Part II

Contents - Previous - Next

Chapter 8: Algeria
Chapter 9: Cyprus
Chapter 10: Egypt
Chapter 11: The islamic republic of Iran
Chapter 12: lraq
Chapter 13: Jordan
Chapter 14: The Libyan Arab Jamahiriya
Chapter 15: Morocco
Chapter 16: Oman
Chapter 17: Pakistan
Chapter 18: Saudi Arabia
Chapter 19: Somalia
Chapter 20: The Sudan
Chapter 21: The Syrian Arab republic
Chapter 22: Tunisia
Chapter 23: Turkey
Chapter 24: The United Arab Emirates
Chapter 25: Yemen

Chapter 8: Algeria

Citriculture in Algeria
Virus and virus-like diseases
Other disease problems
Recommendations
Bibliography

Citrus are among the most popular fruits grown in Algeria. They are of an excellent quality and are greatly appreciated for their nutritional and refreshment value. Furthermore, citrus production represents an important agricultural and economic activity in the country. Oranges and mandarins are traditionally produced for local consumption and also for export.

Total citrus output in Algeria has been declining in the last decade owing to a number of unfavourable factors. Information available indicates yearly total citrus production as shown in Table 24.

Severe droughts reducing the water available for irrigation, unsuitable cultural practices, ageing of existing citrus orchards and increasing problems with pests and diseases, are among the more important factors accounting for lower yields. Old orchards are severely affected by virus diseases and this situation will extend to all existing citrus trees in time.

Productivity of citrus orchards has been fairly low. Considering an average production level of 400 000 to 500 000 tonnes per year in the last decades and the total area dedicated to citrus (somewhere around 40 000 ha), production is about 10 tonnes per hectare. This is a fairly modest output since in many other citrus-growing areas of the world the average annual yield of adult orchards ranges from 30 to 35 tonnes or more per hectare.

Fruit consumption is rapidly increasing in Algeria as a result of the growth in population. However, no matter how much modern orchard management technology is introduced in existing plantations, no great increase in productivity should be expected. Trees are old and diseased. New plantings using superior, virus-free nursery trees are necessary to increase citrus output.

In 1979, the Government of Algeria launched a programme for the propagation and maintenance of healthy citrus materials in the country. It is expected that new trees planted since then will produce virus-free, vigorous and productive citrus orchards. These are mainly nucellar clones of commercial varieties introduced from abroad. Their performance under the local environmental conditions in Algeria is now being studied.

Citriculture in Algeria

Citrus orchards in Algeria are distributed along the coastal area, at altitudes below 400 m, where the climate is mild and frosts rare. The total surface area dedicated to citrus growing is estimated at around 43 000 ha, of which 38 000 ha are used for fruit-bearing trees. The citrus orchards are concentrated in five main areas or wilaya, namely Blida (in the Valley of Mitidja), Mascara, Chlef, Mostaganem and Annaba, which together represent about 80 percent of the total surface of citrus.

TABLE 24 Citrus production in Algeria

Distribution of citrus production is shown in Table 25.

Citrus fruits have been grown commercially in Algeria, both for local consumption and for export since the beginning of the century. The excellent seedless Clementine mandarin, which originated in the garden of an orphanage near Oran, was for many years a major variety grown in the country. However, severe cold weather in 1925 caused extensive damage to citrus orchards and by 1940 oranges had emerged as the main citrus species. Plantings increased rapidly after the Second World War, as did fruit output and exports. However, during the war of independence and the following years, the Algerian economy went through difficult times. By 1974, total citrus exports were 4 000 tonnes, dropping to 34 000 tonnes in 1979. Exports had ceased by 1980, but were restarted in 1984. Ageing of trees, increasing virus disease and pest problems and growing internal consumption are among the major factors contributing to the decline in citrus exports.

Many citrus varieties are grown in Algeria, including oranges (49.1 percent), mandarins (35.4 percent), lemons (2 percent), grapefruits (pomelos) (0.5 percent) and other mixed varieties (13 percent). Among oranges, early ripening varieties account for 36.7 percent of production, mid-season, 50.4 percent and late ripening, 12.9 percent. Among mandarins, the Clementine accounts for 81.8 percent of production, but, of that, over half is the Monreal seedy variety. Lemons are grown only in small orchards and production is considered insufficient to meet local demand, especially during summer months. Grapefruits are not much favoured by local people and the industry only considers them at the end of the season. It is estimated that 20 000 tonnes of citrus fruits are processed every year for the production of juice and preserves. Information available for citrus varieties and area planted is shown in Table 26.

