Wheat was one of thee first plants to be cultivated by mankind, and today it is a major dietary constituent of about a quarter of the world's population, according to the International Wheat Council. It also dominates world cereal trade, with global trade increasing from 35 million tonnes In the 1950's to 100 million tonnes in the Eighties (1988-89, 97.8m).
North American production accounts for 38% of this total. More significantly, wheat has for some time been the greatest cause of a massive shift in food preference throughout the tropics, a shift which has posed an as yet unresolved dilemma for many tropical countries.
Food-deficit nations in Africa and else where have made up for their shortages of locally grown grains by importing cereals, most notably wheat. As a result, the importance of wheat in the diets of many developing countries has grown substantially, and it now provides 27% of their cereal calories and 3% of protein requirements.
Wheat flour is unique in that it contains high levels of gluten. When water is added to wheat flour, the gluten proteins bind with water to make the dough easily work able and a light, palatable loaf results. Flours from other cereals and tubers contain little or no gluten and tend to result in a much more dense loaf. As a result, many people, especially city-dwellers, now want bread made from wheat flour because it is not only more <<convenient>> than traditional staple crops such as cassava, millet or sorghum, it also has a certain <<status>> attached to it. Yet wheat cannot easily be grown in most tropical countries.
The growing demand for wheat has become a major problem for many ACP countries. Wheat imports have been rising steadily to around 20 million tonnes annually representing 80% of requirements. High population growth, rising incomes, income distribution, low prices and simple changes in food preference are all contributory factors and cereal imports into tropical countries are growing faster than the ability of some of the countries to pay. More than 12 million tonnes are imported annually into subSaharan Africa alone, costing in excess of $2.5 billion. More than 20% of all cereals eaten are imported and 25% of export earnings are used up to pay for them.
Wheat is already the most important staple crop in Jamaica and Trinidad and Tobago, so what are the prospects for ACP countries? Can wheat be grown successfully in tropical climates, and is there any real need to expand production when the world already houses surplus stocks of 130 million tonnes?
Wheat is cultivated in a wide range of environments around the world but grows best in temperate zones where there is low to moderate rainfall. More land is devoted to growing wheat - about 230 million ha than to any other commercial crop and more wheat is produced than any other cereal. But 90% of all wheat is grown in the northern hemisphere.
Wheat production in the tropics contributes less than 2% of the total global wheat harvest. In Africa, very little wheat is grown south of the Sahara. What little is produced is grown in rainfed systems in the East African highlands or as irrigated winter season crops in southern Africa. Rainfed wheat is produced only at altitude: Kenya, for example, grows all of its wheat on land above 2000 metres
In west and central Africa, small amounts of wheat have been grown for centuries on small irrigated plots during the dry season in the Sudan and the Sahel. The potential for wheat is improving with the development of irrigation schemes, notably in Nigeria, Chad and Ghana, but local varieties are especially susceptible to stem rust, a major disease of wheat. Other problems are that they are weak-strawed and also unsuitable for baking.
Yet, according to the FAO, 38 million ha in Africa are suitable for wheat production and many African countries are now looking to expand wheat production to try and reduce import bills. Somalia is interested in reducing its annual imports of 180,000 tonnes of wheat flour but, at present, wheat is grown only by smallholders on 4000 ha in the remote northwest highlands. Sudan is attempting to expand wheat production or irrigated clay soils in a double cropping system with cotton. The Institute of Agricultural Research in Ethiopia has developed wheat varieties specifically suited for local conditions, but the supply of water from the Awash river and the availability of sufficient labour to hand-harvest the cotton crop, with which the wheat would be grown have proved restrictive. Nigeria has announced that its production target will be 800,000 tonnes in 1989.
Scientists have been striving for more than 40 years to produce better varieties of wheat and improved high-yield varieties (HYV), adapted to sub-tropical conditions, were developed in Mexico by the International Maize and Wheat Improvement Centre (CIMMYT) has a global mandate to increase productivity in wheat and maize, its research resources being targeted towards improving techniques for resourcepoor farmers.
The use of HYV seeds led to a marked improvement in wheat production throughout the world. Production in India doubled between 1966 and mid-1972 and, virtually within a decade, India changed from being the world's second largest importer of cereals to being self-sufficient. By the 1970s more than half the wheat fields in developing countries were using new varieties which could produce two to three times as much as traditional varieties.
