More than 500 plants species are listed as host of whitefly which transmit at least 19 viral diseases. In Pakistan whitefly (Bemisia tabacci) is becoming increasingly important since the outbreak of cotton leaf curl virus in cotton crop. Based on virus transmission efficiency and biological characteristic of whitefly colonies reared at Plant virology Lab., NARC on cotton plants, it was suspected that perhaps more than one population of whitefly are present. This raised our interest in genetic variation existing among whitefly population. Above 30 random samples were taken from whitefly colony maintained on cotton. Genetic variation among these samples was observed using isozyme electrophoresis patterns of adult whiteflies. Differences in esterase banding patterns have been observed indicating that more than one populations exist.

Fungicides used commercially for control of cotton seedling diseases were evaluated under field conditions during a 3-yr period for their effects on the prevalence of the entomopathogenic fungus Neozygites fresenii (Nowakowski) Batko in the cotton aphid, Aphis gossypii Glover. The susceptibility of N. fresenii to the fungicides varied. Carboxin significantly reduced N. fresenii prevalence during the early season. Furthermore, A. gossypii population levels were significantly greater during the 1993 field test in plots treated with carboxin. In some cases etridiazole and metalaxyl also significantly reduced N. fresenii prevalence during the early season. Conversely, N. fresenii prevalence was generally equivalent to or greater in the fungicide-treated plots than in the control plots during the late season. Although numerous biotic and abiotic factors (that is, environmental or artificial or both) also influence fungal prevalence in field situations, this appears to be the 1st demonstration of reduced entomopathogenic fungal prevalence caused by the application of a granular fungicide at planting. Biological and cultural implications are discussed.

The enlargement of fields in which some horticultural plants are grown in Slovenia outdoors (cucumbers, tomatoes) and in the greenhouse (tomatoes, cucumbers, and to a smaller extent also peppers and eggplants) is accompanied by an increasing and quite regular occurrence of some diseases and pests, such as greenhouse white fly (Trialeurodes vaporariorum Westwood), two-spoted spider mite (Tetranychus urticae Koch.), cotton aphid (Aphis gossypii Glov.), green peach aphid (Myzus persicae Sulz.), thrips (Thrips tabaci Lind.), powdery mildew of cucumber (Erysiphe cichoriacearum DC., Sphaerotheca fuliginea /Schlecht./ Salm.), downy mildew of cucumber (Pseudoperonospora cubensis / Berk. et Curt. / Rost.), and some other pathogenic organisms. On the other hand, some indigenous beneficial species are also found on vegetables such as Aphidius matricariae Hal., Aphidoletes aphidimyza Rond., Chrysoperla carnea Steph. and one year also Encarsia formosa Gahan. These species must be protected with a selective application of pesticides. In many other countries they are already commercially used for the integrated production of horticultural crops. The study discusses up-to-date methods for integrated production and control of the above mentioned vegetables and the current situation in Slovenia.

The agriculture is the leading sector of the Sudanese economy. It consists of three subsectors: the irrigated, the mechanised rainfed and the traditional rainfed. The producers in the Sudan are facing unstable net income from agricultural production. This is attributed mainly to changes in climatic and environmental conditions as well as unstable agriculture policies. This study investigates the causes of fluctuations in output and prices of the major agricultural commodities being the main factros behind the low and the unstable net income of agricultural producers. The study uses linear regression to measure trends and the degree of instability of the major variables that affect agricultural crops grown in Sudan such as total cost of production, gross revenue, prices and yield. The findings of the study are as follows: -Changes in agricultural production are mainly due to fluctuations in productivity per feddan which is influenced not only by technology but also by environmental factors such as the amount and distribution of rainfall, pests and diseases. -Fluctuations in production, yield and area are more pronounced in traditional rainfed crops than in mechanised rainfed crops. -Producer prices of raw export crops (cotton and gum arabic) fluctuate more heavily than those of food crops (grain and oil seeds crops).