TABLE 25 Distribution of citrus production in Algeria

Source: INAF.

Blossoming occurs in April-May and the harvesting season starts with Clementine mandarins in November, continuing until June. Lemons are produced throughout the year. Production per tree is low - an average of 8 to 17 tonnes per hectare according to age, availability of water for irrigation and general cultural practices. Generally, citrus orchards require irrigation every 15 days during summer months, but shortage of water during 1984/85 forced growers to reduce irrigation to three or four times only during the eight dry-months of the year. As a result, fruit production decreased considerably in that period.

TABLE 26 Area covered by citrus varieties in Algeria

Source: Alloum and Bencheik, 1983.

Soil in the areas dedicated to citrus plantings is normally heavy, with a pH ranging from 7.0 to 8.0 and drainage is required during the rainy season. Cleaning the channel system is a constant problem.

Rootstock used in the orchards is nearly always sour orange, Citrus aurantium L. (about 98.4 percent of the total citrus area). Other rootstocks used in a very limited number are: Troyer citrange (0.7 percent), trifoliate orange (0.8 percent) and Cleopatra mandarin (0.1 percent). At present there are 11 official nurseries in the country plus about 50 small private nurseries, concentrated in the Mitidja plain.

A large government programme of reinvigoration of the citrus industry is under way. About 130 000 nursery trees were introduced recently from abroad and distributed to all citrus areas. They were imported (according to available information) from the Bertolami nurseries in Sicily, Italy. Strong support is being given to the production of nursery trees and the planting of new citrus orchards to ensure sufficient citrus output in the near future to cover both domestic requirements and exports.

Virus and virus-like diseases

Destructive diseases caused by virus and virus-like pathogens have been known to occur in citrus trees in Algeria for more than 40 years (Brichet, 1944; Lamour, 1950; Blondel, 1953; Amizet, 1954; Frezal, 1957; Chapot, 1959). A number of attempts have been made to prevent further spread of diseases into new orchards. However, infectious diseases continue to occur in the plantings and are a major factor restraining high-yield crops.

Virus and virus-like diseases reported in citrus trees in Algeria include scaly bark psorosis, concave gum-blind pocket, cachexia-xyloporosis, exocortis, cristacortis, impietratura and stubborn. Most of the disorders are widespread in all citrus areas of the Mediterranean, as indicated by Bové in 1966. Since most citrus propagative material used in Algeria was imported from Mediterranean countries and the United States of America before virus-free budwood was available, it may be assumed that the pathogens responsible for those diseases were inadvertently introduced at the same time.

Salibe, during his visit to Algeria, observed symptoms of virus and virus-like diseases in many trees of. several orchards. He also learned about the recent introduction of healthy nucellar lines of commercial varieties that will serve as a source of budwood for nursery workers and growers.

Scaly bark (psorosis A), concave gum-blind pocket and infectious variegation

Scaly bark psorosis, concave gum-blind pocket and infectious variegation have a worldwide distribution and are found in most orchards of practically all Mediterranean countries. Scaly bark (psorosis A) is a slow-acting disease that may take several years to produce bark scaling symptoms. This disease-and concave gum-blind pocket, as well as cristacortis and impietratura, induce typical vein flecking and/or oak-leaf patterns on young leaves during spring and autumn growth flushes (Klotz, 1973). Scaly bark psorosis causes decline of trees independent of the rootstock and is one of the most damaging citrus virus diseases (Wallace, 1978).

According to the reports of Brichet (1944), Frezal (1949), Lamour (1950), Amizet (1954) and others, these diseases have been found affecting citrus trees in Algeria. Disease is certainly a major factor constraining high production in the older orchards of the country. Salibe observed many trees exhibiting typical bark scaling psorosis and some trunk malformations and flat branches suggestive of concave gum, but no blind pocket. Diseased trees were always orange varieties over 15 years old. In one orchard of Washington navel orange trees located in Boufarik, at least half of the trees were declining because of severe psorosis. Other orange varieties affected were Hamlin, Peretta, Blood and some other, less common, types indicated to be of Spanish origin. Oak-leaf pattern was observed in the leaves of a few Vernia orange and Clementine mandarin trees.