Initially, only wealthy farmers could benefit from using the seeds as they required fertiliser, good water supplies and protection from a wide range of pests and diseases. Led by CIMMYT and the FAO's Seed Improvement and Development Programme (SIDP), which covers more than 118 countries, research is now being directed toward producing new seeds that are not so reliant on expensive inputs. Work is also progressing toward developing seeds designed to grow well in tropical climates.
Tropical wheat systems
Several major constraints will need to be overcome if large-scale wheat fanning is to be introduced successfully in the tropics. In Europe and the Americas wheat is grown in sophisticated farming systems, often using the latest technology. However, in the tropics, it is grown mainly as a high-altitude crop - usually as part of a wheat/dairy farming system - and is not as suitable as other cereals, such as maize, for growing by small-holders, unless they are organised into cooperatives.
Wheat-farming systems in the tropics face a variety of other problems. There is a tendency to burn off straw and stubble after harvesting, which makes ploughing easier and helps prevent the carry-over of disease. But this is counter-productive in areas where poor, light soils could be improved by ploughing in the straw to improve soil structure.
In the tropics, soil erosion may also be a significant factor in curtailing wheat production. Soil loss is particularly damaging, as shown by the situation in the United States where the loss of two cms of topsoil reduced yields by 6%.
Unless new varieties of wheat are developed, the need for a high level of inputs will remain a major drawback. At present, nitrogen fertilizer requirements rise to 150 kg per ha for any sort of economic return on high-yield seeds. And phosphate must also be carefully considered as full response to nitrogen fertilizer is obtained only when phosphorus is not a limiting factor.
Wheat is often grown in rotation with rice, but the two cereals have almost 200 insect pest in common. Also, the bacterium Xanthomanas campestris, which has a worldwide distribution, causes a serious disease of wheat and, to control it in tropical regions, seeds and irrigation water need to be carefully monitored. Stem, leaf and stripe rusts caused by Puccinia fungi are the most serious diseases of wheat. In epidemics, up to 75% of the crop may be destroyed by pests; therefore, effective pest and disease control will require a community-wide crop management programme to avoid pest build-up and minimize losses. This will necessitate a great deal of coordination and expense.
Towards improved production
Fortunately, many wild strains of wheat contain genetic material from which plant breeders can introduce pest and disease resistance. Wild varieties also show drought resistance, salt and heat tolerance, winter hardiness and increased protein content. Consequently, if wheat is to be grown with any degree of economic success in the tropics, plant breeding and biotechnology will have a major role to play.
Wheat yields are sensitive to high temperatures early in the growing season and to even slight deviations from optimal planting dates. Although high temperatures limit yield potential, it is moisture levels and soil acidity that are more critical. Consequently, in the tropics dramatic fluctuations in yields are common. However, field trials of wheat in tropical conditions have shown that yields of 5,000 kg per ha can be achieved.
At harvest, small-holders must cut their wheat manually with hand sickles when the seeds are hard and dry. Cutting semidwarf HYVs is a particularly exhausting task. There are severe storage problems to overcome: high temperatures and relative humidities are not conducive to efficient, low-cost storage methods, particularly as stored wheat grain should have a moisture content of less than 14%.
Additionally, wheat grain generally needs to be milled before use, which requires both equipment and a source of power. The milling process itself also has to be carried out fairly carefully, as all the thiamine (vitamin B1) can be milled out of the grain leading to deficiency diseases such as Beri Beri
Wheat is now being promoted as an additional crop in rotations where there would otherwise be no crop during the cool' dry season, such as in rainfed upland or rice paddies. During 1975-84, wheat production in developing countries increased at 5% per year. higher yields mainly being from the use of HYV seeds. Although the total potential wheat area in the tropics is estimated to be around 3.5 million ha spread through 60 countries, until 1982 no efforts had been made to expand research to over production in tropical climates. Today, several national wheat programmes have been established in ACP countries, including Cote d'Ivoire, Nigeria, Cameroon' and Madagascar.
Particular attention is being paid to the potential of Triticale, a hybrid cereal obtained by crossing wheat and rye, which can be grow on land that is marginal for wheat. Triticale is comparatively disease-resistant and adapted to acid soils. In rice-growing areas, it performs well when grown out of season on rice paddies. In addition, it shows better nutrient efficiency than wheat and is almost as rich in gluten, with the result that Triticale flour can be used for baking bread.