Variation within naturally occurring Townsville stylo (Stylosanthes humilis) population; changes in population structure and some agronomic implications

Abstract

Two populations of Townsville stylo collected from Townsville (T) (rainfall 1140 mm) and from Greenvale (G) (rainfall 640 mm) were grown in small swards at four locations (rainfall 460-869 mm) for 2 years. Phenotypic variation in the original populations and the T-derived populations from seven of the eight location-year combinations was assessed in a pot experiment. Numerical analysis of the data using an agglomerative classification delineated five distinct growth forms. The proportions of these forms differed in the original T and G populations, and the population structure of the T plots changed markedly towards that of the original G population after only one growing season at the four locations. These changes could be related to environmental conditions and weed competition. It is suggested that population heterogeneity may represent an adaptation to varying ecological and climatic conditions. Heterogeneous seed mixtures may therefore be agronomically superior to individual genotypes, and compact growth forms with high seed indices may be more suited to harsher environmental conditions.