Severe symptoms of a scaly bark psorosis were observed by Bové in 1966 on Valencia late sweet orange at Maison Carré, on Thompson navel at Boufarik, and on Clementine at Ferme Blanche (Oued Fodda, Orleanville region, Algeria). Very severe concave gum-blind pocket concavities affected Samson tangelo 2908 at Boufarik. Fruit and leaf symptoms of infectious variegation-crinkly leaf were seen at Boufarik and Oran on Jaffa sweet orange trees on sour orange rootstock, and at Boufarik on Sanguinelli sweet orange top-grafted on Sampson tangelo on sour orange rootstock. The tangelo sandwich showed symptoms of concave gum-blind pocket. indexing with proper indicator test plants is essential to determine the extent of psorosis spread in the commercial orchards, but it is possible that only a few trees will be found free from this debilitating parasite.

Virus-free budwood is being used for the production of nursery plants to try and exclude psorosis from new plantings. Nucellar clones of most varieties are now available, many produced in the country itself and others imported from Corsica. Attention should be given to seed transmission of psorosis virus, found to occur in trifoliate orange and some of its hybrids, such as Troyer and Carrizo citranges.

Cachexia-xyloporosis

Cachexia-xyloporosis is a disease widespread in the mandarin trees of the Mediterranean basin, and the orchards of Algeria are no exception. It was reported to be affecting mandarin trees (Frezal, 1957) and Wekiwa tangelo trees (Amizet, 1959, 1962). In 1966, Bové observed strong symptoms of cachexia on Wekiwa tangelo, Dancy tangerine and Australia mandarin trees at Ferme Blanche. Salibe observed that typical gum pockets, conoid pits and wood pinholing of cachexia-xyloporosis in many Clementine mandarin trees in orchards of the Mitidja. Symptoms ranged from mild to very severe, but not all trees in an orchard were affected, suggesting that more than one source of budwood was used in the formation of the trees. Since cachexia-xyloporosis viroid is perpetuated by the use of infected budwood and no insect vector is known, it can therefore be excluded from new plantings by using only healthy propagative material.

Stubborn

Chapot reported the prevalence of stubborn disease in the citrus orchards of Algeria in 1959. Salibe, in his visits to the citrus orchards of the Mitidja, observed many abnormal and declining trees but none displaying the typical stubborn syndrome.

During his recent tour to citrus areas of Mediterranean countries Salibe found trees exhibiting severe stubborn disease in Cyprus, Egypt, Jordan and the Syrian Arab Republic, but not in Algeria, the Libyan Arab Jamahiriya or Tunisia. An intensive indexing programme is needed to reveal the exact situation of stubborn in these last three countries.

Tristeza

Tristeza disease represents a tremendous threat to the citrus industry of the Mediterranean basin, one of the last areas free from the virus where mainly intolerant scion-rootstock combinations are used. Spain is the first Mediterranean country where extensive spread of tristeza has occurred, more exactly in the Alcira-Carcagente-Corbera district of Valencia, where it started in 1957. More recently, tristeza was discovered in Israel, whereupon an identification and suppression programme was immediately launched (Raccah et al, 1976; Bar-Joseph et al., 1980), but has not met with success.

Apparently, all early cases of tristeza disease found in the citrus areas of the Mediterranean basin can be traced back to the introduction of infected budwood from abroad. All countries which have introduced the Meyer lemon variety have also introduced tristeza (Bové, 1966). Other varieties imported from Australia, South Africa, Japan and the United States of America have also been reported to have introduced tristeza into Mediterranean countries.