For twenty years, the development of biotechnology has given rise to great hopes and has stimulated considerable research effort throughout the world. Today, this effort is producing its first results in agriculture. Although still modest in comparison with the prospects originally envisaged, these achievements should be of interest to both developing and developed countries. No one can afford to ignore the major economic impact that the control and commercial exploitation of some biotechnological procedures could have. Taken in its widest sense, biotechnology encompasses any improvement that makes use of a biological process. Simple examples in agriculture and food processing are brewing and the processing of milk, which have for centuries made use of living organisms such as bacterial and moulds. Farmers, whose work has always been to improve and exploit natural processes, often against considerable odds, could be thought of as the first biotechnologists. Genetic engineering Scientists prefer a more restricted definition of biotechnology. Plant biotechnology can be defined as comprising a range of new methods which lead to varietal improvement, true reproduction and a very large number of individual plants which are exactly the same as the improved parent variety. Even with this more focused definition, there are a great many research and development programmes within the field of biotechnology. A study conducted in 1993 by IBS (Intermediary Biotechnology Service) of ISNAR (International Service for National Agricultural Research) listed 216 separate activities, of which 75% were devoted to plants and, of these, more than 40% were of direct interest to developing countries. By using molecular markers to study plant and animal genetic diversity and genetic engineering to modify genetic inheritance, new varieties can be created, which could not be achieved by natural means. Enriched by genes introduced through Bacillus thuringiensis, a plant can be made toxic to insect pests. The same technology can be used to make tobacco resistant to tobacco mosaic virus and to modify the composition of soya oil. In theory, the range of possibilities is limitless. Some research teams are devoting considerable resources to surprising projects such as creating varieties of banana, which when eaten will provide immunisation against hepatitis or cholera. Given the resources and skills required for genetic engineering, research programmes are led by strong teams, which are becoming increasingly international and collaborative. Some of the transgenic varieties which are of direct importance to many ACP countries now on trial under glass include cotton, rice and cassava. Open field trials of such varieties are not without potential risk. To date, only one variety of tomato and one of cotton, have been officially authorized for widespread cultivation in the United States. The ACP countries can often do little more than express an interest in the direction of international research. Nevertheless, it is important that they should not lose interest in genetic engineering because of the prospects for true reproduction of plant material, and it is this that will have the most impact on agricultural development. Professor Albert Sasson, Special Adviser to the Director General of UNESCO, believes that 'Africa is, without doubt, the region where biotechnology is least developed.' Even if this is true, ACP countries can take advantage of the many laboratory results obtained for temperate plants which are often applicable to many tropical plants. Overcoming nature's obstacles The purpose of cloning is to reproduce from one plant a great number of progeny which are genetically identical to the parent. This parent plant, a banana or a coffee variety for example, will have been chosen for particular performance characteristics that meet the needs of growers. Some plants, such as rice or cotton, are self-fertile and produce daughter plants that are practically identical to the mother plant in performance. Others require cross fertilization between male and female plants of the same species. This is the case with maize and the majority of the principal species of perennial plantation crops such as palm oil, robusta coffee, rubber or cocoa. Progeny of plants that have been cross fertilized may not ' breed true. This is why farmers find that their yields of maize are much lower when they sow seed saved from the previous year's c harvest of a high yielding hybrid. Certain plants, like the cultivated banana, are sterile and cannot reproduce naturally except from side shoots. This hampers varietal improvement by classical methods and limits the availability of good planting material. Biotechnology is opening the way for micropropagation, meristem culture and, more recently, somatic embryogenesis in order to overcome these different obstacles. By making it possible to obtain plantlets from fragments of stem or shoot, micropropagation is no different in principle to classical methods of propagation. In vitro propagation is more sophisticated than the techniques practiced by horticulturalists and it has two distinct advantages: the ability both to produce many more offspring, and to ensure that the plantlets raised are completely healthy. One parent plant can give rise to many hundreds of millions of identical plantlets which are free of viral diseases. Costs of production depends on the level of handling required and this gives countries which have low salary structures, such as those in the ACP regions, an advantage. Some ACP countries already have sizeable production units. Focusing on flowers and bananas In Kenya, where flowers are the third largest export crop after tea and coffee, the Kenya Agricultural Research Institute (KARI) has developed in vitro cultivation of flowering plants. KARI has been working in collaboration with Oserian, one of the three largest private horticultural companies in the country. The company has its own tissue culture laboratory, and since 1994 a staff of 54 people. Varieties are reproduced after being selected for productivity and resistance to pests. The company is planning to commercialize its in vitro plant production for the Kenyan horticultural industry and for export. Côte d'Ivoire, Zimbabwe and Mauritius (which has overtaken Hawaii in anthurium production) have also developed micro-propagation facilities to service their own horticultural sector. It is with bananas and plantains that these techniques have produced the most significant results for ACP countries. A private company based in Santo Domingo, in the Dominican Republic, has developed commercial production of in vitro plants with the support of the Centre for Research and Training in Tropical Agriculture for Central America and the Caribbean (CATIE) which is based in Costa Rica. The company, Luoma Vitrolab, grew out of a family horticultural business and multiplies not only bananas but also many ornamentals and aromatic plants. In addition to its principal research