (1976) and Director of Finance and
Administration
Address: Agricultural Research Cooperation (ARC), Box 126, Wad
Medani, the Sudan

A.M. Yassin

B.Sc. in Agriculture, Khartoum, 1959
M.Sc. in Plant Pathology, St Andrews (United Kingdom), 1965
Career: Pathologist/nematologist
Present status: Research Professor (1975) and Director of Training and
Publications
Address: Agricultural Research Cooperation, Box 126, Wad Medani, the
Sudan