In 1957, Frezal reported that a number of Meyer lemon trees in Algeria were carrying tristeza virus. No natural propagation of the disease was observed at the time, except by bud propagation. During his visit to Algeria, Salibe found indications that tristeza virus is present in some citrus trees in the Mitidja area. The trees affected were two Marsh seedless grapefruits and two Salustiana oranges budded on sour orange, about 22 or 23 years old. The Marsh seedless grapefruit displayed a foliage of normal green colour, but with an overgrowth of the scion-trunk and typical honeycombing below bud-union. The Salustiana orange trees were stunted, with twig-dieback, trunk overgrowth above bud-union and honeycombing in the sour orange trunk.

During a visit to a large, state-owned citrus orchard in Massouma, about 40 orange trees, probably of Verna Peret (Pereta) variety, were encountered showing dieback, leaves with yellow veins and wilting and some trunk honeycombing. In the same orchard, about 500 m away, another group of about ten declining trees of Clementine mandarin and Pereta orange (interplanted) budded on sour orange rootstock was observed. All the trees were over 30 years old, some were dying and a few were dead. The cause of the abnormality was not determined, but it was suggested that ELISA (used for tristeza indexing) should used to index the trees. The INVP virus laboratory in Algiers is well equipped to perform the ELISA test, which can determine within 24 hours whether the virus is present in leaf samples from suspected trees.

At the Virus Indexing Service of the INAF Research Station at Boufarik, the consultant was shown a number of Mexican lime indicator plants inoculated with Cap Nartje orange introduced from South Africa and exhibiting severe stem pitting induced by tristeza virus. No vein corking or vein yellowing had occurred, but symptoms of stem pitting were indicative of a fairly severe form of the virus. A programme for identification and suppression of tristeza virus in Algeria is urgently needed to prevent the possible spread of the problem in the citrus orchards of the country.

Exocortis

Trifoliate orange, used on a small scale as rootstock for citrus in Algeria, is intolerant to exocortis and some trees with Clementine mandarin scions were found to show some symptoms resembling exocortis disease. On the basis of evidence obtained in most citrus-growing areas of the world, exocortis would appear to be the most widely distributed intracellular pathogen of citrus and it is probably infecting many trees in Algeria, reducing vigour and productivity.

At the Boufarik Citrus Experiment Station, Poncirus trifoliata was used as a rootstock in addition to sour orange. Severe symptoms of exocortis bark scaling were observed by Bové in 1966 on P. trifoliata rootstocks carrying Clementine scions (Fig. 316). These Clementine trees were severely stunted (Fig. 317, middle row of trees). The trees in one row were sidegrafted to sour orange seedlings (Fig. 318), and they recovered well (Fig. 317, row of trees on the right). Another interesting case of exocortis was observed by Bové at Ferme Blanche on P. trifoliata trees grafted on sour orange rootstock. This is an unusual combination since most often P. trifoliata occurs as a seedling tree or a rootstock, and almost always exocortis bark scaling is seen on P. trifoliata used as rootstock. Here severe exocortis symptoms were seen when it was used as scion (Figs 320 and 321). Some of the P. trifoliata scions were free of exocortis (Fig. 319), suggesting that the symptomatic trees became infected through mechanical transmission of the exocortis viroid by pruning tools.

Indexing for exocortis is necessary to determine the distribution of the viroid in old plantations and to assure freedom from the pathogen in the selected nucellar mother trees.

Impietratura

Salibe, during his visit to citrus orchards in the Mitidja area, observed no fruit showing signs of impietratura. However, the occurrence of the disease in Algeria was reported by Catara and Scaramuzzi in 1975. It is well known that impietratura-affected trees do not show symptoms regularly each year, which probably explains why Salibe could see no impietratura symptoms.

Cristacortis

Cristacortis disease is present in Algeria, but the number of infected trees in the orchards is not known. Hamlin orange trees exhibiting very conspicuous symptoms of cristacortis were shown to Salibe in the Mitidja area. Bové and Vogel (1975) have already described the presence of cristacortis disease in citrus trees in Algeria.

Gummy bark of sweet orange

Salibe was informed by local scientists that gummy bark disease is probably affecting citrus trees in Algeria, but no survey had been conducted to confirm the presence and the extent of the problem. No diseased trees were found during the consultant's visit.

Rumple

No rumple has been found in the lemon orchards of Algeria. However, local scientists should be aware of the problem and special attention must be paid when introducing lemon budwood from abroad. Careful selection of lemon budwood from disease-free trees is recommended to avoid the spread of the problem in any new orchards in Algeria.

