Focus expansion of bean rust in cultivar mixtures

Radial expansion of foci in mixtures of susceptible and resistant bean cultivars was studied at two sites in Ethiopia. The foci expanded in a wave-like fashion. At Ambo (1990), radial expansion velocity ranged from 6 cm per day in mixtures with 20% susceptible plants to 15 cm per day in plots with the susceptible plants only. At Debre Zeit, the velocity ranged from 3 cm per day in a mixture with 20% susceptible plants to 16 cm per day in plots with 100% susceptible plants. At both sites the radial expansion velocity of foci correlated linearly with the logarithm of the fraction of susceptible plants in the mixture. Velocities of focus expansion at Ambo and Debre Zeit were approximately equal in plots consisting of susceptible plants only. At lower proportions of susceptible plants the velocities at Debre Zeit were lower than at Ambo. Indications were given as to the environmental factors responsible for the observed difference between sites. At each site, the variation between plots showed a clear spatial pattern, probably due to environmental factors.     

Towards Modeling National Preference Formation for Regional Development Policy: Lessons from Developed and Less Developed Countries

National preferences for the development of regional and environmental policy are dependent on the competitive resolution of priorities emanating from four national centers of preference formation, namely: (a) national opinion leaders, (b) society at large, (c) state political institutions, and (d) the private business sector. The viability of national policies for regional development and environmental protection is assumed to be a function of the degree of systemic concordance among these four competing loci of preference formation. The paper explores differences between developed and developing countries in the formation of national preferences and analyzes the process by which competing preferences for regional development and environmental protection are ultimately resolved. It demonstrates that MDCs enjoy a high degree of harmony among their more autonomous centers of preference formation to achieve regional development goals, whereas LDCs are constrained by the dominant and coercive role of the state apparatus.