Research has generally focused on pearl millet, the most important species. Adaptation is a more serious problem in millet than in many other crops. Pearl millet originated in Western Africa, evolving in a harsh environment in association with a number of diseases and insect pests. Local landraces developed through natural and human selection gave poor yields, but showed reasonable tolerance to many of these hazards. Improved varieties introduced from Asia, Eastern Africa or the United States, where these problems are less prevalent, have generally failed to show any superiority over local varieties in Western Africa. Indeed, these introduced materials generally have serious adaptation problems, because of lack of tolerance to high soil temperatures and sandstorms as seedlings, and greater susceptibility than local landraces to diseases and insect pests.
Breeding for drought tolerance, a major problem in all millet environments, is also difficult because it is hard to accurately simulate drought conditions and because manipulating a plant trait to improve tolerance to severe drought stress at one growth stage may result in increased sensitivity to drought at another stage.
These difficulties notwithstanding, national and international research programmes have made significant advances. Improvements in pearl millet yields in the developing countries, mainly in India, have occurred largely due to the development, release and widespread multiplication of improved open-pollinated and hybrid cultivars. Because of their low sowing rates (3-4 kg/ha of seed) and high multiplication rates (200 to 500-fold per generation), these improved cultivars have been adopted fairly widely even by subsistence farmers in specific, relatively favourable, millet environments, e.g., Gujarat, Haryana and Maharashtra in India.
In Africa, hybrids have yet to make a significant impact because extension is inadequate and the seed industry poorly developed. However, there has been some adoption of improved open-pollinated varieties in Southern Africa. These offer marginal gains in grain yield over traditional landraces, and are less prone to end-of-season drought because they mature earlier, thus reducing the risk of crop failure.
The problem of environmental degradation is common for many crops, but particularly serious in millet. Population growth has forced farmers to shorten fallow periods (which in turn has resulted in declining soil fertility) and to expand millet cultivation into more marginal lands. This is most evident in Africa, where millet area has increased and yields have declined over the past 15 years. This problem is less serious in Asia; however, in the harsher environments in Rajasthan, the expansion into more marginal areas will make future productivity increases harder to achieve.
Improving the reliability of grain and stover yields continues to be the major focus of millet research. Current millet research is moving in two broad directions:
· shorter crop life cycles of 70-80 days (as against the more usual 90 days), so that the plant can escape end-of-season drought;
· better tolerance to mid-season drought.
Crop improvement programmes are now integrating farmers more closely than before into the breeding and diffusion process in order to develop technologies that are more accurately targeted at farmers' constraints, and, therefore, more likely to be adopted. The emphasis is on breeding cultivars with durable resistance to downy mildew and foliar diseases. Other important research objectives are to:
· identify Striga resistance sources and develop better crop management technologies to reduce losses due to Striga, particularly in Western Africa;
· develop integrated pest management strategies to reduce losses due to the millet stem borer.