Bud-union crease

Bud-union crease is not a problem in Algeria, but may become a serious setback to the industry should incompatible scion-rootstock combinations be recommended in commercial plantings.

Other disease problems

Phytophthora root rot, anthracnose and mal secco disease are among problems of minor importance affecting citrus orchards in Algeria.

Autumn leaf drop, a serious problem affecting citrus in the Libyan Arab Jamahiriya, Morocco and Tunisia, may also be occurring in certain areas of Algeria. The syndrome is characterized by abnormal leaf drop during the late autumn and winter months. It probably results from a physiological disorder, caused by cold in the mornings (7-8°C) that acts as a form of localized frost. Damaged trees produce low yields.

None of the following virus or virus-like diseases was observed during Salibe's visits to citrus orchards: satsuma dwarf, vein enation-woody gall, citrus tatterleaf, gum pocket, leaf curl, leprosis, yellow vein, citrus blight and citrus decline. Local plant pathologists should, however, be aware of symptoms of these and other undesirable diseases in order to be able to recognize them and promptly eradicate any tree suspected of harbouring their pathogens. Good descriptions of disease problems have been given by Childs et al., (1968), Klotz (1973), Bové and Vogel (1975) and Wallace (1978).

Recommendations

The cultivation of citrus fruits is part of the traditional agriculture of Algeria and it constitutes a large proportion of the country's wealth. Fruit output has decreased in recent years owing to a number of unfavourable conditions. Algeria has the scientific knowledge and the human resources to develop an intensive programme to reverse this situation and to move towards higher yields of citrus. A number of appropriate measures have already been taken and a well-planned scheme for the production of healthy propagative material is being conducted by local scientists. Action has also been taken towards the introduction of sanitary measures to prevent future problems with virus and virus-like diseases. To assist the Algerian Government in its efforts towards an efficient programme of citrus yield improvement and plant protection, a number of recommendations are listed for immediate action.

• The programme of production, conservation, multiplication and control of healthy propagative material of citrus plants should be continued and should receive additional human and financial support in order to realize its aims fully.
• A fully equipped laboratory for shoot-tip grafting should be established at INAF to provide local scientists with the necessary tools for freeing superior local citrus varieties from intracellular pathogens.
• The citrus research programme should be expanded to include comparative trials of healthy, old-line and nucellar clones of commercial citrus varieties, before release of propagative materials to growers.
• New rootstock trials should be established, and should include the many selections of trifoliate orange and new hybrids available in various citrus areas of the world.
• Appropriate installations should be provided for a complete virus indexing programme to ensure freedom from intracellular pathogens of all mother trees producing budwood for nursery workers and growers.
• The programme of diversification of the use of sour orange rootstock should be continued as a safeguard against destruction by tristeza.
• A nationwide identification and suppression programme should be conducted, using modern virus identification technology (the ELISA test) to locate and eradicate all possible sources of tristeza virus from citrus orchards.
• Quarantine regulations should be strictly enforced to prohibit any plant importation into the country by private growers. At the same time, a quarantine station should be established to permit the safe introduction of new citrus varieties and root stocks.
• A programme should be established to allow Algerian citrus growers to visit countries with more advanced citrus industries, such as Brazil, Spain and Italy. Such a programme would give growers the opportunity to learn in situ about modern techniques in the various aspects of citrus production, and would permit an exchange of views with other citrus growers.
• An intensive extension programme for the transference of modern orchard management techniques to citrus growers should be planned and developed. It should include technical meetings, visits, seminars and distribution of technical bulletins prepared by local specialists.
• Opportunity should be given for personnel to train abroad in the identification and indexing of virus and virus-like diseases of citrus, as well as to learn about advances in citrus improvement and protection methods.
• Algeria, in association with all Mediterranean countries, should make a concerted effort to prevent the introduction and diffusion of new pathogens, particularly those of greening disease, tristeza-seedling yellows virus and citrus canker, into the region. In particular, it should be taken into consideration that massive destruction of all existing citrus orchards will occur should the greening bacterium and its efficient vectors invade the country.