activities, the Cameroon-based Regional Centre for Bananas and Plantains (CRBP) also distributes in vitro plants of forty varieties that are used for local consumption. These are cultivated at its station in Njombe from vegetative material supplied by INIBAP whose collections are kept in Leuven, Belgium. The plantlets are sent to a network of development agencies and research centres, specifically in Gabon (AGRO Gabon, IGAD and CENAREST), in Congo (Agri Congo, DGRST) and in the Central African Republic (ICRA). They are used for training technicians to harden the plants for outdoor conditions and set them out in demonstration plots for farmers. By setting up this distribution chain to small producers, the foundations are laid for promising future commercial production. In some large plantation-holding companies, in vitro cultivation techniques has already grown to an industrial scale, particularly in Africa. This has considerable significance in view of their agricultural and economic importance. In Abidjan, the Society for the Study and Development of Bananas, a subsidiary of Terres Rouges, produces a million healthy, nematode-free plants each year for its parent company Even if the distribution of these products to small-scale producers on the continent has yet to be established, trade in in vitro plants is becoming the focus of major international producers. Tropitec, a private company in South Africa, has a commercial agreement to multiply plantain hybrids which are supplied from Honduras by the Honduran Foundation for Agricultural Research. Millions of plantains are then returned in test tubes by air to Honduras where Tropitec has a specialized unit for hardening off the in vitro plants ready for commercial production throughout tropical Latin America. Uganda's test-tube coffee Uganda is the second largest producer of robusta coffee in Africa after Côte d'Ivoire. At the beginning of 1996, a laboratory for in vitro cultivation was established within the Farming Systems Programme, a national programme funded by the KU. One activity of the programme is to replant old coffee trees with higher yielding varieties that are resistant to rust. This medium-sized production unit, which was established within the Institute of Agricultural Research in Kawanda with the technical support of CIRAD, has the capacity to prepare a million micro-propagated coffee plants per year, with a staff of only six. After the initial start-up phase, production will be targeted towards the country's 1.2 million small-scale coffee growers. These growers, who make up 7.5% of the population, grow 250,000 hectares of coffee, which in 1990 brought in 79% of Uganda's export earnings. The Kawanda laboratory will strengthen the Institute of Agricultural Research's traditional nursery, which currently produces several thousand clones each year. These are distributed to propagation units which then multiply them for onward sale to producers. The capacity of this classical horticultural propagation system is far below that required for the Uganda programme, which envisages the replacement of every coffee tree in the country. Given that 2,000 plants are required per hectare, the new laboratory will be able to meet only a small proportion of the demand. It seems likely that private companies will eventually take on this work, therefore the laboratory is already diversifying into meristem culture of local varieties of bananas. Work on cassava may follow. With an annual operational budget of US$150,000, the Kawanda laboratory can produce 500,000 in vitro plants of coffee per year and as many banana plants. Smallscale growers currently pay US 50 cents (US$ 0.5) for a traditionally raised robusta plant. The difference in price allows for marketing costs and a profit on the work of hardening off the in vitro plants: work which a farmer, once trained, can easily master. Back to the future Research is currently well advanced in the technique of cloning by somatic embryogenesis which is far more powerful in terms of productivity than micropropagation. This technique, for example with leaves, consists of taking back differentiated, non-reproductive cells to an undifferentiated state, so that they can each develop as a complete individual plant, genetically identical to the parent. Somatic embryogenesis requires the use of complex hormones and is particularly well adapted for cloning some species, like oil palm, where other in vitro propagation techniques are impractical. Experiments are usually undertaken by collaboration between universities and the major European research centres. Field trials are currently taking place in order to check that each developing plant conforms to type, and particularly to fruit formation. A consortium of agro-processing companies is quietly conducting trials in Brazil and Ecuador of several thousand arabica coffee trees propagated by somatic embryogenesis. To date there appear to be no problems with conformity. Oil palm produced by the same technique is proving equally satisfactory. A research team of scientists drawn from ORSTOM and CIRAD have conducted field trials in Côte d'Ivoire for several years and appear to have achieved a potential productivity gain in the order of 15% to 20%. This has also been observed in Indonesia and Malaysia. Having had their fingers burnt in the past by too hasty forays into industrialization, the scientists will remain cautious for a few more years. But there can be hardly any doubt that somatic embryogenesis is an essential technique for multiplying, and therefore adding value to varieties Improved by genetic engineering. Weak commercial management Many attempts to transfer and adapt technologies in the past, particularly in West Africa, have had no impact beyond that of training scientists and laboratory technicians, although this is not an insignificant achievement in itself. Some of the technologies involved species for which there was no real market. However, research efforts on varieties of major economic importance are beginning to give biotechnology its first significant developments in some ACP countries. Technology and production costs are no longer always the limiting factor to using biotechnology. This has been shown by the experience of large plantation-owning companies and by the intensive floricultural export industry. However, it is also true that the absence of commercial management know-how at the heart of publicly-owned production facilities still restricts the distribution of the products of biotechnology to scattered markets in the villages. As with many other agricultural inputs, it would appear that without the necessary marketing strategy, any attempt within the public sector to adopt new technologies, however sound will always remain a risk. | For twenty years, the development of biotechnology has given rise to great hopes and has stimulated considerable researcheffort throughout the world. Today, this effort is producing its first results in agriculture. Although still modest in...