CASE-STUDIES ON BREEDING SYSTEMS AND ITS CONSEQUENCES FOR GERMPLASM CONSERVATION .1. ISOENZYME DIVERSITY IN WILD LIMA-BEAN POPULATIONS IN CENTRAL COSTA-RICA

This study gives the results of allozyme diversity within and among 20 wild Lima bean populations uniformly distributed throughout the Centr al Valley of Costa Rica. The electrophoretic analysis of seven enzyme systems show five monomorphic loci and a relatively low level of polym orphism for the other loci. This moderate level of polymorphism is une xpected for a species for which a fair amount of allogamy rates has be en reported, at least among the cultivated forms. The genetic paramete rs (mainly percentage of polymorphic loci, mean genetic diversity, per centage of heterozygotes and fixation index) indicate a tendency for a predominantly selfing breeding system in the wild Lima beans although some values range between selfing and mixed-animal breeding systems. Very low within-population diversity is observed while a good diversit y is found among populations. Results also show a departure from Hardy -Weinberg equilibrium on most analyzed populations in the target site This might be due to populations divided into subpopulations among whi ch no natural crosses occur randomly, to weeding practices or to overl ap of generations within some populations. All the results obtained in this work are discussed in view of further studies for the planning o f in situ conservation in a quickly evolving tropical environment.