Bibliography

Alloum, D. & Bencheik El Hocine, N. 1983. Situation générale de l'agrumiculture algérienne. Communication au Colloque de l'Agrumiculture Méditerranéenne (21-26 février). 12 pp.

Amizet, L. 1954. Contribution à l'étude des moyens pratiques de lutte contre certaines maladies virusiformes en Algérie. Fruits et Primeurs, 24(255): 165-168.

Amizet, L. 1959. Contribution to the study of xyloporosis in Algeria. In Citrus virus diseases, p. 125-128. Div. Agric. Sci., Univ. Calif.

Amizet, L. 1962. Contribution à l'étude de la xyloporose en Algérie. In Advances in horticultural sciences and their applications, p. 181 - 184. Oxford, Pergamon.

Bar-Joseph, M., Garnsey, S.M., Gonsalves, D. & Purcifull, D.E. 1980. Detection of citrus tristeza virus. 1. Enzyme-linked immunosorbent assay (ELISA) and SDS-immunodiffusion methods. In Proc. 8th Conf IOCV, p. 1-8. Riverside, Univ. Calif.

Blondel, L. 1953. Influence de la hauteur du point de greffe sur le comportement des agrumes greffés sur Poncirus trifoliata. Ann. Inst. Agric. Algérie, 7(8): 1-12.

Bové, J.M. 1966. Citrus virus diseases in the Mediterranean area. Report presented at the meeting on Phytiatry and Phytopharmacy, Marseilles (France), 1965, updated for the 4th Conf. IOCV. 44 pp. (mimeo)

Bové, J.M. 1985. Greening and stubborn: results and Perspectives. FAO Expert Consultation on Production, Maintenance and Distribution of Virus-free Fruit Tree Planting Material, Rome, FAO. 37 pp.

Bové, J.M. & Vogel, R. 1975. Description and illustration of virus and virus-like diseases of citrus: an IOCV project. Institut Français de Recherches Fruitières Outre-Mer. Paris, Editions SETCO.

Brichet, J. 1944. Une maladie redoutable qui se répand dans nos orangeraies: la psorose "scaly bark" des Américains. Fruits et Primeurs, 14(158): 228-230.

Catara, A. & Scaramuzzi, G. 1975. Impietratura. In J.M. Bové & R. Vogel, eds. Description and illustration of virus and virus-like diseases of citrus: an IOCV project. Institut Français de Recherches Fruitières Outre-Mer. Paris, Editions SETCO.

Chapot, H. 1959. First studies on stubborn diseases in citrus in some Mediterranean countries. In J.M. Wallace, ed. Virus diseases, p. 109-117. Riverside, Univ. Calif.

Chapot, H. 1970. Problèmes de la production des agrumes au Proche-Orient et en Afrique du Nord. FAO Report AT 287. 93 pp.

Childs, J.F.L., Bové, J.M., Calavan, E.C., Fraser, L.R., Knorr, L.C., Nour-Eldin, F., Salibe, A.A., Tanaka, S. & Weathers, L.G. eds. 1968. Indexing procedures for 15 virus diseases of citrus trees. Washington, DC, USDA/ARS Handbook 333.

Frezal, M. 1949. L'agrumiculture algérienne. Réglementation de contrôle de la psorose dans les plantations d'arbres étalons et les pépinières. Rev. Fr. Oranger, 19(22): 154.

Frezal, P. 1957. Sur la présence en Algérie de la tristeza et de la xyloporose de citrus. C.R. Acad. Agric. France, 43: 190-193.

Klotz, L.J. 1973. Color handbook of citrus diseases. Citrus Res. & Agric. Exp. Sta., Riverside, Univ. Calif. 122 pp.

Lamour, R. 1950. Viroses des agrumes en Afrique du Nord. Rev. Fr. Oranger, 20(220): 381-384.

Raccah, B., Loebenstein, G., Bar-Joseph, M. & Oren, Y. 1976. Transmission of tristeza by aphids prevalent on citrus and operation of the tristeza suppression programme in Israel. In Proc. 7th Conf IOCV, p. 47-49. Riverside, Univ. Calif.

Salibe, A.A. 1961. Contribuição ao estudo da doença exocorte dos citros. University of São Paulo, Brazil. 71 pp. (Thesis; mimeo)

Wallace, J.M. 1978. Virus and virus-like diseases. In The citrus industry, vol. IV, p. 67-184. Berkeley, Div. Agric. Sci., Univ. Calif.

