The Eastern Africa root crops workshop was concerned with cassava, sweet potato, yams, and cocoyams, with particular emphasis on the first two crops. None of these crops are indigenous to the area; however, cassava and sweet potato were quickly and widely adapted as important staple-food crops. At present, yields of the root crops in the region are far too low to meet the demand and do not reflect the potential. Researchers have demonstrated that yields can be increased substantially through improved cultural practices and improved varieties. Although opportunities to exchange research findings and views among researchers and policymakers are few, this workshop did prove useful. The areas of research that were considered high priority by the participants were: defining the relevant environmental, socioeconomic, and agronomic constraints to optimum productivity; developing viable cropping systems based on well-defined criteria; establishing economic models to determine the investment potential of different cropping systems; developing and testing improved cultivars with high-yield potential, pest and disease resistance, and good consumer acceptability and storability; designing storage systems appropriate for local conditions; and formulating a wider range of processing techniques for more efficient utilization of present production.

Root system of maize, cowpea, maize and cowpea inter-cropped, cassava, yam and sweet potato were investigated in large boxes 240 x 115 X 20cm. One broad side of these boxes was made of a removable transparent plexiglass sheet. The soil was packed in the boxes at a dry bulk density of 1.28 g cm('-3). Maize roots penetrated to a depth of 135cm in 4 weeks and 240cm in eight weeks after seeding. Total root mass at 4 weeks after seeding was 3.53 and 22.0g per plant for cowpea and maize, respectively. In eight weeks total root mass of cowpea was 130g per plant compared with 292g per plant for maze. The effect of mixed cropping was to increase the total root mass compared with sole crop of maize or cowpea. However, the sum of the root mass of sole maize and cowpea was greater than the total root mass of maize and cowpea grown simultaneously. Among the tuberous crops investigated, cassava has a very deep and prolific root system and sweet potato has a very shallow root system. Results are discussed in terms of agronomic implications towards spacing, optimum plant population, and tillage practices.

The potato, which was introduced into Rwanda about 1900, has become a major food crop in only the past 35 years. Production per unit of land is low (6.8 t/ha) because of a lack of quality seed potatoes of adapted varieties; infections from Phytophthora infestans and Pseudomonas solanacearum; poor agronomic practices; poor preparation of seed potatoes; and an acute lack of technical knowledge among extension personnel and farmers. The Programme national pour l'amelioration de la pomme de terre (PNAP) was established to help remove these constraints to production. A research program with a practical approach to solving problems has been established along with a strong seed production, training, and extension program. The results after 1 year have been encouraging. On one hand, farmers are accepting seed production and storage techniques and see the utility of using fungicides and improved varieties in controlling P. infestans, and, on the other, PNAP scientists have gained valuable information from rural contacts

For one crucial century in the sequence of history, technology and economics created the unique opportunity to unfold their tricks without taking biology seriously into account. This might, in the long run, turn out to be mankind's greatest and most fateful mistake (2). According to Zadoks and Koster (53) the discipline of plant pathology originated during the potato blight of the nineteenth century. In a sense, the discipline was born in the context of technical changes that were incorporated into agricultural practices and thought to be unequivocally positive in their impacts. Yet, as Butler has recognized, the "side-effects of breedings for agronomic features desirable in themselves are well known as the "Green Revolution" (53). Adopting a systems perspective in selection of crop varieties would have made it possible to anticipate many of these secondary impacts. Perhaps the blight problem in Europe was a precursor of things to come. Inadequate attention to basic ecological interactions occurring and changing within a system results in "surprises" that require attention. However, if the attention is given in the strict disciplinary sense, it is quite possible that it will be directed specifically to correcting rather than understanding the totality of the problem being addressed. This has been the lesson of the "green revolution". The commonplace statement that everything is connected to everything else must be understood in its entirety today more than at any time in history. The flexibility with which modern agriculture has to respond to specific needs is more narrow tahn ever before. Much of the diversity that historically characterized the ecological systems that have supported human food production activities has been driven out. Mistakes are often not self-correcting and can easily compound the problem. In this context, the challenge to the plant protection disciplines is not necessarily to adequately respond to specific trangressions, whatever their source; rather, they must understand and document, in a broader context, the evolving system characteristics that will bound and delineate the more specific responses. Genetic engineering might produce dramatic gains in the direct response to specific maladies. Yet, if such engineering is undertaken with little or no understanding at the system level, it merely becomes a "band-aid" approach to the problem. The seemingly inevitable increase in the human population will require increased attention to global food production and distribution. If we focus on increased production, without understanding the indirect and subtle ramifications of the techniques employed in raising production, we will run the unthinkable risk of facilitating population growth in the short-run that we will be unable to maintain in the long-run. This would result in a veritable cul de sac for the world. From 1850 to 1925 plant pathology has focused on the fungus, the host, and environmental interaction, respectively (53). More recently, plant pathology, and more generally, the plant protection disciplines, have concentrated their efforts on integrated management or plant protection. This concentration implicitly recognize the failure of post World War II synthetic chemicals to achieve long-term stability in agricultural production. In many respects, this system sacrificed ecological stability for maximum yields, a trade-off we are beginning to seriously question