Evolution and adaptedness in a facultatively apomictic grass, Poa pratensis L.

Summary Facultative apomixis confers great adaptedness and evolutive potential on biotypes belonging to the Poa pratensis L. agamic complex. Pioneering and recent research have dealt with and sometimes elucidated different aspects of apomictic expression, such as cytological mechanisms, distribution patterns, genetic control and environmental effects, in this species. We carried out an investigation on the mode of reproduction expressed in Italian natural populations, cultivars and selected genotypes together with an extensive time (56 years) and space (six countries) review in order to obtain a comprehensive picture of apomixis expression in P. pratensis. Histograms of the estimations were prepared. They showed that, due to breeder and natural selection, both cultivars and natural populations very frequently expressed a high degree of apomixis. Variations in the degree of apomixis across generations, different pollen donors, environments and estimation levels were generally low. It would, therefore, seem that the tenet which holds that apomixis in P. pratensis is strongly influenced by external factors should be reconsidered. Despite the fact that little is known of the genetic, physiological and molecular control underlying apomixis, the overall picture that emerges from our study helps to explain how the balance between sexual and asexual reproduction confers extreme versatility, adaptedness and evolutive capacity on this remarkable grass.