Chapter 9: Cyprus

Citrus growing
Incidence of virus and virus-like diseases in citrus orchards
Bibliography

Citrus fruits, the "yellow gold" of Cyprus, and potatoes are by far the most important of the country's export crops. Citrus orchards occur throughout the coastal areas, enjoy a mild climate and produce high-quality fruit. Most of the fruit production, over 70 percent of all citrus, is exported in the form of fresh fruit to European markets. New plantings are being made in many areas of the island and an increase in production is likely in the near future.

Most young and old citrus orchards benefit from appropriate cultural practices and modern technology is being used in the pest control programmes. However, the establishment and management of a successful and highly productive citrus industry depend on a series of factors. One of these, which is frequently overlooked and is of paramount importance, is the sanitary status of the orchards.

Virus and virus-like diseases are known to cause severe yield losses, which occur even in the so-called tolerant scion-rootstock combinations. In some instances, these diseases can cause extensive tree losses and render large areas unsuitable for citrus growing.

Many infectious diseases, such as psorosis, exocortis, xyloporosis and impietratura, are known to occur in most Mediterranean citrus areas, including Cyprus. They can reduce productivity of trees by half. Although these diseases are of viral aetiology, natural vectors are not known. Consequently, their introduction into new orchards can be avoided by their detection in and eradication from mother tree collections, and by distributing only healthy stocks to growers.

Some other diseases are very difficult to control. Tristeza (of viral nature), stubborn (caused by the helical mycoplasma Spiroplasma citri), greening (caused by an intracellular bacterium) and blight (of unknown cause) are especially destructive to citrus trees. Tristeza, stubborn and greening have efficient air-borne vectors and thus a tremendous potential for rapid spread into new areas if not properly controlled.

Citrus growing

Cyprus is a large island, the third in size in the Mediterranean Sea, with an area of 9 251 km². Its maximum length is 225 km (east to west) and its maximum width is 97 km (north to south). The country enjoys a mild climate with relatively hot, dry summers and rainy winters. The agricultural sector is recognized as the backbone of the economy because of the importance of its exports and its employment of a high proportion of the population. The general aim of the government's agricultural policy has been to ensure the steady rise in the prosperity and income of the farming community (Louca, 1981).

Tree crops grown in Cyprus include olive, carob, vines, nuts, citrus and other fruits, which covered about 63 000 ha in 1981. The citrus plantations amount to about 10 percent of the total tree-crop area and are concentrated in the warm littoral regions of the island. Most orchards are small plantations, but a few cover areas as large as 600 ha. Many orchards have trees more than 30 or 40 years old, especially in the Nicosia, Famagusta and Limassol areas. In the Paphos area, citrus plantings are a new enterprise and trees are relatively young. The citrus species most commonly grown are grapefruit, sweet orange, lemon and mandarin. Marsh seedless is practically the only grapefruit variety grown.

Among oranges, Valencias and navels are extensively grown. Several lemon varieties are cultivated, including Lisbon and Eureka, as well as several local selections. Among mandarins, the most appreciated is Clementine. Other varieties grown include Shamouti orange, Willowleaf mandarin, Ortanique (Mandora) tangor and Minneola tangelo. Local citrus varieties include a lemon called Lapithos and a non-acid sweet orange known as Shekerika orange. Practically all citrus trees are grafted on sour orange rootstock and are therefore susceptible to tristeza disease.

For 1980 for the area under Greek-Cypriot control, Louca (1981) reported that the total area under citrus was about 5 400 ha, producing 6 300 tonnes, with a value of £C 8 268 000.

In 1981, this yield represented an increase of 15.7 percent over 1980 production. Exports were 85 900 tonnes, a 21.8 percent increase over the previous year. The main outlets for citrus exports were the countries of the European Economic Community which, in terms of value, accounted for 77.2 percent of total exports. Production and exports of citrus fruit in 1981 are shown by species in Table 27.

Exports thus reached £C 11 million in 1981, compared with £C 8.2 million in 1980. Citrus exports were expected to continue to increase in the near future.

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